KR20230007753A - Image decoding apparatus for sea surface based on airborn and method of decoding image using the same - Google Patents

Abstract

An aircraft-based sea surface image restoration device comprises a waveform generator, a distributor, an antenna member, a first mixer, a first raw data generating unit, a delay signal value generating unit, a shortened signal value generating unit, a delay signal correction unit, a second mixer, a second raw data generating unit, a reverse projection unit, and an image restoration unit. The delay signal value generating unit receives a signal generated from the waveform generator and generates a delay signal value linked to a beat frequency. The shortened signal value generating unit generates a shortened signal value corresponding to the delay signal value. The delay signal correction unit receives the delay signal value and the shortened signal value and generates a shortened delay signal. The second mixer mixes a reception wave with the shortened delay signal to generate a second demodulated signal. The second raw data generating unit generates second raw data from the second demodulated signal. The reverse projection unit calculates a function value for each pixel in a composite aperture surface. The image restoration unit restores an image in the composite aperture surface. According to the present invention, the image restoration device can construct a radar system that is not affected by the total reflection characteristics of the sea surface.

Description

Aircraft-based sea level image restoration device and image restoration method using the same

The present invention relates to an aircraft-based sea level image restoration device and an image restoration method using the same, and more particularly, to a sea level image in an emergency using FMCW-SAR (Frequency Modulated Continuous Wave - Synthetic Aperture Radar) measured by an aircraft. It relates to an image restoration device capable of restoring and an image restoration method using the same.

Global environment research is a field that investigates the geology, ocean, and ecology of a vast area, and includes field investigations, indoor experiments, and remote sensing.

On-site investigation includes direct site visits such as surface exploration, boring, and physical exploration, and surveys using the naked eye or various survey equipment. Because of its high accuracy, field surveys are still widely used when precise measurements are required. In indoor experiments, chemical and physical properties that are difficult to directly measure in the field are measured using precision measuring equipment in the laboratory. Field investigations and indoor experiments have the advantage of high accuracy, but due to temporal and spatial constraints, it is not easy to apply them to large areas, remote areas, remote areas, and the ocean.

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

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

In the case of aircraft, compared to satellites, it has the advantage of being able to measure short distances at a relatively low price. However, continuous fluctuations and vibrations occur due to atmospheric conditions, weather, engines, etc. while operating the aircraft. The shaking and vibration of the aircraft degrades the quality of the data, but it is impossible to completely eliminate them due to the nature of the aircraft flying in the air.

Among these problems, there is a problem in that the sea surface is displayed in black due to the total reflection characteristic of the sea surface.

In order to solve this problem, there is a method of separately extracting the backscatter coefficient and comparing it with distance-Doppler 2-dimensional data, such as Korean Patent Registration No. 1784178 ("scatter system for ocean displacement observation"). However, in the case of the above Korean Patent Registration No. 1784178, there is a problem in that a separate laying hen system for ocean displacement observation must be built instead of a general FMCW-SAR radar system.

Conventional technologies include Korean Patent Registration No. 10-1839041 ("FMCW-SAR system using continuous movement effect correction technique and method for restoring SAR image of this system"), Korean Patent Registration No. 10-2192332 ("Leakage signal in FMCW radar") Advanced method for attenuation and radar system using the same"), Republic of Korea Patent Registration No. 10-2156489 ("Aircraft-based image restoration device and image restoration method using the same"), Republic of Korea Patent Registration No. 10-2156490 ("Aircraft-based segmented image Restoration apparatus and split image restoration method using the same") have been developed to correct errors occurring in ground observation using aircraft, such as aircraft shaking and beam angle errors.

However, even according to the above inventions, the problem of the sea surface appearing black due to the total reflection characteristic of the sea surface cannot be solved.

Korean Registered Patent No. 10-1784178 (2017.9.27.) Korean Registered Patent No. 10-1839041 (2018.3.9.) Korean Registered Patent No. 10-2192332 (2020.12.11.) Korean Registered Patent No. 10-2156489 (2020.9.9.) Korean Registered Patent No. 10-2156490 (2020.9.9.) Korean Registered Patent No. 10-2258202 (2021.5.24.)

An object of the present invention is to provide an image restoration device capable of restoring a sea level image in an emergency using FMCW-SAR (Frequency Modulated Continuous Wave-Synthetic Aperture Radar) measured by an aircraft.

An object of the present invention is to provide an image restoration method using an image restoration device capable of restoring a sea level image in an emergency using FMCW-SAR (Frequency Modulated Continuous Wave - Synthetic Aperture Radar) measured by an aircraft.

An aircraft-based sea level image restoration apparatus according to an embodiment of the present invention includes a waveform generator, a divider, an antenna member, a first mixer, a first raw data generator, a delay signal value generator, a shortened signal value generator, and a delay signal corrector. , a second mixer, a second raw data generator, a back projection unit, and an image restoration unit. The waveform generator generates a signal of the same waveform as the transmission wave. The divider is connected to the waveform generator, 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 divided signal from the splitter and transmitting the transmit wave to the ground surface, and a receive antenna for receiving the receive wave reflected from the ground surface. The first mixer is connected to the divider and the reception antenna, and generates a first demodulation signal by mixing the divided signal received from the divider and the reception wave received from the reception antenna. The first raw data generator is connected to the first mixer and generates first raw data from the first demodulated signal generated by the first mixer. The delay signal value generator is connected to the divider, receives the signal generated from the waveform generator, and generates a delay signal value linked to the bit frequency of the signal received from the waveform generator. The shortened signal value generating unit is connected to the delayed signal value generating unit and generates a shortened signal value corresponding to the delayed signal value applied from the delayed signal value generating unit. The delay signal correction unit is connected to the delay signal value generator and the shortened signal value generator, receives the delayed signal value and the shortened signal value from the delayed signal value generator and the shortened signal value generator, respectively, and shortens the signal. generate a delayed signal. The second mixer is connected to the reception antenna and the delay signal correction unit, and generates a second demodulation signal by mixing the received wave applied from the reception antenna and the shortened delay signal received from the delay signal correction unit. . The second raw data generator is connected to the second mixer and generates second raw data from the second demodulation signal applied from the second mixer. The back projection unit receives the first raw data and the second raw data and calculates a function value for each pixel within the composite aperture. The image restoration unit is connected to the back projection unit, and restores an image within the composite aperture using the function value for each pixel applied from the back projection unit.

In one embodiment, the second demodulation signal may have a lower incident angle than the first demodulation signal.

In one embodiment, the first raw data generator and the second raw data generator are connected, and the first raw data and the second raw data are obtained from the first raw data generator and the second raw data generator. A raw data summing unit configured to receive data and generate summed raw data may be further included, and the back-projection unit may be connected to the raw data summator to receive the summed raw data.

In one embodiment, the transmission wave is represented as a function of time as in [Equation 1] (in [Equation 1], t represents time, S ₀ (t) represents the transmission wave, f ₀ represents the center frequency, , K _r represents the modulation rate),

[Equation 1]

The received wave may be expressed as a function of time and the position (u) of the antenna member as shown in [Equation 2] (in [Equation 2], t represents time, and u represents the position of the antenna members 110 and 120 , S _r (t, u) represents a transmission wave, f ₀ represents a center frequency, K _r represents a modulation rate, and τ represents a delay time).

[Equation 2]

In one embodiment, the first raw data generator may generate the first raw data corresponding to a synthetic aperture image corresponding to a half-power beam width region before and after the incident angle of the transmission wave using [Equation 3]. (In [Equation 3], τ(u) represents the target delay time and is obtained by [Equation 4]. In [Equation 4], R(u) represents the distance between the aircraft's position (u) and the target. (x,y,z) represent the coordinates of the target, (u _x ,u _y ,u _z ) represent the coordinates of the aircraft, and c represent the speed of light).

[Equation 3]

[Equation 4]

In one embodiment, the delay signal value generator may generate 1/2 of the bit frequency as a delay signal value. In addition, the delay signal value generation unit may set the delay signal value as shown in [Equation 6] (in [Equation 6], R _d represents the straight line distance between the aircraft and the ground, and c represents the speed of light).

[Equation 6]

In one embodiment, the short signal value generation unit may set the short signal value using [Equation 8] (in [Equation 8], H ₀ represents the altitude of the aircraft and c represents the speed of light).

[Equation 8]

In one embodiment, the shortened signal value generator may set a value obtained by multiplying the delayed signal value by 0.1 to 0.2 as the shortened signal value. Also, the shortened signal value generator may set a value obtained by multiplying the delayed signal value by 0.15 as the shortened signal value.

In one embodiment, the shortened signal value generating unit may set an angle of a transmission wave generating the second demodulation signal to be 3.5° to 35°.

In one embodiment, the delay signal correction unit may generate a shortened delay signal using [Equation 9] (in [Equation 9], f ₀ represents the center frequency, t represents time, and d represents the delay represents a signal value, Δd represents a shortened signal value, and K _r represents a modulation rate).

[Equation 9]

In one embodiment, the second raw data generator may generate the second raw data from the second demodulation signal using [Equation 10] (in [Equation 10], t represents time, and u is represents the position of the aircraft, Sr(t,u) represents the received wave, S _sd *(t,u) represents the matched filter of the second demodulation signal, f ₀ represents the center frequency, K _r represents the modulation rate , d represents the delay signal value, Δd represents the shortened signal value, and τ(u) is the target delay time, which can be expressed as in [Equation 4] above).

[Equation 10]

In one embodiment, the back projection unit may calculate a function value for each pixel using [Equation 11] (in [Equation 11], f(x _i ,y _j ) represents the function value of the ij th pixel, , P represents the number of total pixels, p represents the number of pixels corresponding to each function value, Wp represents the magnitude function of the p-th received signal, t represents time, and u _p represents the p-th received signal represents the position of the corresponding antenna member, S _sddc (t, u _p ) represents the demodulation signal corresponding to the shortened delay signal, and S ^* _M (t _d (u _p )) represents the demodulation corresponding to the shortened delay signal represents a matched filter of the signal).

[Equation 11]

An aircraft-based sea level image restoration apparatus according to an embodiment of the present invention includes a waveform generator, a divider, an antenna member, a delay signal value generator, a shortened signal value generator, a delay signal corrector, a second mixer, and a second raw data generator. , a back projection unit, and an image restoration unit. The waveform generator generates a signal of the same waveform as the transmission wave. The divider is connected to the waveform generator, 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 divided signal from the splitter and transmitting the transmit wave to the ground surface, and a receive antenna for receiving the receive wave reflected from the ground surface. The delay signal value generator is connected to the divider, receives the signal generated from the waveform generator, and generates a delay signal value linked to the bit frequency of the signal received from the waveform generator. The shortened signal value generating unit is connected to the delayed signal value generating unit and generates a shortened signal value corresponding to the delayed signal value applied from the delayed signal value generating unit. The delay signal correction unit is connected to the delay signal value generator and the shortened signal value generator, receives the delayed signal value and the shortened signal value from the delayed signal value generator and the shortened signal value generator, respectively, and shortens the signal. generate a delayed signal. The second mixer is connected to the reception antenna and the delay signal correction unit, and generates a second demodulation signal by mixing the received wave applied from the reception antenna and the shortened delay signal received from the delay signal correction unit. . The second raw data generator is connected to the second mixer and generates second raw data from the second demodulation signal applied from the second mixer. The back projection unit receives the second raw data and calculates a function value for each pixel in the composite aperture. The image restoration unit is connected to the back projection unit, and restores an image within the composite aperture using the function value for each pixel applied from the back projection unit. The delay signal correction unit generates a shortened delay signal using [Equation 9], and the second raw data generation unit generates the second raw data from the second demodulation signal using [Equation 10] ([ In Equation 9], f ₀ represents the center frequency, t represents time, d represents the delay signal value, Δd represents the shortened signal value, K _r represents the modulation rate, and in [Equation 10], t represents time, u represents the position of the aircraft, Sr(t,u) represents the received wave, S _sd *(t,u) represents the matched filter of the second demodulation signal, f ₀ represents the center frequency , where K _r represents the modulation rate, d represents the delay signal value, Δd represents the shortened signal value, and τ(u) represents the target delay time as shown in [Equation 4], in [Equation 4] , R(u) represents the distance between the position (u) of the aircraft and the target, (x,y,z) represents the coordinates of the target, (u _x ,u _y ,u _z ) represents the coordinates of the aircraft , c represents the speed of light).

[Equation 4]

[Equation 9]

[Equation 10]

In the image restoration method using the aircraft-based sea level image restoration device according to an embodiment of the present invention, the aircraft-based sea level image restoration device is connected to a waveform generator for generating a signal of the same waveform as a transmission wave and the waveform generator, An antenna member including a divider receiving and distributing the signal generated from the waveform generator, a transmit antenna connected to the divider for transmitting a transmit wave, and a receive antenna for receiving a receive wave, connected to the divider and the receive antenna a first mixer for generating a first demodulation signal; a first raw data generating unit connected to the first mixer and generating first raw data; and a delayed signal value connected to the divider and generating a delayed signal value. a delay signal value generator connected to the delayed signal value generator and generating a shortened signal value; and a delay signal connected to the delay signal value generator and the shortened signal value generator to generate a shortened delay signal. A correction unit, a second mixer connected to the reception antenna and the delay signal correction unit and generating a second demodulation signal; a second raw data generator that generates raw data; an inverse projection unit that is connected to the first raw data generator and the second raw data generator and calculates a function value for each pixel within the composite aperture; and an image restoration unit that is connected to and restores an image within the composite aperture using the function value for each pixel applied from the back projection unit. In the aircraft-based sea level image restoration method, first, the transmission wave is transmitted onto the ground surface using the transmission antenna, and the reception wave reflected from the land surface is received through the reception antenna. Subsequently, the first demodulation signal is generated by mixing the signal distributed from the divider and the received wave received from the reception antenna using the first mixer. Thereafter, the first raw data is generated from the first demodulation signal using the first raw data generator. Then, by using the delay signal value generation unit, the signal generated from the waveform generator is applied and the delay signal value linked to the bit frequency of the signal applied from the waveform generator is generated. Subsequently, the shortened signal value corresponding to the delayed signal value is generated using the shortened signal value generator. Thereafter, the shortened delay signal is generated using the delay signal value and the shortened signal value by using the delay signal correction unit. Subsequently, the second demodulation signal is generated by mixing the received wave and the shortened delayed signal using the second mixer. Subsequently, the second raw data is generated from the second demodulated signal using the second raw data generator. Thereafter, the first raw data and the second raw data are applied using the back projection unit, and a function value for each pixel within the composite aperture is calculated. Subsequently, the image in the composite aperture is restored using the function value for each pixel applied from the back projection unit by using the image restoration unit.

According to the present invention as described above, it is possible to build a radar system that is not affected by the total reflection characteristics of the sea level in the aircraft-based sea level image restoration device.

In addition, it is possible to easily remove the effect of the total reflection characteristics of the sea surface by simple modification by applying a shortened delay signal value without the need to build a separate expensive equipment. Since most of the components of the existing FMCE-SAR radar system can be used as is, exploration cost and time are reduced.

In addition, in order to accurately observe phenomena occurring in various areas of the sea surface, a shortened signal value is applied in addition to the delay signal value, so that points on the sea surface can be observed freely without being bound to the preset delay signal value according to the signal of the waveform generator. there is.

In addition, through actual aircraft experiments, the aircraft-based sea level image restoration device having the configuration of the present invention can acquire high-quality sea level images with appropriate resolution and total reflection characteristics removed in the range of the transmission wave angle from 3.5 ° to 35 °. . In addition, in order to obtain a high-quality sea surface image with appropriate resolution and total reflection characteristics removed, the delay signal value is 1/2 of the sampling frequency, and the shortened signal value may have a value obtained by multiplying the delay signal value by 0.1 to 0.2.

In addition, since the delayed signal value and the shortened signal value are simultaneously applied, it is possible to easily remove an area with low resolution generated when only the delayed signal value is applied.

In addition, even when it is impossible to arbitrarily adjust the delayed shortened distance, sea level observation can be easily performed by adjusting the altitude of the aircraft.

1 is a conceptual diagram illustrating a marine observation method to which an aircraft-based image restoration apparatus according to a comparative embodiment of the present invention is applied.
FIG. 2 is an image showing a synthetic aperture image obtained using the aircraft-based sea level image restoration apparatus shown in FIG. 1 .
FIG. 3 is a graph showing signal strength of line II′ of FIG. 2 .
4 is a block diagram showing an aircraft-based sea level image restoration apparatus according to an embodiment of the present invention.
FIG. 5 is a graph showing a first demodulation signal output from a first mixer of the aircraft-based sea level image restoration apparatus shown in FIG. 1 .
FIG. 6 is an image showing a region processed by the first demodulation signal shown in FIG. 5 .
7 is a graph showing a demodulation signal generated using only delay signal values in another embodiment.
FIG. 8 is a graph showing a second demodulation signal output from a second mixer of the aircraft-based sea level image restoration apparatus shown in FIG. 1 .
FIG. 9 is an image showing a region processed by the second demodulation signal shown in FIG. 8 .
10 is a flowchart illustrating an image restoration method using the aircraft-based sea level image restoration apparatus shown in FIG. 4 .
11 is a block diagram showing an aircraft-based sea level image restoration apparatus according to another embodiment of the present invention.
12 is a flowchart illustrating an image restoration method using the aircraft-based sea level image restoration apparatus shown in FIG. 11 .
13 is a conceptual diagram illustrating an image restoration method using an aircraft-based sea level image restoration apparatus according to another embodiment of the present invention.
14 to 19 are graphs illustrating Experimental Example 1 using the aircraft-based sea level image restoration apparatus shown in FIG. 4 .
FIG. 20 is an image showing the position of the composite aperture of Experimental Example 2 using the aircraft-based sea level image restoration apparatus shown in FIG. 4 .
FIG. 21 is an image showing a terrestrial observation image obtained by reconstructing a first demodulation signal corresponding to a terrestrial observation area indicated by a normal setup in FIG. 20 .
FIG. 22 is an image showing a sea level observation image indicated as a near zone in FIG. 20 .
23 is an image obtained by using the aircraft-based sea level image restoration apparatus shown in FIG. 4 to observe an area where the angle of a transmitted wave is 0° to 49° on the ground surface.
FIG. 24 is a graph showing resolution in the horizontal direction of the image shown in FIG. 23 .
FIG. 25 is a graph showing the resolution in the horizontal direction and the resolution in the vertical direction of the image shown in FIG. 23 together.
FIG. 26 is an image showing a sea level image restored using the first demodulation signal of the aircraft-based sea level image restoration apparatus shown in FIG. 4 .
FIG. 27 is a graph showing function values for each pixel of the image shown in FIG. 26 by overlapping cross-sectional views.
28 is an image showing a sea level image restored using the second demodulation signal of the aircraft-based image restoration apparatus shown in FIG. 4 .
FIG. 29 is a graph showing function values for each pixel of the image shown in FIG. 28 by overlapping cross-sectional views.
30 is an image showing a sea level image restored using a second demodulation signal in which the aircraft-based sea level image restoration apparatus shown in FIG. 4 is configured to have two channels.
FIG. 31 is a graph showing the overlapping function values of each pixel of the image shown in FIG. 30 .
32 is an image showing phase components by interferometry signal processing on signals generated from two channels.
FIG. 33 is a graph showing the overlapping function values of each pixel of the image shown in FIG. 32 .
34 is an image showing coherence by performing interferometry signal processing on signals generated from two channels.
35 to 40 are images obtained by restoring sea level images using the aircraft-based sea level image restoration apparatus shown in FIG. 4 by flying an aircraft over various sea levels.

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

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

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this application, terms such as "comprise" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should 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 defined otherwise, 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 unless explicitly defined in the present application, they should not be interpreted in an ideal or excessively formal meaning. don't

1 is a conceptual diagram illustrating a marine observation method to which an aircraft-based image restoration apparatus according to a comparative embodiment of the present invention is applied. In FIG. 1, the aircraft performs observation along the coastline in the sea adjacent to the coastline, θ _i,sea represents the angle of incidence when the transmitted wave is irradiated for maritime observation, and θ _i,land represents the incident angle when the transmitted wave is irradiated for terrestrial observation. Indicates the angle of incidence when irradiated for

FIG. 2 is an image showing a synthetic aperture image obtained using the aircraft-based sea level image restoration apparatus shown in FIG. 1 . 2, the horizontal axis represents the distance direction (m), and the vertical axis represents the azimuth direction (m).

FIG. 3 is a graph showing signal strength of line II′ of FIG. 2 . In FIG. 3, the horizontal axis represents the distance direction (m), and the vertical axis represents the signal strength (dB).

1 to 3, since the aircraft-based sea level image restoration apparatus according to the comparative embodiment is optimized for the purpose of ground observation, it is easy to observe the terrain or structures on the ground, but the radio response characteristics of the sea surface Since it is very low, there is a problem in that the sea level is displayed in black on the synthetic aperture.

4 is a block diagram showing an aircraft-based sea level image restoration apparatus according to an embodiment of the present invention.

Referring to FIG. 4, the aircraft-based sea level image restoration apparatus includes antenna members 110 and 120, a waveform generator 150, a divider 160, a first mixer 205, a first raw data generator 210, a delay A signal value generator 301, a shortened signal value generator 3030, a delayed signal corrector 305, a second mixer 307, a second raw data generator 310, a raw data adder 320, It includes a back projection unit 230 and an image restoration unit 240 .

The waveform generator 150 generates a signal of the same waveform as the transmission wave 2. The waveform generator 150 may generate various signals such as a triangular wave, a sawtooth wave, and the like. For example, a sawtooth wave refers to a waveform whose frequency constantly increases with time, and then the frequency is initialized and then constantly increased again at predetermined intervals. Since the sawtooth wave can directly measure the Doppler frequency according to distance, it can provide speed information according to distance.

The divider 160 is connected to the waveform generator 150, the transmission antenna 110 of the antenna members 110 and 120, the first mixer 205, and the delay signal value generator 301. The divider 160 receives the signal generated from the waveform generator 150 and distributes it to the transmission antenna 110, the first mixer 205, and the delay signal value generator 301.

The antenna members 110 and 120 transmit the transmission wave 2 of the signal applied from the distributor 160 and receive the reception wave 4 reflected from the sea level. In this embodiment, 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.

The transmission wave 2 transmitted through the transmission antenna 110 of the antenna members 110 and 120 can be expressed as a function of time as shown in [Equation 1].

[Equation 1]

In [Equation 1], t represents time, S ₀ (t) represents a transmission wave, f ₀ represents a center frequency, and K _r represents a modulation rate.

The received wave 4 received through the reception antenna 120 of the antenna members 110 and 120 can be expressed as a function of time and the position u of the antenna members 110 and 120 as shown in [Equation 2]. .

[Equation 2]

In [Equation 2], t represents time, u represents the position of the antenna members 110 and 120, S _r (t, u) represents the transmitted wave, f ₀ represents the center frequency, and K _r represents represents the modulation rate, and τ represents the delay time.

The first mixer 205 is connected to the splitter 160 and the receiving antenna 120, mixes the divided signal and the received wave 4 received from the splitter 160 and the receiving antenna 120, and performs first demodulation. generate a signal

FIG. 5 is a graph showing a first demodulation signal output from a first mixer of the aircraft-based sea level image restoration apparatus shown in FIG. 1 . 5, the horizontal axis represents the frequency, the vertical axis represents the signal strength (dB), d represents the delay signal value, Δd represents the signal shortening * shortened signal value, f _s represents the sampling frequency, f _b represents the beat frequency.

Referring to FIG. 5 , in the first mixer 205, an area (left part) displayed as a solid line graph indicates an area where first raw data is generated by the first mixer 205. An area (right part) indicated by a dotted line graph represents an area out of the processing range of the first mixer 205 .

The first mixer 205 mixes the signal of the waveform generator 150 and the received wave 4 as they are through the first mixer 205 without considering the delay signal value d or the shortened signal value Δd. do.

The first raw data generator 210 is connected to the first mixer 205 and generates first raw data from the first demodulation signal generated by the first mixer 205 using [Equation 3]. The first raw data corresponds to a composite aperture image corresponding to the half power beam width (HPBW _θ ) region before and after the incident angle of the transmission wave 2, and represents a terrestrial observation image in the present invention.

[Equation 3]

In [Equation 3], τ(u) is the target delay time and can be expressed as in [Equation 4].

[Equation 4]

FIG. 6 is an image showing a region processed by the first demodulation signal shown in FIG. 5 . In FIG. 6, the incident angle of the transmission wave 2 is 45°, HPBW _θ represents the half-power beam width, H ₀ represents the altitude of the aircraft, and R _d represents the aircraft corresponding to the minimum incident angle of the transmission wave 2 and Represents the ground range between ground surfaces, R _g represents the distance on the ground surface, R _g,c represents the distance to the center of the ground observation, R _g,1 represents the minimum distance of the ground observation, R _g,2 represents the longest distance for ground observation.

5 and 6, the first demodulation signal generated by the first mixer 205 is applied to the reflected wave 4 centered at a preset angle of incidence (eg, θ _i = 45°) among the reflected waves 4. Corresponds. The area to be observed (eg, the ground surface) is arranged between the minimum distance (R _g,1 ) and the maximum distance (R _g,2 ) of ground observation.

Referring again to FIG. 4, the delayed signal value generator 301 is connected to the divider 160 and receives the signal generated from the waveform generator 150, and receives the bit frequency (f) of the signal received from the waveform generator 150. A delay signal value (d) corresponding to _b ) is generated. In an embodiment of the present invention, the delay signal value (d) may be expressed in a unit of frequency. In one embodiment, the delay signal value generator 301 may set a value corresponding to 1/2 of the bit frequency f _b as the delay signal value d.

The delay signal considering the delay signal value d can be expressed as a function of time t as shown in [Equation 5].

[Equation 5]

In [Equation 5], the delay signal value (d) is the linear distance between the aircraft and the ground corresponding to the minimum incident angle of the transmitted wave (2) (Ground Range; R _g ) and the speed of light (c) as shown in [Equation 6] below. can be expressed as a function of

[Equation 6]

7 is a graph showing a demodulation signal generated using only delay signal values in another embodiment. In FIG. 7, the horizontal axis represents the frequency, the vertical axis represents the signal strength (dB), d represents the delay signal value, f _s represents the sampling frequency, and f _b represents the bit frequency.

Referring to FIG. 7, the delay demodulation signal S _ddc (t, u) generated by demodulating the received wave 4 represented by [Equation 2] and the delay signal represented by [Equation 5] is 7].

[Equation 7]

In [Equation 7], τ(u) is the target delay time and can be expressed as in [Equation 4].

In FIG. 7, an area (left part) indicated by a solid line graph indicates an area where raw data is generated using the delayed demodulation signal S _ddc (t, u). A region (right part) indicated by a dotted line graph represents a region out of the processing range of the delay mixer S _ddc (t, u).

When the delay demodulation signal S _ddc (t, u) is generated by applying only the delay signal value d, it is possible to observe the sea surface area adjacent to the aircraft by changing the observation range. However, since the delay signal value (d) is a value preset by the waveform generator 150 as an intermediate value of the beat frequency (f _b ), it is impossible to arbitrarily adjust the incident range and reflection range of the radio waves 2 and 4. . In addition, it is difficult to properly recognize a reconstructed image within a synthesized aperture because the resolution rapidly decreases near the delay signal value d, which is an intermediate value of the bit frequency f _b .

In an embodiment of the present invention, in order to accurately observe phenomena occurring in various areas of the sea surface, a short signal value Δd is additionally applied to the delay signal value d. In an embodiment of the present invention, the shortened signal value (Δd) may be expressed in a unit of frequency. In the embodiment of the present invention, the sea surface area at a desired point can be accurately observed by simultaneously applying the delay signal value d and the shortened signal value Δd to the second mixer 307 . Hereinafter, a configuration in which the delay signal value d and the shortened signal value Δd are simultaneously applied to the second mixer 307 will be described.

Referring back to FIG. 4, the shortened signal value generator 303 is connected to the delayed signal value generator 301, and the shortened signal corresponding to the delayed signal value d received from the delayed signal value generator 301. Produces a value (Δd). For example, the shortened signal value (Δd) or the shortened delayed signal value (d−Δd) can be determined using the following [Equation 8].

[Equation 8]

In [Equation 8], H ₀ represents the altitude of the aircraft, and c represents the speed of light.

In another embodiment, the shortened signal value Δd may be determined by multiplying the delayed signal value d by a preset shortening ratio (eg, 0.1 to 0.2). At this time, if the shortened signal value (Δd) is smaller than 0.1 of the delayed signal value (d), there is a problem that the resolution of the restored image is lowered, and if it has a value larger than 0.2, the image is displayed in black. there is Preferably, the shortened signal value (Δd) may be a value obtained by multiplying the delayed signal value (d) by 0.15.

In another embodiment, the shortened signal value Δd may be changed according to an area to be detected by the aircraft-based sea level image restoration device within the composite aperture. For example, the delayed shortened signal value (d-Δd) may be set so that the angle (thick dotted line in FIG. 9) of the transmission wave (2 in FIG. 4) generating the second demodulation signal is 3.5° to 35°. can If the angle of the transmission wave is smaller than 3.5°, the distance direction resolution of the reconstructed image rapidly deteriorates and the displayed image cannot be interpreted. When the angle of the transmitted wave is greater than 35°, the sea surface appears black due to the total reflection characteristic of the sea surface.

The delay signal correction unit 305 is connected to the delay signal value generation unit 301 and the short signal value generation unit 303, and the delayed signal value generation unit 301 and the short signal value generation unit 303 respectively output the delayed signals. The value d and the shortened signal value Δd are applied. The delay signal correction unit 305 subtracts the shortened signal value (Δd) from the delay signal value (d) and uses the shortened delay signal value (d-Δd = d') to obtain a shortened delay signal (S _sd (t) )) to generate

The shortened delay signal S _sd (t) generated by the delay signal correction unit 305 can be expressed using [Equation 9].

[Equation 9]

The second mixer 307 is connected to the reception antenna 120 and the delayed signal correction unit 305, and transmits the received wave 4 received from the reception antenna 120 and the shortened signal received from the delay signal correction unit 305. A second demodulation signal is generated by mixing the delay signal S _sd (t). The second mixer 307 applies the second demodulation signal to the second raw data generator 310 .

FIG. 8 is a graph showing a second demodulation signal output from a second mixer of the aircraft-based sea level image restoration apparatus shown in FIG. 1 . 8, the horizontal axis represents the frequency, the vertical axis represents the signal strength (dB), d represents the delay signal value, Δd represents the signal shortening * shortened signal value, f _s represents the sampling frequency, f _b represents the beat frequency.

Referring to FIGS. 1 and 8 , an area (left part) indicated by a solid line graph indicates an area where second raw data is generated by the second mixer 307 . An area (right part) indicated by a dotted line graph represents a region outside the processing range of the second mixer 307.

The second mixer 307 delays the received wave 4 using a shortened delay signal value (d-Δd) generated by simultaneously considering the delay signal value (d) and the shortened signal value (Δd).

Referring back to FIG. 4 , the second raw data generator 310 is connected to the second mixer 307 and generates second raw data such as [Equation 10] from the second demodulated signal.

[Equation 10]

In [Equation 10], t represents time, u represents the position of the aircraft, Sr(t,u) represents the received wave, S _sd *(t,u) represents the matched filter of the second demodulation signal, , f ₀ denotes the center frequency, K _r denotes the modulation rate, d denotes the delay signal value, Δd denotes the shortened signal value, and τ(u) denotes the target delay time. can be shown together.

FIG. 9 is an image showing a region processed by the second demodulation signal shown in FIG. 8 . In FIG. 9, the incident angle of the transmission wave 2, the half power beam width (HPVW _θ ), and the aircraft altitude (H ₀ ) are the same as those in FIG. 6, but the minimum distance (R' _g,1 ) of ground observation and ground observation The longest distance (R' _g,2 ) is moved in a direction adjacent to the aircraft compared to FIG. 6 due to the shortened delay signal value (d-Δd = d'). Therefore, the straight line distance between the aircraft and the ground corresponding to the minimum incident angle of the transmission wave (2) has a delayed short distance (R' _d ) that is less than the ground observation distance (Ground Range, R _d ). That is, the delayed shortened distance (R' _d ) has a smaller value than the ground observation distance (R _d ) (R' _d <R _d ).

Referring back to FIG. 4 , the raw data summing unit 320 is connected to the first raw data generator 210 and the second raw data generator 310, so that the first raw data generator 210 and the second raw data generator 210 The first raw data and the second raw data are respectively applied from the raw data generating unit 310 to generate summed raw data. The summed raw data includes first raw data representing the shape of the ground and second raw data representing the shape of the sea surface. In another embodiment, the raw data summing unit 320 is omitted, and the first raw data and the second raw data respectively generated from the first raw data generator 210 and the second raw data generator 310 are directly It may be applied to the back projection unit.

The back projection unit 230 is connected to the raw data summing unit 320 and receives the summed raw data to calculate a function value for each pixel. The back projection unit 230 calculates the calculated function value for each pixel by performing the operation of [Equation 11].

[Equation 11]

In [Equation 11], f(x _i ,y _j ) denotes the function value of the ij th pixel, P denotes the total number of pixels, p denotes the number of pixels corresponding to each function value, and Wp is p Represents the magnitude function of the th received signal, t represents time, u _p represents the position of the antenna member corresponding to the p th received signal, S _sddc (t, u _p ) is a demodulation signal corresponding to the shortened delay signal , and S ^* _M (t _d (u _p )) represents a matched filter of a demodulation signal corresponding to the shortened delay signal.

The image restoration unit 240 is connected to the back projection unit 230 and restores an image within the synthetic aperture using the function value for each pixel applied from the back projection unit 230 .

10 is a flowchart illustrating an image restoration method using the aircraft-based sea level image restoration apparatus shown in FIG. 4 .

4 and 10, in the image restoration method using the aircraft-based sea level image restoration device, first, a signal having the same waveform as the transmission wave 2 is generated using a waveform generator 150, and a divider 160 The signal received from the waveform generator 150 is distributed using (S100). Specifically, the divided signal is transmitted to the transmission antenna 110, the first mixer 205, and the delayed signal value generator 301 using the divider 160.

Subsequently, a transmission wave 2 is generated from the distributed signal using the transmission antenna 110 and transmitted to the target (S110). The transmission wave 2 can be expressed as a function of time t as in [Equation 1]. The transmission wave 2 is reflected from the target and a reception wave 4 is generated. The received wave 4 can be expressed as a function of the time t and the position u of the antenna members 110 and 120 as shown in [Equation 2].

Then, the reception wave 4 reflected from the target is received using the reception antenna 120 (S120).

Subsequently, the first raw data is generated by mixing the signal distributed through the divider 160 and the received wave 4 (S130). Specifically, the signal distributed through the divider 160 is mixed with the received wave 4 received through the reception antenna 120 using the first mixer 205 . The first raw data generation unit 210 generates first raw data corresponding to the inverse inverse beam width before and after the incident angle from the signal received from the first mixer 205 using [Equation 3]. The first raw data corresponds to the solid line graph part in FIG. 5 and the in-line part in FIG. 6 .

Subsequently, a delayed signal value is generated from the distributed signal using the delayed signal value generator 301 (S140). Specifically, the delay signal value generator 301 uses the ground range (R _g ) between the aircraft and the ground surface corresponding to the minimum incident angle of the transmission wave (2) and the light speed (c) as shown in [Equation 6] A delay signal value (d) can be generated.

Thereafter, the shortened signal value Δd corresponding to the delayed signal value d is generated using the shortened signal value generator 303 (S150). For example, the shortened signal value (Δd) can be obtained using the altitude (H ₀ ) of the aircraft and the speed of light (c) as shown in [Equation 8].

Subsequently, a shortened delay signal is generated using the delay signal correction unit 305 (S160). Specifically, the delay signal shortened by applying the delay signal value (d) and the shortened signal value (Δd) generated from the delay signal value generator 301 and the shortened signal value generator 303 to [Equation 9], respectively. A signal delayed by the value (d-Δd = d') is generated.

Subsequently, second raw data is generated by mixing the shortened delay signal generated through the delay signal correction unit 305 and the received wave 4 (S170). Specifically, the second mixer 307 is used to mix the shortened delay signal generated through the delay signal correction unit 305 with the received wave 4 received through the reception antenna 120 . The second raw data generator 310 generates second raw data corresponding to the sea surface area by decreasing the incident angle from the signal received from the second mixer 307 using [Equation 10]. The second raw data corresponds to the solid line graph part in FIG. 8 and the in-line part in FIG. 9 .

Then, the first raw data received from the first raw data generator 210 and the second raw data received from the second raw data generator 310 are summed using the raw data summing unit 320 ( S180). Specifically, the raw data summing unit 320 sums the first raw data corresponding to the terrestrial area and the second raw data corresponding to the sea surface area to generate summed raw data representing both the land and the sea level. In another embodiment, only the sea surface area may be observed by omitting the first raw data and using only the second raw data.

Subsequently, the summation raw data is back-projected onto the synthesis aperture using the back-projection unit 230 (S190). Specifically, the back projection unit 230 calculates function values corresponding to each pixel on the composite aperture including both the land area and the sea level area by using [Equation 11].

Finally, images of the land area and the sea surface area are generated from the function values applied from the back projection unit 230 using the image restoration unit 240 (S200). Specifically, the image restoration unit 240 reconstructs images of the land area and the sea level area by projecting the function value for each pixel applied from the back projection unit 230 onto a composite aperture including the land area and the sea level area.

11 is a block diagram showing an aircraft-based sea level image restoration apparatus according to another embodiment of the present invention. In FIG. 11, except for the point where the first mixer 205, the first raw data generator 210, and the raw data summing unit 320 are omitted, the remaining components are the same as those of the embodiment shown in FIGS. 4 to 10. Since they are the same, duplicate descriptions of the same components will be omitted. In FIG. 11, the mixer 307 and the raw data generator 310 have the same components as the second mixer 307 and the second raw data generator 310 of FIG. 4, but are expressed as 'second' for convenience of description. is omitted.

Referring to FIG. 11, the aircraft-based sea level image restoration device includes antenna members 110 and 120, a waveform generator 150, a divider 160, a delay signal value generator 301, a shortened signal value generator 3030, It includes a delay signal correction unit 305, a mixer 307, a raw data generator 310, an back projection unit 230, and an image restoration unit 240.

The waveform generator 150 generates a signal of the same waveform as the transmission wave 2.

The divider 160 is connected to the waveform generator 150, the transmission antenna 110 of the antenna members 110 and 120, and the delay signal value generator 301, receives the signal generated from the waveform generator 150, and transmits the signal. distributed to the antenna 110 and the delayed signal value generator 301.

The antenna members 110 and 120 transmit the transmission wave 2 of the signal applied from the distributor 160 and receive the reception wave 4 reflected from the sea level.

The delay signal value generator 301 is connected to the divider 160 and receives the signal generated from the waveform generator 150, and receives the delay signal corresponding to the bit frequency f _b of the signal applied from the waveform generator 150. produces a value (d).

The delay signal considering the delay signal value (d) can be expressed as a function of time (t) as in [Equation 5], and the delay signal value (d) is the minimum incident angle of the transmission wave (2) as in [Equation 6]. It can be expressed as a function of the ground range (R _g ) and the speed of light (c) between the aircraft and the ground surface corresponding to .

The shortened signal value generator 303 is connected to the delayed signal value generator 301, and the shortened signal value corresponding to the delayed signal value d applied from the delayed signal value generator 301 as shown in [Equation 8] (Δd).

The delay signal correction unit 305 is connected to the delay signal value generation unit 301 and the short signal value generation unit 303, and the delayed signal value generation unit 301 and the short signal value generation unit 303 respectively output the delayed signals. The value d and the shortened signal value Δd are applied. The delay signal correction unit 305 subtracts the shortened signal value (Δd) from the delay signal value (d) and uses the shortened delay signal value (d-Δd = d') as shown in [Equation 9]. Generates a signal S _sd (t).

The mixer 307 is connected to the receiving antenna 120 and the delayed signal correcting unit 305, and receives the received wave 4 and the shortened delayed signal S _sd from the receiving antenna 120 and the delayed signal correcting unit 305, respectively. (t)) is authorized. The second mixer 307 mixes the received wave 4 and the shortened delay signal S _sd (t) and applies the mixture to the raw data generator 310.

The raw data generation unit 310 is connected to the mixer 307, and uses the received wave 4 and the shortened delay signal S _sd (t) received from the mixer 307 to generate the following [Equation 10] and generate the same demodulation signal. In an embodiment of the present invention, the raw data corresponds to the shape of the sea surface.

The back projection unit 230 is connected to the raw data generator 310 and receives the raw data, and calculates the function value for each pixel by performing the operation of [Equation 11].

The image restoration unit 240 is connected to the back projection unit 230 and restores an image within the composite aperture representing the sea level area using the function value for each pixel applied from the back projection unit 230 .

12 is a flowchart illustrating an image restoration method using the aircraft-based sea level image restoration apparatus shown in FIG. 11 .

Referring to FIGS. 11 and 12, in the image restoration method using the aircraft-based sea level image restoration device, first, a signal having the same waveform as the transmission wave 2 is generated using a waveform generator 150, and a divider 160 The signal received from the waveform generator 150 is distributed using (S300).

Subsequently, a transmission wave 2 is generated from the distributed signal using the transmission antenna 110 and transmitted to the target (S310).

Then, the reception wave 4 reflected from the target is received using the reception antenna 120 (S320).

Subsequently, a delayed signal value is generated from the distributed signal using the delayed signal value generator 301 (S330).

Thereafter, a shortened signal value Δd corresponding to the delayed signal value d is generated using the shortened signal value generator 303 (S340).

Subsequently, a shortened delay signal is generated using the delay signal correction unit 305 (S350).

Subsequently, second raw data is generated by mixing the shortened delay signal generated through the delay signal corrector 305 and the received wave 4 using the mixer 307 and the raw data generator 310 (S360). ).

Thereafter, the summation raw data is back-projected onto the synthesis aperture using the back-projection unit 230 (S370). Specifically, the back projection unit 230 calculates function values corresponding to each pixel on the synthetic aperture representing the sea level area using [Equation 11].

Finally, an image of the sea surface area is generated from the function values applied from the back projection unit 230 using the image restoration unit 240 (S380).

13 is a conceptual diagram illustrating an image restoration method using an aircraft-based sea level image restoration apparatus according to another embodiment of the present invention. In FIG. 13, the aircraft-based sea level image restoration device uses the image restoration device shown in FIGS. 4 to 12, and an altitude correction unit (not shown) connected to the delay signal correction unit 305 and changing the altitude of the aircraft. may be further included.

Referring to FIG. 13, in the image restoration method using the aircraft-based sea level image restoration device, an altitude correction unit (not shown) is used to set the aircraft altitude to the ground observation distance (Rd) and the ground observation distance (Rd) at the ground observation altitude (H ₀ ). A step of setting the marine observation altitude (H ₂ ) having the delayed shortened distance (R'd) having the same value is further included.

Specifically, the ground range (Ground Range, R _d ) is the minimum distance between the aircraft and the ground corresponding to the minimum incident angle set in consideration of the half-power beam width (HPBW _θ ) at the incident angle (eg, 45°) of the transmission wave (2). Indicates the distance, and the delayed shortened distance R′ _d represents the minimum distance between the aircraft and the ground surface corresponding to the minimum incident angle at which the transmission antenna 110 is set to observe the sea level.

In this embodiment, in order to set the delayed shortened distance (R' _d ) and the ground observation distance (R _d ) to the same value, the altitude of the aircraft is increased by a predetermined value (ΔH) from the ground observation altitude (H ₀ ) Just change it to the altitude for sea level observation (H ₂ ). For example, by changing the altitude value of [Equation 8], the setting for ground observation can be changed to the setting for sea level observation.

Thereafter, sea level observation may be performed by performing the steps shown in FIG. 10 or FIG. 12 . Subsequent steps are the same as those shown in FIG. 10 or 12, and therefore, duplicate descriptions of the same components are omitted.

According to the present embodiment as described above, even when it is impossible to arbitrarily adjust the delayed shortened distance R′ _d , it is possible to easily perform sea level observation by adjusting the altitude of the aircraft.

Experimental Example 1

14 to 19 are graphs illustrating Experimental Example 1 using the aircraft-based sea level image restoration apparatus shown in FIG. 4 . 4, 14 to 21, the frequency of the transmission wave (2) was 10.25 GHz, the bandwidth of the transmission wave (2) was 500 MHz, and the transmission power of the transmission wave (2) was 1 Watt (30 dBm) at most , the sampling rate was 1.2 MHz, the resolution was 0.3 m based on the slant range, the data collection time was 30 seconds, the pulse repetition frequency (PRF) was 1 KHz, and the half-power beam width ( HPBW) was 11.4° in the E-field and 37.9° in the H-field, horizontal polarization was used, the receiving channel was 2 channels with a baseline of 48.26 cm, and the flight altitude (H ₀ ) was 500 m.

Hereinafter, the signal attenuation characteristics on the sea level of the transmission wave (2 in FIG. 4) are analyzed.

The signal attenuation characteristic (A(θ _inc )) on the sea level can be expressed as a function of the incident angle (θ _inc ) as shown in [Equation 12].

[Equation 12]

In [Equation 12], θ _inc represents the incident angle, σ ° represents the backscattering coefficients, R represents the distance along the distance direction, and H represents the altitude. The signal attenuation characteristic (A(θ _inc )) can be obtained by multiplying the radio wave response characteristic on the sea level, the radiation pattern, and the distance attenuation. In an embodiment of the present invention, the propagation response characteristics can be represented by backscattering coefficients (σ°).

14 is a graph showing backscattering coefficients (σ°) according to the incident angle (θ _inc ) of the transmission wave 2 of the aircraft-based sea level image restoration apparatus shown in FIG. 4, and FIG. 15 is shown in FIG. It is a graph showing the radio wave response characteristics of the transmitted wave (2) of the aircraft-based sea level image restoration device divided into vertical polarization (VV) and horizontal polarization (HH). In FIG. 14, HH represents the response of horizontal polarization, IEM-exp. represents the integral equation model (IEM) experimental model, and IEM-Gaus. represents the integral equation Gaussian experimental model. Indicates, Exp. + Gaus. indicates an experimental model that combines the above two methods, and Means. indicates that the angle of incidence of the transmission wave 2 in the aircraft-based sea level image restoration device shown in FIG. 4 is 0 ° and 10 °, respectively. , the actual measured values of the backscattering coefficients (σ°) at 20°, 30°, 40°, and 50°. In FIG. 15, VV represents a response of vertical polarization, and HH represents a response of horizontal polarization. In FIGS. 14 and 15, the horizontal axis represents the incident angle (θ _inc ), and the vertical axis represents backscattering coefficients (σ°).

Referring to FIG. 14 , backscattering coefficients (σ°) representing radio wave response characteristics on the sea level decreased as the incident angle (θ _inc ) increased. The radio wave response characteristics (square symbols) of the aircraft-based sea level image restoration device shown in FIG. ) gave similar results.

Referring to FIG. 15, the response of vertical polarization (VV) of vertical polarization showed higher propagation response characteristics than the response of horizontal polarization (HH).

16 is a graph showing antenna radiation patterns (dB) according to elevation angles (θ _ev ) of the aircraft-based sea level image restoration apparatus shown in FIG. 4, and FIG. 17 is a radio wave response shown in FIGS. 14 and 15 It is a graph showing the signal strength obtained by multiplying the characteristics by the radiation pattern of FIG. 16. In FIG. 16, the horizontal axis represents elevation angles (θ _ev ), and the vertical axis represents the radiation pattern (dB). In FIG. 15, the horizontal axis represents the incident angle (θ _inc ), and the vertical axis represents the signal strength (dB) considering both the radio response characteristics and the radiation pattern.

Referring to FIG. 16, when the elevation angle (θ _ev ) of the transmission antenna 110 is 0°, there is no effect of the radiation pattern, but the elevation angle (θ _ev ) is far from 0°. As the radiation pattern increased, the effect of the radiation pattern increased.

Referring to FIG. 17, considering the radio wave response characteristics of FIGS. 14 and 15 and the radiation pattern of FIG. 16, the signal strength gradually increased as the incident angle (θ _inc ) increased.

18 is a graph showing sea level radio wave response characteristics (or signal attenuation characteristics) for each incident angle considering the radio wave response characteristics, radiation patterns, and distance attenuation shown in FIGS. 14 to 17 in the aircraft-based sea level image restoration apparatus shown in FIG. 4 19 is a graph showing sea level radio wave response characteristics (or signal attenuation characteristics) for each ground range considering the radio wave response characteristics, radiation patterns, and distance attenuation shown in FIGS. 14 to 18 together. In FIG. 19, the horizontal axis represents the ground range relative to the aircraft, and the vertical axis represents the normalized attenuation of range (dB). 18 and 19, the horizontal axis represents the incident angle (θ _inc ), the vertical axis represents the normalized attenuation of range (dB), and the thick solid line represents the polarization of the vertical polarization calculated by [Equation 12] It represents the response characteristic (VV), the thick dotted line represents the polarization response characteristic (HH) of horizontal polarization calculated by [Equation 12], the thin solid line represents the normalized signal attenuation characteristic of vertical polarization, and the thin dotted line represents the horizontal polarization represents the normalized signal attenuation characteristics of

Referring to FIG. 18, the distance attenuation increased as the incident angle (θ _inc ) increased, and when the threshold of signal attenuation for sea level image restoration was set to -25 dB, sea level image restoration was possible in the range of 30 ° or less of the incident angle .

Referring to FIG. 19, the distance attenuation increased as the ground range increased, and when the threshold of signal attenuation for sea level image restoration was set to -25 dB, the flight altitude (H ₀ ) was 500 m above the ground surface Sea level image restoration was possible in the range of 300 m or less in the ground range. In this Experimental Example 1, the distance on the ground surface where sea level image restoration is possible based on the aircraft showed a value of 60% or less of the flight altitude (H ₀ ).

Experimental Example 2

In this Experimental Example 2, the image was restored using data obtained while flying the aircraft-based sea level image restoration apparatus shown in FIG. 4 over the sea surface separated by a distance of 200 m from the coastline.

FIG. 20 is an image showing the position of the composite aperture of Experimental Example 2 using the aircraft-based sea level image restoration apparatus shown in FIG. 4 . 4 and 20, the frequency of the transmission wave 2 was 10.25 GHz, the bandwidth of the transmission wave 2 was 500 MHz, the transmit power of the transmission wave 2 was a maximum of 1 Watt (30 dBm), and the sampling The speed was 1.2 MHz, the resolution was 0.3 m based on the slant range, the data collection time was 30 seconds, the pulse repetition frequency (PRF) was 1 KHz, and the half power beam width (HPBW) was It was 11.4° in the E-field, 37.9° in the H-field, HH-polarization was used, the receiving channel was 2 channels with a baseline of 48.26 cm, and the flight altitude (H ₀ ) was 500 m, the flight distance was 1 km, and it flew over the sea surface at an average distance of 200 m from the coastline.

In the first demodulation signal output from the first mixer 205 of the aircraft-based sea level image restoration apparatus, the minimum ground observation distance (R _g,1 in FIG. 6) of the transmission wave (2 in FIG. 4) was 300 m, and the ground observation The maximum distance (R _g,2 in FIG. 6 ) was 1,000 m, the angle of the transmission wave corresponding to the half power beam width (HPBW _θ in FIG. 6 ) was 30° to 63°, the resolution was 0.3 m, and the reconstructed image The noise signal of was less than -22.5 dB.

The delay time (dechirp-delay, d) of the second demodulation signal output from the second mixer 307 of the aircraft-based sea level image restoration device was 3.9 μs, and the shortened signal value (Δd) was 0.6 μs. , the shortened delay time (d-Δd), which is the shortened delay signal value, was 3.3 μs (2H ₀ /c, H ₀ is altitude, c is light speed). The minimum ground observation distance (R' _g,1 in FIG. 9) of the transmission wave (2 in FIG. 4) was 30 m, and the maximum ground observation distance (R' _g,2 in FIG. 9) was 600 m and the shortened delay signal The angle of the transmitted wave for observing the sea level after being corrected by the value was 3.5° to 49°, but the maximum distance of the sea level at which a meaningful sea level image can be observed through the second demodulation signal is up to 350 m based on the position of the aircraft on the ground. and the maximum incident angle at which significant sea level images could be acquired was 35°. The resolution of the sea level image reconstructed through the second demodulation signal was 0.5 m to 3.5 m, and the noise signal of the reconstructed image was -22.5 dB or less.

20 is an image showing an experimental area of Experimental Example 2 using the aircraft-based sea level image restoration apparatus shown in FIG. 4 . In FIG. 20, the aircraft traveled along a line spaced about 200 m from the coastline toward the sea, where Az represents an azimuth direction and Rg represents a distance direction (or ground range). The area indicated by the normal setup on the right (white dotted line) indicates an area where the ground observation image is restored by the first demodulation signal output from the first mixer 205, and the adjacent area on the left (near zone ) (yellow dotted line) is an area where the sea level observation image is restored by the second demodulation signal output from the second mixer 307, and represents a so-called emergency setup. The beam center indicates the center line of the area observed by the transmission wave (2 in FIG. 4).

FIG. 21 is an image showing a terrestrial observation image obtained by restoring a first demodulation signal corresponding to the terrestrial observation area indicated by the normal setup of FIG. 20, and FIG. It is an image representing an observation image. 21 and 22, the horizontal axis represents the ground range from the aircraft, the vertical axis represents the azimuth distance, and the bar on the right represents the function value (dB) obtained by [Equation 11] for each pixel. ).

Referring to FIG. 21, the image of the ground portion was easily restored, but the sea surface portion was displayed in black due to the total reflection characteristics of the sea surface.

Referring to FIG. 22, the image of the sea level is not displayed in black, but gray and black are displayed like spots according to the state of the sea level.

Experimental Example 3

In order to explain the reason why the angle of the transmission wave for observing the sea level is 3.5° or more, corrected by the shortened delay signal value, an experiment of restoring the ground surface image from the area where the angle of the transmission wave is 0° to the area where the angle is 49° Example 3 was performed. In Experimental Example 3, only the surface image was observed and restored in order to remove the total reflection characteristics of the sea surface.

Except for the fact that only the angle of the transmission wave and the ground surface image were restored in Experimental Example 3, the rest of the experimental conditions are the same as those in Experimental Example 2, so duplicate descriptions of the same components will be omitted. In Experimental Example 3, in the area where the angle of the transmission wave is 0 ° to 49 °, the minimum ground observation distance (R' _g,1 in FIG. 9) of the transmission wave (2 in FIG. 4) is 0 m and the maximum ground observation distance is 0 m. This corresponds to a region where the distance (R′ _g,2 in FIG. 9 ) is 600 m.

23 is an image obtained by using the aircraft-based sea level image restoration apparatus shown in FIG. 4, observing an area where the angle of the transmitted wave is 0° to 49° on the ground surface, and FIG. 24 is an image shown in FIG. 23 25 is a graph showing the resolution in the horizontal direction and the resolution in the vertical direction of the image shown in FIG. 23 together. 23 and 25, the horizontal axis represents the distance direction, and the vertical axis represents the azimuth direction. In FIG. 24, the horizontal width represents the distance direction, and the vertical axis represents the resolution. In FIG. 25, ΔRg(R) is a distance direction resolution expressed as a function of distance (R), and ΔAz(R) is an azimuth direction resolution expressed as a function of distance (R).

23 to 25, as the angle of the transmission wave approaches 0°, the resolution in the distance direction rapidly decreases, and when the angle of the transmission wave is smaller than 3.5°, the resolution in the distance direction exceeds 3.5 m and the reconstructed image was displayed distorted. Also, as the angle of the transmitted wave increased, the azimuth resolution slightly increased.

According to Experimental Example 3 as described above, image restoration is possible only when the shortened delay signal value (d-Δd, 3.3 μs) is set so that the angle of the transmission wave generating the second demodulation signal maintains 3.5° or more. .

Experimental Example 4

In order to explain why the angle of the transmission wave for observing the sea level is set to 35 ° or less, which is corrected by the shortened delay signal value, the sea level image is restored from the region where the angle of the transmission wave is 3.5 ° to the region of 49 ° Experimental Example 4 was performed. In Experimental Example 4, the entire area was configured as the sea level area and observed in order to consider the total reflection characteristics of the sea level.

Except for the fact that only the angle of the transmission wave and the sea level image were restored in Experimental Example 4, the rest of the experimental conditions are the same as those in Experimental Example 2, so duplicate descriptions of the same components will be omitted.

26 is an image showing a sea level image restored using the first demodulation signal of the aircraft-based sea level image restoration apparatus shown in FIG. 4, and FIG. 27 is a cross-sectional view of function values for each pixel of the image shown in FIG. 28 is an image showing a sea level image restored using the second demodulation signal of the aircraft-based image restoration apparatus shown in FIG. 4, and FIG. 29 is a function value for each pixel of the image shown in FIG. 28 It is a graph showing superimposed cross-sectional view. 26 and 28, the horizontal axis represents the distance direction, the vertical axis represents the azimuth direction, and the bar on the right represents the function value (dB) for each pixel obtained by [Equation 11]. 27 and 29, the horizontal axis represents the distance direction, and the vertical axis represents the function value (dB) for each pixel obtained by [Equation 11], and the solid line represents the average value of function values having the same ground observation distance in the distance direction.

Referring to FIGS. 26 and 27 , since the angle of the transmission wave of the first demodulation signal exceeds 30°, sea level images are not properly displayed except for a very small portion on the left side.

Referring to FIGS. 28 and 29 , in the case of the second demodulation signal, the function value increased at a distance of less than 350 m corresponding to a transmission wave angle of 35°. Therefore, it was displayed as a visible sea level image.

According to Experimental Example 4 as described above, image restoration is possible only when the shortened delay signal value (d-Δd, 3.3 μs) is set so that the angle of the transmission wave generating the second demodulation signal is maintained at 35° or less. .

Experimental Example 5

In order to explain the reason for setting the angle of the transmission wave corrected by the shortened delay signal value and observing the sea level to 3.5 ° or more and 35 ° or less, the aircraft-based sea level image restoration device shown in FIG. 4 has two channels The configured Experimental Example 5 was performed.

In this Experimental Example 5, except that the aircraft-based sea level image restoration device has two channels, the rest of the experimental conditions are the same as those of Experimental Example 4, so duplicate descriptions of the same components are omitted.

30 is an image showing a sea level image reconstructed using a second demodulation signal in which the aircraft-based sea level image restoration apparatus shown in FIG. 4 is configured to have two channels, and FIG. 31 is each pixel of the image shown in FIG. 30 32 is an image showing phase components by interferometric signal processing of signals generated from two channels, and FIG. 33 is a graph of the image shown in FIG. 34 is an image showing coherence by interferometric signal processing of signals generated from two channels. 30, 32, and 34, the horizontal axis represents the distance direction (range), and the vertical axis represents the azimuth direction (azimuth). The right bar shapes in FIGS. 30, 32, and 34 represent the function value for each pixel obtained by [Equation 11], the closeness value for each pixel using interferometric signal processing, and the phase component for each pixel using interferometric signal processing. indicate 31 and 33, the horizontal axis represents the incident angle of the transmitted wave, and the vertical axis represents the function value for each pixel, and the solid line represents the average value of function values having the same ground observation distance in the distance direction.

Referring to FIGS. 30 to 34 , when the angle of the transmission wave exceeds 35°, the reliability of coherence analysis and phase analysis using interferometry signal processing is rapidly reduced.

Therefore, sea level image restoration is possible only when the shortened delay signal value (d-Δd, 3.3 μs) is set so that the angle of the transmission wave generating the second demodulation signal is maintained at 35° or less.

Experimental Example 6

To verify the aircraft-based sea level image restoration device shown in FIG. 4, the sea level image was restored by flying the aircraft over various sea levels.

In this Experimental Example 6, except that the aircraft was flown on various sea levels, the rest of the experimental conditions are the same as those of Experimental Example 2, so duplicate descriptions of the same components are omitted.

35 to 40 are images obtained by restoring sea level images using the aircraft-based sea level image restoration apparatus shown in FIG. 4 by flying an aircraft over various sea levels.

Referring to FIGS. 35 to 40, a good sea surface image was reconstructed in a region of 30 m to 350 m (when the aircraft altitude (H ₀ ) is 500 m) where the incident angle of the transmitted wave is 3.5° or more and 35° or less.

According to the present invention as described above, it is possible to build a radar system that is not affected by the total reflection characteristics of the sea level in the aircraft-based sea level image restoration device.

In addition, it is possible to easily remove the effect of the total reflection characteristics of the sea surface by simple modification by applying a shortened delay signal value without the need to build a separate expensive equipment. Since most of the components of the existing FMCE-SAR radar system can be used as is, exploration cost and time are reduced.

In addition, in order to accurately observe phenomena occurring in various areas of the sea surface, a shortened signal value is applied in addition to the delay signal value, so that points on the sea surface can be observed freely without being bound to the preset delay signal value according to the signal of the waveform generator. there is.

In addition, through actual aircraft experiments, the aircraft-based sea level image restoration device having the configuration of the present invention can acquire high-quality sea level images with appropriate resolution and total reflection characteristics removed in the range of the transmission wave angle from 3.5 ° to 35 °. . In addition, in order to obtain a high-quality sea surface image with appropriate resolution and total reflection characteristics removed, the delay signal value is 1/2 of the sampling frequency, and the shortened signal value may have a value obtained by multiplying the delay signal value by 0.1 to 0.2.

In addition, since the delayed signal value and the shortened signal value are simultaneously applied, it is possible to easily remove an area with low resolution generated when only the delayed signal value is applied.

In addition, even when it is impossible to arbitrarily adjust the delayed shortened distance, sea level observation can be easily performed by adjusting the altitude of the aircraft.

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

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

2: transmit wave 4: receive wave
110, 120: antenna member 150: waveform generator
160: distributor 205: first mixer
301: delay signal value generation unit d: delay signal value
303: short signal value generating unit △d: short signal value
305: delay signal correction unit 307: second mixer
210: first raw data generator 310: second raw data generator
320: raw data summation unit 230: back projection unit
240: image restoration unit

Claims (6)

a waveform generator for generating a signal of the same waveform as the transmission wave;
a divider connected to the waveform generator and receiving and distributing the signal generated from the waveform generator;
an antenna member connected to the distributor, including a transmission antenna for receiving the divided signal from the distributor and transmitting the transmission wave to the ground surface, and a reception antenna for receiving the reception wave reflected from the ground surface;
a first mixer connected to the divider and the reception antenna and generating a first demodulation signal by mixing the divided signal received from the divider and the received wave received from the reception antenna;
a first raw data generator connected to the first mixer and configured to generate first raw data from the first demodulated signal generated by the first mixer;
a delay signal value generation unit connected to the divider, receiving the signal generated from the waveform generator and generating a delay signal value linked to the bit frequency of the signal received from the waveform generator;
a shortened signal value generating unit connected to the delayed signal value generating unit and configured to generate a shortened signal value corresponding to the delayed signal value applied from the delayed signal value generating unit;
It is connected to the delayed signal value generator and the shortened signal value generator, and generates a shortened delay signal by receiving the delay signal value and the shortened signal value from the delayed signal value generator and the shortened signal value generator, respectively. a delay signal correction unit;
a second mixer connected to the reception antenna and the delayed signal compensator, mixing the received wave applied from the reception antenna with the shortened delay signal received from the delay signal compensator to generate a second demodulation signal;
a second raw data generator connected to the second mixer and configured to generate second raw data from the second demodulation signal applied from the second mixer;
an inverse projection unit which receives the first raw data and the second raw data and calculates a function value for each pixel within a composite aperture; and
An aircraft-based sea level image restoration device comprising an image restoration unit connected to the back projection unit and restoring an image within the synthetic aperture using the function value for each pixel applied from the back projection unit. The method of claim 1, connected to the first raw data generator and the second raw data generator, wherein the first raw data and the second raw data are obtained from the first raw data generator and the second raw data generator. The aircraft-based sea surface image restoration apparatus, characterized in that it further comprises a raw data summing unit for receiving raw data and generating summed raw data, wherein the reverse projection unit is connected to the raw data summing unit and receives the summed raw data. The shortened signal value according to claim 1, wherein the delayed signal value generating unit generates 1/2 of the bit frequency as the delayed signal value, and the shortened signal value generating unit multiplies the delayed signal value by 0.1 to 0.2 as the shortened signal value. Aircraft-based sea level image restoration device, characterized in that for setting. The aircraft-based sea level image restoration apparatus according to claim 1, wherein the shortened signal value generator sets the angle of the transmission wave generating the second demodulation signal to be 3.5° to 35°. a waveform generator for generating a signal of the same waveform as the transmission wave;
a divider connected to the waveform generator and receiving and distributing the signal generated from the waveform generator;
an antenna member connected to the distributor, including a transmission antenna for receiving the divided signal from the distributor and transmitting the transmission wave to the ground surface, and a reception antenna for receiving the reception wave reflected from the ground surface;
a delay signal value generation unit connected to the divider, receiving the signal generated from the waveform generator and generating a delay signal value linked to the bit frequency of the signal received from the waveform generator;
a shortened signal value generating unit connected to the delayed signal value generating unit and configured to generate a shortened signal value corresponding to the delayed signal value applied from the delayed signal value generating unit;
It is connected to the delayed signal value generator and the shortened signal value generator, and generates a shortened delay signal by receiving the delay signal value and the shortened signal value from the delayed signal value generator and the shortened signal value generator, respectively. a delay signal correction unit;
a mixer connected to the reception antenna and the delayed signal correction unit, mixing the received wave applied from the reception antenna with the shortened delay signal received from the delay signal correction unit to generate a demodulation signal;
a raw data generator connected to the mixer and configured to generate raw data from the demodulation signal received from the mixer;
an inverse projection unit that receives the raw data and calculates a function value for each pixel within the composite aperture; and
An image restoration unit connected to the back projection unit and restoring an image within the composite aperture using the function value for each pixel applied from the back projection unit,
The delay signal correction unit generates a shortened delay signal using [Equation 1] (in [Equation 1], f ₀ represents the center frequency, t represents time, d represents the delay signal value, and Δd denotes the shortened signal value, and K _r denotes the modulation rate),
[Equation 1]

The aircraft-based sea level image restoration device, characterized in that the raw data generator generates the raw data from the demodulation signal using [Equation 2].
[Equation 2]

(In [Equation 2], t represents time, u represents the position of the aircraft, Sr (t, u) represents the received wave, and S _sd * (t, u) represents the matched filter of the second demodulation signal where f ₀ represents the center frequency, K _r represents the modulation rate, d represents the delay signal value, Δd represents the shortened signal value, and τ(u) is the target delay time as shown in [Equation 3] can show)
[Equation 3]

(In [Equation 3], R(u) represents the distance between the position (u) of the aircraft and the target, (x, y, z) represents the coordinates of the target, (u _x , u _y , u _z ) denotes the coordinates of the aircraft, and c denotes the speed of light) A waveform generator for generating a signal of the same waveform as the transmitted wave, a divider connected to the waveform generator and receiving and distributing the signal generated from the waveform generator, a transmit antenna connected to the divider and transmitting a transmit wave, and a receive wave An antenna member including a receiving antenna for receiving, a first mixer connected to the splitter and the receiving antenna and generating a first demodulation signal, and a first source connected to the first mixer and generating first raw data A data generator, a delayed signal value generator connected to the divider and configured to generate a delayed signal value, a shortened signal value generator connected to the delayed signal value generator and configured to generate a shortened signal value, and a delayed signal value generator a delay signal correction unit connected to the receiving antenna and the delay signal correction unit and connected to the received antenna and the delay signal correction unit to generate a second demodulation signal; 2 a second raw data generator connected to a mixer and configured to generate second raw data from the second demodulation signal applied from the second mixer, and connected to the first raw data generator and the second raw data generator and an image restoration unit connected to the back projection unit and restoring an image within the synthesis aperture using the function value for each pixel applied from the back projection unit. In the image restoration method using an aircraft-based sea level image restoration device comprising:
transmitting the transmission wave onto the ground surface using the transmission antenna, and receiving the reception wave reflected from the ground surface through the reception antenna;
generating the first demodulation signal by mixing the distributed signal received from the divider and the received wave received from the reception antenna using the first mixer;
generating the first raw data from the first demodulated signal using the first raw data generator;
receiving the signal generated from the waveform generator and generating the delay signal value linked to the bit frequency of the signal received from the waveform generator, using the delay signal value generator;
generating the shortened signal value corresponding to the delayed signal value by using the shortened signal value generator;
generating the shortened delay signal using the delay signal value and the shortened signal value by using the delay signal correction unit;
generating the second demodulation signal by mixing the received wave and the shortened delay signal using the second mixer;
generating the second raw data from the second demodulation signal using the second raw data generator;
receiving the first raw data and the second raw data using the back-projection unit and calculating a function value for each pixel within the composite aperture; and
and restoring an image within the composite aperture using the function value for each pixel applied from the back projection unit by using the image restoration unit.

Images