A high orbit satellite TOPS SAR working mode design method

Abstract

The application belongs to the field of synthetic aperture radar, and discloses a high-orbit satellite TOPS SAR working mode design method, which comprises the following steps: step one, determining the azimuth imaging resolution of a TOPS SAR working mode sub-swath and an antenna beam scanning angular velocity; step two, determining the beam dwell time of each sub-swath; step three, determining the sub-swath beam scanning angle according to the beam scanning angular velocity and the sub-swath beam dwell time; step four, scanning each sub-swath to obtain each sub-swath image; and performing distance and azimuth image splicing on all sub-swath images to obtain a TOPS SAR image. The application can realize the calculation of the beam scanning speed and the beam scanning angle of the high-orbit SAR TOPS working mode, thereby greatly improving the level and efficiency of the high-orbit SAR system design and the precision of the SAR system working mode design.

Description

Technical Field

[0001] This invention belongs to the field of synthetic aperture radar and relates to a design method for the working mode of TOPS SAR for high-orbit satellites. Background Technology

[0002] The TOPS mode was proposed by E. Attema (ESA-ESTEC, European Space Technology Centre) and F. Rocca (POLIMI, Polytechnic University of Milan, Italy), and fully described by FDZan and AM Guarnieri (POLIMI) in their paper, naming this working mode TOPS. Currently, the TOPS mode, as an experimental mode on TerraSAR-X, has successfully acquired TOPS images. These images have not undergone residual scalloping correction, but the scalloping effect is no longer visible. According to publicly available literature, in addition to the general TOPS mode, the inverse TOPS mode has also been tested on TerraSAR-X. Besides TerraSAR-X, Radarsat-2 also conducted TOPS mode experiments to support the Sentinel-1 satellite in implementing TOPS. The Sentinel-1 satellite, currently receiving considerable attention, is a relatively new SAR satellite in ESA's GMES program, primarily aimed at monitoring sea ice and the marine environment, and mapping forests, water, and soil on the Earth's surface. Because Sentinel-1 satellites are designed for large-scale environmental monitoring, they require a high revisit period. Therefore, TOPS mode became the primary operating mode for Sentinel-1.

[0003] The paper "Design and Imaging Processing Technology of Low-Earth Orbit Spaceborne Multi-Mode SAR System" presents a conventional design method for the TOPS (Top-Down-Side) working mode of low-Earth orbit SAR and proposes a frequency domain imaging algorithm specifically for TOPS mode. To address the issues of large range migration and high echo data redundancy in TOPS mode, a variable PRF (Range-Reference Frame) technique is proposed for echo storage. To address the problem of aperiodic and non-uniform azimuth sampling in the variable PRF SAR working mode, a method combining the extended omega-K algorithm and a time-frequency scale transformation imaging algorithm is proposed. This method first performs uniform sampling of the unambiguous azimuth signal in the time domain, then uses the omega-K algorithm for range migration correction, and finally employs azimuth frequency scale transformation to process the remaining phase. However, this TOPS design suffers from azimuth image misalignment in the sub-band stitched images.

[0004] The paper "Multi-channel Beampointing High-Resolution SAR and Moving Target Imaging Technology" proposes two methods for simultaneously processing TOPSSAR. The first method is based on the azimuth preprocessing convolution operation in the two-step processing of spotlight SAR, modifying the azimuth dealiasing operation to make it well-suited for these two new SAR systems. After recovering the two-dimensional spectrum, an azimuth Doppler domain algorithm is used to correct signal migration. Finally, an azimuth deskewing and recalibrating focusing algorithm is proposed to focus the signal in the azimuth frequency domain. The second method is based on azimuth-calibrated PFA, or generalized PFA. Generalized PFA combines the efficiency of traditional PFA algorithms in signal processing with the effectiveness of azimuth recalibration in avoiding azimuth ambiguity in the two-step method. It can simultaneously process sliding spotlight and TOPSSAR data by selecting a reference function. However, this paper also fails to provide design parameters for the azimuth rotation rate and angle in the case of high-orbit satellites, and suffers from azimuth image misalignment in the stitched images of different sub-bands.

[0005] In summary, current TOPS design methods are not suitable for high-orbit SAR, and there is also the problem of azimuth image misalignment in the stitched images of each sub-band. Therefore, there is an urgent need to propose a new design method for high-orbit TOPS SAR operating modes. Summary of the Invention

[0006] The purpose of this invention is to provide a design method for the working mode of high-orbit satellite TOPS SAR, so as to solve the problem that the traditional TOPS SAR working mode design method is not applicable to high-orbit SAR and the azimuth image misalignment of sub-band stitched images.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A design method for the operating mode of a high-orbit satellite TOPS SAR includes the following steps:

[0009] Step 1: Determine the azimuth imaging resolution of the sub-strip in TOPS SAR operating mode, and determine the scanning angular rate of the antenna beam based on the azimuth imaging resolution of the sub-strip.

[0010] Step 2: Determine the dwell time of each sub-mapping beam based on the imaging resolution requirements;

[0011] Step 3: Based on the scanning angular rate of the beam obtained in Step 1 and the dwell time of each sub-mapping beam obtained in Step 2, determine the scanning angle of each sub-mapping beam.

[0012] Step 4: Scan each sub-mapped area according to the scanning angle of each sub-mapped area beam obtained in Step 3 to obtain an image of each sub-mapped area; stitch the range images of all sub-mapped areas together, and then stitch the azimuth images together to obtain a TOPS SAR image. At this point, the design of the TOPS SAR working mode for high-orbit satellites is completed.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] Current TOPS SAR operating mode design methods are not applicable to high-orbit SAR TOPS operating mode design. This invention considers the impact of high-orbit SAR resolution improvement factors on sub-mapped area resolution design and solves the azimuth image misalignment problem in the stitched images of each sub-mapped area by adjusting the beam scanning angle of each sub-mapped area. This invention can calculate the beam scanning speed and beam scanning angle of high-orbit SAR TOPS operating mode, thereby greatly improving the design level and efficiency of high-orbit SAR systems. Similarly, this method can be extended to platforms such as medium-orbit SAR, which can greatly improve the accuracy of SAR system operating mode design and has important application prospects.

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 A flowchart illustrating the design method for the TOPS SAR working mode of a high-orbit satellite according to the present invention;

[0017] Figure 2 For sub-mapping, the scanning angular rate with antenna is measured;

[0018] Figure 3 For sub-mapping, beam scanning and dwell time;

[0019] Figure 4 The beam scanning angle for the first sub-mapping zone;

[0020] Figure 5 The second sub-mapping band beam scanning angle;

[0021] Figure 6 The beam scanning angle for the third sub-mapping zone. Detailed Implementation

[0022] like Figure 1 As shown, the present invention provides a design method for the TOPS SAR working mode of high-orbit satellites, including the following steps:

[0023] Step 1: Determine the azimuth imaging resolution of the sub-mapped area in the TOPS SAR working mode, and determine the scanning angular rate of the antenna beam based on the azimuth imaging resolution of the sub-mapped area.

[0024] Specifically, the azimuth resolution of the sub-mapping strip in TOPS SAR working mode The expression is as follows:

[0025]

[0026] In the formula:

[0027] —Radar range;

[0028] —The scanning angular rate of the antenna beam;

[0029] —Satellite flight speed;

[0030] —Antenna aperture;

[0031] —High-orbit SAR resolution improvement factor (0.15 in this embodiment);

[0032] From the above formula, we can obtain:

[0033]

[0034] Calculated from the above It is positive because ,in This is the azimuth resolution for standard strip mode.

[0035] Step 2: Determine the dwell time of each sub-mapping beam based on the imaging resolution requirements;

[0036] Specifically, the following formula needs to be satisfied:

[0037]

[0038]

[0039]

[0040] In the formula:

[0041] —No. n Individual mapping beam scanning angular rate;

[0042] —From the antenna beam center to the n The distance of each survey zone;

[0043] — nInitial beamwidth of the antenna in each sub-mapping zone;

[0044] —No. n Individual mapping satellite flight speed;

[0045] —No. n The dwell time of each sub-survey area;

[0046] —The sum of the dwell time of the beam and the beam scanning time in the first sub-mapping zone;

[0047] —Total period of TOPS SAR beam switching;

[0048] —The total beam switching time for each survey zone;

[0049] —No. n Individual mapping beam switching time.

[0050] Step 3: Based on the scanning angular rate of the beam obtained in Step 1 and the dwell time of each sub-mapping beam obtained in Step 2, determine the scanning angle of each sub-mapping beam.

[0051] Specifically, the formula for calculating the scanning angle of the first sub-mapping band beam is as follows:

[0052]

[0053] In the formula:

[0054] —The left-end scanning angle of the first sub-mapping zone beam;

[0055] —The scanning angle at the right end of the first sub-mapping band beam;

[0056] At this time, the beam scanning angle of the first sub-mapping zone is [ , Starting from the second sub-mapped area, the formula for calculating the scanning angle of the beam in each sub-mapped area is as follows:

[0057]

[0058] In the formula:

[0059] —No. n The scanning angle at the left end of the sub-mapping beam;

[0060] —No. nThe scanning angle at the right end of the sub-mapping beam;

[0061] —The serial number of the sub-survey zone;

[0062] —The sum of the beam dwell time in the first sub-mapped area and the beam scanning time;

[0063] At this time, the n The scanning angle of the sub-mapping beam is [ , ].

[0064] Step 4: Scan each sub-mapped area according to the scanning angle of each sub-mapped area beam obtained in Step 3 to obtain an image of each sub-mapped area; stitch the range images of all sub-mapped areas together, and then stitch the azimuth images together to obtain a TOPS SAR image. This completes the design of the TOPS SAR working mode for high-orbit satellites.

[0065] To verify the effectiveness of the proposed method, the following parameters were selected for simulation verification: satellite orbital altitude 42164km, orbital inclination 20°, eccentricity 0°, perigee argument 88°, true perigee 180°, right-side look-ahead observation, carrier frequency 1.25GHz, radar antenna downward viewing angle 3°, antenna aperture 30m, sub-mapped area azimuth resolution 10m, TOPS SAR working mode sub-mapped area elevation side-reversal zone 500km, azimuth zone 1500km, totaling 3 sub-mapped areas. Figure 2 A comparative diagram of the operating modes of conventional and high-orbit TOPS SAR is provided. Figures 3-6 The simulation results for each of the four steps are presented.

[0066] As shown in the simulation results in the attached figures, for the near-geometry time 0, the beam scanning angle of the first sub-mapped zone is [-1.18, 1.18], the beam scanning angle of the second sub-mapped zone is [-1.53, 0.83], and the beam scanning angle of the third sub-mapped zone is [-1.88, 0.48]. The simulation results demonstrate that the method provided by this invention achieves accurate calculation of beam scanning speed and beam scanning angle in the high-orbit SAR TOPS operating mode, thereby significantly improving the design level and efficiency of high-orbit SAR systems.

[0067] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A design method for the working mode of a high-orbit satellite TOPS SAR, characterized in that, Includes the following steps: Step 1: Determine the azimuth imaging resolution of the sub-mapped area in TOPS SAR operating mode, and determine the antenna beam scanning angular rate based on the azimuth imaging resolution of the sub-mapped area; where the azimuth resolution of the sub-mapped area in TOPS SAR operating mode is... The expression is as follows: In the formula: —Radar range; —The scanning angular rate of the antenna beam; —Satellite flight speed; —Antenna aperture; —High-orbit SAR resolution improvement factor, set to 0.15; From the above formula, we can obtain: Calculated from the above It is positive because ,in This is the azimuth resolution for standard strip mode; Step 2: Determine the dwell time of each sub-mapping beam based on the imaging resolution requirements; the following formula must be satisfied: In the formula: — No. n Individual mapping beam scanning angular rate; —From the antenna beam center to the n The distance of each survey zone; —The initial beamwidth of the antenna for the n sub-mapping zones; —The flight speed of the satellite in the nth sub-mapping zone; —No. n The dwell time of each sub-survey area; —The sum of the dwell time of the beam and the beam scanning time in the first sub-mapping zone; —Total period of TOPS SAR beam switching; —The total beam switching time for each survey zone; —No. n Individual mapping beam switching time; Step 3: Based on the scanning angular rate of the beam obtained in Step 1 and the dwell time of each sub-mapping band beam obtained in Step 2, determine the scanning angle of each sub-mapping band beam; wherein, the formula for calculating the scanning angle of the first sub-mapping band beam is: In the formula: —The left-end scanning angle of the first sub-mapping zone beam; —The scanning angle at the right end of the first sub-mapping band beam; At this time, the beam scanning angle of the first sub-mapping zone is [ , Starting from the second sub-mapped area, the formula for calculating the scanning angle of the beam in each sub-mapped area is as follows: In the formula: —The scanning angle at the left end of the nth sub-mapping band beam; —The scanning angle at the right end of the nth sub-mapping zone beam; —The serial number of the sub-survey zone; —The sum of the beam dwell time in the first sub-mapped area and the beam scanning time; At this time, the n The scanning angle of the sub-mapping beam is [ , ]; Step 4: Scan each sub-mapped area according to the scanning angle of each sub-mapped area beam obtained in Step 3 to obtain an image of each sub-mapped area; stitch the range images of all sub-mapped areas together, and then stitch the azimuth images together to obtain a TOPS SAR image. At this point, the design of the TOPS SAR working mode for high-orbit satellites is completed.

Images