KR102408991B1 - High resolution image decoding system based on squint sar and method of decoding image using the same - Google Patents

Abstract

The directional angle SAR-based high-resolution image restoration system includes a waveform generator, a divider, an antenna member, a mixer, a raw data generating member, a directional angle correction member, an image restoration unit, and an operating range setting member. The operating range setting member analyzes the Doppler frequency error of the corrected raw data according to the change in the beam width of the beam and the inversion power of the transmission wave, and the maximum error orientation angle and maximum error inversion power that do not exceed the threshold value of the Doppler frequency error A non-linear error analysis unit for setting the beam width, and a resolution analysis unit for analyzing the restored preliminary image and setting the beam width and the beam width at which the resolution according to the change in the beam angle and the half power beam width does not exceed the critical resolution; By combining the analysis result of the nonlinear error analysis unit and the analysis result of the resolution analysis unit, the Doppler frequency error does not exceed the threshold value and the resolution of the reconstructed preliminary image does not exceed the threshold resolution. to include an operating range setting unit for controlling the antenna member and the waveform generator.

Description

HIGH RESOLUTION IMAGE DECODING SYSTEM BASED ON SQUINT SAR AND METHOD OF DECODING IMAGE USING THE SAME}

The present invention relates to a directional angle SAR-based high-resolution image restoration system and an image restoration method using the same, and more particularly, to an optimal squint SAR system in a Squint-Synthetic Aperture Radar (Squint-SAR) image restoration system measured by an aircraft. It relates to an orientation angle SAR-based high-resolution image restoration system with reduced errors and improved economic feasibility and resolution by determining the operating range, and an image restoration method using the same.

The global environmental survey is a field that investigates the geology, ocean, and ecology of a vast area, and includes field surveys, indoor experiments, and remote sensing.

Field surveys include direct visits to the site, such as surface exploration, boring, and physical exploration, and surveys using the naked eye or various survey equipment. Since field surveys have high accuracy, they are still widely used when precise measurements are required. In an indoor experiment, chemical and physical properties that are difficult to measure directly in the field are measured using precision measuring equipment in the laboratory. Field surveys and indoor experiments have the advantage of high accuracy, but they are not easy to apply to large areas, remote areas, remote areas, and the ocean due to time and spatial constraints.

Recently, due to the development of remote sensing technology, remote sensing using an aircraft is widely used. In particular, remote sensing is very useful in disaster situations such as volcanic eruptions, earthquakes, typhoons, and environmental monitoring such as glaciers, tides, waves, and marine pollution.

Common remote sensing equipment uses satellites or radars mounted on aircraft. In the case of satellites, it is possible to measure a large area from a distance, but it is difficult to obtain precise data because it costs a lot and the distance from the measurement point is long.

In the case of an aircraft, it has the advantage of being able to measure close range at a relatively low price compared to satellites. However, during the operation of the aircraft, continuous fluctuations and vibrations occur due to factors such as atmospheric conditions, weather, and engines. The fluctuations and vibrations of the aircraft degrade the quality of data, but it is impossible to completely eliminate them due to the nature of the aircraft operating in the air.

Among these problems, especially in the case of Squint-SAR data, which is caused by the radar irradiation direction being twisted, the azimuth and distance directions are twisted at the same time due to the fact that the data obtained through the aircraft has a three-dimensional shape, There is a problem in that the restored data is distorted. In particular, since various variables such as atmospheric conditions, weather, engine, etc. are involved while operating an aircraft, as well as physical characteristics of the radar itself such as synthetic aperture length, flight altitude, radio wave incidence angle, and orientation angle, the orientation angle SAR The underlying system has no choice but to basically behave non-linearly.

Since it is difficult to predict the occurrence of errors in nonlinear behavior and it is also difficult to correct the errors, the cost and time increase because it is necessary to repeat the measurement several times or use a complex numerical analysis technique to obtain the desired result. In addition, if the error range is out of the critical value, it is impossible to reuse the survey results even after correction. Due to the unpredictability of error generation, it is difficult to predict the accuracy of inspection results.

Republic of Korea Patent No. 10-2028323 (2019. 9. 27.) Republic of Korea Patent No. 10-2028324 (2019. 9. 27.)

It is an object of the present invention to determine the optimal operating range of the Squint-SAR system in the Squint-Synthetic Aperture Radar (SAR) image restoration system measured by an aircraft, thereby reducing errors and improving economic efficiency and resolution. to provide a recovery system.

An object of the present invention is to provide an image restoration method using the directional angle SAR-based high-resolution image restoration system.

A directional angle SAR-based high-resolution image restoration system according to an embodiment of the present invention includes a waveform generator, a divider, an antenna member, a mixer, a raw data generating member, a directional angle correction member, an image restoration unit, and an operating range setting member. The waveform generator generates a signal having the same waveform as the transmission wave. The divider is connected to the waveform generator, and receives and distributes the signal generated from the waveform generator. The antenna member is connected to the splitter and includes a transmit antenna for receiving the distributed signal from the splitter to transmit the transmit wave to the ground surface and a receive antenna for receiving the receive wave reflected from the ground surface, the aircraft moving direction It is inclined as much as the orientation angle based on the direction perpendicular to . The mixer is connected to the splitter and the receive antenna, and mixes the distributed signal applied from the splitter and the receive wave received from the receive antenna. The raw data generating member is connected to the mixer, receives the mixed signal from the mixer, measures a distance from the target center of the ground surface, and generates raw data indicating the location of the target center. The orientation angle correcting member is connected to the raw data generating member, and changes the raw data into corrected raw data on the distance-Doppler frequency domain rotated by the orientation angle, and converts the corrected raw data to displacement according to the movement of the aircraft. Reconstructed image data for each pixel is generated by compensating for the rotation as much as the orientation angle. The image restoration unit projects the restored image data for each pixel to restore a preliminary image of a virtual target center or a final image obtained by scanning real terrain. The operating range setting member is connected to the antenna member, the waveform generator, the directivity angle correcting member, and the image restoration unit, and the Doppler frequency of the corrected raw data according to the change in the directivity angle and the reverse power beam width of the transmitted wave. A nonlinear error analysis unit that analyzes an error to set a maximum error directivity angle and maximum error reversal power beam width that do not exceed the threshold of the Doppler frequency error, and the reconstructed preliminary image is analyzed to change the directivity angle and reversal power beam width A resolution analysis unit that sets the beam width and the beam width of a beam whose resolution does not exceed the critical resolution according to And it includes an operating range setting unit for controlling the antenna member and the waveform generator by setting the beam width and the beam width of the reversal power at which the resolution of the restored preliminary image does not exceed the critical resolution.

In an embodiment, the nonlinear error analysis unit uses [Equation 1] to determine the effective length of the synthetic aperture (L in FIG. 2), the antenna reverse power beam width (φ _BW ), the flight altitude (H ₀ ), and the radio wave incident angle (θ _i ). ), and the center frequency (f ₀ ) can be determined.

[Equation 1]

(L represents the effective length of the composite aperture, H ₀ represents the flight altitude, θ _i represents the incident angle, and φ _BW represents the half force beam width)

In an embodiment, the nonlinear error analyzer may obtain the Doppler frequency error using a root mean square (RMS) method as shown in [Equation 2], [Equation 3], and [Equation 4].

[Equation 2]

(In [Equation 2], N is the number of samples indicating the positions of the antenna members 110 and 120 in the composite aperture, and u' _n is the coordinate system rotated by the beam angle ( Φ _sq ) in the composite aperture (u') Corresponds to each position (sample) of the antenna members 110 and 120 according to the movement of the aircraft on the plane, k _u '(u') corresponds to [Equation 3], and the fit(u') function is approximated by a linear equation (fitting) is a function)

[Equation 3]

(In [Equation 3], k u ' represents the Doppler frequency rotated by the beam angle in the Fourier-transformed distance-Doppler domain, f0 represents the center frequency, f represents the beat frequency, and u' represents the rotation angle by the beam angle. It represents the azimuth distance on the coordinate system, and A(u') is represented by [Equation 4])

[Equation 4]

(In [Equation 4], c represents the speed of light, and R ₀ represents the distance between the virtual position of the aircraft and the center of the target when the heading angle is 0°)

In one embodiment, the resolution analyzer analyzes the beam angle and the azimuth resolution using [Equation 3] and [Equation 5] to set the range of the beam width and the range of the beam width in the azimuth direction within the critical resolution, characterized in that A high-resolution image restoration system based on directional angle SAR.

[Equation 3]

(In [Equation 3], k u ' represents the Doppler frequency rotated by the beam angle in the Fourier-transformed distance-Doppler domain, f0 represents the center frequency, f represents the beat frequency, and u' represents the rotation angle by the beam angle. It represents the azimuth distance on the coordinate system, and A(u') is represented by [Equation 4])

[Equation 4]

(In [Equation 4], c represents the speed of light, and R ₀ represents the distance between the virtual position of the aircraft and the center of the target when the heading angle is 0°)

[Equation 5]

△u=2π/BW _ku'

(In [Equation 5], BW _ku' represents the frequency bandwidth)

In an embodiment, the operating range setting member may further include a control motor connected to the antenna member to control the orientation angle.

In one embodiment, the orientation angle correction information material is connected to a first Fourier transform unit that is connected to the raw data generating member and performs a first-order Fourier transform with respect to time on the raw data, and is connected to the first Fourier transform unit, A raw data preprocessor for generating first corrected raw data by rotating the first Fourier-transformed raw data by the orientation angle, connected to the raw data preprocessor, and rotated by the orientation angle to the first corrected raw data A second Fourier transform unit for generating second corrected raw data by performing a Fourier transform on the aircraft position variable on the coordinate system, and the second Fourier transform unit connected to the second Fourier transform unit to rotate the displacement according to the movement of the aircraft by the orientation angle a trajectory characteristic function generator generating third corrected raw data by compensating for the state and additionally compensating for a distance difference caused by the rotation, and directing the generated mixed data by multiplying the third corrected raw data by a matched filter An inverse Fourier transform unit generating fourth correction data according to coordinates on the earth's surface by performing inverse Fourier transform with the Doppler frequency rotated by the angle, and the inverse Fourier transform unit is connected to the inverse Fourier transform unit and inversely rotates the fourth correction data by the orientation angle to restore image data It may include a data reverse rotation unit to generate

In the image restoration method using the directional angle SAR-based high-resolution image restoration system according to an embodiment of the present invention, the directional angle SAR-based high-resolution image restoration system includes a waveform generator that generates a signal of the same waveform as a transmission wave, and the waveform generator a divider connected to and receiving and distributing the signal generated from the waveform generator; a transmitting antenna connected to the divider and receiving the distributed signal from the divider to transmit the transmission wave to the ground; An antenna member including a receiving antenna for receiving a wave, but inclined as much as a directivity angle with respect to a direction perpendicular to the direction of movement of the aircraft, the splitter and the receiving antenna connected to the splitter and the received signal and the receiving antenna A mixer that mixes the received wave received from the mixer, is connected to the mixer, receives the mixed signal from the mixer, measures the distance from the target center of the ground surface, and generates raw data indicating the location of the target center a raw data generating member, connected to the raw data generating member to change the raw data into corrected raw data on a distance-Doppler frequency domain rotated by the orientation angle, and converting the corrected raw data to displacement according to the movement of the aircraft The orientation angle correction member for generating reconstructed image data for each pixel by compensating for the rotation as much as the orientation angle, and by projecting the reconstructed image data for each pixel to restore as a preliminary image about the virtual target center or to scan the actual terrain An image restoration unit that restores an image, the antenna member, the waveform generator, the directivity angle correction member, and the image restoration unit are connected to the image restoration unit and analyze the Doppler frequency error according to the input beam angle and the reverse power beam width. It includes an operating range setting member including a resolution analysis unit for analyzing the resolution according to the portion and the input beam angle and the reversing power beam width, and an operating range setting unit for setting the operating range of the heading angle and the reversing power beam width. In the image restoration method using the directional angle SAR-based high-resolution image restoration system, first, the scope of the directional angle and the range of the half-power beam width are set for analyzing the virtual target center by using the operation range setting unit. Then, an arbitrary value is set within the range of the set half-power beam width by using the operating range setting unit, and a plurality of different beam angle values are set within the range of the set beam width. Thereafter, preliminary images corresponding to the respective beam angle values and the set half-power beam width value are reconstructed using the raw data generating member, the orientation angle correction member, and the image restoration unit. Subsequently, a Doppler frequency error corresponding to each of the beam angle values and the set half-power beam width value is detected using the nonlinear error analysis unit. Next, a directivity angle at which the detected Doppler frequency error becomes the maximum value is calculated using the nonlinear error analysis unit and is set as the maximum error directivity angle. Thereafter, the maximum error directivity angle is set as a directivity angle value by using the operating range setting unit, and a plurality of different half-power beamwidth values are set within the range of the set half-power beamwidth. Subsequently, preliminary images corresponding to each of the maximum error directivity angle value and each of the half-power beamwidth values are restored using the raw data generating member, the orientation angle correction member, and the image restoration unit. Next, the reconstructed preliminary images are analyzed using the nonlinear error analyzer to set the maximum error inversion power beam width corresponding to the threshold value of the Doppler frequency error. Thereafter, the range of the beam angle and the half-power beam width within a preset critical resolution are set using the resolution analysis unit. Subsequently, the Doppler frequency error does not exceed the threshold value by combining the analysis result of the nonlinear error analysis unit and the analysis result of the resolution analysis unit using the operating range setting unit, and the resolution of the restored preliminary image is the threshold resolution. The antenna member and the waveform generator are controlled by setting the directivity angle and the reverse power beam width not to exceed. Then, the actual topography is scanned by applying the beam angle and the half-power beam width to the beam beam SAR-based high-resolution image restoration system, and the final image on the composite aperture is restored by combining the reconstructed image data for each pixel.

In one embodiment, the image restoration method uses [Equation 16] to determine the effective length of the synthetic aperture (Fig. 2) and the antenna reversal power beam width (φ _BW ), flight altitude (H ₀ ), radio wave incidence angle (θ _i ), and determining the center frequency (f ₀ ) may be further included.

[Equation 1]

(L represents the effective length of the composite aperture, H ₀ represents the flight altitude, θ _i represents the incident angle, and φ _BW represents the half force beam width)

In an embodiment, the detecting of the Doppler frequency error may include obtaining the Doppler frequency error using a root mean square (RMS) method as shown in [Equation 2].

[Equation 2]

(In [Equation 2], N is the number of samples indicating the positions of the antenna members 110 and 120 in the composite aperture, and u' _n is the coordinate system rotated by the beam angle ( Φ _sq ) in the composite aperture (u') Corresponds to each position (sample) of the antenna members 110 and 120 according to the movement of the aircraft on the plane, k _u '(u') corresponds to [Equation 12], and the fit(u') function is approximated by a linear equation (fitting) is a function)

[Equation 3]

(In [Equation 3], k u ' represents the Doppler frequency rotated by the beam angle in the Fourier-transformed distance-Doppler domain, f0 represents the center frequency, f represents the beat frequency, and u' represents the rotation angle by the beam angle. It represents the azimuth distance on the coordinate system, and A(u') is represented by [Equation 4])

[Equation 4]

(In [Equation 4], c represents the speed of light, and R ₀ represents the distance between the virtual position of the aircraft and the center of the target when the heading angle is 0°)

In one embodiment, the step of setting the range of the beam angle and the half-power beam width within the preset critical resolution comprises analyzing the beam angle and the azimuth resolution using [Equation 3] and [Equation 5] to determine the threshold It is possible to set the range of the beam direction and the range of the reversal beam width within the resolution.

[Equation 3]

(In [Equation 3], k u ' represents the Doppler frequency rotated by the beam angle in the Fourier-transformed distance-Doppler domain, f0 represents the center frequency, f represents the beat frequency, and u' represents the rotation angle by the beam angle. It represents the azimuth distance on the coordinate system, and A(u') is represented by [Equation 4])

[Equation 4]

(In [Equation 4], c represents the speed of light, and R ₀ represents the distance between the virtual position of the aircraft and the center of the target when the heading angle is 0°)

[Equation 5]

△u=2π/BW _ku'

(In [Equation 5], BW _ku' represents the frequency bandwidth)

In one embodiment, the step of setting the maximum error reversal power beam width comprises analyzing the reconstructed preliminary images and halfway between the reversal power beam width of a point forming a single cross and the reversing power beam width of a point forming two cross shapes It may be a step of setting a value to the maximum error inversion power beam width.

In an embodiment, the method may further include setting a Doppler frequency error corresponding to the maximum error directivity angle and the maximum error half-power beam width as a threshold value of the Doppler frequency error using the nonlinear error analysis unit.

In an embodiment, the restoring of the preliminary images may include: generating a signal corresponding to the half-power beam width using the waveform generator; applying the signal to the transmitting antenna, transmitting the transmitted wave rotated by the directivity angle onto the ground surface, and receiving the received wave reflected from the ground surface through the receiving antenna; mixing the signal distributed from the divider with the reception wave received from the reception antenna using the mixer; generating raw data indicating the position of the center of the target by measuring a distance from the mixed signal to the center of the target on the ground surface using the raw data generating member; performing a first-order Fourier transform with respect to time on the raw data using the first Fourier transform unit; generating first corrected raw data by rotating the first-order Fourier-transformed raw data by the orientation angle using the raw data preprocessor; generating second corrected raw data by performing a Fourier transform on the aircraft position variable on the coordinate system rotated by the orientation angle on the first corrected raw data by using the second Fourier transform unit; Compensating the displacement according to the movement of the aircraft in a rotated state by the orientation angle using the trajectory characteristic function generator, and further compensating for a distance difference caused by the rotation to generate third corrected raw data; ; generating fourth corrected data according to coordinates on the earth's surface by using the inverse Fourier transform unit to Fourier inversely transform the generated mixed data obtained by multiplying the third corrected raw data by a matched filter with a Doppler frequency rotated by the orientation angle; generating restored image data by using the data reverse rotation unit to reversely rotate the fourth correction data by the orientation angle; and projecting the restored image data for each pixel by using the image restoration unit to restore a preliminary image on the synthetic aperture with respect to the virtual target center.

In an embodiment, the anti-reverse force beam width may be an azimuth anti-reverse force beam width or a distance-direction anti-reverse force beam width.

In an embodiment, the generating of the first corrected raw data includes: generating mixed data by multiplying the first-order Fourier-transformed raw data by a baseband transform filter; and generating the first corrected raw data by rotating the mixed data by the orientation angle.

According to the present invention as described above, by adjusting the physical characteristics of the radar in advance in the Squint-SAR image restoration system, the error of the directional angle SAR (Squint-SAR) data caused by twisting the irradiation direction, and the range of the reverse power beam width It can be set in advance so that raw data within a range that can be corrected is generated by controlling in advance the occurrence of errors caused by not setting properly.

In addition, in the nonlinear behavior of the Squint-SAR image restoration system, which is difficult to predict and correct for errors, the accuracy of inspection results is improved by setting the error range within a threshold in advance.

In addition, in setting variables such as the orientation angle ( Φ _sq ), the effective length of the composite aperture (L), the half-power beam width ( Φ _BW ), etc., the reconstructed image of excellent quality can be obtained without trial and error considering the Doppler frequency error and resolution. can create

In addition, since the Squint-SAR image restoration system itself is controlled in advance so that the raw data converges within a correctable error range, it has the advantage of being applicable to various image restoration techniques.

In addition, with respect to the raw data converged within the error range, the rotational resampling unit, the second Fourier transform unit, the trajectory characteristic function (Range Cell Migration; RCM) generation unit, and the data reverse rotation unit are used for 4 times by using the orientation angle. By correcting the influence, the accuracy of the restored image is improved.

1 is a block diagram illustrating a directional angle SAR-based high-resolution image restoration system according to an embodiment of the present invention.
2 is a diagram showing the geometry of an aircraft on which a directional angle SAR-based high-resolution image restoration system according to an embodiment of the present invention is mounted.
FIG. 3 is a block diagram illustrating the orientation angle correcting member shown in FIG. 1 .
FIG. 4 is a conceptual diagram illustrating a process of rotating raw data by the raw data preprocessor shown in FIG. 3 .
5 is a block diagram illustrating the operating range control member shown in FIG. 1 .
6A is a graph showing a relationship between an azimuth distance and a Doppler frequency according to Comparative Example 1 of the present invention.
6B is a graph showing a relationship between an azimuth direction distance and a Doppler frequency error according to Comparative Example 2 of the present invention.
7A is a graph illustrating the relationship between the azimuth distance and the Doppler frequency analyzed by the nonlinear error analyzer of FIG. 5 .
FIG. 7B is a graph showing the relationship between the azimuth direction distance and the Doppler frequency error analyzed by the nonlinear error analyzer of FIG. 5 .
8 is a graph illustrating a synthetic aperture length, a directivity angle, and a Doppler frequency error analyzed by the nonlinear error analyzer of FIG. 5 .
9A and 9B are diagrams showing geometric structures of the behavior of the nonlinear error analyzer shown in FIG. 5 according to various flight altitudes and radio wave incident angles.
10A and 10B are graphs showing the synthesized aperture length, the orientation angle, and the Doppler frequency error analyzed by the nonlinear error analyzer of FIG. 5 when the flight altitude of the aircraft is different.
11A and 11B are graphs showing a composite aperture length, a directivity angle, and a Doppler frequency error analyzed by the nonlinear error analyzer of FIG. 5 when the aircraft radio wave incident angles are different.
12A and 12B are graphs illustrating a composite aperture length, a directivity angle, and a Doppler frequency error analyzed by the nonlinear error analyzer of FIG. 5 when the aircraft radio wave incident angles are different.
13 is a graph showing the Doppler frequency error (Δk _u ') according to the azimuth reverse force beam width (Azimuth HPBW, φ _BW ) and the beam angle ( φ _sq ) analyzed by the nonlinear error analyzer of FIG. 5 .
14 to 19 are images showing reconstructed images respectively corresponding to (1) to (6) of FIG. 13 .
20 is a graph comparing the results analyzed by the resolution analyzer shown in FIG. 5 and the theoretical performance analysis results.
FIG. 21 is a graph illustrating azimuth resolution analyzed by the resolution analyzer shown in FIG. 5 .
22 is a graph illustrating Doppler frequency error and azimuth resolution analyzed by the operating range setting unit shown in FIG. 5 .
23 is a graph showing a cross-section in the distance direction of the reconstructed image of point (1) shown in FIG. 22 .
24 is a graph showing an azimuth cross-section of the reconstructed image of point (1) shown in FIG. 22 .
25 is a flowchart illustrating an image restoration method using the directional angle SAR-based high-resolution image restoration system shown in FIG. 1 .
FIG. 26 is a block diagram illustrating a step of reconstructing the preliminary image of FIG. 25 .

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. Since the present invention can have various changes and can have various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

In describing each figure, like reference numerals have been used for like elements. In the accompanying drawings, the dimensions of the structures are enlarged than the actual size for clarity of the present invention.

Terms such as first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component. The singular expression includes the plural expression unless the context clearly dictates otherwise.

In the present application, terms such as "comprise" or "have" are intended to designate that a feature, number, step, operation, component, part, or a combination thereof described in the specification exists, but one or more other features It is to be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof.

In addition, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

1 is a block diagram illustrating a directional angle SAR-based high-resolution image restoration system according to an embodiment of the present invention.

Referring to FIG. 1 , the high-resolution image restoration system based on the directional angle SAR includes the antenna members 110 and 120 , the waveform generator 150 , the divider 160 , the mixer 205 , the raw data generating member 210 , and the orientation angle correction. It includes a member 220 , an image restoration unit 240 , and an operating range setting member 300 .

The waveform generator 150 generates a signal having the same waveform as the transmission wave 2 . In an embodiment of the present invention, the waveform generator 150 is connected to the divider 160 and the operating range setting member 300 to generate a signal having a frequency characteristic set by the operating range setting member 300 to generate the divider 160 . send to The waveform generator 150 may generate various signals such as a triangular wave, a sawtooth wave, and the like. For example, the sawtooth wave refers to a waveform in which the frequency is constantly increased according to time, the frequency is initialized every predetermined period, and then the frequency is increased again. Since the sawtooth wave can directly measure the Doppler frequency according to the distance, it can provide velocity information according to the distance.

The splitter 160 is connected to the waveform generator 150 , the transmit antennas 110 of the antenna members 110 and 120 , and the mixer 205 . The divider 160 receives the signal generated from the waveform generator 150 and distributes it to the transmitting antenna 110 and the mixer 205 .

The antenna members 110 and 120 transmit a signal received from the distributor 160 as a transmission wave 2 and receive a reception wave 4 reflected from the ground surface. The antenna members 110 and 120 include a transmission antenna 110 for transmitting the transmission wave 2 and a reception antenna 120 for receiving the reception wave 4 .

In the embodiment of the present invention, the transmitting antenna 110 is connected to the operating range setting member 300, the squint angle ( Φ _sq ) can be adjusted by the control of the operating range setting member 300 .

The mixer 205 mixes the signal transmitted through the divider 160 and the reception wave 4 received from the reception antenna 120 and transmits it to the raw data generating member 210 .

2 is a diagram showing the geometry of an aircraft equipped with a directional angle SAR-based high-resolution image restoration system according to an embodiment of the present invention.

축은 항공기의 진행방향,

은 경사거리방향을 나타내는 것으로 항공기 진행방향에서 목표물 중심(f(x_c,y_c))으로 향하는 방향으로 항공기의 진행방향(

)에 수직한 방향을 나타낸다.

축,

축,

축은 각각 지표면을 기준으로 하는 직교좌표계에서 항공기의 진행방향(

축), 항공기의 진행방향에 수직하고 지표면에 평행한 방향(

축), 지상으로부터 항공기로부터 향하는 수직방향(

축)을 나타낸다. f(x_c,y_c)은 지표면 상에서 레이더의 전자파를 반사하는 물체가 존재하는 목표물 중심을 나타내고, u_c는 안테나부재(110, 120)가 탑재된 항공기의 실제위치이며, u₀는 지향각(Φ _sq )이 0°인 경우에 항공기가 위치해야 하는 이상적인 위치이다. R_c는 항공기의 실제위치(u_c)와 목표물 중심(f(x_c,y_c)) 사이의 거리를 나타내고, R₀는 지향각(Φ _sq )이 0°인 경우에 항공기의 가상위치(u₀)와 목표물 중심(f(x_c,y_c)) 사이의 거리를 나타내며, Rc는 항공기의 실제위치(u_c)와 목표물 중심(f(x_c,y_c)) 사이의 거리를 나타낸다. Φ _BW 는 반전력빔폭을 나타내며, H ₀ 는 항공기의 비행고도를 나타내고, θ _i 는 전파 입사각을 나타낸다.2,

The axis is the direction of the aircraft,

is the direction of the inclination distance, from the direction of the aircraft to the center of the target (f(x _c , y _c )).

) is the direction perpendicular to the

axis,

axis,

Each axis represents the direction of travel (

axis), the direction perpendicular to the direction of travel of the aircraft and parallel to the ground surface (

axis), the vertical direction from the ground to the aircraft (

axis). f(x _c ,y _c ) represents the center of the target where an object reflecting electromagnetic waves of the radar exists on the ground surface, u _c is the actual position of the aircraft on which the antenna members 110 and 120 are mounted, and u ₀ is the orientation angle This is the ideal position where the aircraft should be located if ( Φ _sq ) is 0°. R _c represents the distance between the actual position of the aircraft (u _c ) and the center of the target (f(x _c , y _c )), and _{R 0} is the virtual position ( represents the distance between u ₀ ) and the center of the target (f(x _c ,y _c )), and Rc represents the distance between the actual position of the aircraft (u _c ) and the center of the target (f(x _c ,y _c )) . Φ _BW represents the reverse force beam width, H ₀ represents the flight altitude of the aircraft, and θ _i represents the radio wave incident angle.

방향으로 이동한다. 조사 대상이 되는 목표물 중심 f(x_c, y_c)은 지표면상(z_c=0)에 위치한다.A directional angle SAR-based high-resolution image restoration system according to an embodiment of the present invention is carried out in a state of being mounted on an aircraft.

move in the direction The target center f(x _c , y _c ) to be investigated is located on the earth's surface (z _c = 0).

1 and 2 , the raw data generating member 210 measures the distance between the receiving antenna 120 and the target center f(x _c , y _c ) of the ground surface from the signal received from the mixer 205, Generate raw data indicating the position of the target center f(x _c , y _c ).

For example, the target center corresponds to each of the pixels (x _i , y _j ) in the composite aperture, and the raw data generating member 210 corresponds to each of the pixels (x _i , y _j ) in the composite aperture. You can create raw data.

The raw data may be Frequency Modulated Continuous Wave - Synthetic Aperture Radar (FMCW-SAR) data (s(t,u)) measured by the aircraft. The raw data s(t, u) may be expressed as a variable of time t and the position u of the antenna members 110 and 120 mounted on the aircraft. For example, the raw data (s(t,u)) includes a sampling time (t), a center frequency (f ₀ ), a modulation rate (K _r ), a position (u) of the antenna members 110 and 120, and a target delay. It may also be expressed in the form of an exponential function related to time (τ), signal strength components, etc. (Republic of Korea Patent Registration No. 10-2090318).

[Equation 1] shows the FMCW signal-based directional angle SAR received signal model representing the received signal.

[Equation 1]

In [Equation 1], S ₀ (t) represents the received signal data as a function of time (t), f ₀ represents the center frequency, and K _r represents the modulation rate.

Using [Equation 1] as a reference signal and applying the target delay time τ ₀ (u) according to the position (u) of the antenna members 110 and 120 mounted on the aircraft, the received signal S _r is [Equation 2] ], it can be expressed as a function of time (t) and position (u).

[Equation 2]

In addition, when 'delayed de-chirp' is applied by applying a delay time (d) to time (t) for signal processing, the reference signal (S _d ) is time (t) as in [Equation 3] can be expressed as a function of

[Equation 3]

If frequency down conversion is applied to the received signal using [Equation 2] and [Equation 3], it can be expressed as [Equation 4].

[Equation 4]

[Equation 5] represents the target delay time τ(u) to which the 'delayed de-chirp' of [Equation 4] is applied.

[Equation 5]

[Equation 4] represents the raw data (s(t, u)) generated by the raw data generating member 210 as a time domain received signal model including a beat frequency component.

The orientation angle correcting member 220 receives the raw data from the raw data generating member 210 and corrects an error due to the orientation angle. In this embodiment, the orientation angle correcting member 220 is connected to the raw data generating member 210, and the raw data s(t, u) is rotated by the orientation angle φ _sq on the distance-Doppler frequency domain. Change the third corrected raw data (s'(f,k _u ')) and change the corrected third corrected raw data (s'(f,k _u ')) to the displacement according to the movement of the aircraft, the orientation angle ( φ _sq ) It is compensated in the state rotated as much as possible. Hereinafter, the directivity angle correcting member 220 will be described in detail.

FIG. 3 is a block diagram illustrating the orientation angle correcting member shown in FIG. 1 .

') 상의 위치를 나타내며, s(f,u')는 회전 리샘플링부(227)에 의해 지향각(Φ _sq)만큼 회전시킨 좌표계(

') 상으로 투영된 제1 보정 원시데이터를 나타내고, k_u'은 푸리에 변환된 거리-도플러 영역 상에서 지향각(Φ _sq)만큼 회전된 도플러 주파수를 나타내며, s(f,k'_u)는 푸리에 변환된 거리-도플러 영역으로 투영된 회전된 제2 보정 원시데이터를 나타내고, s'(f,k'_u)는 궤적 특성함수(Range Cell Migration; RCM) 생성부(231)에 의해 생성된 제3 보정 원시데이터를 나타내며, S'_M(f,k'_u)은 제3 보정 원시데이터(s'(f,k'_u))에 대응되는 정합필터(matched filter)를 나타내며, f'(x,y)는 (x,y)위치에서의 각 화소별로 보정된 제4 보정 데이터를 나타내며, f_c(x,y)는 데이터 역회전부(237)에 의해 제4 보정 데이터(f'(x,y))를 지향각(Φ _sq )만큼 역회전시켜서 생성되는 복원된 예비영상 데이터 또는 복원된 최종영상 데이터를 나타낸다. 예비영상 데이터는 안정영역(도 22의 c)내의 지향각(φ _sq ) 및 방위방향 반전력빔폭(φ_BW)을 구하는 과정에서 예비적으로 복원되는 영상을 위한 데이터를 의미하고, 최종영상 데이터는 안정영역(도 22의 c)내의 지향각(φ _sq ) 및 방위방향 반전력빔폭(φ_BW)을 구한 이후에 최종적으로 복원되는 영상을 위한 데이터를 의미한다. 이하, '복원영상' 이라고 하면, 예비영상 및 최종영상 중의 어느 하나를 의미하는 것으로 해석될 수 있다.In FIG. 3 , t represents time, u represents the positions of the antenna members 110 and 120 according to the traveling direction of the aircraft, and s(t, u) represents the raw data generated by the raw data generating member 210. where f represents frequency (or bit frequency), S _BB (f,u) represents baseband conversion, and Fourier transforms raw data (s(t,u)) with respect to time (t) For one data, it has a relation of a kind of matched filter, u' is the coordinates (u) of the antenna members 110 and 120 according to the traveling direction of the aircraft by the raw data rotation resampling unit 227. The coordinate system rotated by Φ _sq (

') represents the position on the image, and s(f,u') is the coordinate system rotated by the orientation angle Φ _sq by the rotation resampling unit 227 (

') represents the first corrected raw data projected onto the image, k _u ' represents the Doppler frequency rotated by the orientation angle Φ _sq on the Fourier-transformed distance-Doppler domain, and s(f,k' _u ) is the Fourier transform represents the rotated second corrected raw data projected to the transformed distance-Doppler region, and s'(f,k' _u ) is the third generated by the Range Cell Migration (RCM) generator 231 . Represents the corrected raw data, S' _M (f,k' _u ) represents a matched filter corresponding to the third corrected raw data (s'(f,k' _u )), f'(x, y) denotes the fourth correction data corrected for each pixel at the (x,y) position, and f _c (x,y) denotes the fourth correction data (f'(x,y) by the data reverse rotation unit 237 . ))) is reversely rotated by the orientation angle ( Φ _sq ) to indicate the restored preliminary image data or the restored final image data. Preliminary image data means data for an image that is preliminarily reconstructed in the process of obtaining an orientation angle ( φ _sq ) and an azimuth reverse power beam width (φ _BW ) within the stable region (c in FIG. 22), and the final image data is It means data for an image that is finally reconstructed after obtaining the directional angle ( φ _sq ) and the azimuth reverse force beam width (φ _BW ) in the stable region (c in FIG. 22 ). Hereinafter, the word 'reconstructed image' may be interpreted as meaning any one of a preliminary image and a final image.

1 to 3 , the orientation angle correcting member 220 includes a first Fourier transform unit 221 , a raw data preprocessor 223 , a second Fourier transform unit 229 , and a trajectory characteristic function (Range Cell Migration). ; RCM) includes a generator 231 , a second data mixing unit 233 , an inverse Fourier transform unit 235 , and an inverse data rotation unit 237 .

The first Fourier transform unit 221 performs a first Fourier transform with respect to time t on the raw data s(t, u) received from the raw data generator 210 to perform a first Fourier transform Transform data (s(f, u)) is generated.

FIG. 4 is a conceptual diagram illustrating a process of rotating raw data by the raw data preprocessor shown in FIG. 3 .

축은 지표면을 기준으로 하는 직교좌표계에서 항공기의 진행방향을 나타내는 것으로

축으로 표시되는 항공기의 진행방향과 동일하다.

은 경사거리방향을 나타내는 것으로 항공기 진행방향에서 목표물 중심(f(x_c,y_c))으로 향하는 방향을 나타내며, 항공기의 진행방향(

)에 수직한 방향을 나타낸다. (x_c,y_c)는 목표물 중심의 좌표를 나타낸다.

는 전파진행방향의 벡터성분을 나타내며,

는 안테나부재(110, 120)가 탑재된 항공기 진행방향의 벡터성분을 나타내며,

는 항공기 진행방향의 벡터(

)를 지향각(Φ _sq)만큼 회전시킨 벡터성분을 나타내며,

는 전파진행방향의 벡터(

)를 지향각(Φ _sq)만큼 회전시킨 벡터성분을 나타낸다. u₀는 지향각오류가 없는 경우에 항공기가 위치하는 이상적인 위치를 나타내며, u_c는 안테나부재(110,120)가 탑재된 항공기의 실제 위치를 나타내며, Rc는 항공기의 실제위치(u_c)와 목표물 중심(f(x_c,y_c)) 사이의 거리를 나타낸다.2 and 4,

The axis represents the direction of travel of the aircraft in the Cartesian coordinate system with respect to the earth's surface.

It is the same as the direction of travel of the aircraft indicated by the axis.

denotes the direction of the inclination distance, indicating the direction from the aircraft's moving direction to the target center (f(x _c ,y _c )), and the aircraft's moving direction (

) is the direction perpendicular to the (x _c ,y _c ) represents the coordinates of the target center.

represents the vector component of the propagation direction,

represents the vector component of the traveling direction of the aircraft on which the antenna members 110 and 120 are mounted,

is the vector of the aircraft's travel direction (

) represents the vector component rotated by the orientation angle ( Φ _sq ),

is the vector of the propagation direction (

) represents the vector component rotated by the orientation angle ( Φ _sq ). u ₀ represents the ideal position where the aircraft is located when there is no orientation angle error, u _c represents the actual location of the aircraft equipped with the antenna members 110 and 120, and Rc is the actual position of the aircraft (u _c ) and the center of the target. It represents the distance between (f(x _c ,y _c )).

)을 고려하여 비틀린 좌표로 표현된 항공기 이동에 따른 거리방정식(range cell migration; RCM) 기준궤적을 나타내고, '(3) squint (rotated grid)'는 목표물 중심(R₀, y_c)을 기준으로 지향각(Φ _sq)만큼 회전시킨 좌표정보와 RCM 궤적을 나타낸다.In FIG. 4, '(1) zero-squint' represents a range cell migration (RCM) reference trajectory when the directivity angle ( Φ _sq ) is 0°, and '(2) squint (skewed grid)' is the propagation direction (

), the range cell migration (RCM) reference trajectory according to the aircraft movement expressed in twisted coordinates is shown, and '(3) squint (rotated grid)' is based on the target center (R ₀ , y _c ). Coordinate information and RCM trajectory rotated by the orientation angle ( Φ _sq ) are shown.

The raw data preprocessor 223 rotates the first Fourier transform data s(f, u) by the orientation angle Φ _sq by the first Fourier transform unit 221 to rotate the first corrected raw data s(f) ,u')).

Specifically, the raw data preprocessor 223 includes a first data mixing unit 225 and a rotation resampling unit 227 .

The first data mixing unit 225 performs a first-order mixing function by multiplying the first-order Fourier-transformed data by a baseband conversion filter (S _BB (f, u)) to generate first mixed data. The baseband transform filter S _BB (f, u) has a kind of matched filter relation with respect to the first-order Fourier transform data.

The rotation resampling unit 227 rotates the first mixed data first mixed by the first data mixing unit 225 by the orientation angle Φ _sq to generate the first corrected raw data (s(f, u')) create Hereinafter, the function of the rotation resampling unit 227 will be described in detail.

'(3) squint (rotated grid)' of FIG. 4 corresponds to the coordinate information (R',u') rotated by the orientation angle Φ _sq , and the rotation resampling unit 227 expresses the following [Equation 6] Corresponding to the coordinate information (R',u') rotated by the orientation angle ( Φ _sq ) by using it can be expressed by the orientation angle SAR distance equation (R'(u')).

[Equation 6]

In [Equation 6], A(u'), and u' may be represented as in [Equation 7] and [Equation 8] below.

[Equation 7]

[Equation 8]

[Equation 6] shows the directivity angle SAR distance equation (R'(u')) when the directivity angle ( Φ _{sq )} is not 0°. ] can be seen as the same expression.

The rotation resampling unit 227 applies the directivity angle SAR distance equation (R'(u')) of [Equation 6] to the following [Equation 9] to rotate the primary mixed data by the directivity angle ( Φ _sq ). The first corrected raw data s(f, u') is generated.

[Equation 9]

') 상의 안테나 부재(110, 120) 위치를 나타내며, τ'은 목표물 지연시간을 나타내며, R'(u')는 지향각(Φ _sq)만큼 회전시킨 좌표계(

') 상의 안테나부재(110, 120)의 위치(u')를 변수로 하는 궤적 특성함수를 나타낸다. 궤적 특성함수는 후술될 궤적 특성함수(Range Cell Migration; RCM) 생성부(231)에 관한 설명에서 상술한다.In [Equation 8], f represents the frequency, and u' is the coordinate system rotated by the orientation angle ( Φ _sq ) (

') represents the position of the antenna _members 110 and 120 on

') represents a trajectory characteristic function with the position (u') of the antenna members 110 and 120 on it as a variable. The trajectory characteristic function will be described in detail in the description of the trajectory characteristic function (Range Cell Migration; RCM) generator 231, which will be described later.

3 and [Equation 9], the second Fourier transform unit 229 is the first corrected raw data rotated by the orientation angle Φ _sq by the rotation resampling unit 227 (s(f, u') ) is applied, and the second corrected raw data (s(f,k' _u )) is obtained by performing Fourier transformation on the aircraft position variable (u') on the coordinate system rotated by the orientation angle ( Φ _sq ). create

The data transformed by the second Fourier transform unit 229 is the rotated second corrected raw data s(f,k' _u ) in the Range-Doppler region rotated by the orientation angle Φ _sq . The rotated second corrected raw data s(f,k' _u ) in the Range-Doppler region rotated by the orientation angle Φ _sq is calculated by the frequency f and the orientation angle Φ _sq . It can be expressed as a function of the rotated Doppler frequency (k' _u ).

') 상의 안테나 부재(110, 120) 위치(u')를 거리-도플러(Range-Doppler) 영역 내에서 지향각(Φ _sq)만큼 회전된 도플러 주파수(k_u')로 변환한다. 이론에 의해 본 발명의 권리범위를 제한하려는 것은 아니지만, [식 10]는 [식 4]에 [식 6] 내지 [식 8]을 대입한 푸리에변환 적분식을 나타내며, 정지위상근사법(Principle of Stationary Phase; POSP)을 이용한다. 다른 실시예에서, 다양한 수치적 분석기법(예, interpolation, curve-fitting, re-sampling 등)이 사용될 수도 있다.[ _Equation 10 The coordinate system rotated by the orientation angle ( Φ _sq ) using

') of the antenna members 110 and 120 on the position (u') is converted into a Doppler frequency (k _u ') rotated by a beam angle Φ _sq in a Range-Doppler region. Although it is not intended to limit the scope of the present invention by theory, [Equation 10] represents a Fourier transform integral expression by substituting [Equation 6] to [Equation 8] in [Equation 4], Phase; POSP) is used. In another embodiment, various numerical analysis techniques (eg, interpolation, curve-fitting, re-sampling, etc.) may be used.

[Equation 10]

') 상의 안테나 부재(110, 120) 위치(u', 방위방향샘플)과 도플러주파수(Ku')의 관계식인 [식 12]을구할 수 있다. 본 실시예에서, [식 10]에서 위상함수의 2차항(τ'²(u'))은 잔류 비디오 위상(Residual Video Phase; RVP) 필터과정으로 제거될 수 있으며, 그 값이 작아서 영상복원과정에서 무시될 수도 있다.According to the stationary _phase approximation method, the coordinate system (

[Equation 12], which is a relational expression between the position (u', azimuth sample) of the antenna members 110 and 120 on ') and the Doppler frequency (Ku'), can be obtained. In this embodiment, the quadratic term (τ' ² (u')) of the phase function in [Equation 10] can be removed by a residual video phase (RVP) filter process, and its value is small, so the image restoration process may be ignored in

[Equation 11]

')와 거리방정식(R'(u'))을 적용한 지향각 SAR 기반 고해상도 영상복원 시스템에 최적화된 방위방향샘플(u')과 도플러주파수(K_u')의 관계식은 [식 12]과 같이 나타낸다.In an embodiment of the present invention, the coordinate system rotated by the orientation angle Φ _sq (

') and the distance equation (R'(u')) are applied to the azimuth direction sample (u') and the Doppler frequency (K _u ') optimized for the SAR-based high-resolution image restoration system, as shown in [Equation 12]. indicates.

[Equation 12]

The range cell migration (RCM) generator 231 uses [Equation 12] and [Equation 13] to rotate the second corrected raw data on the distance-Doppler region (s(f,k _u ')) The third corrected raw data (s'(f,k _u ')) is generated by compensating for the displacement according to the aircraft position variable (u') on the coordinate system rotated by the orientation angle ( Φ _sq ).

[Equation 13]

In [Equation 13], A(Ku') and B are the same as [Equation 14] below.

[Equation 14]

In one embodiment, the trajectory characteristic function generator 231 may further include a function of correcting the trajectory characteristic function by the distance difference ΔR' rotated by the orientation angle Φ _sq using [Equation 15]. have.

[Equation 15]

') 상의 안테나부재(110, 120)의 위치(u')를 변수로 하는 궤적 특성함수를 나타내며, R'(k_u')는 거리-도플러(Range-Doppler) 영역 내의 보정된 궤적 특성함수를 나타내고, R₀는 지향각(Φ _sq)만큼 회전시킨 좌표계 내에서 중심거리를 나타낸다.In [Equation 13] and [Equation 15], k _u ' represents the Doppler frequency rotated by the orientation angle Φ _sq on the Fourier transformed distance-Doppler domain, and u' is the antenna member 110, 120) represents the position on the coordinate system in which the coordinates u are rotated by the orientation angle Φ _sq by the rotation resampling unit 227, and A(k _u ') and A(u') are respectively [Equation 14] and [Equation 7] is shown, and R'(u') is a coordinate system rotated by an orientation angle ( Φ _sq ) (

') represents a trajectory characteristic function using the position ( _u ') of the antenna members 110 and 120 on and R ₀ represents the center distance within the coordinate system rotated by the orientation angle ( Φ _sq ).

As described above, the trajectory characteristic function generator 231 calculates the displacement according to the amount of movement of the aircraft from the second corrected raw data s(f,k _u ') using [Equation 13] and [Equation 15] described above. By compensating, the third corrected raw data s'(f,k _u ') is generated.

The second data mixing unit 233 is matched with the third corrected raw data s'(f,k _u ') on the distance-Doppler region in which the displacement according to the amount of movement of the aircraft is compensated by the trajectory characteristic function generating unit 231 . Multiply by filter (S _M '(f,k _u ')).

The inverse Fourier transform unit 235 includes the third corrected raw data s'(f,k _u ') on the distance-Doppler region mixed by the second data mixing unit 233 and the matched filter S _M '(f, k _u '))), the generated second mixed data is inversely transformed into a Doppler frequency (k _u ') rotated by the orientation angle ( Φ _sq ), and the fourth correction data (f) according to the coordinates (x,y) on the earth's surface '(x,y)) is created.

The data reverse rotation unit 237 reversely rotates the fourth correction data f'(x,y) by the orientation angle Φ _sq to generate the restored image data f _c (x,y). In an embodiment of the present invention, the restored image data f _c (x, y) may be image data for the coordinates (x, y) of each pixel on the composite aperture.

The image restoration unit 240 restores image data for each pixel about the virtual target center by the directivity angle ( Φ _sq ) and the azimuth reverse force beam width ( Φ _BW ) set by the operating range control member 300 to be described later. Restoring it as a preliminary image on the composite aperture, or using the orientation angle ( Φ _sq ) and the azimuth reverse force beam width ( Φ _BW ) in the stable region ('c' in FIG. 22) set by the operating range control member 300 It is possible to restore the final image on the composite aperture by combining the reconstructed image data for each pixel that has been scanned for the real terrain.

The operating range control member 300 is connected to the antenna members 110 and 120, the waveform generator 150, the directivity angle correction member 220, and the image restoration unit 240 so that the raw data converge within a correctable range. The antenna members 110 and 120 and the directivity angle correction member 220 are controlled.

5 is a block diagram illustrating the operating range control member shown in FIG. 1 .

1 and 5 , the operating range control unit 300 includes a nonlinear error analysis unit 310 , a resolution analysis unit 320 , and an operating range setting unit 330 .

The nonlinear error analysis unit 310 analyzes the nonlinear characteristic of the Doppler frequency (k _u ') of [Equation 12] according to the effective length of the synthetic aperture (L in FIG. 2) so that the raw data come within a preset error range. Variables such as the directivity angle ( ϕ _sq ), the azimuth direction reversal force beam width (ϕ _BW ), the maximum error directivity angle, the maximum error reversal force beam width, and the combined aperture effective length (L in FIG. 2 ) are primarily determined. The maximum error directivity angle means the directivity angle ( φ _sq ) at which the Doppler frequency error (Δk _u ') has the maximum value, and the maximum error reversal power beam width is the direction in which the Doppler frequency error (Δk _u ') has the maximum value. The direction reversal force beam width (φ _BW ) will be described later with reference to FIG. 13 .

In one embodiment, the nonlinear error analysis unit 310 uses [Equation 16] to determine the effective length of the composite aperture (L in FIG. 2), the antenna reverse power beam width (φ _BW ), the flight altitude (H ₀ ), and the radio wave incident angle. Variables such as (θ _i ) and center frequency (f ₀ ) may be determined.

[Equation 16]

Specifically, the nonlinear error analysis unit ₃₁₀ is an _azimuth direction distance ( By analyzing the Doppler frequency error (Δk _u ') according to azimuth, u'), the orientation angle ( φ _sq ) at which the Doppler frequency error (Δk _u ') does not exceed the threshold value, the azimuth reverse force beam width (φ _BW ) ), the maximum error direction angle, the maximum error half-power beam width, the effective length of the composite aperture (L), and the center frequency (f ₀ ) are determined. The threshold value may be set by inputting a preset value to the nonlinear error analysis unit 310 or the nonlinear error analysis unit 310 using the restored image restored by the image restoration unit 240 to set the threshold value.

For example, the nonlinear error analyzer 310 may analyze the Doppler frequency error (Δk _u ') using a root mean square (RMS) method as shown in [Equation 17] below.

[Equation 17]

In [Equation 17], N is the number of samples indicating the positions of the antenna members 110 and 120 in the composite aperture plane, and u' _n is the coordinate system (u') rotated by the orientation angle Φ _sq in the composite aperture plane. Corresponds to each position (sample) of the antenna members 110 and 120 according to the movement of the aircraft, k _u '(u') corresponds to [Equation 12], and the fit(u') function is approximated by a linear equation ( fitting) function.

The nonlinear error analysis unit 310 uses [Equation 12] to [Equation 17], the orientation angle ( Φ _sq ) at which the Doppler frequency error (Δk _u ') is distributed within the critical point, and the effective length of the synthetic aperture (L) ), the half-power beam width ( Φ _BW ), the center frequency (f ₀ ), the maximum error directivity angle, and the maximum error half-power beam width are determined. For example, the critical point of the Doppler frequency error (Δk _u ') may be 1.5 rad/m, the directivity angle ( Φ _sq ), the effective length of the composite aperture (L), the half-force beam width ( Φ _BW ), and the center frequency In (f ₀ ), the Doppler frequency error (Δk _u ') may be reduced by first adjusting the beam angle ( φ _sq ) and/or the azimuth reverse force beam width (φ _BW ).

In an embodiment of the present invention, when the Doppler frequency error (Δk _u ') does not fall within the critical point even by adjusting the beam angle ( φ _sq ) and/or the azimuth reverse force beam width (φ _BW ), the effective length of the composite aperture (L) and/or the center frequency (f ₀ ) can be adjusted. The reason for first adjusting the directivity angle ( φ _sq ) and/or the azimuth reversing force beam width (φ _BW ) is the directivity angle ( φ _sq ) and/or the azimuth direction reversing power beam width (φ _BW ) is the antenna member (110, 120) A relatively accurate setting is possible by changing the direction of the waveform generator 150, but the effective length of the composite aperture (L) and/or the center frequency (f ₀ ) are secondary numerical values that are changed according to the setting change. This is because it is not easy to set an exact value in advance.

Hereinafter, the function of the nonlinear error analysis unit 310 will be described in more detail through comparative examples and examples of the present invention.

Comparative Example 1

6A is a graph showing a relationship between an azimuth distance and a Doppler frequency according to Comparative Example 1 of the present invention. In FIG. 6A , the horizontal axis represents the azimuth distance (azimuth, u), and the vertical axis represents the Doppler frequency (k _u ).

In this comparative example 1, the orientation angle ( φ _sq ) is 0°, the flight altitude (H ₀ ) is 1 km, the synthetic aperture length (L) is 372 m, and the virtual position of the aircraft (u ₀ in FIG. 2 ) The distance (R ₀ ) between the target and the center of the target (f(x _c ,y _c )) was 1,414 m, and a SAR-based high-resolution image restoration system with an orientation angle with a half-power beam width (φ _BW ) of 15° was used. The high-resolution image restoration system based on the directional angle SAR was an X-band radar system.

Referring to FIG. 6a, when solving by applying the case where the directivity angle ( φ _sq ) is 0° to [Equation 10] to [Equation 12] using [Equation 4] and [Equation 5], the Doppler frequency (k _u ) can be expressed as in [Equation 18] below.

[Equation 18]

In [Equation 18], k denotes a propagation constant, and φ denotes an observation angle between the antenna members 110 and 120 and the target center f(x _c , y _c ).

The Doppler frequency (k _u ) increased linearly as the azimuth distance (azimuth, u) increased.

Comparative Example 2

6B is a graph showing a relationship between an azimuth direction distance and a Doppler frequency error according to Comparative Example 2 of the present invention. In FIG. 6B , the horizontal axis represents the azimuth distance (azimuth, u), and the vertical axis represents the Doppler frequency error (Δk _u ).

In the X-band radar system of Comparative Example 2, the heading angle ( φ _sq ) is 0°, the flight altitude (H ₀ ) is 1 km, and the virtual position of the aircraft (u ₀ in FIG. 2 ) and the target center (f) The distance (R ₀ ) between (x _c , y _c )) was 1,414 m, which was the same as in Comparative Example 1, but the reverse force beam width (φ _BW ) was changed to 3°, 6°, 9°, 12°, 15° By changing it, the Doppler frequency error (Δk _u ) was examined. As the reverse force beam width (φ _BW ) was changed to 3°, 6°, 9°, 12°, and 15°, the composite aperture length (L) was also changed to 74m, 148m, 222m, 297m, and 372m.

Referring to FIG. 6b , when the effect by the orientation angle ( φ _sq ) is removed, the Doppler frequency error (Δk _u ) is 0 at a point where the azimuth distance (azimuth, u) is 0m, and the azimuth distance As (azimuth, u) moved away from 0 m, the Doppler frequency error (Δk _u ) increased gently while drawing a parabola, then decreased again, and then rapidly increased again.

The reason that the Doppler frequency error (Δk u ) shows 0 at a point where the azimuth distance (azimuth, _u ) is 0 m is because the azimuth angle ( φ _sq ) is 0°.

According to Comparative Examples 1 and 2 of the present invention, when the effect by the directivity angle ( φ _sq ) is removed, the reverse force beam width (φ _BW ) is changed to 3° to 15°, and the composite aperture length (L) is Even if it is changed to 74m to 372m, the Doppler frequency error (Δk _u ) does not exceed the threshold value of 1.5 rad/m.

Experimental Example 1

7A is a graph illustrating the relationship between the azimuth distance and the Doppler frequency analyzed by the nonlinear error analyzer of FIG. 5 . In FIG. 7A , the horizontal axis represents the azimuth distance (azimuth, u') in the coordinate system tilted by the orientation angle ( φ _sq ), and the vertical axis represents the Doppler frequency (k _u ') in the coordinate system tilted by the orientation angle ( φ _sq ). ) is indicated.

In this Experimental Example 1, the orientation angle ( φ _sq ) is 15°, the flight altitude (H ₀ ) is 1 km, the synthetic aperture length (L) is 372 m, and the virtual position of the aircraft (u ₀ in FIG. 2 ) and The distance (R ₀ ) between the target centers (f(x _c ,y _c )) was 1,414 m, and a SAR-based high-resolution image restoration system with an orientation angle of 15° with a half-power beam width (φ _BW ) was used. The high-resolution image restoration system based on the directional angle SAR was an X-band radar system.

Referring to FIG. 7A , the Doppler frequency k _u ' linearly increased as the azimuth distance (azimuth, u') increased.

Experimental Example 2

FIG. 7B is a graph showing the relationship between the azimuth direction distance and the Doppler frequency error analyzed by the nonlinear error analyzer of FIG. 5 . In FIG. 7B , the horizontal axis represents the azimuth distance (azimuth, u') in the coordinate system tilted by the orientation angle φ _sq , and the vertical axis represents the Doppler frequency error (Δk) in the coordinate system tilted by the orientation angle φ _sq . _u ').

In the X-band radar system of Experimental Example 2, the heading angle ( φ _sq ) is 15°, the flight altitude (H ₀ ) is 1 km, the virtual position of the aircraft (u ₀ in FIG. 2 ) and the target center (f(x) The distance (R ₀ ) between _c , y _c )) was 1,414 m, which was the same as in Example 1, but the reverse force beam width (φ _BW ) was changed to 3°, 6°, 9°, 12°, 15° to Doppler The frequency error (Δk _u ) was examined. As the reverse force beam width (φ _BW ) was changed to 3°, 6°, 9°, 12°, and 15°, the composite aperture length (L) was also changed to 74m, 148m, 222m, 297m, and 372m.

Referring to FIG. 7B , when the directivity angle ( φ _sq ) is 15°, the Doppler frequency error (Δk _u ) exhibits a nonlinear behavior, and as the azimuth distance (azimuth, u) increases in the negative (-) direction, The Doppler frequency error (Δk _u ) showed a pattern of increasing gently while drawing a parabola and then decreasing again.

The reason that the Doppler frequency error (Δk _u ) shows the minimum value (0) at the point where the azimuth distance (azimuth, u') is negative (-) is that the directivity angle ( φ _sq ) is 15°, so the antenna members 110, 120 ) because the actual position (u _c in FIG. 2 ) and the shortest distance position (u ₀ in FIG. 2 ) are different from each other.

According to Comparative Examples 1 and 2 of the present invention, the directivity angle ( φ _sq ) is 15°, the half-force beam width (φ _BW ) is 15°, and the combined aperture length (L) is 372 m. Doppler frequency error ( Δk _u ) was found to exceed the critical value of 1.5 rad/m.

Example 1

8 is a graph illustrating a synthetic aperture length, a directivity angle, and a Doppler frequency error analyzed by the nonlinear error analyzer of FIG. 5 .

In FIG. 8 , the horizontal axis represents the directivity angle ( φ _sq ), the vertical axis represents the azimuth reverse force beam width (Azimuth HPBW, φ _BW ), and the height axis represents the square mean of the Doppler frequency error (Δk _u ', rad/m). (Root Mean Square; RMS).

In the X-band radar system of Example 1, the flight altitude (H ₀ ) is 1 km, the radio wave incidence angle (θ _i ) of the transmitted wave (2 in FIG. 1 ) is 45°, and the virtual position of the aircraft (u in FIG. 2 ) The distance (R ₀ ) between ₀ ) and the target center (f(x _c ,y _c )) was 1,414 m, and the center frequency (f ₀ ) was 9.65 GHz. The beam angle ( φ _sq ) was changed from 0° to 80° and the azimuth reverse force beam width (φ _BW ) was changed from 0° to 15°, and the Doppler frequency error (Δk _u ', rad/m) was analyzed. .

Referring to FIG. 8 , the Doppler frequency error (Δk _u ', rad/m) behaved non-linearly according to changes in the beam angle ( φ _sq ) and the azimuth reverse force beam width (φ _BW ), and the beam angle ( φ _sq ) ) was 30° and the azimuth reverse force beam width (φ _BW ) was 15°, showing the maximum value of 1.15 rad/m of Doppler frequency error (Δk _u ').

Hereinafter, the function of the nonlinear difference analysis unit according to various flight altitudes and radio wave incidence angles will be described along with various embodiments.

9A and 9B are diagrams showing geometric structures of the behavior of the nonlinear error analyzer shown in FIG. 5 according to various flight altitudes and radio wave incident angles.

9a and 9b, L ₁ , L ₂ represent the composite aperture length, θ _i , θ _i1 , θ _i2 represent the radio wave incident angle, H ₀ , H ₁ , H ₂ represent the flight altitude of the aircraft, Φ _BW represents the reverse force beam width, and R ₀ represents the distance between the virtual position of the aircraft and the center of the target.

Although not intended to limit the scope of the present invention by theory, the function of the nonlinear error analysis unit according to the change of the flight altitude and the radio wave incidence angle will be described with reference to FIGS. 10A to 12B.

Example 2

In Embodiment 2, when the flight altitudes (H ₁ , H ₂ ) are changed, the function of the nonlinear error analysis unit 310 will be described.

10A and 10B are graphs showing the synthesized aperture length, the orientation angle, and the Doppler frequency error analyzed by the nonlinear error analyzer of FIG. 5 when the flight altitude of the aircraft is different.

9A and 10A , the horizontal axis represents the directivity angle ( φ _sq ), the vertical axis represents the azimuth reverse force beam width (Azimuth HPBW, φ _BW ), and the height axis represents the Doppler frequency error (Δk _u ', rad/ m) represents the root mean square (RMS).

In the X-band radar system of FIG. 9A, the flight altitude (H ₀ ) is 1 km, the radio wave incidence angle (θ _i ) of the transmitted wave (2 in FIG. 1) is 45°, and the virtual position of the aircraft (u ₀ in FIG. 2) ) and the distance (R ₀ ) between the target center (f(x _c ,y _c )) was 1,414 m, and the center frequency (f ₀ ) was 9.65 GHz. The beam angle ( φ _sq ) was changed from 0° to 80°, and the azimuth reverse force beam width (φ _BW ) was changed from 0° to 15°, and the Doppler frequency error (Δk _u ', rad/m) was analyzed. .

The Doppler frequency error (Δk _u ', rad/m) behaved nonlinearly according to changes in the beam angle ( φ _sq ) and the azimuth reverse force beam width (φ _{BW )} . The direction reversal force beam width (φ _BW ) showed the maximum value of 1.15 rad/m of Doppler frequency error (Δk _u ') at 15°.

In FIG. 10b, except that the flight altitude (H ₀ ) is 5 km, the remaining numerical values are the same as in FIG. 10a.

The Doppler frequency error (Δk _u ', rad/m) behaved nonlinearly according to the change of the beam angle ( φ _sq ) and the azimuth reverse force beam width (φ _BW ), and the beam angle ( φ _sq ) was 30° and the azimuth The direction reversal force beam width (φ _BW ) showed the maximum value of 1.15 rad/m of Doppler frequency error (Δk _u ') at 15°.

The Doppler frequency error (Δk _u ') of FIG. 10B was the same as that of FIG. 10A.

Referring to FIGS. 10A and 10B , there was no change in the Doppler frequency error (Δk _u ') even if the flight altitude (H ₀ ) was changed.

Example 3

In the third embodiment, when the radio wave incident angles θ _i1 and θ _i2 are changed, the function of the nonlinear error analyzer 310 will be described.

11A and 11B are graphs showing a composite aperture length, a directivity angle, and a Doppler frequency error analyzed by the nonlinear error analyzer of FIG. 5 when the aircraft radio wave incident angles are different.

9B and 11A , the horizontal axis represents the directivity angle ( φ _sq ), the vertical axis represents the azimuth reverse force beam width (Azimuth HPBW, φ _BW ), and the height axis represents the Doppler frequency error (Δk _u ', rad/ m) represents the root mean square (RMS).

In the X-band radar system of FIG. 11A , the flight altitude (H ₀ ) is 1 km, the radio wave incidence angle (θ _i1 ) of the transmitted wave (2 in FIG. 1) is 30°, and the virtual position of the aircraft (u ₀ in FIG. 2) ) and the distance (R ₀ ) between the target center (f(x _c ,y _c )) was 1,414 m, and the center frequency (f ₀ ) was 9.65 GHz. The beam angle ( φ _sq ) was changed from 0° to 80° and the azimuth reverse force beam width (φ _BW ) was changed from 0° to 15°, and the Doppler frequency error (Δk _u ', rad/m) was analyzed. .

The Doppler frequency error (Δk _u ', rad/m) behaved nonlinearly according to changes in the beam angle ( φ _sq ) and the azimuth reverse force beam width (φ _{BW )} . The direction reversal force beam width (φ _BW ) showed the maximum value of 1.15 rad/m of Doppler frequency error (Δk _u ') at 15°.

In FIG. 11B , the other numerical values were the same as those of FIG. 11A except that the radio wave incident angle θ _i2 was 60°.

The Doppler frequency error (Δk _u ', rad/m) behaved nonlinearly according to changes in the beam angle ( φ _sq ) and the azimuth reverse force beam width (φ _{BW )} . The direction reversal force beam width (φ _BW ) showed the maximum value of 1.15 rad/m of Doppler frequency error (Δk _u ') at 15°.

The Doppler frequency error (Δk _u ') of FIG. 11B was the same as that of FIG. 11A.

Referring to FIGS. 11A and 11B , even when the radio wave incident angles θ _i1 , θ _i2 are changed, the Doppler frequency error Δk _u ′ did not change.

Example 4

In the fourth embodiment, when the center frequency f ₀ is changed, the function of the nonlinear error analysis unit 310 will be described.

12A and 12B are graphs illustrating a composite aperture length, a directivity angle, and a Doppler frequency error analyzed by the nonlinear error analyzer of FIG. 5 when the aircraft radio wave incident angles are different.

Referring to FIG. 12A , the horizontal axis represents the directivity angle ( φ _sq ), the vertical axis represents the azimuth reverse force beam width (Azimuth HPBW, φ _BW ), and the height axis represents the Doppler frequency error (Δk _u ', rad/m). It represents the root mean square (RMS).

In the X-band radar system of FIG. 12A , the flight altitude (H ₀ ) is 1 km, the radio wave incidence angle (θ _i1 ) of the transmitted wave (2 in FIG. 1) is 30°, and the virtual position of the aircraft (u ₀ in FIG. 2) ) and the distance (R ₀ ) between the target center (f(x _c ,y _c )) was 1,414 m, and the center frequency (f ₀ ) was 1.25 GHz. The beam angle ( φ _sq ) was changed from 0° to 80° and the azimuth reverse force beam width (φ _BW ) was changed from 0° to 15°, and the Doppler frequency error (Δk _u ', rad/m) was analyzed. .

The Doppler frequency error (Δk _u ', rad/m) behaved nonlinearly according to changes in the beam angle ( φ _sq ) and the azimuth reverse force beam width (φ _{BW )} . The direction reversal force beam width (φ _BW ) showed the maximum value of 0.15 rad/m of Doppler frequency error (Δk _u ') at 15°.

In FIG. 12b , the center frequency f ₀ is the same as that of FIG. 12a except that it is 15 GHz.

The Doppler frequency error (Δk _u ', rad/m) behaved nonlinearly according to changes in the beam angle ( φ _sq ) and the azimuth reverse force beam width (φ _{BW )} . The maximum value of the Doppler frequency error (Δk _u ') exceeded 2 rad/m when the direction reversal force beam width (φ _BW ) was 15°.

In FIG. 12b, the region in which the Doppler frequency error (Δk _u ') exceeded 1.15 rad/m was a region in which the directivity angle ( φ _sq ) was 17° to 50° and the azimuth reverse force beam width (φ _BW ) was 12° or more. .

12A and 12B , as the center frequency f ₀ increased, the Doppler frequency error Δk _u ′ rapidly increased.

Although not intending to limit the scope of the present invention by theory, the point at which the Doppler frequency error (Δk _u ') increases with the change of the center frequency (f ₀ ) is rotated by the orientation angle ( φ _sq ) in [Equation 12] This is because the Doppler frequency (k _u ') on the coordinate system is affected by the magnitude component (-4π/c-(f ₀ +f))) including the center frequency (f ₀ ). This is because the effective length of the composite aperture compared to the wavelength increases as the center frequency (f ₀ ) increases in the composite aperture having the same length (L), so the Doppler frequency error (Δk _u ') acting nonlinearly can be interpreted as increasing.

9A to 12B, the high-resolution image restoration system based on the directional angle SAR according to an embodiment of the present invention changes the geometric structure such as flight altitude (H ₁ , H ₂ ), radio incidence angle (θ _i1 , θ _i2 ), etc. , and has a characteristic that is dependent on the center frequency (f ₀ ).

Example 5

13 is a graph showing the Doppler frequency error (Δk _u ') according to the azimuth reverse force beam width (Azimuth HPBW, φ _BW ) and the beam angle ( φ _sq ) analyzed by the nonlinear error analyzer of FIG. 5 . In FIG. 13 , the horizontal axis represents the azimuth reverse force beam width (Azimuth HPBW, φ _BW ) and the vertical axis represents the directivity angle ( φ _sq ).

A high-resolution image restoration system based on an azimuth angle SAR having the specifications in [Table 1] was used.

Setting items set value note frequency band X-band BW=500 MHz Modulation rate (K _r ) 5e ^ll Hz/s t _sweep = 1ms Number of samples in the distance direction (Range bins) 1,252 samples fs≒1.2 MHz Azimuth bins 2001 samples Direction angle ( φ _sq ) 0° to 75° Reverse force beam width (φ _BW ) 1° to 15° Composite aperture length (L) 25m to 372m Antenna incident angle (θ _inc ) 45° Flight Altitude (H ₀ ) 1km (Based on ground distance)

13 and [Table 1], the directional angle SAR-based high-resolution image restoration system is an X-band radar system, the half-power beam width was 500 MHz, and the frequency modulation rate (Kr) is 5e ¹¹ Hz/s, which is irradiated every 1 ms. (t _sweep = 1ms), the number of samples in the distance direction (Range bins) was 1,252, and each sample had a frequency of 1.2 MHz (fs ≒ 1.2 MHz), and the number of samples in the azimuth direction (Azimuth bins) was 2,001, and transmission The wave incident angle (θ _inc ) of the wave (2 in FIG. 1) was 45°, the flight altitude (H ₀ ) was 1 km based on the ground distance, and the virtual position of the aircraft (u ₀ in FIG. 2 ) and the center of the target (f ( The distance (R ₀ ) between x _c ,y _c )) was 1,414 m. The Doppler frequency error (Δk _u ', rad/m) was analyzed while changing the beam angle ( φ _sq ) from 0° to 75° and the half-force beam width (φ _BW ) from 1° to 15°.

Referring to FIG. 13 , the nonlinear error analyzer 310 sets the threshold of the Doppler frequency error (Δk _u ', rad/m) to 0.15 rad/m. The threshold of the Doppler frequency error (Δk _u ', rad/m) is determined by comparing the restored images by variously changing the azimuth reverse power beam width (φ _BW ) while the beam angle ( φ _sq ) is the same. saved A method of obtaining a threshold of the Doppler frequency error (Δk _u ', rad/m) will be described later with reference to FIGS. 14 to 16 .

In FIG. 13 , the Doppler frequency error (Δk _u ', rad/m) exhibited the maximum value when the directivity angle ( φ _sq ) was 30° and the azimuth reverse force beam width was 6°. For example, in FIG. 13 , the beam angle ( φ _sq ) and the azimuth reverse force beam width (φ _BW ) at the apex (p) of the parabola where the Doppler frequency error (Δk _u ', rad/m) is a threshold value, respectively It becomes the maximum error directivity angle, and the maximum error reverse power beam width.

When the directivity angle ( φ _sq ) and the half-power beam width (φ _BW ) corresponding to the threshold value of the Doppler frequency error (Δk _u ', rad/m) are plotted, a parabolic shape is shown as shown by the solid line in FIG. 13 .

14 to 19 are images showing reconstructed images respectively corresponding to (1) to (6) of FIG. 13 .

In the case of (1), (2), (3) of FIG. 13, the Doppler frequency by changing the azimuth reverse force beam width (φ _BW ) to 5°, 7.5°, and 10°, respectively, at the same directivity angle ( φ _sq ) 30° The error (Δk _u ', rad/m) was measured. The Doppler frequency errors (Δk _u ') of (1), (2) and (3) of FIG. 13 were 0.08 rad/m, 0.22 rad/m, and 0.46 rad/m, respectively.

Referring to FIG. 14 , the reconstructed image of FIG. 13 ( 1 ) has a cross shape, so that the position of the center of the target can be specified.

On the other hand, referring to FIGS. 15 and 16 , the reconstructed images of FIGS. 13 (2) and (3) showed two crosses, so that the location of the center of the target could not be specified. The reason that the position of the target center cannot be specified with the restored images of (2) and (3) of FIG. 13 is that the Doppler frequency error (Δk _u ', rad/m) exceeds the threshold.

In this embodiment, the threshold value of the Doppler frequency error (Δk _u ', rad/m) is shown in (1) of FIG. 13 that can specify the position of the center of the target and that of FIG. 13 that cannot specify the position of the center of the target. (2) is located between Therefore, the nonlinear error analysis unit 310 is a threshold value of the Doppler frequency error (Δk _u ', rad/m) in FIG. 13 (1), the Doppler frequency error (Δk _u ') 0.08 rad/m and FIG. 13 The Doppler frequency error (Δk _u ') in (2) was set to 0.15 rad/m, which is the median value of 0.22 rad/m.

14 and 17 to 19 , in the case of (1), (4), (5), and (6) of FIG. 13, the Doppler frequency error (Δk _u ', rad/m) does not deviate from the threshold value. Therefore, the restored images showed a single cross. The reason the reconstructed image is tilted is because the antenna members 110 and 120 are irradiated with the transmission wave 2 in a state where the antenna members 110 and 120 are rotated by the directional angle φ _sq .

15 and 16, in the case of (2) and (3) of FIG. 13, the Doppler frequency error (Δk _u ', rad/m) exceeds the threshold, so that the reconstructed image does not form a single cross. The two crosses were superimposed on each other. When the reconstructed image shows two crosses, the reconstructed image could not be used because the location of the center of the target could not be specified.

In the case of (1), (4), and (5) of FIG. 13, the Doppler frequency was changed to 10°, 30°, and 60°, respectively, by changing the directivity angle ( φ _sq ) to 5° in the same azimuth direction reverse power beam width (φ _BW ) The error (Δk _u ', rad/m) was measured. The Doppler frequency errors (Δk _u ') of (1), (4), and (5) of FIG. 13 were 0.08 rad/m, 0.05 rad/m, and 0.04 rad/m, respectively.

Referring to FIGS. 14, 17, and 18 , the Doppler frequency error (Δk _u ', rad/m) did not exceed the threshold, so that the reconstructed image exhibited a single cross shape based on the center of the target. However, as the orientation angle ( φ _sq ) increased, the reconstructed image showed a distorted shape and the resolution was lowered. The function of controlling the resolution of the reconstructed image will be described using the resolution analyzer 320, which will be described later.

Referring back to FIG. 5 , the resolution analysis unit 320 analyzes the orientation angle ( φ _sq ) and the azimuth resolution (Azimuth resolution, Δu , m) using [Equation 12] and [Equation 19] below, and , determine the range of the beam angle ( φ _sq ) within the critical resolution and the azimuth reverse force beam width (φ _BW ). In the present embodiment, the resolution analyzer 320 analyzes the azimuth resolution, but the resolution analyzer 320 may also analyze the range resolution. In this embodiment, the threshold resolution may be a preset value. For example, the critical resolution may be 0.3m as shown in (r) of FIG. 21 .

[Equation 19]

△u=2π/BW _ku'

In [Equation 19], BW _ku' represents a frequency bandwidth.

Experimental Example 6

20 is a graph comparing the results analyzed by the resolution analyzer shown in FIG. 5 and the theoretical performance analysis results. In FIG. 14 , the horizontal axis represents the orientation angle ( φ _sq ), the left vertical axis represents the Doppler frequency bandwidth (rad/m), and the right vertical axis represents the length of the azimuth resolution.

The orientation angle SAR-based high-resolution image restoration system used in Experimental Example 6 has a flight altitude (H ₀ ) of 1 km, a synthetic aperture length (L) of 123 m, and a virtual position of the aircraft (u ₀ in FIG. 2 ) and The distance (R ₀ ) between the target centers (f(x _c ,y _c )) was 1,414 m, and an X-band radar system (X-band) with an anti-power beam width (φ _BW ) of 15° was used.

In FIG. 20, the lower graph (a) shows the azimuth resolution (m) according to the change in the orientation angle ( φ _sq ), and the graph (b) directed from the upper left to the lower right is the Doppler frequency bandwidth (Doppler frequency) bandwidth, red/m). The solid line parts (a, b) of the graph represent the results of the theoretical performance analysis, and the dotted lines represent the results analyzed by the resolution analyzer of the orientation angle SAR-based high-resolution image restoration system shown in FIG. 1 .

Referring to the graph a of FIG. 20 , as the orientation angle φ _sq increased, the length m of the azimuth resolution increased. That is, as the orientation angle φ _sq increased, the azimuth direction resolution decreased.

Referring to the graph b of FIG. 20 , the Doppler frequency bandwidth (rad/m) decreased as the directivity angle φ _sq increased.

Experimental Example 7

FIG. 21 is a graph illustrating azimuth resolution analyzed by the resolution analyzer shown in FIG. 5 . In FIG. 21 , the horizontal axis represents the azimuth reverse force beam width (Azimuth HPBW, φ _BW ), and the vertical axis represents the directional angle (Squint angle, φ _sq ).

The directional angle SAR-based high-resolution image restoration system used in Experimental Example 7 has a flight altitude (H ₀ ) of 1 km, a radio incident angle (θ _i ) is 45°, and the virtual position of the aircraft (u ₀ in FIG. 2 ) and An X-band radar system (X-band) with a distance (R ₀ ) between the target centers (f(x _c ,y _c )) of 1,414 m was used. The azimuth reverse power beam width (φ _BW ) was changed from 0° to 15°, and the beam angle ( φ _sq ) was changed from 0° to 75° to measure the length (m) of the azimuth resolution.

5 and 21 , the resolution analyzed by the resolution analyzer 320 was lowered as the directivity angle φ _sq increased, and improved as the azimuth reverse force beam width φ _BW increased.

Although it is not intended to limit the scope of the present invention by theory, the reason that the resolution decreases as the beam angle ( φ _sq ) increases is that as the beam angle ( φ _sq ) increases, the effective length of the synthesized aperture becomes shorter, so that the bandwidth of the Doppler frequency is reduced. decreases. As the Doppler frequency bandwidth decreases, the resolution decreases.

On the other hand, referring to [Equation 12] and [Equation 19], if the azimuth reverse force beam width (φ _BW ) increases, the effective length of the composite aperture becomes longer and thus the bandwidth of the Doppler frequency increases. As the Doppler frequency bandwidth increases, the resolution improves.

Referring back to FIG. 21 , the azimuth resolution in the upper left corner with a large beam angle ( φ _sq ) and a small azimuth reverse force beam width (φ _BW ) exhibited a low resolution of about 1 m in length.

On the other hand, the azimuth resolution in the lower right corner with a small beam angle ( φ _sq ) and a large azimuth reverse force beam width (φ _BW ) showed high resolution of 0.1 m or less.

Referring back to FIG. 5 , the operating range setting unit 330 is electrically connected to the nonlinear error analysis unit 310 and the resolution analysis unit 320 , so that the Doppler frequency error (Δk _u ') does not exceed the threshold value. The azimuth resolution sets the beam width ( φ _sq ) and the azimuth reverse power beam width (φ _BW ) at which the azimuth resolution does not exceed the critical resolution.

22 is a graph illustrating Doppler frequency error and azimuth resolution analyzed by the operating range setting unit shown in FIG. 5 . 22 is an overlapping view of FIGS. 13 and 21 , wherein the horizontal axis represents the azimuth reverse force beam width (Azimuth HPBW, φ _BW ), and the vertical axis represents the directional angle (Squint angle, φ _sq ).

The orientation angle SAR-based high-resolution image restoration system used in FIG. 22 has a flight altitude (H ₀ ) of 1 km, a radio incidence angle (θ _i ) is 45°, and the virtual position of the aircraft (u ₀ in FIG. 2 ) and the target center An X-band radar system (X-band) with a distance (R ₀ ) between (f(x _c ,y _c )) of 1,414 m was used. The azimuth reverse power beam width (φ _BW ) was changed from 0° to 15°, and the beam angle ( φ _sq ) was changed from 0° to 75° to measure the length (m) of the azimuth resolution.

Referring to FIG. 22 , the region analyzed by the operating range setting unit 330 is a 'high error region (High) within the azimuth reverse power beam width (Azimuth HPBW, φ _BW )-Squint angle ( φ _sq ) region. It is divided into an error zone (I))', an 'error zone (II)', an unstable region (d), and a stable region (c).

13 (2), (3), 15, 16, and 22 , the 'high error zone (I)' is Doppler analyzed by the nonlinear error analysis unit 310 . The frequency error (Δk _u ') represents the range of the azimuth reverse power beam width (Azimuth HPBW, φ _BW )-Squint angle ( φ _sq ) beyond the threshold. In the 'high error zone (I)', since the reconstructed image shows two crosses, the position of the center of the target cannot be specified.

13 (6), 19, and 22, the 'error zone (II)' is a Doppler frequency error (Δk _u ') analyzed by the nonlinear error analysis unit 310 is Although it does not exceed the threshold, the directivity angle ( ϕ _sq ) and the azimuth direction reversal force beam width (ϕ _BW ) represent a larger range than the maximum error directivity angle and maximum error reversal force beam width, respectively. In the 'Error zone (II)', the reconstructed image shows a single cross, so the location of the center of the target can be specified, but the quality of the reconstructed image is deteriorated due to low resolution.

13 (5), 18, and 22, in the 'unstable region (d)', the Doppler frequency error (Δk _u ') analyzed by the nonlinear error analysis unit 310 does not exceed the threshold value. , but indicates a range in which the azimuth resolution analyzed by the resolution analyzing unit 320 does not reach the critical resolution. In this embodiment, the critical resolution is 0.3 m. In the 'unstable region (d)', the reconstructed image shows a single cross, so the location of the center of the target can be specified, but the quality of the reconstructed image is deteriorated due to low resolution.

13 (1), 14, and 22, in the 'stable region (c)', the Doppler frequency error (Δk _u ') analyzed by the nonlinear error analysis unit 310 does not exceed the threshold value. and the azimuth resolution analyzed by the resolution analyzer 320 represents a range superior to the critical resolution. In the 'stable region (c)', the reconstructed image shows a single cross to specify the location of the center of the target, and the quality of the reconstructed image is good due to the good resolution.

23 is a graph showing a cross-section in the distance direction of the reconstructed image of point (1) shown in FIG. 22 . In FIG. 23 , the horizontal axis represents the distance direction resolution (m), and the vertical axis represents an impulse response function (IRF).

Referring to FIG. 23 , when the directivity angle ( φ _sq ) is 30° and the azimuth reverse force beam width (φ _BW ) is 5°, the distance direction resolution (ΔR) was 0.286 m and the peak-side ratio (peak-side ratio) lobe ratio; PSLR) was -15dB.

24 is a graph showing an azimuth cross-section of the reconstructed image of point (1) shown in FIG. 22 . In FIG. 24 , the horizontal axis represents the azimuth resolution (m), and the vertical axis represents an impulse response function (IRF).

Referring to FIG. 24 , at the same beam angle ( φ _sq ) and azimuth reverse power beam width (φ _BW ), the azimuth resolution (Δu) was 0.225 m and the peak-side lobe ratio (PSLR) was It was -13.3 dB.

22 and 24 , when the directivity angle ( φ _sq ) is 30° and the azimuth reverse force beam width (φ _BW ) is 5°, the Doppler frequency error (Δk _u ') does not exceed the threshold and the resolution was also good.

In one embodiment, it is physically connected to the antenna members 110 and 120 to physically control the orientation angle. For example, the operating range setting unit 330 includes a control motor 335 for controlling the antenna members 110 and 120 to control the directional angle φ _sq of the antenna members 110 and 120, and a waveform generator. By controlling the frequency generated by being connected to (150), the azimuth direction reverse force beam width ( φ _BW ) can be controlled.

The image restoration unit 240 restores image data for each pixel about the virtual target center by the directivity angle ( Φ _sq ) values and the azimuth reverse power beam width ( Φ _BW ) values set by the nonlinear error analysis unit 310 . Orientation angle ( Φ _sq ) and azimuth reverse force beam width ( Φ _BW ) in the stable region ('c' in FIG. 22) finally set by the operation range setting unit 330 or restored with preliminary images on the composite aperture It is possible to restore the final image on the composite aperture by combining the reconstructed image data for each pixel that has been scanned for the real topography using .

How to restore video

Hereinafter, an image restoration method using a directional angle SAR-based high-resolution image restoration system according to an embodiment of the present invention will be described.

25 is a flowchart illustrating an image restoration method using the directional angle SAR-based high-resolution image restoration system shown in FIG. 1 .

1, 5, and 25, first, the range of the beam angle (φ _sq ) for analyzing the virtual target center (f(x _c , y _c )), the azimuth reversal force beam width (φ _BW ) Set the range of (step S110). In an embodiment, the Doppler frequency error (Δk _u ') may set the threshold value and the threshold resolution together.

Specifically, the operating range setting unit 330 sets the range of the directional angle (φ _sq ) to 0° to 80° and sets the range of the azimuth reverse force beam width (φ _BW ) to 0° to 15°.

Subsequently, the operating range setting unit 330 is an arbitrary azimuth reverse power beam width (φ _BW ) within a preset azimuth direction reversal force beam width (φ _BW ) range as shown in (1), (4), (5) of FIG. 13 . For a value (eg, 5°), a plurality of different directivity angle (φ _sq ) values (10°, 30°, 60°) within a range of a preset directivity angle (φ _sq ) are set (step S120 ). Preferably, the plurality of different directional angle (φ _sq ) values are set to be evenly distributed within the preset directional angle (φ _sq ) range by the operating range setting unit 330 .

In this embodiment, the operating range setting unit 330 controls the antenna members 110 and 120 to change the directional angle φ _sq to set values, and controls the waveform generator 150 to control the azimuth reverse power beam width ( It generates a signal corresponding to φ _BW ).

Thereafter, using the antenna members 110 and 120, the raw data generating member 210, the orientation angle correction member 220, and the image restoration unit 240, each Preliminary images corresponding to the orientation angle (φ _sq ) and the azimuth reverse force beam width (φ _BW ) are restored ( S130 ). The step of reconstructing the preliminary images will be described in detail with reference to FIG. 26 .

FIG. 26 is a block diagram illustrating a step of reconstructing the preliminary image of FIG. 25 .

1, 3, and 26 , first, a transmission wave 2 is transmitted to the target center f(x _c , y _c ) on the ground surface according to a preset directivity angle φ _sq ( S131 ).

In order to generate the transmission wave 2 , a signal having the same waveform as the transmission wave 2 is generated using the waveform generator 150 . A signal having the same waveform as the transmission wave 2 generated from the waveform generator 150 is distributed to the transmission antenna 110 and the mixer 205 using the divider 160 . Among the signals distributed using the divider 160 , the signal applied to the transmission antenna 110 becomes the transmission wave 2 and is transmitted to the target center f(x _c , y _c ) on the ground surface.

Subsequently, the reception wave 4 reflected from the target center f(x _c , y _c ) of the ground surface is received using the reception antenna 120 (S132).

Next, raw data is generated from the received wave 4 (S133).

In order to generate raw data from the reception wave 4 , the distributed signal received from the divider 160 and the reception wave 4 received from the reception antenna 120 are mixed using the mixer 205 . The raw data generating member 210 is used to measure the distance for each pixel on the ground surface from the signal mixed by the mixer 205 to generate raw data s(t,u) indicating the distance for each pixel.

Subsequently, an error due to the orientation angle is corrected in the raw data s(t, u) by using the orientation angle correction member 220 . A step of generating preliminary image data by correcting an error due to an orientation angle in the raw data s(t, u) will be described in detail.

In order to correct the error due to the orientation angle, first, the first Fourier transform data (s) by performing a first Fourier transform with respect to time on the raw data (s(t,u)) using the first Fourier transform unit 221 . (f, u)) is generated (S134).

Next, the first corrected raw data (s(f,u')) is generated by rotating the first Fourier transform data (s(f,u)) by the orientation angle Φ _sq using the raw data preprocessor 223 generated (S135).

In order to generate the first corrected raw data s(f,u'), the first-order Fourier-transformed data using the first data mixing unit 225 of the raw data pre-processing unit 223 is subjected to baseband transformation (Baseband). Conversion) filter (S _BB (f, u)) is multiplied to perform a first mixing function to generate first mixed data.

Then, by using the rotation resampling unit 227 of the raw data preprocessor 223 to rotate the first mixed data by the orientation angle Φ _sq , the first corrected raw data (s(f, u') as in [Equation 9] )) is created.

Thereafter, using the second Fourier transform unit 229, the first corrected raw data (s(f, u')) is subjected to a Fourier transform for the aircraft position variable (u') on the coordinate system rotated by the orientation angle Φ _sq . (Fourier Transformation) is performed to generate second corrected raw data s(f,k' _u ) as in [Equation 10] (S136).

Then, the orientation angle according to [Equation 12] and [Equation 13] in the second corrected raw data s(f,k _u ') using the Range Cell Migration (RCM) generator 231 The third corrected raw data (s'(f,k _u ')) is generated by compensating for the displacement according to the aircraft position variable (u') on the coordinate system rotated by ( Φ _sq ) (S137). In an embodiment of the present invention, the method further includes correcting the trajectory characteristic function by the correction value (Equation 15).

Next, the third corrected raw data s'(f,k _u ') is multiplied by the matched filter S _M '(f,k _u ') using the second data mixing unit 233 to obtain the second mixed data to create

Thereafter, by using the inverse Fourier transform unit 235 to inversely transform the second mixed data into the Doppler frequency k _u ' rotated by the orientation angle Φ _sq , the fourth correction according to the coordinates (x, y) on the ground surface Data (f'(x,y)) is generated (S138).

Subsequently, the preliminary image data (f _c (x, y)) restored by reverse-rotating the fourth correction data f'(x,y) by the orientation angle Φ _sq using the data reverse rotation unit 237 to generate (S139).

Next, the image restoration unit 240 is used to combine the restored image data f _c (x,y) for each pixel generated by the data reverse rotation unit 237 to restore a preliminary image on the composite aperture (S139). ).

1, 5, 13, and 25 again, thereafter, the nonlinear error analysis unit 310 uses [Equation 12] to [Equation 17] to each directivity angle (φ _sq ) values and half Doppler frequency errors (Δk _u ') for the power beam width (φ _BW ) value are detected (S140).

Subsequently, as shown in FIG. 13 , the directivity angle φ _sq at which the Doppler frequency error Δk _u ' has the maximum value is calculated and set as the maximum error directivity angle ( S150 ). For example, the maximum error directivity angle may be set by approximating the Doppler frequency error Δk _u ' corresponding to each of the directivity angles φ _sq . For example, in (1) of FIG. 13, when the directivity angle φ _sq is 30°, the Doppler frequency error Δk _u ' represents 0.08, which is the maximum value, so 30° becomes the maximum error directivity angle. In another embodiment, when there are two different directional angles having a maximum Doppler frequency error (Δk _u '), an intermediate value of the two directional angles may be set as the maximum error directional angle. Those with ordinary knowledge and experience in the art can determine the maximum error directivity angle by applying various approximations to the Doppler frequency errors (Δk _u ') corresponding to the plurality of directivity angles (φ _sq ). will be readily available.

Then, the operating range setting unit sets the directing angle (φ _sq ) as the maximum error directing angle, and sets a plurality of different azimuth reverse power beam width (φ _BW ) values within the preset azimuth direction reversing power beam width (φ _BW ) range. (Step S160). For example, as shown in (1), (2), (3) of FIG. 13 , azimuth reverse force beam width (φ _BW ) values of 5°, 7.5°, and 10° can be set for the maximum error directivity angle of 30°. have. Preferably, the plurality of different azimuth reversing force beam width (φ _BW ) values are set to be evenly distributed within a preset azimuth direction reversing force beam width (φ _BW ) range by the operation range setting unit 330 .

Thereafter, the preliminary image corresponding to the maximum error directivity angle and the plurality of azimuth reverse power beam width (φ _BW ) values is reconstructed ( S170 ). Since the step of reconstructing the preliminary image ( S160 ) is the same as the above-described step S130 , a redundant description will be omitted.

Subsequently, by analyzing the reconstructed preliminary images, the maximum error half-power beam width corresponding to the threshold value of the Doppler frequency error (Δk _u ') is set (S180).

In order to set the maximum error reversal power beam width, the reconstructed preliminary images are analyzed and the azimuth reversal force beam width (φ _BW ) of the point forming one cross shape and the azimuth reversing force beam width (φ) at the point forming two cross shapes _BW ) is set as the maximum error half-power beam width. For example, as shown in (1), (2) of FIG. 13, the azimuth direction reverse force beam width (φ _BW ) of the point (1) forming one cross shape and the orientation of the point (2) forming two cross shapes 6.25°, which is the middle value of the direction reversal force beam width (φ _BW ), can be set as the maximum error reversal force beam width.

In one embodiment, without using a threshold value for the preset Doppler frequency error (Δk _u '), the nonlinear error analysis unit 310 generates a Doppler frequency error (Δ) corresponding to the maximum error directivity angle and the maximum error inversion power beam width. It may further include the step of setting k _u ') as a threshold value. For example, since the Doppler frequency error (Δk _u ') in (1) and (2) of FIG. 13 is 0.08 rad/m and 0.22 rad/m, respectively, the median value of 0.15 rad/m is the Doppler frequency error ( Δk _u ') may be set as a threshold value.

Next, a range of a directivity angle (φ _sq ) and an azimuth direction reverse power beam width (φ _BW ) range within the preset critical resolution are set ( S190 ).

In order to determine the range of the beam angle (φ _sq ) and the azimuth reverse power beam width (φ _BW ) within the preset critical resolution, the resolution analysis unit 320 using [Equation 12] and [Equation 19] is Determine the range of the directional angle (φ _sq ) and the azimuth reverse power beam width (φ _BW ) corresponding to the critical resolution. For example, as shown in (r) of FIG. 21 , the preset critical resolution is 0.3 m, and the range of the directivity angle (φ _sq ) range and the azimuth reverse power beam width (φ _BW ) corresponding to the critical resolution is critical in FIG. It may be the lower right area of the resolution graph (r).

After that, the range of the orientation angle (φ _sq ) and the azimuth reversal force in the stable region (c) where the Doppler frequency error (Δk _u ') does not exceed the threshold and the azimuth resolution does not exceed the critical resolution The range of the beam width φ _BW is set ( S200 ).

Specifically, the operating range setting unit 330 overlaps the Doppler frequency error range analyzed by the nonlinear error analysis unit 310 and the resolution range analyzed by the resolution analysis unit 320, and the Doppler frequency error (Δk _u ) ') does not exceed the threshold value and the azimuth resolution does not exceed the threshold resolution (φ _sq ) and the azimuth reverse power beam width (φ _BW ) are set.

For example, as in FIG. 22 , the operating range setting unit 330 sets the azimuth reverse force beam width (Azimuth HPBW, φ _BW )-Squint angle (φ _sq ) region to a ‘high error zone’ (I))', 'error zone (II)', unstable zone (d), and stable zone (c) can be divided.

In the 'stable region (c)', the Doppler frequency error (Δk _u ') analyzed by the nonlinear error analysis unit 310 does not exceed a threshold value, and the azimuth resolution analyzed by the resolution analysis unit 320 (Azimuth resolution) ) indicates a range superior to the critical resolution. In an embodiment of the present invention, the 'stable region (c)' is at the bottom of the critical resolution (r) graph of the azimuth resolution based on the point (p) set by the maximum error reversal power beam width and the maximum error directivity angle. It may be a region in which the Doppler frequency error (Δk _u ') is located outside the threshold value (t) graph.

In the 'stable region (c)', the reconstructed preliminary image shows a single cross so that the position of the center of the target can be specified, and the quality of the reconstructed preliminary image is good due to good resolution.

Then, by applying the azimuth reverse force beam width (Azimuth HPBW, φ _BW ) and the directional angle (Squint angle, φ _sq ) corresponding to the stable region (c) to the waveform generator 150 and the antenna members 110 and 120, respectively, , finally set the high-resolution image restoration system based on the directional angle SAR.

Thereafter, the actual terrain is scanned using a high-resolution image restoration system based on the azimuth angle SAR in which the azimuth reverse power beam width (φ _BW ) and the beam angle (φ _sq ) are set within the stable region, and the restored image data for each pixel (f _c (x , y)) is combined to restore the final image on the composite aperture (S210).

According to the embodiment of the present invention as described above, by adjusting the physical characteristics of the radar in advance in the Squint-SAR image restoration system, the directional angle SAR (Squint-SAR) data error caused by twisting the irradiation direction, the reverse power beam width It can be set in advance so that raw data within a range that can be corrected is generated by controlling in advance the occurrence of errors caused by failing to set the range of .

In addition, in the nonlinear behavior of the Squint-SAR image restoration system, which is difficult to predict and correct for errors, the accuracy of inspection results is improved by setting the error range within a threshold in advance.

In addition, in setting variables such as the orientation angle ( Φ _sq ), the effective length of the composite aperture (L), the half-power beam width ( Φ _BW ), etc., the reconstructed image of excellent quality can be obtained without trial and error considering the Doppler frequency error and resolution. can create

In addition, since the Squint-SAR image restoration system itself is controlled in advance so that the raw data converges within a correctable error range, it has the advantage of being applicable to various image restoration techniques.

In addition, with respect to the raw data converged within the error range, the rotational resampling unit, the second Fourier transform unit, the trajectory characteristic function (Range Cell Migration; RCM) generation unit, and the data reverse rotation unit are used for 4 times by using the orientation angle. By correcting the influence, the accuracy of the restored image is improved.

The present invention has industrial applicability that can be used for purposes such as aerial view, topographical mapping, ocean exploration, remote sensing, artificial satellite exploration, aircraft exploration, exploration using a floating experimental device, bird exploration, meteorological exploration, military use, and the like.

Although the above has been described with reference to the embodiments, those skilled in the art can variously modify and change the present invention within the scope without departing from the spirit and scope of the present invention described in the following utility model registration claims. You will understand that there is

110, 120: antenna member 150: waveform generator
160: divider 205: mixer
210: raw data generating member 220: orientation angle correction member
20: raw data transform unit 221: first Fourier transform unit
223: raw data preprocessor 225: first data mixing unit
227: rotation resampling unit 229: second Fourier transform unit
231: Range Cell Migration (RCM) generation unit
233: second data mixing unit 33: data mixing unit
235, 35: third Fourier transform unit 237: data inverse rotation unit
240: image restoration unit 300: operating range control material
310: non-linear error analysis unit 320: resolution analysis unit
330: operating range setting unit

Claims (10)

a waveform generator for generating a signal having the same waveform as that of the transmission wave;
a divider connected to the waveform generator and receiving and distributing the signal generated from the waveform generator;
It is connected to the splitter and includes a transmit antenna for receiving the distributed signal from the splitter to transmit the transmit wave to the ground surface and a receive antenna for receiving the receive wave reflected from the ground surface, the direction perpendicular to the direction of movement of the aircraft An antenna member inclined as much as a directivity angle with respect to ;
a mixer connected to the splitter and the receiving antenna and mixing the distributed signal applied from the splitter and the receiving wave received from the receiving antenna;
a raw data generating member connected to the mixer, receiving the mixed signal from the mixer, measuring a distance from the center of the target on the ground surface, and generating raw data indicating the location of the center of the target;
It is connected to the raw data generating member to change the raw data into corrected raw data on the distance-Doppler frequency domain rotated by the orientation angle, and convert the corrected raw data to the displacement according to the movement of the aircraft by the orientation angle. an orientation angle correction member for generating reconstructed image data for each pixel by compensating for the state;
an image restoration unit that projects the restored image data for each pixel to restore a preliminary image about a virtual target center or restores a final image obtained by scanning real terrain;
It is connected to the antenna member, the waveform generator, the directivity angle correction member, and the image restoration unit, and analyzes the Doppler frequency error of the corrected raw data according to the change in the directivity angle and the inverse power beam width of the transmitted wave to analyze the Doppler A non-linear error analysis unit that sets a maximum error directivity angle and maximum error reversal power beam width that do not exceed the threshold of frequency error, and a resolution according to a change in the directivity angle and the reversal power beam width by analyzing the restored preliminary image is a critical resolution A resolution analysis unit that sets a beam-width of the beam angle and half-power not exceeding A directional angle SAR-based high-resolution image restoration system comprising an operating range setting unit including an operating range setting unit for controlling the antenna member and the waveform generator by setting a beam width and a beam width whose resolution does not exceed the critical resolution. According to claim 1, wherein the non-linear error analysis unit, the orientation angle SAR-based high resolution, characterized in that the RMS (Root Mean Square) method as in [Equation 1], [Equation 2], [Equation 3] to obtain the Doppler frequency error. video restoration system.
[Equation 1]

(In [Equation 1], N is the number of samples indicating the positions of the antenna members 110 and 120 in the composite aperture, and u' _n is the coordinate system rotated by the beam angle ( Φ _sq ) in the composite aperture (u') Corresponds to each position (sample) of the antenna members 110 and 120 according to the movement of the aircraft on the plane, k _u '(u') corresponds to [Equation 2], and the fit(u') function is approximated by a linear equation (fitting) is a function)
[Equation 2]

(In [Equation 2], k u ' represents the Doppler frequency rotated by the beam angle on the Fourier-transformed distance-Doppler domain, f0 represents the center frequency, f represents the beat frequency, and u' represents the rotation angle by the beam angle. It represents the azimuth distance on the coordinate system, and A(u') is represented by [Equation 3])
[Equation 3]

(In [Equation 3], c represents the speed of light, and R ₀ represents the distance between the virtual position of the aircraft and the center of the target when the heading angle is 0°) The method of claim 1, wherein the resolution analyzer analyzes the beam angle and azimuth resolution using [Equation 2] and [Equation 4] to set the range of the beam width and the range of the beam width in the azimuth direction within the critical resolution. A high-resolution image restoration system based on directional angle SAR.
[Equation 2]

(In [Equation 2], k u ' represents the Doppler frequency rotated by the beam angle on the Fourier-transformed distance-Doppler domain, f0 represents the center frequency, f represents the beat frequency, and u' represents the rotation angle by the beam angle. It represents the azimuth distance on the coordinate system, and A(u') is represented by [Equation 3])
[Equation 3]

(In [Equation 3], c represents the speed of light, and R ₀ represents the distance between the virtual position of the aircraft and the center of the target when the heading angle is 0°)
[Equation 4]
△u=2π/BW _ku'
(In [Equation 4], BW _ku' represents the frequency bandwidth) According to claim 1, wherein the orientation angle correction information,
a first Fourier transform unit connected to the raw data generating member and performing a first Fourier transform with respect to time on the raw data;
a raw data preprocessing unit connected to the first Fourier transform unit and configured to generate first corrected raw data by rotating the first Fourier transformed raw data by the orientation angle;
a second Fourier transform unit connected to the raw data pre-processing unit and generating second corrected raw data by performing a Fourier transform on the aircraft position variable on the coordinate system rotated by the orientation angle on the first corrected raw data;
Connected to the second Fourier transform unit, compensating for displacement according to the movement of the aircraft in a state rotated by the orientation angle, and further compensating for a distance difference caused by the rotation to generate third corrected raw data trajectory characteristic function generator;
an inverse Fourier transform unit for generating fourth corrected data according to coordinates on the earth's surface by inverse Fourier transforming the generated mixed data obtained by multiplying the third corrected raw data by a matched filter with a Doppler frequency rotated by the orientation angle; and
and a data inverse rotator connected to the inverse Fourier transform unit to generate reconstructed image data by inversely rotating the fourth correction data by the orientation angle. a waveform generator for generating a signal having the same waveform as a transmission wave; a divider connected to the waveform generator to receive and distribute a signal generated from the waveform generator; An antenna member including a transmission antenna for transmitting a transmission wave to the ground surface and a reception antenna for receiving a reception wave reflected from the ground surface, the antenna member being inclined as much as a directivity angle with respect to a direction perpendicular to the direction of movement of the aircraft, the splitter and the reception antenna a mixer connected to and mixing the distributed signal received from the divider and the received wave received from the receiving antenna, and connected to the mixer and receiving the mixed signal from the mixer a raw data generating member that measures a distance to generate raw data indicating the position of the center of the target; an orientation angle correction member for generating reconstructed image data for each pixel by changing the corrected raw data and compensating for displacement according to the movement of the aircraft to a state rotated by the orientation angle, and projecting the restored image data for each pixel to create a virtual An image restoration unit that restores a preliminary image about the target center of the image restoration unit or restores a final image obtained by scanning the actual terrain, and the antenna member, the waveform generator, the orientation angle correction member, and the orientation inputted by the antenna member A nonlinear error analysis unit that analyzes the Doppler frequency error according to the angle and the half-power beam width, a resolution analyzer that analyzes the resolution according to the input beam angle and the half-power beam width, and the operating range of the beam angle and the half-power beam width are set In an image restoration method using a directional angle SAR-based high-resolution image restoration system including an operating range setting member including an operating range setting unit,
setting a range of an orientation angle and a range of a half-power beam width for analyzing a virtual target center using the operating range setting unit;
setting an arbitrary value within the range of the set half-power beam width using the operating range setting unit and setting a plurality of different beam angle values within the range of the set beam angle;
reconstructing preliminary images corresponding to each of the beam angle values and the set half-power beam width value using the raw data generating member, the beam angle correction member, and the image restoration unit;
detecting a Doppler frequency error corresponding to each of the beam angle values and the set reversal power beam width value using the nonlinear error analysis unit;
calculating a directivity angle at which the detected Doppler frequency error has a maximum value using the nonlinear error analysis unit and setting it as a maximum error directivity angle;
setting the maximum error directivity angle as a directivity angle value using the operating range setting unit and setting a plurality of different semi-power beamwidth values within the range of the set half-power beamwidth;
reconstructing preliminary images corresponding to each of the maximum error directivity angle values and the respective half-power beam width values by using the raw data generating member, the orientation angle correction member, and the image restoration unit;
analyzing the reconstructed preliminary images using the nonlinear error analyzer to set a maximum error inversion power beam width corresponding to a threshold value of the Doppler frequency error;
setting a range of an orientation angle range and a half-power beam width within a preset critical resolution using the resolution analyzer;
By combining the analysis result of the nonlinear error analysis unit and the analysis result of the resolution analysis unit using the operating range setting unit, the Doppler frequency error does not exceed the threshold value and the resolution of the restored preliminary image does not exceed the threshold resolution controlling the antenna member and the waveform generator by setting the angle and the reverse power beam width; and
An image comprising the step of applying the beam angle and the half-power beam width to the beam angle SAR-based high-resolution image restoration system to scan the real topography, and combining the restored image data for each pixel to restore the final image on the composite aperture How to restore. The method of claim 5, wherein the detecting of the Doppler frequency error comprises obtaining the Doppler frequency error using a root mean square (RMS) method as shown in [Equation 1].
[Equation 1]

(In [Equation 1], N is the number of samples indicating the positions of the antenna members 110 and 120 in the composite aperture, and u' _n is the coordinate system rotated by the beam angle ( Φ _sq ) in the composite aperture (u') Corresponds to each position (sample) of the antenna members 110 and 120 according to the movement of the aircraft on the plane, k _u '(u') corresponds to [Equation 2], and the fit(u') function is approximated by a linear equation (fitting) is a function)
[Equation 2]

(In [Equation 2], k u ' represents the Doppler frequency rotated by the beam angle on the Fourier-transformed distance-Doppler domain, f0 represents the center frequency, f represents the beat frequency, and u' represents the rotation angle by the beam angle. It represents the azimuth distance on the coordinate system, and A(u') is represented by [Equation 3])
[Equation 3]

(In [Equation 3], c represents the speed of light, and R ₀ represents the distance between the virtual position of the aircraft and the center of the target when the heading angle is 0°) The method of claim 5, wherein the setting of the range of the beam angle and the half-power beam width within the preset critical resolution comprises analyzing the beam angle and the azimuth resolution using [Equation 2] and [Equation 3] to determine the threshold. Image restoration method, characterized in that setting the range of the beam angle range and the half-power beam width within the resolution.
[Equation 2]

(In [Equation 2], k u ' represents the Doppler frequency rotated by the beam angle on the Fourier-transformed distance-Doppler domain, f0 represents the center frequency, f represents the beat frequency, and u' represents the rotation angle by the beam angle. It represents the azimuth distance on the coordinate system, and A(u') is represented by [Equation 3])
[Equation 3]

(In [Equation 3], c represents the speed of light, and R ₀ represents the distance between the virtual position of the aircraft and the center of the target when the heading angle is 0°)
[Equation 4]
△u=2π/BW _ku'
(In [Equation 4], BW _ku' represents the frequency bandwidth) The method of claim 5, further comprising setting a Doppler frequency error corresponding to the maximum error directivity angle and the maximum error half-power beam width as a threshold value of the Doppler frequency error using the nonlinear error analysis unit. How to restore video. The method of claim 5, wherein the restoring of the preliminary images comprises:
generating a signal corresponding to the half-power beam width using the waveform generator;
applying the signal to the transmitting antenna, transmitting the transmitted wave rotated by the directivity angle onto the ground surface, and receiving the received wave reflected from the ground surface through the receiving antenna;
mixing, using the mixer, the signal distributed from the divider and the reception wave received from the reception antenna;
generating raw data indicating the position of the center of the target by measuring a distance from the mixed signal to the center of the target on the ground surface using the raw data generating member;
performing a first-order Fourier transform with respect to time on the raw data using a first Fourier transform unit;
generating first corrected raw data by rotating the first-order Fourier-transformed raw data by the orientation angle using the raw data preprocessor;
generating second corrected raw data by performing a Fourier transform on the aircraft position variable on the coordinate system rotated by the orientation angle on the first corrected raw data by using a second Fourier transform unit;
generating third corrected raw data by using a trajectory characteristic function generator to compensate for displacement according to the movement of the aircraft in a rotated state by the orientation angle, and additionally compensate for a distance difference caused by the rotation;
generating fourth corrected data according to coordinates on the earth's surface by using the inverse Fourier transform unit to Fourier inversely transform the generated mixed data obtained by multiplying the third corrected raw data by a matched filter with a Doppler frequency rotated by the orientation angle;
generating restored image data by using the data reverse rotation unit to reversely rotate the fourth correction data by the orientation angle; and
and projecting the restored image data for each pixel by using the image restoration unit to restore a preliminary image on the synthetic aperture with respect to the virtual target center. The method of claim 9, wherein the generating of the first corrected raw data comprises:
generating mixed data by multiplying the first-order Fourier-transformed raw data by a baseband transform filter; and
and generating the first corrected raw data by rotating the mixed data by the orientation angle.

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