A method and device for testing SAR satellite backscatter coefficient image

Abstract

The present invention provides a SAR satellite backscatter coefficient image inspection method and device, including: remote control adjustment of an automatic corner reflector fixedly arranged in an authenticity inspection site according to observation parameters during SAR satellite transit imaging; obtaining a SAR satellite backscatter coefficient image according to a SAR image synchronously acquired by the SAR satellite and the attitude angle of the automatic corner reflector after adjustment; obtaining a radar scattering cross-sectional area measurement value of the automatic corner reflector according to the characteristics of the automatic corner reflector in the backscatter coefficient image; and obtaining a SAR satellite backscatter coefficient image inspection result by analyzing the measurement value using a theoretical value of the radar scattering cross-sectional area of ​​the automatic corner reflector. The method is used to solve the defects of the prior art that the model for inspecting the radiation characteristics of SAR satellite backscatter coefficient images is complex, the calculation is cumbersome, and the application requirements cannot be effectively met under the background of complex terrestrial objects, and the SAR satellite backscatter coefficient image inspection under the background of complex terrestrial objects is realized, and the model is simple and easy to implement.

Description

Technical Field

[0001] The present invention relates to the technical field of SAR satellite image radiation characteristic inspection, and in particular to a SAR satellite backscatter coefficient image inspection method and device. Background Art

[0002] Synthetic Aperture Radar (SAR) has the ability to observe the earth all day and all weather, and is not affected by bad weather such as clouds and rain. It is of great significance for disaster emergency monitoring, agricultural monitoring, land and resources survey, topographic measurement, and ocean dynamic environment measurement, which have high timeliness requirements. With the continuous improvement of SAR resolution and performance, the qualitative analysis of SAR images using image position, texture, shape and other information can no longer meet the application needs of many industries. Therefore, it is urgent to promote the quantitative research of SAR images to further broaden the application scope of SAR and tap the application potential of SAR. The radiation characteristics of SAR images will affect the effect of the final quantitative application and are directly related to the user's application field. Analyzing and verifying the image characteristic indicators can optimize the SAR payload system more specifically to ensure the accuracy requirements of the user's quantitative application.

[0003] SAR satellite backscatter coefficient images are the basic images for SAR quantitative applications. Using ground point targets to verify the radiation characteristics of SAR satellite backscatter coefficient images can provide strong support for SAR quantitative applications. Existing methods for verifying the radiation characteristics of SAR satellite backscatter coefficient images are mainly used in the ocean, and meteorological buoys are required to obtain sea surface wind field information, and further spatiotemporal registration is required. Therefore, the model is complex and the calculation is cumbersome, which cannot effectively meet the application requirements under the background of complex land objects.

[0004] SAR radiation characteristic inspection methods based on point targets include methods using active calibrators (ARC) and passive point targets (such as corner reflectors). Corner reflectors (CRs) are commonly used passive point targets with the advantages of simple structure, stable performance, convenient deployment and low cost. They can be used as ground point targets with accurately known radar cross-sectional areas and are practical equipment for inspecting SAR images. However, in the process of using corner reflectors, how to ensure the azimuth and elevation pointing accuracy is the core issue. Traditional deployment requires calculating the azimuth and elevation angles based on satellite orbit parameters and the position coordinates of CR, and then manually adjusting the actual elevation angle of the corner reflector with the help of the electronic level measurement results, and then using the mechanical compass to measure and adjust the actual azimuth angle of the corner reflector. This work is time-consuming and labor-intensive, and it is very difficult to carry out an experiment. Therefore, there is currently a lack of long-term inspection methods. Summary of the invention

[0005] The present invention provides a SAR satellite backscatter coefficient image inspection method and device, which are used to solve the defects of the prior art in that the model for inspecting the radiation characteristics of the SAR satellite backscatter coefficient image is complex, the calculation is cumbersome, and the application requirements under the background of complex terrestrial objects cannot be effectively met. The SAR satellite backscatter coefficient image inspection under the background of complex terrestrial objects is realized, and the model is simple and easy to implement.

[0006] The present invention provides a method for testing a SAR satellite backscatter coefficient image, comprising:

[0007] According to the observation parameters of the SAR satellite during the transit imaging, the attitude of the automatic corner reflector fixedly deployed in the authenticity inspection site is remotely controlled and adjusted;

[0008] Obtaining the SAR satellite backscatter coefficient image according to the SAR image covering the automatic corner reflector synchronously acquired by the SAR satellite and the adjusted attitude angle of the automatic corner reflector;

[0009] Obtaining a radar cross-sectional area measurement value of the automatic corner reflector according to the characteristics of the automatic corner reflector in the backscatter coefficient image;

[0010] The radar cross-sectional area theoretical value of the automatic corner reflector is used to analyze the radar cross-sectional area measurement value to obtain the inspection result of the SAR satellite backscatter coefficient image.

[0011] According to a SAR satellite backscatter coefficient image inspection method provided by the present invention, the attitude of an automatic corner reflector fixedly arranged in an authenticity inspection site is remotely controlled and adjusted according to observation parameters of the SAR satellite during transit imaging, specifically comprising:

[0012] According to the observation parameters of the SAR satellite during transit imaging, the azimuth pointing angle and the elevation pointing angle of the automatic corner reflector are remotely controlled and adjusted through the automatic corner reflector fixedly arranged in the authenticity verification site until the normal direction of the automatic corner reflector is consistent with the incident beam direction of the SAR satellite.

[0013] According to a SAR satellite backscatter coefficient image verification method provided by the present invention, the SAR satellite backscatter coefficient image is obtained based on a SAR image covering an automatic corner reflector synchronously acquired by a SAR satellite and an adjusted attitude angle of the automatic corner reflector, specifically comprising:

[0014] Performing SAR image antenna pattern correction according to imaging results of each automatic corner reflector arranged in the SAR satellite range direction, so as to perform relative radiation correction on the SAR image;

[0015] The SAR image after relative radiation correction is combined with a calibration equation and an absolute radiation calibration constant to calculate the SAR satellite backscatter coefficient image.

[0016] According to a SAR satellite backscatter coefficient image inspection method provided by the present invention, obtaining the radar cross-sectional area measurement value of the automatic corner reflector according to the characteristics of the automatic corner reflector in the backscatter coefficient image specifically includes:

[0017] According to the longitude and latitude of the automatic corner reflector in the authenticity verification site, obtaining the row and column coordinates of the automatic corner reflector in the backscatter coefficient image;

[0018] A predetermined range is selected with the row and column coordinates as the center as a buffer zone, a region with the largest sum of backscatter coefficient values ​​in the buffer zone is selected using a sliding window method, and the center point of the region is used as the center point of the imaging region of the automatic corner reflector;

[0019] Based on the automatic corner reflector imaging area in the backscatter coefficient image determined by the imaging area center point of the automatic corner reflector, a SAR image point target radar scattering cross-sectional area measurement method based on the peak method and / or the integral method is derived with the help of a point target response energy calculation method;

[0020] The radar cross-sectional area measurement value of the automatic corner reflector is obtained from the backscatter coefficient image using the SAR image point target radar cross-sectional area measurement method.

[0021] According to a method for inspecting a SAR satellite backscatter coefficient image provided by the present invention, the radar scatter cross-sectional area measurement value is analyzed by using the radar scatter cross-sectional area theoretical value of the automatic corner reflector to obtain the inspection result of the SAR satellite backscatter coefficient image, which specifically includes:

[0022] Performing statistical analysis on radar cross-sectional area measurement values ​​of a plurality of automatic corner reflectors having the same radar cross-sectional area theoretical value and fixedly arranged in the authenticity verification site, and using the obtained analysis results as relative accuracy verification results of the SAR satellite backscatter coefficient image; and / or

[0023] The radar cross-sectional area measurement value of the automatic corner reflector is subtracted from the corresponding radar cross-sectional area theoretical value of the automatic corner reflector, and the absolute value of the difference is used as the absolute accuracy test result of the SAR satellite backscatter coefficient image.

[0024] The present invention also provides a device for testing a SAR satellite backscatter coefficient image, comprising:

[0025] An adjustment unit is used to remotely control and adjust the attitude of an automatic corner reflector fixedly arranged in the authenticity inspection site according to observation parameters of the SAR satellite during transit imaging;

[0026] An image generating unit, configured to obtain the SAR satellite backscatter coefficient image according to a SAR image covering the automatic corner reflector and synchronously acquired by the SAR satellite and the adjusted attitude angle of the automatic corner reflector;

[0027] A calculation unit, used to obtain a radar cross-sectional area measurement value of the automatic corner reflector according to the characteristics of the automatic corner reflector in the backscatter coefficient image;

[0028] The analysis unit is used to analyze the radar cross-sectional area measurement value using the radar cross-sectional area theoretical value of the automatic corner reflector to obtain the inspection result of the SAR satellite backscatter coefficient image.

[0029] The present invention also provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the steps of the method for verifying the SAR satellite backscatter coefficient image as described in any one of the above are implemented.

[0030] The present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the steps of the method for verifying the SAR satellite backscatter coefficient image as described in any one of the above are implemented.

[0031] The present invention also provides a computer program product, comprising a computer program, wherein when the computer program is executed by a processor, the steps of any of the above-mentioned methods for verifying the SAR satellite backscatter coefficient image are implemented.

[0032] The present invention provides a method and device for verifying a SAR satellite backscatter coefficient image. The method and device verify the backscatter coefficient image by fixedly arranging an automatic corner reflector in an authenticity verification site. During the entire process, it is only necessary to remotely control and adjust the attitude of the automatic corner reflector according to the observation parameters of the SAR satellite during transit imaging, and calculate and analyze the relevant data obtained by the automatic corner reflector and the SAR satellite itself, so as to obtain the verification result of the SAR satellite backscatter coefficient image. There is no need to obtain more external space-time matching auxiliary data, and the model is simple and easy to implement.

[0033] The present invention performs accuracy inspection of SAR satellite backscatter coefficient images based on an automatic corner reflector fixedly deployed at a ground authenticity inspection site, and can remotely control and adjust the working posture of the corner reflector according to the requirements of different images, effectively reducing manual repetitive work in field inspection experiments.

[0034] The present invention utilizes automatic corner reflectors fixedly deployed at ground authenticity verification sites to conduct quantitative evaluation and inspection of SAR satellite backscatter coefficient images, supports long-term deployment and automated operation under complex land backgrounds, and periodically verifies the characteristic accuracy of SAR satellite backscatter coefficient images, providing strong technical support for the quantitative application of SAR images. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 This is one of the flow charts of a method for testing a SAR satellite backscatter coefficient image provided by the present invention;

[0037] Figure 2 The present invention provides a flow chart of obtaining the radar cross-sectional area measurement value of the automatic corner reflector according to the characteristics of the automatic corner reflector in the backscatter coefficient image by using the SAR image point target radar cross-sectional area measurement value calculation method based on the peak method or the integral method;

[0038] Figure 3 It is a schematic diagram of the principle of selecting the center point of the imaging area of ​​the automatic corner reflector by using the sliding window method provided by the present invention;

[0039] Figure 4 It is a rectangular integral window structure diagram of the imaging area of ​​the automatic corner reflector provided by the present invention in the backscattering coefficient image;

[0040] Figure 5 It is a structural schematic diagram of a SAR satellite backscatter coefficient image inspection device provided by the present invention;

[0041] Figure 6 It is a structural schematic diagram of the electronic device provided by the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] With the continuous improvement of SAR resolution and performance, the qualitative analysis of SAR images using information such as image position, texture, and shape can no longer meet the application requirements of many industries. Therefore, it is urgent to promote the quantitative research of SAR images to further broaden the application scope of SAR and tap the application potential of SAR. The radiation characteristics of SAR images will affect the effect of the final quantitative application and are directly related to the user's application field. Analyzing and verifying the image characteristic indicators can optimize the SAR payload system more targeted to ensure the accuracy requirements of the user's quantitative application. SAR satellite backscatter coefficient images are the basic images for SAR quantitative applications. Using ground point targets to test the radiation characteristics of SAR satellite backscatter coefficient images can provide strong support for SAR quantitative applications. However, the existing methods for testing the radiation characteristics of SAR satellite backscatter coefficient images are mainly used in the ocean range and cannot effectively meet the application requirements under the background of complex land objects. In response to this problem, an embodiment of the present invention provides a method for testing SAR satellite backscatter coefficient images, so that the testing requirements for SAR satellite backscatter coefficient images can be met when facing the background of complex land objects.

[0044] Combine the following Figure 1-Figure 4 A method for checking a SAR satellite backscatter coefficient image of the present invention is described, and the method comprises the following steps:

[0045] 101. According to the observation parameters of the SAR satellite during transit imaging, the attitude of the automatic corner reflector fixedly deployed in the authenticity inspection site is remotely controlled and adjusted.

[0046] 102. Obtain a backscatter coefficient image of the SAR satellite according to a SAR image covering an automatic corner reflector and synchronously acquired by the SAR satellite and the adjusted attitude angle of the automatic corner reflector.

[0047] 103. Obtain a radar cross-sectional area measurement value of the automatic corner reflector according to the features of the automatic corner reflector in the backscatter coefficient image.

[0048] 104. Analyze the radar cross-sectional area measurement value using the radar cross-sectional area theoretical value of the automatic corner reflector to obtain the inspection result of the SAR satellite backscatter coefficient image.

[0049] Specifically, the automatic corner reflector is equipped with an intelligent gimbal, which can automatically perform parameter setting, state detection and attitude control through remote control software in the case of unattended operation. In the application background of the complex ground surface environment, the automatic corner reflector is applied to the inspection method of the SAR satellite backscatter coefficient image, which can realize the remote control adjustment of the corner reflector attitude, thereby overcoming the disadvantage that the traditional corner reflector needs to be manually adjusted according to the satellite orbit parameters when it is deployed, thereby consuming a lot of manpower and financial resources. By fixedly deploying the automatic corner reflector that supports remote control, unattended operation, and self-powered at the ground authenticity inspection site, when the SAR satellite passes the authenticity inspection site, the high-precision adjustment of the attitude of the automatic corner reflector is realized by remote control according to the SAR satellite and imaging geometric parameters, and the accuracy inspection of the SAR satellite backscatter coefficient image is realized through satellite-ground matching based on the position information of the automatic corner reflector, which effectively reduces the manual repetitive work in the field inspection experiment, and supports long-term deployment and automatic operation under complex land background, so as to periodically verify the characteristic accuracy of the SAR satellite backscatter coefficient image, and provide strong technical support for the quantitative application of SAR images. At the same time, the pointing accuracy of traditional manually placed corner reflectors is controlled at around 1°, while the automatic corner reflector that uses mechanically controlled angle adjustment has higher accuracy and stability than manual control. Its azimuth and elevation pointing accuracy can reach 0.1°, reducing the impact of the deviation of the radar wave incident direction from the normal direction of the corner reflector on the radar scattering cross-sectional area.

[0050] Furthermore, when the SAR satellite passes by for imaging, the attitude of the automatic corner reflector at the authenticity verification site can be remotely adjusted according to the satellite's observation parameters to meet the needs of different images. At the same time, the automatic corner reflector is equipped with safety protection measures such as a protective cover and a video monitoring system to ensure its safe and normal operation during the mission. As a ground reference, the automatic corner reflector can provide an accurately known radar cross-sectional area (RCS), that is, the theoretical value of RCS, because by accurately measuring the side length a of the automatic corner reflector, the theoretical value of RCS of the automatic corner reflector can be calculated in theory. For example, for a three-sided corner reflector, the theoretical calculation formula for the peak RCS is shown in Formula 1:

[0051]

[0052] Where σ is the theoretical RCS value of the corner reflector, in m 2 ; a is the length of the right-angle side of the corner reflector, in m; λ is the wavelength of the radar payload, in m.

[0053] It is understandable that when a SAR satellite backscatter coefficient image inspection method of the present invention is applied on the ground, first of all, according to the layout principle of the field experiment corner reflector, the automatic corner reflector should be laid out in the authenticity inspection station according to a reasonable layout plan, and the equipment accuracy and quantity should meet the requirements of the backscatter coefficient accuracy inspection, and the automatic corner reflector layout geographic coordinates, shape, side length and other information should be recorded at the same time. Usually, under ideal conditions, the authenticity inspection equipment layout plan is designed as a "cross", that is, the automatic corner reflector is evenly laid out in the distance-azimuth direction in the imaging coverage area of ​​the SAR satellite. At the same time, in order to improve the accuracy of the inspection result, the layout position needs to meet the requirements of the background terrain being flat, no surrounding buildings, mountains and other obstructions, no smoke or dust enterprises, no strong target signals or electromagnetic interference, etc., to ensure that the equipment meets the effective condition of the signal-to-noise ratio not less than 20dB. In addition, in order to facilitate the layout of the automatic corner reflector, the layout site also needs to ensure the normal passage of equipment transportation vehicles. At the same time, in order to ensure that the instruments and equipment are placed stably, the selected layout points and their surroundings must also have a certain degree of stability, so as to facilitate the implementation of infrastructure construction such as equipment base construction, protective cover installation, and video surveillance system.

[0054] Furthermore, the SAR satellite backscatter coefficient image is related to the SAR image acquired by the SAR satellite and the incident angle of the SAR satellite relative to the automatic corner reflector. Therefore, in the calculation of the SAR satellite backscatter coefficient image, it is necessary to process and calculate the SAR image of the authenticity verification site acquired synchronously by the satellite, combined with the known calibration equation, absolute radiation calibration constant, and incident angle, to obtain the backscatter coefficient image.

[0055] After the SAR satellite backscatter coefficient image is obtained, the radar cross-sectional area measurement value of the automatic corner reflector can be calculated according to the characteristics of the automatic corner reflector in the backscatter coefficient image.

[0056] Finally, the RCS theoretical value of the automatic corner reflector obtained by theoretical calculation is compared and analyzed with the radar cross-sectional area measurement value of the automatic corner reflector extracted from the backscatter coefficient image to obtain the inspection result of the SAR satellite backscatter coefficient image.

[0057] It should be noted that the existing method needs to use meteorological buoys to obtain sea surface wind field data, and further time-space registration is required, so the calculation is complex and cannot effectively meet the application requirements under the background of complex land objects. The present invention is based on the automatic corner reflector fixedly deployed at the ground authenticity inspection site to perform radiation characteristic inspection of the backscatter coefficient image. The whole process only needs to clarify the approximate layout position of the automatic corner reflector, and then the satellite-ground matching can be performed to select the automatic corner reflector imaging area to realize the inspection process. Therefore, the model is simple and easy to implement, and can adapt to a variety of quantitative application requirements under complex land backgrounds, and provide strong support for the long-term and periodic inspection of the radiation characteristics of the SAR satellite backscatter coefficient image.

[0058] In one embodiment of the present invention, based on the observation parameters of the SAR satellite during transit imaging, the azimuth pointing angle and the elevation pointing angle of the automatic corner reflector are remotely controlled and adjusted through an automatic corner reflector fixedly arranged in the authenticity verification site until the normal direction of the automatic corner reflector is consistent with the incident beam direction of the SAR satellite.

[0059] Specifically, the fixedly deployed automatic corner reflector can remotely control the azimuth and elevation pointing angle of the corner reflector according to the requirements of different images, so that the normal direction of the automatic corner reflector is as consistent as possible with the incident beam direction of the SAR satellite, which can further reduce the impact of the deviation of the radar wave incident direction from the normal direction of the corner reflector on the RCS.

[0060] Since the change of the antenna pointing angle may cause the radiation deviation of the SAR image in the range direction, in another embodiment of the present invention, the SAR image antenna pattern correction is performed according to the imaging results of each automatic corner reflector arranged in the range direction of the SAR satellite, so as to perform relative radiation correction on the SAR image;

[0061] The SAR image after relative radiation correction is combined with a calibration equation and an absolute radiation calibration constant to calculate the SAR satellite backscatter coefficient image.

[0062] Specifically, according to the SAR image covered with automatic corner reflector synchronously acquired by SAR satellite, combined with calibration equation, known absolute radiation calibration constant, incident angle and other related parameters, relative correction of SLC data and calculation of backscatter coefficient are performed, and abnormal values ​​in the image are inspected and corrected to ensure the quality of the obtained SAR satellite backscatter coefficient image. That is, firstly, the antenna pattern correction is performed on the SAR image to eliminate the radiation deviation in the range direction of the image caused by the change of antenna pointing angle, and then after relative radiation correction, the SAR image backscatter coefficient is calculated in combination with calibration equation and absolute radiation calibration constant. The commonly used backscatter coefficient calculation formula is shown in Formula 2:

[0063]

[0064] Among them, σ 0 is the backscattering coefficient corresponding to the ground object; DN 2 is the intensity value corresponding to the SAR image. For SLC data, the DN value is calculated from the real part I and the imaginary part Q, that is, DN 2 =I 2 +Q 2 ; K is the absolute radiation calibration constant value.

[0065] In addition, if it is necessary to convert the backscatter coefficient linear value σ 0 Convert to dB form σ dB , can be based on σ dB =10×lg(σ 0 ) is used for conversion. At the same time, due to the limitations of the conversion formula, when σ 0 =0, abnormal values ​​will appear in the backscatter coefficient conversion result, that is, null values ​​will appear in the backscatter coefficient image. Therefore, interpolation is required before conversion to eliminate the influence of abnormal values ​​on the result.

[0066] Furthermore, if Figure 2 As shown, in one embodiment, a specific method for obtaining the radar cross-sectional area measurement value of the automatic corner reflector according to the characteristics of the automatic corner reflector in the backscatter coefficient image in step 103 is provided, including:

[0067] 1031. Obtain row and column coordinates of the automatic corner reflector in the backscatter coefficient image according to the longitude and latitude of the automatic corner reflector in the authenticity verification site;

[0068] 1032. Select a predetermined range with the row and column coordinates as the center as a buffer zone, select a zone with the largest sum of backscatter coefficient values ​​in the buffer zone by using a sliding window method, and use the center point of the zone as the center point of the imaging zone of the automatic corner reflector;

[0069] 1033. Based on the automatic corner reflector imaging area in the backscatter coefficient image determined by the imaging area center point of the automatic corner reflector, a SAR image point target radar scattering cross-sectional area measurement method based on the peak method and / or the integral method is derived with the aid of a point target response energy calculation method;

[0070] 1034. Obtain a radar cross-sectional area measurement value of the automatic corner reflector from a backscatter coefficient image using the SAR image point target radar cross-sectional area measurement method.

[0071] Specifically, when inspecting the backscatter coefficient image, it is necessary to clearly identify the corresponding position of the automatic corner reflector on the image. Therefore, when the automatic corner reflector is fixedly deployed on the ground, the longitude and latitude of each point needs to be accurately measured. The longitude and latitude of the automatic corner reflector measured on the spot are converted into the row and column coordinates of the backscatter coefficient image through the affine transformation matrix, and this point is used as the center of the buffer zone. The center point of the sliding window with the largest sum of backscatter coefficient values ​​is selected within a certain buffer zone as the corresponding position of the automatic corner reflector on the image.

[0072] Specific selection method: Figure 3 As shown in FIG. 1 , the sliding window method is used to automatically select the center point position. First, a sliding window of a fixed size is used to slide in the buffer at a set step speed, and the sum of the backscatter coefficient values ​​in the sliding window is calculated. The center point of the sliding window with the largest sum is regarded as the center point of the imaging area of ​​the automatic corner reflector. Then, based on the selected center point of the imaging area of ​​the automatic corner reflector, Figure 4 Determine the imaging area of ​​the automatic corner reflector in the backscatter coefficient image.

[0073] It can be understood that after the relative radiation correction processing, the automatic corner reflector response energy ε p , absolute radiation calibration constant K, and radar cross-sectional area σ, the relationship between the three is shown in formula 3:

[0074] ε p =Kσ Formula 3;

[0075] Therefore, the impulse response energy ε of the automatic corner reflector can be used p The corresponding radar scattering cross-sectional area σ is calculated, and the pulse response energy of the automatic corner reflector can be calculated by the integral method or the peak method.

[0076] That is, based on the latitude and longitude coordinates of the automatic corner reflector, satellite-ground matching can realize the accurate selection of the center point of the automatic corner reflector imaging window, and extract the imaging window of the automatic corner reflector in the backscatter coefficient image. With the help of the point target response energy calculation method, a SAR image point target radar scattering cross-sectional area measurement method based on the peak method and the integral method is derived, and the radar scattering cross-sectional area measurement value of the automatic corner reflector is obtained from the backscatter coefficient image.

[0077] Among them, the method of calculating the radar cross-sectional area measurement value of the automatic corner reflector using the integration method is:

[0078] Take the center point of the imaging area of ​​the extracted automatic corner reflector as the window center and extract 2 c ×2 c The rectangular integral window data of the imaging area of ​​size, where c is taken as a natural number greater than 2 according to the actual situation, such as Figure 4As shown, taking c=5 as an example, Figure 4 The P in represents the size of a pixel, where area 1 is the main lobe area, areas 2 and 3 are the azimuth side lobe areas, and areas 4 and 5 are the range side lobe areas.

[0079] The integral method response energy calculation is to integrate the results of 8 times FFT interpolation of the pixels within the integral window of the automatic corner reflector. The specific formula is shown in the following formula 4:

[0080]

[0081] Among them, ε integral The energy response of the automatic corner reflector integration method; is the intensity value corresponding to the pixel of the automatic corner reflector in the SAR image; A is the integration area of ​​the automatic corner reflector; N A is the number of pixels corresponding to the integral area; B is the background calculation area of ​​the automatic corner reflector; N B is the number of pixels corresponding to the background calculation area; δ a and δ r They are the pixel spacing sizes in azimuth and distance directions respectively.

[0082] Combining formulas 2, 3, and 4, we can derive formula 5:

[0083]

[0084] Among them, RCS integral The radar cross-sectional area measured by the automatic corner reflector integration method, in m 2 ; σ i is the backscattering coefficient (linear value) corresponding to each pixel in the automatic corner reflector window.

[0085] Therefore, the RCS measurement value calculation of the automatic corner reflector integration method based on the backscatter coefficient image is based on the SAR image point target radar scattering cross-sectional area measurement method based on the integration method derived with the help of the point target response energy calculation method. The radar scattering cross-sectional area measurement value of the automatic corner reflector is obtained by performing 8 times FFT interpolation on the automatic corner reflector imaging window in the backscatter coefficient image and then integrating it.

[0086] The method for calculating the radar cross-sectional area measurement value of the automatic corner reflector using the peak method is:

[0087] The peak response energy calculation is to obtain the pulse response energy by multiplying the peak response energy of the automatic corner reflector by the equivalent resolution unit area. Figure 4, in the corner reflector imaging area in the SAR image, 8 times FFT interpolation is used to obtain the interpolated automatic corner reflector impulse response, find the DN value corresponding to the peak position, and calculate the peak method response energy. The specific formula is shown in Formula 6:

[0088]

[0089] Among them, ε peak It is the peak method response energy of the automatic corner reflector; is the intensity value corresponding to the pixel at the peak point of the automatic corner reflector in the SAR image; a and r are the width of the antenna 3dB pulse response in azimuth and range, respectively.

[0090] Therefore, by combining formulas 2, 3, and 6, it is found that the calculation of the RCS measurement value of the automatic corner reflector peak method based on the backscatter coefficient image is based on the backscatter coefficient peak value of the automatic corner reflector imaging area to obtain the radar cross-sectional area of ​​the automatic corner reflector. Specifically, 8 times FFT interpolation is performed on the automatic corner reflector imaging area in the backscatter coefficient image, and the backscatter coefficient value corresponding to the peak position is selected. The radar cross-sectional area corresponding to the automatic corner reflector is obtained by calculating the backscatter coefficient peak value of the automatic corner reflector imaging area and the equivalent resolution unit area, as shown in Formula 7:

[0091] RCS peak =σ p arδ a δ b Formula 7;

[0092] Among them, RCS peak The measured value of the radar cross-sectional area by the automatic corner reflector peak method, in m 2 ; σ p is the peak backscattering coefficient of the automatic corner reflector imaging area (linear value); a and r are the width of the antenna 3dB pulse response in azimuth and range, respectively.

[0093] In another embodiment, the specific contents of analyzing the radar cross-sectional area measurement value by using the radar cross-sectional area theoretical value of the automatic corner reflector to obtain the inspection result of the SAR satellite backscatter coefficient image are also provided, including:

[0094] Performing statistical analysis on radar cross-sectional area measurement values ​​of a plurality of automatic corner reflectors having the same radar cross-sectional area theoretical value and fixedly arranged in the authenticity verification site, and using the obtained analysis results as relative accuracy verification results of the SAR satellite backscatter coefficient image; and / or

[0095] The radar cross-sectional area measurement value of the automatic corner reflector is subtracted from the corresponding radar cross-sectional area theoretical value of the automatic corner reflector, and the absolute value of the difference is used as the absolute accuracy test result of the SAR satellite backscatter coefficient image.

[0096] Specifically, the SAR satellite backscatter coefficient image verification method of the present invention provides two backscatter coefficient image verification results, namely, relative accuracy and absolute accuracy.

[0097] In order to keep the RCS measurement value and the ground reference theoretical value in the same calculation dimension, the linear value is generally converted to a result in dBsm. The conversion formula is shown in Formula 8:

[0098] RCS dB =10*lg(RCS) Formula 8.

[0099] More specifically, for relative accuracy, ideally, automatic corner reflectors with the same RCS theoretical value in the backscatter coefficient image should have equal RCS measurement values. Therefore, a certain number of automatic corner reflectors with the same RCS theoretical value are deployed in the authenticity verification site. By calculating the radar cross-sectional area measurement value of each reference automatic corner reflector and performing statistical analysis on the measurement values ​​of multiple automatic corner reflectors with the same radar cross-sectional area theoretical value, the relative accuracy of the SAR image covered with automatic corner reflectors can be obtained, as shown in Formula 9:

[0100]

[0101] Among them, Δ R is the relative accuracy; N is the number of automatic corner reflectors used for inspection; is the radar cross-sectional area measurement value corresponding to the i-th automatic corner reflector, in dBsm; It is the average value of radar cross-sectional area measurement corresponding to N automatic corner reflectors, in dBsm.

[0102] For absolute accuracy, this indicator reflects the absolute difference between the measured value and the theoretical value. The absolute accuracy of the SAR image covered with the automatic corner reflector is obtained by taking the difference between the RCS measured value of the automatic corner reflector and the corresponding RCS theoretical value and taking the absolute value, as shown in Formula 10:

[0103]

[0104] Among them, Δ A is the absolute accuracy; is the radar cross-sectional area measurement value of the i-th automatic corner reflector, in dBsm; RCS iis the theoretical value of the radar cross-section of the ith automatic corner reflector, in dBsm.

[0105] In response to the urgent need for quantitative application of SAR images, the present invention proposes a method for testing the radiation characteristics of SAR satellite backscatter coefficient images based on automatic corner reflectors deployed at ground inspection stations. Taking the airborne SAR data of Huanghekou Town, Dongying City, Shandong Province, the Yellow River Delta, acquired on November 25, 2019 as an example, the method of the present invention is used to test the radiation characteristics of SAR satellite backscatter coefficient images based on automatic corner reflectors. The results show that the radiation inspection based on the automatic corner reflector has a good effect and can effectively reflect the accuracy of the radiation characteristics of the SAR backscatter coefficient image. The relative accuracy of the SAR satellite backscatter coefficient image obtained by the method provided by the present invention is 0.546, and the absolute accuracy is 0.664, which can meet the basic requirements of the radiation quality of the SAR satellite backscatter coefficient image required for the measurement accuracy of various earth parameters.

[0106] Combine the following Figure 5 A SAR satellite backscatter coefficient image inspection device provided by the present invention is described. The SAR satellite backscatter coefficient image inspection device described below and the SAR satellite backscatter coefficient image inspection method described above can correspond to each other.

[0107] like Figure 5 As shown, a SAR satellite backscatter coefficient image inspection device provided by the present invention includes an adjustment unit 510, an image generation unit 520, a calculation unit 530 and an analysis unit 540; wherein,

[0108] The adjustment unit 510 is used to remotely control and adjust the attitude of the automatic corner reflector fixedly arranged in the authenticity inspection site according to the observation parameters of the SAR satellite during the transit imaging;

[0109] The image generation unit 520 is used to obtain the SAR satellite backscatter coefficient image according to the SAR image covering the automatic corner reflector and the adjusted attitude angle of the automatic corner reflector synchronously acquired by the SAR satellite;

[0110] The calculation unit 530 is used to obtain a radar cross-sectional area measurement value of the automatic corner reflector according to the characteristics of the automatic corner reflector in the backscatter coefficient image;

[0111] The analysis unit 540 is used to analyze the radar cross-sectional area measurement value using the radar cross-sectional area theoretical value of the automatic corner reflector to obtain the inspection result of the SAR satellite backscatter coefficient image.

[0112] The inspection device provided by the present invention inspects the SAR satellite backscatter coefficient image through a remotely controllable automatic corner reflector fixedly arranged in the authenticity inspection site. During the whole process, it is only necessary to remotely control and adjust the attitude of the automatic corner reflector according to the observation parameters of the SAR satellite during transit imaging, and calculate and analyze the relevant data obtained by the automatic corner reflector and the SAR satellite itself, so as to obtain the inspection result of the SAR satellite backscatter coefficient image. It is not necessary to obtain more external space-time matching auxiliary data, and the model is simple and easy to implement. At the same time, the layout of the automatic corner reflector can fully meet the needs of various quantitative applications on land, and provide convenient quantitative data support for the verification of the SAR satellite backscatter coefficient image.

[0113] Figure 6 An example of a physical structure diagram of an electronic device is shown in FIG. Figure 6 As shown, the electronic device may include: a processor 610, a communication interface 620, a memory 630 and a communication bus 640, wherein the processor 610, the communication interface 620 and the memory 630 communicate with each other through the communication bus 640. The processor 610 may call the logic instructions in the memory 630 to execute the SAR satellite backscatter coefficient image verification method, which includes:

[0114] 101. According to the observation parameters of the SAR satellite during transit imaging, the attitude of the automatic corner reflector fixedly deployed in the authenticity inspection site is remotely controlled and adjusted.

[0115] 102. Obtain a backscatter coefficient image of the SAR satellite according to a SAR image covering an automatic corner reflector and synchronously acquired by the SAR satellite and the adjusted attitude angle of the automatic corner reflector.

[0116] 103. Obtain a radar cross-sectional area measurement value of the automatic corner reflector according to the features of the automatic corner reflector in the backscatter coefficient image.

[0117] 104. Analyze the radar cross-sectional area measurement value using the radar cross-sectional area theoretical value of the automatic corner reflector to obtain the inspection result of the SAR satellite backscatter coefficient image.

[0118] In addition, the logic instructions in the above-mentioned memory 630 can be implemented in the form of a software functional unit and can be stored in a computer-readable storage medium when it is sold or used as an independent product. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program codes.

[0119] On the other hand, the present invention further provides a computer program product, the computer program product comprising a computer program, the computer program can be stored in a non-transitory computer-readable storage medium, when the computer program is executed by a processor, the computer can execute the SAR satellite backscatter coefficient image verification method provided by the above methods, the method comprising:

[0120] 101. According to the observation parameters of the SAR satellite during transit imaging, the attitude of the automatic corner reflector fixedly deployed in the authenticity inspection site is remotely controlled and adjusted.

[0121] 102. Obtain a backscatter coefficient image of the SAR satellite according to a SAR image covering an automatic corner reflector and synchronously acquired by the SAR satellite and the adjusted attitude angle of the automatic corner reflector.

[0122] 103. Obtain a radar cross-sectional area measurement value of the automatic corner reflector according to the features of the automatic corner reflector in the backscatter coefficient image.

[0123] 104. Analyze the radar cross-sectional area measurement value using the radar cross-sectional area theoretical value of the automatic corner reflector to obtain the inspection result of the SAR satellite backscatter coefficient image.

[0124] In another aspect, the present invention further provides a non-transitory computer-readable storage medium having a computer program stored thereon, which is implemented when the computer program is executed by a processor to perform the SAR satellite backscatter coefficient image verification method provided by the above methods, the method comprising:

[0125] 101. According to the observation parameters of the SAR satellite during transit imaging, the attitude of the automatic corner reflector fixedly deployed in the authenticity inspection site is remotely controlled and adjusted.

[0126] 102. Obtain a backscatter coefficient image of the SAR satellite according to a SAR image covering an automatic corner reflector and synchronously acquired by the SAR satellite and the adjusted attitude angle of the automatic corner reflector.

[0127] 103. Obtain a radar cross-sectional area measurement value of the automatic corner reflector according to the features of the automatic corner reflector in the backscatter coefficient image.

[0128] 104. Analyze the radar cross-sectional area measurement value using the radar cross-sectional area theoretical value of the automatic corner reflector to obtain the inspection result of the SAR satellite backscatter coefficient image.

[0129] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0130] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for testing a SAR satellite backscatter coefficient image, characterized in that: include: According to the observation parameters of the SAR satellite during the transit imaging, the attitude of the automatic corner reflector fixedly deployed in the authenticity inspection site is remotely controlled and adjusted; Obtaining the SAR satellite backscatter coefficient image according to the SAR image covering the automatic corner reflector synchronously acquired by the SAR satellite and the adjusted attitude angle of the automatic corner reflector; Obtaining a radar cross-sectional area measurement value of the automatic corner reflector according to the characteristics of the automatic corner reflector in the backscatter coefficient image; Analyzing the radar cross-sectional area measurement value using the radar cross-sectional area theoretical value of the automatic corner reflector to obtain the inspection result of the SAR satellite backscatter coefficient image; The remote control adjustment of the attitude of the automatic corner reflector fixedly arranged in the authenticity inspection site according to the observation parameters of the SAR satellite during the transit imaging specifically includes: According to the observation parameters of the SAR satellite during transit imaging, the azimuth pointing angle and the elevation pointing angle of the automatic corner reflector are remotely controlled and adjusted through the automatic corner reflector fixedly arranged in the authenticity verification site until the normal direction of the automatic corner reflector is consistent with the incident beam direction of the SAR satellite; The step of obtaining the SAR satellite backscatter coefficient image based on the SAR image covering the automatic corner reflector synchronously acquired by the SAR satellite and the adjusted attitude angle of the automatic corner reflector specifically includes: Performing SAR image antenna pattern correction according to imaging results of each automatic corner reflector arranged in the SAR satellite range direction, so as to perform relative radiation correction on the SAR image; The SAR image after relative radiation correction is combined with a calibration equation and an absolute radiation calibration constant to calculate the SAR satellite backscatter coefficient image; The step of obtaining a radar cross-sectional area measurement value of the automatic corner reflector according to the feature of the automatic corner reflector in the backscatter coefficient image specifically includes: According to the longitude and latitude of the automatic corner reflector in the authenticity verification site, obtaining the row and column coordinates of the automatic corner reflector in the backscatter coefficient image; A predetermined range is selected with the row and column coordinates as the center as a buffer zone, a region with the largest sum of backscatter coefficient values ​​in the buffer zone is selected using a sliding window method, and the center point of the region is used as the center point of the imaging region of the automatic corner reflector; Based on the automatic corner reflector imaging area in the backscatter coefficient image determined by the imaging area center point of the automatic corner reflector, a SAR image point target radar scattering cross-sectional area measurement method based on the peak method and / or the integral method is derived with the help of a point target response energy calculation method; Obtaining a radar cross-sectional area measurement value of the automatic corner reflector from a backscatter coefficient image using the SAR image point target radar cross-sectional area measurement method; The method of analyzing the radar cross-sectional area measurement value by using the radar cross-sectional area theoretical value of the automatic corner reflector to obtain the inspection result of the SAR satellite backscatter coefficient image specifically includes: Performing statistical analysis on radar cross-sectional area measurement values ​​of a plurality of automatic corner reflectors having the same radar cross-sectional area theoretical value and fixedly arranged in the authenticity verification site, and using the obtained analysis results as relative accuracy verification results of the SAR satellite backscatter coefficient image; and / or The radar cross-sectional area measurement value of the automatic corner reflector is subtracted from the corresponding radar cross-sectional area theoretical value of the automatic corner reflector, and the absolute value of the difference is used as the absolute accuracy test result of the SAR satellite backscatter coefficient image.

2. A SAR satellite backscatter coefficient image inspection device, characterized in that: include: An adjustment unit is used to remotely control and adjust the attitude of an automatic corner reflector fixedly arranged in the authenticity inspection site according to observation parameters of the SAR satellite during transit imaging; The remote control adjustment of the attitude of the automatic corner reflector fixedly arranged in the authenticity inspection site according to the observation parameters of the SAR satellite during the transit imaging specifically includes: According to the observation parameters of the SAR satellite during transit imaging, the azimuth pointing angle and the elevation pointing angle of the automatic corner reflector are remotely controlled and adjusted through the automatic corner reflector fixedly arranged in the authenticity verification site until the normal direction of the automatic corner reflector is consistent with the incident beam direction of the SAR satellite; An image generating unit, configured to obtain the SAR satellite backscatter coefficient image according to a SAR image covering the automatic corner reflector and synchronously acquired by the SAR satellite and the adjusted attitude angle of the automatic corner reflector; The step of obtaining the SAR satellite backscatter coefficient image based on the SAR image covering the automatic corner reflector synchronously acquired by the SAR satellite and the adjusted attitude angle of the automatic corner reflector specifically includes: Performing SAR image antenna pattern correction according to imaging results of each automatic corner reflector arranged in the SAR satellite range direction, so as to perform relative radiation correction on the SAR image; The SAR image after relative radiation correction is combined with a calibration equation and an absolute radiation calibration constant to calculate the SAR satellite backscatter coefficient image; A calculation unit, used to obtain a radar cross-sectional area measurement value of the automatic corner reflector according to the characteristics of the automatic corner reflector in the backscatter coefficient image; The step of obtaining a radar cross-sectional area measurement value of the automatic corner reflector according to the feature of the automatic corner reflector in the backscatter coefficient image specifically includes: According to the longitude and latitude of the automatic corner reflector in the authenticity verification site, obtaining the row and column coordinates of the automatic corner reflector in the backscatter coefficient image; A predetermined range is selected with the row and column coordinates as the center as a buffer zone, a region with the largest sum of backscatter coefficient values ​​in the buffer zone is selected using a sliding window method, and the center point of the region is used as the center point of the imaging region of the automatic corner reflector; Based on the automatic corner reflector imaging area in the backscatter coefficient image determined by the imaging area center point of the automatic corner reflector, a SAR image point target radar scattering cross-sectional area measurement method based on the peak method and / or the integral method is derived with the help of a point target response energy calculation method; Obtaining a radar cross-sectional area measurement value of the automatic corner reflector from a backscatter coefficient image using the SAR image point target radar cross-sectional area measurement method; An analysis unit, used to analyze the radar cross-sectional area measurement value using the radar cross-sectional area theoretical value of the automatic corner reflector to obtain the inspection result of the SAR satellite backscatter coefficient image; The method of analyzing the radar cross-sectional area measurement value by using the radar cross-sectional area theoretical value of the automatic corner reflector to obtain the inspection result of the SAR satellite backscatter coefficient image specifically includes: Performing statistical analysis on radar cross-sectional area measurement values ​​of a plurality of automatic corner reflectors having the same radar cross-sectional area theoretical value and fixedly arranged in the authenticity verification site, and using the obtained analysis results as relative accuracy verification results of the SAR satellite backscatter coefficient image; and / or The radar cross-sectional area measurement value of the automatic corner reflector is subtracted from the corresponding radar cross-sectional area theoretical value of the automatic corner reflector, and the absolute value of the difference is used as the absolute accuracy test result of the SAR satellite backscatter coefficient image.

3. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the steps of the method for verifying the SAR satellite backscatter coefficient image as claimed in claim 1 are implemented.

4. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for verifying the SAR satellite backscatter coefficient image as claimed in claim 1 are implemented.

5. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method for verifying the SAR satellite backscatter coefficient image as claimed in claim 1 are implemented.

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