KR100252345B1 - Distortion complement method of radar system - Google Patents

Abstract

PURPOSE: A method of correcting topographical distortion in a synthetic aperture radar system is provided which corrects the topographical distortion due to foreshortening with regard to reflectivity of a corresponding point when a video signal is reconstructed in the SAR system. CONSTITUTION: The position of a ground range image is calculated using the start point and end point of the shortest range image with respect to a synthetic aperture radar system when a signal obtained by correcting RF measurement distortion for a target is applied(301). The height of a predetermined ground control point within the ground range image is calculated with reference to a digital elevation map of a corresponding area(302). The shortest range corresponding to the ground control point is calculated using the distance between the actual position of the ground control point in the ground range and the synthetic aperture radar system(303). The reflectivity of the ground control point is calculated for a pixel placed in the shortest range(304). A value obtained by multiplying the reflectivity by the pixel value located in the shortest range is mapped into the pixel value of the ground control point(305). The step of calculating the height information to the mapping step are repeated until the mapping of the ground range image for the obtained shortest range image is completed(306).

Description

Terrain Distortion Correction Method in Synthetic Opening Radar System

The present invention relates to a method of correcting topographical distortion in a Synthetic Aperture Radar (hereinafter referred to as SAR) system. It relates to a distortion correction method.

SAR system can maintain constant azimuth resolution regardless of distance, and because it acquires image using ultra high frequency, it can get information about desired area without being affected by visible light, weather and cloud. . In particular, the Doppler effect is used to achieve much higher resolution in the azimuth direction than the existing SLAR (Side Looking Aperture Radar) system.

Since the SAR system acquires the image based on the shortest range (Slant Range) for the target as shown in FIG. 1, the shortest distance image is different from the ground range image by the height H of the SAR system. Have. In particular, when there is an inclined surface such as α in the SAR system direction as shown in FIG. 1, the length a 'of the shortest distance image is smaller than the length a of the image on the ground distance to the α inclined surface. This phenomenon is called four shortening.

In order to correct the topographical distortion due to the shortening, the existing SAR system uses the digital elevation map (DEM), which is composed of sampled height information of the area previously acquired, to ground the shortest distance image. Map to distance image. For example, for the point b in the ground distance image, the height h is obtained by referring to the DEM. The shortest distance b 'is calculated using the height h obtained. The calculated pixel value of the shortest distance image at point b 'is substituted into the pixel value b of the ground distance image.

However, in the case of the inclined surface such as α shown in FIG. 1, as described above, since the distance a on the ground distance is larger than the distance a 'on the shortest distance, several points on the ground distance are gathered at one point of the shortest distance image and thus on the shortest distance. It is highly possible to increase the pixel value. That is, when the shortest distance is calculated with reference to the above-described DEM for the adjacent points existing on the inclined plane in addition to the b point on the ground distance, and when the b 'point corresponds to the b' point, the reflected point of the adjacent point including the above-described b point is reflected. The pixel value at point b 'on the shortest distance is determined by the signal, and the pixel value at point b' has a large value, and the large pixel value at point b 'includes the point b on the ground distance by the above-described mapping process. Mapping to pixel values of adjacent points, topographical distortion is generated in which the pixel values of adjacent points, including point b of the ground-distance image, are represented by larger values than the original pixel values.

The present invention has been made to solve the above-described drawbacks, and provides a topographic distortion correction method for correcting topographical distortion due to shortening when reconstructing an image signal in a SAR system in consideration of reflectivity of a corresponding point. There is a purpose.

In order to achieve the above object, the topographical distortion correction method according to the present invention is a method for correcting topographical distortion in a synthetic opening radar system for obtaining an image by mapping the shortest distance image acquired for a predetermined target to a ground distance image. The method of claim 1, further comprising: calculating a position of the ground distance image using a start point and an end point of the shortest distance image of the synthesized opening radar system when a signal corrected for the high frequency measurement distortion of the target is applied; Calculating a height of a predetermined ground control point in the ground distance image by referring to a map (DEM) of sampled height information of a corresponding region; Calculating a shortest distance corresponding to a predetermined ground control point by using the height of the predetermined ground control point obtained in the height calculation step using a distance between the actual position on the ground distance of the predetermined ground control point and the synthetic opening radar system; Calculating reflectivity of a predetermined ground control point with respect to the pixel located at the shortest distance; Mapping a value obtained by multiplying a reflectance degree by a pixel value corresponding to the shortest distance to a pixel value of a predetermined ground control point; Comprising the step of repeating the step of calculating the height information until the mapping of the ground distance image to the obtained shortest distance image is completed, characterized in that it is performed.

1 is a view illustrating a geometric model of an image obtained through a conventional synthetic opening radar system,

2 is a schematic block diagram of a general synthetic opening radar system;

3 is an operation flowchart of a topographic distortion correction method according to the present invention applied to a synthetic opening radar system;

4 is an exemplary view of a geometric model of an image obtained through a synthetic opening radar system for explaining the operation according to the operation flowchart of FIG.

<Description of the symbols for the main parts of the drawings>

200: raw signal providing unit 210: compressed signal processing unit

220: high-frequency measurement distortion correction unit 230: terrain distortion correction unit

The above and other objects and various advantages of the present invention will become more apparent from the preferred embodiments of the invention described below with reference to the accompanying drawings by those skilled in the art.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a block diagram of a general synthetic opening radar system (hereinafter, referred to as SAR) system, and includes: an original signal providing unit 200 for generating and providing a predetermined raw signal by receiving a reflected signal of a very high frequency emitted to a desired terrain; ), The compression signal processing unit 210 to improve the resolution by performing distance-direction compression and azimuth compression processing on the original signal provided from the original signal providing unit 200, and to the original signal compressed by the compression signal processing unit 210. The high frequency measurement distortion correction unit 220 and the high frequency measurement distortion correction unit 220 correcting and outputting the high frequency measurement distortion such as the output change, the receiver gain conversion, the antenna pattern and the loss according to the distance It is composed of a topographic distortion correction unit 230 for correcting the topographical distortion of the original signal according to the present invention.

3 is a flowchart illustrating a topographic distortion correction method according to the present invention, and FIG. 4 is a diagram illustrating a geometric model of a SAR image for explaining the topographic distortion correction according to the present invention.

Next, the embodiment according to the present invention shown in FIG. 3 will be described in detail with reference to FIGS. 2 and 4.

First, since the original signal providing unit 200, the compressed signal processing unit 210, and the high frequency measurement distortion correction unit 220 are the same as those of the conventional SAR system, a detailed description thereof will be omitted, and the topographic distortion correction unit ( The operation of 230 will be described below.

That is, when the image distortion-corrected image is transmitted from the high frequency measurement distortion correction unit 220, the topographic distortion correction unit 230 proceeds to step 301 to calculate the position of the image of the ground distance. The position of the image of the ground distance is calculated using the start point and the end point of the image of the shortest distance. That is, the point on the ground distance that corresponds to the distance between the start point of the image on the shortest distance from the SAR system and the point on the ground distance having the distance on the ground distance and the corresponding SAR system as the start point of the ground distance image, and the point on the ground distance that matches the end point of the image on the shortest distance. Is the end point of the ground distance image.

When the position of the ground distance image is calculated as described above, the terrain distortion correction unit 230 proceeds to step 302 to calculate the height of the current ground control point. The current ground control point is sequentially selected to any one of the starting point and the ending point of the ground distance image. For example, when the current ground control point is point c as shown in FIG. 4, the topographic distortion correction unit 230 calculates a height corresponding to h ′. As described above, the height refers to a DEM composed of sampled height information about a corresponding region acquired in advance.

That is, since the DEM holds sampled height information on the terrain in the form of a two-dimensional map, the DEM information is accessed using the two-dimensional coordinate system of the current ground control point on the ground distance image. At this time, if there is no DEM information for the corresponding coordinate point, the height information obtained by interpolation of adjacent height information is obtained as the height h 'at the current ground control point. When the height h 'is obtained, the topographical distortion correction unit 230 proceeds to step 303.

In step 303, the topographic distortion correction unit 230 calculates a corresponding shortest distance R _A ′. This shortest distance calculation is obtained by calculating the distance R _A between the SAR system and the actual ground control point obtained using the height h 'obtained at point c. In other words, since the distance R _A is the same as the shortest distance R _A ', the distance between the SAR system and the shortest distance is obtained when the distance between the point h' on the ground distance and the SAR system is obtained. This distance calculation is based on the value of the corresponding pixel on the shortest distance ( P _{c ′} To obtain). However, in this case, when the pixel value does not exist at the corresponding point, the pixel value is determined by interpolation of the pixels raised at the adjacent position.

The flow proceeds to step 304 to calculate the reflectivity of the point c with respect to the pixel value c 'having the shortest distance R _A '. At this time, the reflectivity is calculated in consideration of the reflectivity of adjacent points on the ground distance calculated as the shortest distance. The point detection that forms the same pixel value on the shortest distance is to find the point with the shortest distance like the ground control point by calculating the shortest distance for all points existing from the start point to the end point of the ground distance image as in step 303. Is done. That is, in the case of FIG. 4, since c, d, and e points are reflected from the ground distance to the c 'point on the shortest distance, the reflectivity of the c' c point of the c point is calculated as in Equation 1.

Such reflectivity may be calculated by the numerator of γ _c in γ _d When calculated for point e, the numerator of Equation 1 is γ _c in γ _e It is changed to and calculated.

When the reflectivity of the point c is calculated, the flow proceeds to step 305 where the value of c'pixel located on the shortest distance calculated in step 303 is obtained. P _{c ′} And the reflectivity of the reflector calculated in step 304 are combined as shown in Equation 2 to determine a pixel value to be mapped to point c of the ground distance.

This completes the mapping process between the shortest-range images of point c on the ground distance.

However, in order to process the mapping with the shortest-range image of all the pixels on all ground distances, the terrain distortion correction proceeds to step 306 to check whether the pixel values on all ground distances are determined, and if not, to step 302. It proceeds and repeats the above process. At this time, the next ground control point is determined by the scanning order. As a result of the check in step 306, when all the pixel values of the terrestrial distance image are determined, the terrain distortion correction operation is terminated.

As described above, the present invention is a value close to the original value by correcting the topographical distortion due to the shortening in the composite opening radar system using the reflectivity of the ground distance point with respect to the pixel value of the shortest distance. There is an advantage that can obtain a SAR image having a.

Although the present invention has been described as the above-described embodiment, those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention. For example, the above-described embodiment illustrates the case where three points on the ground distance have the same shortest distance, but when there are less than three points or three or more points having the same shortest distance, the reflectivity is calculated in the same manner. Can be. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (2)

In the method for correcting the topographical distortion in a synthetic opening radar system for obtaining an image by mapping the shortest distance image obtained for a predetermined target to a ground distance image, Calculating a position of the ground distance image by using a start point and an end point of the shortest distance image with respect to the synthesis opening radar system when a signal corrected for the high frequency measurement distortion of the target is applied; Calculating a height of a predetermined ground control point in the ground distance image with reference to a map (DEM) of sampled height information of a corresponding region; Using the height of the predetermined ground control point obtained in the height calculation step, the shortest distance corresponding to the predetermined ground control point is calculated using the actual position on the ground distance of the predetermined ground control point and the distance between the synthetic opening radar system. Doing; Calculating a reflectivity of the predetermined ground control point for the pixel located at the corresponding shortest distance; Mapping a value obtained by multiplying the reflectivity by the pixel value located at the corresponding shortest distance to the pixel value of the predetermined ground control point; Comprising the step of repeating the step of calculating the height information until the mapping of the ground distance image to the obtained shortest distance image is completed, characterized in that it is performed Terrain Distortion Correction Method The method of claim 1, wherein the calculating of the reflectivity of the reflector comprises: reflectance of the point having the shortest distance equal to the predetermined ground control point on the ground distance; γ _n ) And the reflectivity of the predetermined ground control point ( γ _c Topographic distortion correction method for a synthetic opening radar system, characterized in that it is calculated by considering the following equation.

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