KR20100126979A - Imaging method for arc synthetic aperture radar system using polar coordinates - Google Patents

Abstract

PURPOSE: A method for imaging the polar coordinate of an arc synthetic aperture radar system is provided to efficiently obtain images by dividing the radar system into a scanning mode and a spot mode. CONSTITUTION: A microwave antenna moves on a circular rail. The microwave antenna transmits microwave using a spot mode and receives the microwave from a target. A received signal is compacted in a range direction. A range migration calculation is performed using the distance function of a target point. A Deramp function multiplied to the received signal, and a hamming filtering in an azimuth direction is performed. A Fourier transformation is calculated. A geometric correction is performed.

Description

Polar coordinate imaging method of arc composite diameter radar system {IMAGING METHOD FOR ARC SYNTHETIC APERTURE RADAR SYSTEM USING POLAR COORDINATES}

The present invention relates to a new imaging method for imaging in an arc composite diameter radar system in which an antenna moves along a circular trajectory rather than a straight line.

Synthetic Aperture Radar (weak SAR) system is implemented using Doppler effect, it can maintain constant azimuth resolution regardless of distance, and it can obtain image using ultra-high frequency and weather In addition, it is possible to obtain information on desired areas without being affected by clouds. In particular, because of the Doppler effect, the system achieves much higher resolution in the azimuth direction than the existing side-looking aperture radar (SLAR).

When such a SAR system reconstructs an image from a received signal, the compression of a portion related to the distance signal processing included in the received signal and the compression of the portion related to the azimuth signal processing may be reduced. After that, it is configured to correct the high frequency measurement distortion.

GB-SAR (Ground-Based Synthetic Aperture Radar) is an image radar that obtains high resolution two-dimensional images by synthetic aperture by controlling the position of the antenna on the ground. It is a kind of radar scanner that uses the principle of.

It is possible to precisely control the movement of the antenna through uniaxial movement on a platform fixed to the ground such as rail, so that the repeatability is very high, unlike a general SAR system mounted on aircraft and satellites. In addition, it is possible to accurately find the geometric positional relationship between the antenna and the scatterer, so that optimal SAR imaging can be achieved, and the baseline length in the SAR interference technique can be zero by measuring the antenna repeatedly at the same position. ) Can be maintained.

GB-SAR is easy to maintain and repair, and can realize various microwave wavelengths, polarizations, angles of incidence, etc., so that it can not only be used for ground calibration and concept design of aircraft and satellite SAR, but also find new applications independently. It is a promising technology. To monitor the characteristics and changes of scatterers responding to microwaves of various wavelengths and polarizations at high resolution, or to determine the stability of artificial and natural structures such as ground subsidence measurement, slope stability evaluation, and avalanche detection by monitoring the phase change for a long time. Can also be used as.

However, the rail-type GB-SAR has a high resolution that can detect deformations within mm through repeated measurement, but for this purpose, the rail must be fixed at the monitoring position, and the manufacturing cost of the high precision rail is very expensive. Installation is also a very complicated task.

In order to solve this problem, the inventors of the present invention have developed a new arc composite diameter radar system in which the antenna moves along a circular rail mounted on a vehicle, rather than a straight rail type GB-SAR system, The new system has the advantages of low manufacturing cost, fast start-up of the measuring device, and expansion of the image area by increasing the length of the composite sphere.

However, the new arc composite diameter radar system has a problem that imaging cannot be achieved by conventional data processing methods because the antenna moves along a circular trajectory rather than a straight line.

In order to solve the above problems, an object of the present invention is to provide an imaging method in a new arc composite diameter radar system in which the antenna moves along a circular trajectory rather than a straight line.

Polar coordinate imaging method of the arc composite diameter radar system of the present invention for achieving the above object, (a) a microwave antenna moves over a circular rail and transmits the microwave to the target in spot mode and from the target Receiving the reflected microwaves to obtain a received signal; (b) performing a range compression operation of compressing the received signal applied in polar coordinates in a range direction through a Hamming filter in a range direction and performing inverse Fourier transform; (c) performing a range migration operation to align in a range direction using a distance function with respect to a target point; (d) performing a Fourier transform operation by multiplying the received signal by a Deramp function through a Hamming filter in an azimuth direction; (e) geocoding the imaging results.

At this time, in the step (b), the received signal applied to the polar coordinates is represented by the following equation.

[Equation]

,

,

) 이며, θ_L는 자료가 얻어진 아크의 각도 영역이고, λ는 파장이다.)Where R is range, θ is the angle of the antenna, θ _c and R _c are the antenna angle and Range (

Θ _L is the angular region of the arc from which the data is obtained, and λ is the wavelength.)

에서 영상화가 이루어지며 해상도는

로 나타난다.In addition, in the step (d), imaging is performed using Equation A below, and Equation A is integrated into the integral section [CL _s / 2, C + L _S / 2] (C is used to illuminate the target from the rail. The center position of the antenna, L _S is the length of the arc, which is the width of the corresponding rail section of the antenna) is represented by the following equation B, wherein

Imaging is done at

Appears.

Equation A

, R"(0)은 R(θ)를 θ=0을 중심으로 테일러 급수로 전개한 근사치이고, θ는 안테나의 각도, u는 wavenumber, λ는 파장이다.)(In the above equation,

, R "(0) is an approximation of R (θ) developed by Taylor series around θ = 0, θ is the angle of the antenna, u is the wavenumber, and λ is the wavelength.)

Equation B

)와 azimuth이며, r은 회전축이 되는 원점에서 안테나까지의 반경, C는 레일에서 타겟을 비추는 안테나의 중심위치, L_S는 안테나의 해당 레일 구간의 폭인 아크의 길이, u는 wavenumber이다.)Where R and x are Range and azimuth, and R _c and x _c are range (

) And azimuth, r is the radius from the origin of the rotation axis to the antenna, C is the center position of the antenna projecting the target from the rail, L _S is the length of the arc, the width of the corresponding rail section of the antenna, u is the wavenumber.)

Another polar coordinate imaging method of the arc composite diameter radar system of the present invention for achieving the above object, (a) the microwave antenna is moved on a circular rail and transmits the microwave to the target in the scan mode (scan mode) Receiving a microwave reflected from a target to obtain a received signal; (b) performing a range compression operation of compressing the received signal applied in polar coordinates in a range direction through a Hamming filter in a range direction and performing inverse Fourier transform; (c) performing a range migration operation that undergoes an azimuth Fourier transform and aligns in a range direction using a distance function with respect to the target; (e) performing an inverse Fourier transform operation after passing through an azimuth matched filter, applying a Hamming filter in the direction of Azure, and performing an inverse Fourier transform; and (f) geocoding the imaging results.

At this time, in the step (b), the received signal applied to the polar coordinates is represented by the following equation.

[Equation]

)이며,

와

은 wavenumber Doppler parameter이며 R(θ)를 θ=θ_c 를 중심으로 테일러 급수로 전개하여 parameter 변환하면

,

이고, θ_L는 자료가 얻어진 아크의 각도 영역, L_x는 아크의 길이, λ는 파장이다.)Where θ _c and R _c are the antenna angle and the range (

),

Wow

Is the wavenumber Doppler parameter and R (θ) is transformed into a Taylor series with θ = θ _c as the parameter

,

Where θ _L is the angular region of the arc from which the data is obtained, L _x is the length of the arc, and λ is the wavelength.)

에서 영상화가 이루어지며 해상도는

로 나타난다.In addition, in the step (e), imaging is performed using Equation A 'below, and the equation A' is integrated into the integral section [CL _s / 2, C + L _S / 2] (C is a target on the rail. The center position of the antenna, L _S is the length of the arc, which is the width of the corresponding rail section of the antenna.

Imaging is done at

Appears.

Equation A '

, 이고, θ는 안테나의 각도이다.)(In the above equation,

Is the angle of the antenna.)

Equation B '

)와 azimuth이며, r은 회전축이 되는 원점에서 안테나까지의 반경, C는 레일에서 타겟을 비추는 안테나의 중심위치, L_S는 안테나의 해당 레일 구간의 폭인 아크의 길이이다.)In the above equation, R _c and x _c are range (

) And azimuth, r is the radius from the origin of the rotation axis to the antenna, C is the center position of the antenna projecting the target from the rail, and L _S is the length of the arc, which is the width of the corresponding rail section of the antenna.)

 According to the present invention, it is possible to provide an efficient polar coordinate imaging method in a new arc composite diameter radar system in which an antenna moves along a circular trajectory rather than a straight line.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention.

The new arc composite diameter radar system developed by the inventors of the present invention is to position the microwave antenna at the end of the circular rail and move to the arc shape to obtain data by continuously transmitting and receiving microwaves, and to achieve the image through a constant data processing. Unlike the conventional synthetic aperture radar, the arc composite aperture radar system cannot achieve imaging by the conventional data processing method because the antenna moves along a circular trajectory rather than a straight line. Therefore, the present invention has developed a new imaging method of the arc composite diameter radar system.

The arc composite diameter radar system uses the Scan Mode (see Fig. 1) to fix the antenna to the end of the boom and obtain an omni-directional continuous image, and acquire data through a circular trajectory with the antenna directed in a constant direction. It is divided into a spot mode (see FIG. 2).

(1) Arc-SAR Spot Mode Imaging

) 이다. 도 3에서와 같이, 직교좌표에서는 (R₀,x_c)에 위치한 한 타겟인 점산란체는 극좌표상에서는 (R_c,θ_c)로 표현된다. First, the polar coordinate representation for the spot mode is as follows. 3 shows Arc-SAR image geometry. In Figure 3, the circle is a circular rail to which the antenna moves, θ is the angle of the antenna, r is the radius from the origin to the antenna axis of rotation, θ _c and R _c is the antenna angle and range for the target scatterer (target) Range)

) to be. As shown in FIG. 3, the scatterer, which is a target located at (R ₀ , x _c ) in the rectangular coordinate, is represented by (R _c , θ _c ) on the polar coordinate.

Arc-SAR raw data obtained from this scatterer is base-banded and then subjected to inverse Fourier transform to range compression, resulting in the following equation (1). In the actual data processing, a Hamming filter is applied in the range direction to emphasize only the main peak of the sinc function, and then range compression is performed using an Inverse Fast Fourier Transform (iFFT).

,

,

Where θ is the angle of the antenna, θ _L is the angular region of the arc from which the material was obtained in the spot mode, and λ is the wavelength of the microwave. When the length from the center of the circular rail to the antenna r, the distance from the antenna to the target point can be represented by the following equation (2).

If Equation 2 is developed into a Taylor series centering on θ = 0, the following Equation 3 is obtained.

When Equation 3 is calculated, Equations 4 to 6 are obtained.

In spot mode, the Fourier transform is used by default, which is first aligned in the range direction using a function of distance to a single target point. This process is called range migration.

Next, a deramp function for imaging is defined by Equation 7 as follows.

Imaging is performed using Equation 7 below using Equation 7.

Here, the defined region of the received signal may be represented by [CL _s / 2, C + L _S / 2]. Where C is the center position of the antenna projecting the scatterer on the rail, and L _s is the length of the arc, which is the width of the corresponding rail section of the antenna. If Equation 8 is calculated using the definition region as an integration period, Equation 9 is obtained.

에서 최대 피크를 가지며 half power width로 정의되는 해상도는

을 가진다. 따라서

에서 영상화가 이루어지며 해상도는

와 같이 된다. In other words, the sinc function above

The maximum peak at and the resolution defined by half power width

Has therefore

Imaging is done at

Becomes

로 만들어 간소화 시킨다. 이 때문에 스팟 영상의 중심 영역인 θ_c=0 에서 정확하며, 주변으로 갈수록 약간의 영상 왜곡이 생긴다. 따라서 본 실시예에서 설명한 방법은 영상의 폭이 좁은 ArcSAR 스팟 모드에 적합하다. 그리고 일정한 각도 영역을 가지는 여러 개의 영상을 조합하여 전방위적인 영상으로 합성하여 ArcSAR 스캔 모드 영상화를 이룬다. In order to improve the processing speed, assuming that the Deramp function is θ _c = 0

Simplify it. Therefore, it is accurate at θ _c = 0, which is the center region of the spot image, and slight image distortion occurs toward the periphery. Therefore, the method described in this embodiment is suitable for the ArcSAR spot mode of narrow image width. ArcSAR scan mode imaging is achieved by combining multiple images with a certain angular area into omnidirectional images.

In the actual data processing, after the Range Migration, the Deramp function is multiplied and passed through the Hamming filter to be imaged through the Azimuth FFT.

Using the method described above, the imaging processing time and the computer memory usage are relatively reduced.

(2) Arc-SAR Scan Mode Imaging

Since the Arc-SAR scan mode continuously acquires data along the circular rail and requires omnidirectional imaging, unlike the aforementioned spot mode, the data is used based on the continuity.

Since data are obtained based on polar coordinates, a new equation development is required, followed by a process in which imaging is first obtained in the polar coordinate region and then moved to the rectangular coordinate region. Arc-SAR image geometry is referenced to FIG. 3 as in spot mode.

The data processing of the new polar coordinate technique for scatterers at one point (R _c , x _c ) is as follows. As in the spot mode, the data after range compression is expressed by Equation 10 below.

,

,

As in the spot mode, the distance from the antenna to the target point may be represented by Equation 2 above. Unlike in the spot mode, Equation 2 can be approximated as shown in Equation 11 below by expanding the Taylor expression into a Taylor series around θ = θ _c .

By calculating this, the following equations (12) to (14) can be represented.

If the above equation is changed to the wavenumber Doppler parameter, it is expressed by Equation 15 below.

,

,

,

,

Therefore, the received signal is represented by Equation 16 below.

This signal forms an azimuth linear chirp.

As a filter for imaging in the polar coordinate algorithm according to the present embodiment, the following expression (17) is used.

,

,

SAR focusing is performed by using the following matched filtering.

In Equation 18, when the center of the corresponding integration section is C and the width thereof is the arc of the composite sphere, L _s , the integration section may be represented by [CL _s / 2, C + L _S / 2]. Where C is the center position of the antenna projecting the scatterer on the rail, and L _s is the width of the arc of the antenna. When the Equation 18 is calculated, the imaging is performed as shown in Equation 19 below.

, 해 상도는

이다. 위상은

로 되기 때문에 기하보정이 필요하다. 실제 자료처리는 FFT(Fast Fourier Transform)를 이용하여 수행하게 된다. At θ = θ _c , the maximum value L _s , and azimuth bandwidth

, The resolution is

to be. Phase

Geometric correction is required. Actual data processing is performed by using Fast Fourier Transform (FFT).

In order to speed up the calculation of Equation 18, the imaging program uses azimuth FFT to perform range migration and multiply the frequency domain values of the azimuth matched filter. In addition, after applying the Hamming filter in the azimuth direction to emphasize only the main peak of the sinc function, the SAR imaging is completed by returning back to the time domain using the azimuth iFFT.

Embodiments have been disclosed in the drawings and the specification as above. Although specific terms have been used herein, they are used only for the purpose of describing the present invention and are not used to limit the scope of the present invention as defined in the meaning or claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a diagram illustrating a scan mode in an arc composite diameter radar system.

2 is a view showing a spot mode in the arc composite diameter radar system.

3 is a view showing the image geometry of the arc composite diameter radar.

Claims (6)

(a) moving a microwave antenna over a circular rail and transmitting a microwave to a target in spot mode, and receiving a microwave reflected from the target to obtain a received signal; (b) performing a range compression operation of compressing the received signal applied in polar coordinates in a range direction through a Hamming filter in a range direction and performing inverse Fourier transform; (c) performing a range migration operation to align in a range direction using a distance function with respect to a target point; (d) performing a Fourier transform operation by multiplying the received signal by a Deramp function through a Hamming filter in an azimuth direction; (e) geocoding the imaging results; Imaging method of the arc composite diameter radar system comprising a. The method of claim 1, In the step (b), the received signal applied to the polar coordinates is represented by the following equation. [Equation]

,

Where R is range, θ is the angle of the antenna, θ _c and R _c are the antenna angle and Range (

Θ _L is the angular region of the arc from which the data is obtained, and λ is the wavelength.) The method of claim 1, In the step (d), imaging is performed using Equation A below, and Equation A is integrated into the integral section [CL _s / 2, C + L _S / 2] (C is the center of the antenna shining the target on the rail. Where L _S is the length of the arc, which is the width of the corresponding rail section of the antenna).

Imaging is done at

Imaging method of the arc composite diameter radar system, characterized in that represented by. Equation A

(In the above equation,

, R "(0) is an approximation of R (θ) developed by Taylor series around θ = 0, θ is the angle of the antenna, u is the wavenumber, and λ is the wavelength.) Equation B

Where R and x are Range and azimuth, and R _c and x _c are range (

) And azimuth, r is the radius from the origin of the rotation axis to the antenna, C is the center position of the antenna projecting the target from the rail, L _S is the length of the arc, the width of the corresponding rail section of the antenna, u is the wavenumber.) (a) moving a microwave antenna over a circular rail and transmitting a microwave to a target in a scan mode and receiving a microwave reflected from the target to obtain a received signal; (b) performing a range compression operation of compressing the received signal applied in polar coordinates in a range direction through a Hamming filter in a range direction and performing inverse Fourier transform; (c) performing a range migration operation that undergoes an azimuth Fourier transform and aligns in a range direction using a distance function of a target point; (e) performing an inverse Fourier transform operation after passing through an azimuth matched filter, applying a Hamming filter in the direction of Azure, and performing an inverse Fourier transform; (f) geocoding the imaging results; Imaging method of the arc composite diameter radar system comprising a. The method of claim 4, wherein In the step (b), the received signal applied to the polar coordinates is represented by the following equation. [Equation]

Where θ _c and R _c are the antenna angle and the range (

),

Wow

Is the wavenumber Doppler parameter and R (θ) is transformed into a Taylor series with θ = θ _c as the parameter

,

Where θ _L is the angular region of the arc from which the data is obtained, L _x is the length of the arc, and λ is the wavelength.) The method of claim 4, wherein In the step (e), imaging is performed using Equation A 'below, and Equation A' is integrated into the integral section [CL _s / 2, C + L _S / 2] (C is an antenna for illuminating the target on the rail. Where the center position, L _S is the length of the arc, which is the width of the corresponding rail section of the antenna.

Imaging is done at

Imaging method of the arc composite diameter radar system, characterized in that represented by. Equation A '

(In the above equation,

Is the angle of the antenna.) Equation B '

In the above equation, R _c and x _c are range (

) And azimuth, r is the radius from the origin of the rotation axis to the antenna, C is the center position of the antenna projecting the target from the rail, and L _S is the length of the arc, which is the width of the corresponding rail section of the antenna.)

Images