A design method to improve the beam coverage of high-orbit SAR scanning mode

Abstract

The present invention discloses a design method for improving the beam coverage of a high-orbit SAR scanning working mode: Step 1: Calculate the scanning angle and scanning azimuth of the antenna beam of the high-orbit SAR required for satellite yaw guidance; Step 2: Use the scanning angle and scanning azimuth to perform yaw angle correction; Step 3: Divide the imaging surveying belt into multiple sub-surveying belts according to the width requirement of the distance-upward imaging surveying belt; Step 4: Calculate the time for a high-orbit SAR to continuously image in each sub-surveying belt in the scanning working mode according to the preset resolution requirement; Step 5: Calculate the scanning time of the high-orbit SAR satellite; Step 6: Complete the image splicing of all sub-surveying belts in the distance-upward scanning mode to obtain a surveying belt image. The present invention can realize the orderly splicing of the sub-surveying belts scanned by the high-orbit SAR, and can effectively avoid the dislocation of the splicing of the sub-surveying belts.

Description

Technical Field

[0001] The present invention belongs to the field of synthetic aperture radar, and specifically provides a design method for improving the beam coverage of a high-orbit SAR scanning working mode. Background Art

[0002] The ScanSAR mode was first implemented on the Radarsat satellite launched by Canada in 1995. The SAR satellite uses a beam angle that can be changed within a certain range, and can image any target within the beam illumination area. In this way, a defined area can be observed multiple times by the satellite in one orbital cycle, and multiple sub-survey bands can be obtained in parallel through the change of antenna angle to obtain a larger ground observation area. The radars carried by the current spaceborne SAR satellites in orbit, such as Envisat, ALOS, and TerraSAR-X, all have ScanSAR mode.

[0003] In low-orbit SAR satellites, the scanning mode is designed to obtain a large mapping swath by switching the beam in the range upward within a synthetic aperture time. Since low-orbit SAR is less affected by the rotation of the earth, its beam footprint is in a positive side-view observation on the ground, so there is no misalignment problem in the splicing of its range-up width. However, during the design of the high-orbit 20mSAR scanning working mode, it was found that due to the great influence of the earth's rotation, the antenna beam is in an oblique observation state on the ground. At this time, if the beam is not adjusted, it will cause misalignment in the scanning mode image splicing process at certain orbital moments.

[0004] Currently, the public literature has not conducted a detailed analysis of the design of the high-orbit SAR scanning working mode. Some public literature has touched on some aspects of it, but it cannot solve the problems encountered in the high-orbit SAR scanning working mode.

[0005] The document “Research on Imaging Algorithms of Typical Working Modes of Geosynchronous Orbit SAR” introduces the working schematic of the scanning mode of geosynchronous orbit SAR, but does not give a specific implementation method of the scanning mode in combination with the antenna beam, nor does it consider the problem of scanning mode splicing misalignment caused by the rotation of the earth.

[0006] In the document "Multi-transmitter and multi-receiver Scan Mode to Realize High-resolution Wide-swath SAR Imaging", a SAR imaging method based on multi-transmitter and multi-receiver scanning mode is proposed to address the contradiction between high-resolution and wide-swath imaging of traditional satellite-mounted synthetic aperture radar. This method controls the beam pointing so that it periodically illuminates multiple sub-swaths in the range direction, thereby obtaining a wide swath in the range direction. At the same time, in order to ensure the resolution in azimuth, multi-antenna reception and beamforming are used to achieve Doppler ambiguous signal reconstruction at a low azimuth repetition frequency. However, this method is mainly used in the case of low-orbit SAR, and does not cause the problem of inconsistent overlapping sizes of swaths with different viewing angles in high-orbit SAR.

[0007] Based on the above typical literature, the currently available relevant literature has not conducted a detailed analysis of the specific implementation process of the high-orbit SAR scanning mode. The existing scanning working mode design method is mainly aimed at the low-orbit SAR. However, the low-orbit SAR does not have the problem of inconsistent overlapping sizes of mapping strips from different perspectives caused by the influence of the earth's rotation in the high-orbit SAR. Summary of the invention

[0008] The purpose of the present invention is to provide a design method for improving the beam coverage of the high-orbit SAR scanning working mode to solve the following technical problems: the high-orbit SAR is easily affected by the rotation of the earth, causing the antenna beam to be oblique on the ground. In the scanning mode, if the width is spliced ​​according to the traditional pitch sub-surveying strips, the sub-surveying strips will be misaligned at certain orbital moments.

[0009] In order to achieve the above object, the present invention adopts the following technical solution:

[0010] A design method for improving the beam coverage of a high-orbit SAR scanning mode includes the following steps:

[0011] Step 1: Calculate the scanning angle and scanning azimuth of the antenna beam of the high-orbit SAR required for satellite yaw guidance;

[0012] Step 2: Use the scanning angle and scanning azimuth obtained in step 1 to correct the yaw angle;

[0013] Step 3: Divide the imaging swath into The antenna beam pointing angle switches along the range direction for a scanning time period. -1;

[0014] Step 4: Calculate the resolution of the high-orbit SAR in the scanning mode according to the preset resolution requirements. i The time of a continuous imaging in a sub-mapping zone ;

[0015] Step 5: Calculate the scanning time of the high-orbit SAR satellite. The calculation formula is as follows:

[0016] ;

[0017] Where:

[0018] —The scanning time of the antenna beam of the high-orbit SAR;

[0019] N s —Number of sub-surveying zones;

[0020] —High-orbit SAR in i The time of continuous imaging in a sub-mapping zone;

[0021] — Antenna beam pointing angle switching time;

[0022] Step 6: Complete the stitching of all sub-surveying strip images in the scanning mode distance upward to obtain the surveying strip image, that is, the high-orbit SAR scanning mode image.

[0023] Furthermore, step one includes the following sub-steps:

[0024] Step 11, calculate the antenna beam pointing angle of the high-orbit SAR before satellite yaw guidance, the formula is as follows:

[0025] ;

[0026] Where:

[0027] —Antenna beam pointing angle of high-orbit SAR before satellite yaw guidance;

[0028] —initial azimuth;

[0029] —Yaw angle of high-orbit SAR;

[0030] — Initial viewing angle;

[0031] u t 、u p 、u r —Unit vectors corresponding to the X, Y, and Z axes in the satellite orbit coordinate system;

[0032] Step 12, calculating the antenna beam pointing angle of the high-orbit SAR after satellite yaw guidance;

[0033] ;

[0034] Where: Q c —Antenna beam pointing angle of high-orbit SAR before satellite yaw guidance;

[0035] Step 13, give the representation of the antenna beam pointing angle in the antenna coordinate system:

[0036] ;

[0037] Where:

[0038] - Scanning angle of view;

[0039] - scanning azimuth;

[0040] The antenna beam pointing angle is converted equally between the satellite orbit coordinate system and the antenna coordinate system to obtain the following expression:

[0041] ;

[0042] Step 14, calculate the scanning angle of the antenna beam of the high-orbit SAR required for satellite yaw guidance in the antenna coordinate system through the expression in step 13, and the scanning angle includes the scanning viewing angle and the scanning azimuth angle:

[0043]

[0044] ;

[0045] Where:

[0046] —Yaw angle of high-orbit SAR satellite;

[0047] - Scanning angle of view;

[0048] —Scanning azimuth.

[0049] Furthermore, in step 4, the current scanning time period satisfies the following conditions:

[0050] ;

[0051] Where:

[0052] - synthetic aperture time of the beam full aperture;

[0053] —The scanning time of the antenna beam of the high-orbit SAR.

[0054] The beneficial effects of the present invention compared with the prior art are as follows:

[0055] In view of the problem of the dislocation of the sub-strips in the high-orbit SAR scanning mode, the present invention provides a design method for improving the beam coverage of the high-orbit SAR scanning working mode. The method uses antenna beam scanning to correct the yaw angle. At the same time, the dwell time of each sub-strip in the scanning working mode is calculated according to the resolution requirement; the scanning time of the high-orbit SAR satellite is calculated according to the dwell time and the switching time. On this basis, in order to ensure that the strips between the adjacent sub-strips in the azimuth of the next cycle can be spliced ​​normally, the scanning time in the current scanning time period must be less than the synthetic aperture time of the beam full aperture, so as to achieve the orderly splicing of the sub-strips scanned by the high-orbit SAR. According to the test, the method of the present invention can effectively avoid the dislocation of the sub-strips. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 A flow chart of a design method for improving beam coverage of a high-orbit SAR scanning working mode according to the present invention;

[0057] Figure 2 The yaw angle required for the full orbit of the high-orbit SAR satellite;

[0058] Figure 3 The scanning angle of the antenna beam required for yaw steering;

[0059] Figure 4 The scanning azimuth angle of the antenna beam required for yaw steering;

[0060] Figure 5 It is the dwell time of a sub-survey swath during one continuous imaging of the high-orbit SAR in the scanning working mode;

[0061] Figure 6 The full-track beam coverage area is adopted in the traditional high-orbit SAR scanning mode;

[0062] Figure 7 It is the beam coverage area obtained by adopting the method of the present invention.

[0063] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0064] The technical idea of ​​the method of the present invention is to use antenna beam scanning to correct the yaw angle, and at the same time, calculate the dwell time of each sub-surveying band in the scanning working mode according to the resolution requirement, and then calculate the antenna beam adjustment and scanning speed according to the beam scanning angle and the dwell time, so as to realize the orderly splicing of the high-orbit SAR scanning sub-surveying bands.

[0065] The design method for improving the beam coverage of the high-orbit SAR scanning working mode provided by the present invention has the following process: Figure 1 As shown, the specific steps include:

[0066] Step 1: Calculate the scanning angle and azimuth of the antenna beam of the high-orbit SAR required for satellite yaw guidance.

[0067] Step 11, calculate the antenna beam pointing angle of the high-orbit SAR before satellite yaw guidance, the specific calculation formula is as follows:

[0068] ;

[0069] Where:

[0070] —Antenna beam pointing angle of high-orbit SAR before satellite yaw guidance;

[0071] —initial azimuth;

[0072] —Yaw angle of high-orbit SAR;

[0073] — Initial viewing angle;

[0074] u t 、u p 、u r —Unit vectors corresponding to the X, Y, and Z axes in the satellite orbit coordinate system;

[0075] Step 12, calculating the antenna beam pointing angle of the high-orbit SAR after satellite yaw guidance.

[0076] After the yaw control is adopted for the high-orbit SAR satellite, the initial azimuth angle of the antenna beam in the satellite orbit coordinate system , so the antenna beam pointing angle of the high-orbit SAR after satellite yaw guidance is expressed as:

[0077] ;

[0078] Where: Q c —Antenna beam pointing angle of high-orbit SAR before satellite yaw guidance;

[0079] Step 13, give the representation of the antenna beam pointing angle in the antenna coordinate system:

[0080] ;

[0081] Where: - Scanning angle of view; - scanning azimuth;

[0082] The antenna beam pointing angle is converted equally between the satellite orbit coordinate system and the antenna coordinate system to obtain the following expression:

[0083] ;

[0084] Step 14, calculate the scanning angle of the antenna beam of the high-orbit SAR required for satellite yaw guidance in the antenna coordinate system through the expression in step 13, and the scanning angle includes the scanning viewing angle and the scanning azimuth angle:

[0085] , ;

[0086] Where:

[0087] —Yaw angle of high-orbit SAR;

[0088] - Scanning angle of view;

[0089] —Scanning azimuth.

[0090] Step 2: Use the scanning angle and scanning azimuth obtained in step 1 to correct the yaw angle;

[0091] Step 3: Divide the imaging swath into The antenna beam pointing angle switches along the range direction for a scanning time period. -1;

[0092] Step 4: Calculate the resolution of the high-orbit SAR in the scanning mode according to the preset resolution requirements. i The time of continuous imaging within a sub-survey band (burst) (usually called the Burst dwell time) is recorded as .

[0093] Step 5: Calculate the scanning time of the high-orbit SAR satellite. The calculation formula is as follows:

[0094] ;

[0095] Where:

[0096] —The scanning time of the antenna beam of the high-orbit SAR;

[0097] N s —Number of sub-surveying zones;

[0098] —High-orbit SAR ini The time of continuous imaging in a sub-mapping zone;

[0099] — Antenna beam pointing angle switching time;

[0100] Preferably, in order to ensure that the mapping strips between adjacent sub-mapping strips in azimuth in the next scanning time period can be normally spliced, the scanning time of the antenna beam of the high-orbit SAR in the current scanning time period needs to meet the following conditions:

[0101] ;

[0102] Where: is the synthetic aperture time of the full aperture of the beam.

[0103] Step 6: Complete the stitching of all sub-surveying strip images in the scanning mode distance upward to obtain the surveying strip image, that is, the high-orbit SAR scanning mode image.

[0104] It should be noted that the contents not described in detail in the specification of the present invention are well-known technologies for those skilled in the art.

[0105] The effect of the present invention is further illustrated by simulation experiments. In order to verify the effectiveness of the method, the following parameters are selected for simulation verification. The satellite orbit altitude is 42164 km, the orbit inclination is 16°, the eccentricity is 0°, the perigee angle is 88°, the true anomaly is 180°, the right side observation, the number of sub-surveying and mapping strips is 3, the antenna downward viewing angle is 4.5°~6.5°, the antenna aperture is 20m, and the azimuth resolution is 10m.

[0106] In order to calculate the pitch angle and azimuth angle required for the antenna beam to be viewed sideways, the yaw angle required for the satellite's full orbit is first calculated, such as Figure 2 As shown, on this basis, according to the calculation method of step 1, the scanning viewing angle and scanning azimuth angle of the antenna beam required for yaw guidance are as follows: Figure 3 and Figure 4 shown.

[0107] On the basis of obtaining the scanning angle and scanning azimuth required for antenna beam yaw guidance correction, under the requirement of azimuth resolution of 10m, the dwell time of each sub-surveying band during one continuous imaging of high-orbit SAR in scanning working mode is calculated, as follows: Figure 5 As shown in the figure, at a resolution of 10 m, the dwell time of each sub-survey band in one continuous imaging is 830s-1800s.

[0108] Assuming that the beam switching time is 10us, in order to ensure that the mapping strips between adjacent sub-mapping strips in the azimuth of the next cycle can be spliced ​​normally, the synthetic aperture time of the beam full aperture needs to be greater than 2490s-5400s. At this point, the high-orbit SAR scanning mode design is completed.

[0109] Figure 6 To cover the area with full-track beam in traditional SAR scanning mode, Figure 6 The different lines in the figure represent different sub-survey belts, from the near end to the far end, they are the first sub-survey belt, the second sub-survey belt, and the third sub-survey belt. Figure 6 It can be seen that due to the influence of the earth's rotation, the beam footprints of its various sub-surveying bands are not regular rectangles like conventional low-orbit SAR. The lower half of the entire "tear drop-shaped" beam coverage area is folded and covered at different angles, which brings great difficulties to the scanning mode imaging stitching process.

[0110] Figure 7 The beam coverage obtained by the method of the present invention under the same parameters is: Figure 7 The different lines in the figure represent different sub-survey belts, from the near end to the far end, they are the first sub-survey belt, the second sub-survey belt, and the third sub-survey belt. Figure 7 It can be seen that the problem of mutual folding of the high-orbit SAR beam coverage areas has been solved, proving that the method of the present invention can achieve orderly splicing of high-orbit SAR scanning sub-surveying swaths.

[0111] The following table shows the calculation results of the full-track beam coverage area obtained by using the traditional SAR scanning mode and a high-orbit SAR scanning working mode antenna beam adjustment method under the same parameters. It can be seen from Table 1 that the method of the present invention increases the observation area by nearly 4 times compared with the traditional scanning mode.

[0112] Table 1 Comparison of ground coverage area between the method of the present invention and the traditional scanning mode beam

[0113]

Claims

1. A design method for improving the beam coverage of a high-orbit SAR scanning mode, characterized in that: The specific steps include: Step 1: Calculate the scanning angle and scanning azimuth of the antenna beam of the high-orbit SAR required for satellite yaw guidance, including the following sub-steps: Step 11, calculate the antenna beam pointing angle of the high-orbit SAR before satellite yaw guidance, the formula is as follows: ； Where: —Antenna beam pointing angle of high-orbit SAR before satellite yaw guidance; —initial azimuth; —Yaw angle of high-orbit SAR; — Initial viewing angle; ut、u p , ur—unit vector corresponding to the X, Y, and Z axes in the satellite orbit coordinate system; Step 12, calculating the antenna beam pointing angle of the high-orbit SAR after satellite yaw guidance; ； Where: Q c —Antenna beam pointing angle of high-orbit SAR after satellite yaw guidance; Step 13, give the representation of the antenna beam pointing angle in the antenna coordinate system: ； Where: - Scanning angle of view; - scanning azimuth; The antenna beam pointing angle is converted equally between the satellite orbit coordinate system and the antenna coordinate system to obtain the following expression: ； Step 14, calculate the scanning angle of the antenna beam of the high-orbit SAR required for satellite yaw guidance in the antenna coordinate system through the expression in step 13, and the scanning angle includes the scanning viewing angle and the scanning azimuth angle: ； Where: —Yaw angle of high-orbit SAR; - Scanning angle of view; - scanning azimuth; Step 2: Use the scanning angle and scanning azimuth obtained in step 1 to correct the yaw angle; Step 3: Divide the imaging swath into The antenna beam pointing angle switches along the range direction for a scanning time period. -1; Step 4: Calculate the resolution of the high-orbit SAR in the scanning mode according to the preset resolution requirements. i The time of a continuous imaging in a sub-mapping zone ; Step 5: Calculate the scanning time of the high-orbit SAR satellite. The calculation formula is as follows: ； Where: —The scanning time of the antenna beam of the high-orbit SAR; N —Number of sub-surveying zones; —High-orbit SAR in i The time of one continuous imaging in a sub-mapping band; — Antenna beam pointing angle switching time; Step 6: Complete the stitching of all sub-surveying strip images in the scanning mode distance upward to obtain the surveying strip image, that is, the high-orbit SAR scanning mode image.

2. The design method for improving the beam coverage of the high-orbit SAR scanning working mode as claimed in claim 1, characterized in that: In step 5, the scanning time of the antenna beam of the high-orbit SAR meets the following conditions: ； Where: - synthetic aperture time of the beam full aperture; —The scanning time of the antenna beam of the high-orbit SAR.

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