Satellite-borne SAR complete polarization scanning mode implementation method based on time-sharing coding

Abstract

The invention provides a spaceborne SAR complete polarization scanning mode implementation method based on time-sharing coding, and relates to the technical field of radar imaging, and the method comprises the steps: firstly, determining a first spatial resolution and a first imaging breadth of an SAR satellite system in a spaceborne SAR complete polarization strip mode, so as to determine the number of surveying and mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode; further determining a second spatial resolution and a second imaging breadth in a satellite-borne SAR scanning mode, and when an imaging index is met, enabling the SAR satellite system to execute an observation process in the satellite-borne SAR scanning mode by using a time-sharing coding mode; and after the observation process is completed, imaging is carried out on the full-polarization SAR echo data scanned by each surveying and mapping sub-band, and finally, a full-polarization SAR scanning image is spliced. According to the invention, the defects that the observation breadth of a satellite-borne SAR full-polarization strip mode is limited and a satellite-borne SAR scanning mode only supports single polarization or dual polarization are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of radar imaging, and in particular, to a method for implementing a full-polarization scanning mode of spaceborne SAR based on time-division coding. Background Art

[0002] Spaceborne synthetic aperture radar (SAR) is an active microwave remote sensing radar that can achieve high-resolution observation of the ground, is not affected by illumination and weather, and has the ability to work all day and all weather. In this field, spaceborne SAR is developing towards high resolution, large swath width, and multi-polarization. Polarimetric SAR can obtain different polarization scattering characteristics of ground targets by transmitting and receiving horizontal (H) and vertical (V) polarization waves. In particular, full-polarization SAR can obtain four polarization information of HH, HV, VH, and VV, which greatly expands the dimension of information obtained by spaceborne SAR and has important application value and significance in target recognition and classification, forest resource monitoring, crop growth assessment, disaster monitoring, etc.

[0003] Traditional full-polarization SAR implementation methods include time division, code division, and frequency division, which require two transceiver channels to transmit H-polarization signals and V-polarization signals respectively, and can receive H-polarization signals and V-polarization signals to obtain full-polarization signals. Time-division full-polarization SAR obtains four-polarization information by alternately transmitting H-polarization signals and V-polarization signals, but it is necessary to increase the pulse repetition frequency (PRF) close to twice that of single-polarization SAR, which limits the imaging swath width. Frequency-division full-polarization SAR simultaneously transmits H-polarization signals and V-polarization signals with different carrier frequencies. Although it does not require an increase in PRF, due to the difficulty of filtering received signals, different polarization signals cannot be well separated, resulting in unstable full-polarization scattering performance. Code-division full-polarization SAR is similar to frequency-division full-polarization SAR, and simultaneously transmits H-polarization signals and V-polarization signals after orthogonal coding. However, in actual work, completely orthogonal coding signals cannot be obtained, and there is a certain cross-correlation noise between the coding signals, so the cross-polarization suppression is insufficient, affecting the imaging quality.

[0004] Some full-polarization working methods of SAR satellites have been proposed to solve the above problems. The full-polarization implementation method of "time division + code division" is adopted, which can achieve the effect of suppressing cross-polarization range ambiguity while obtaining stable full-polarization scattering information. However, there are still some defects in these full-polarization working methods of SAR satellites. All spaceborne full-polarization SARs adopt the strip observation mode to achieve, with a small observation swath width and low observation efficiency, which cannot meet the observation requirements of large-scale areas such as the ocean and forests. The spaceborne SAR scanning mode can achieve wide-swath observation through range-direction beam scanning. The scanning mode can be implemented by Scanner Synthetic Aperture Radar (ScanSAR) and Terrain Observation by Progressive (TOPS). However, the current spaceborne SAR scanning mode only supports single-polarization or dual-polarization working methods and cannot obtain the full-polarization scattering information of the target. Summary of the Invention

[0005] The present invention provides a method for implementing a spaceborne SAR full-polarization scanning mode based on time-division coding to solve the defects existing in the full-polarization working methods of SAR satellites in the prior art.

[0006] The present invention provides a method for implementing a spaceborne SAR full-polarization scanning mode based on time-division coding, including: Determining the first spatial resolution and the first imaging swath width of the SAR satellite system in the spaceborne SAR full-polarization strip mode based on preset SAR satellite parameters; Determining the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode according to the first spatial resolution and the first imaging swath width; Determining the second spatial resolution and the second imaging swath width of the spaceborne SAR scanning mode according to the number of mapping sub-bands. When the second spatial resolution and the second imaging swath width meet the preset imaging indexes, enabling the SAR satellite system to perform the observation process in the spaceborne SAR scanning mode by means of time-division coding; After the observation process is completed, performing imaging processing on the full-polarization SAR echo data scanned for each mapping sub-band to obtain the corresponding full-polarization SAR image; Performing stitching processing on the full-polarization SAR images corresponding to each mapping sub-band to obtain a full-polarization SAR scanning image.

[0007] In some embodiments, the determining the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode according to the first spatial resolution and the first imaging swath width includes: Obtaining the observation swath width and the second azimuth resolution of the SAR satellite system in the spaceborne SAR scanning mode; Determine the ratio of the beam dwell time to the synthetic aperture time of the mapping sub-band in the spaceborne SAR scanning mode according to the first azimuth resolution and the second azimuth resolution included in the first spatial resolution; Determine the overlapping width of the mapping sub-band in the spaceborne SAR scanning mode, and construct a width relationship equation based on the number of mapping sub-bands according to the overlapping width, the observation width, and the first imaging width; Determine the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode based on the ratio and the width relationship equation.

[0008] In some embodiments, the SAR satellite system performs the observation process in the spaceborne SAR scanning mode by means of time-division coding, including: Cyclically observe each mapping sub-band in the spaceborne SAR scanning mode; Within each mapping sub-band, alternately transmit the encoded H-polarized pulse signal and the encoded V-polarized pulse signal through the H-polarization channel and the V-polarization channel in a time-division manner, and receive four full-polarization SAR echo data during the gap time of the transmitted signal.

[0009] In some embodiments, the cyclically observing each mapping sub-band in the spaceborne SAR scanning mode includes: Determine the beam direction of the antenna range-direction beam of the SAR satellite system according to the number of mapping sub-bands and the second imaging width; During the sub-band scan return time, switch the mapping sub-band pointed to by the antenna range-direction beam according to the beam direction; Perform observation on the mapping sub-band pointed to by the antenna range-direction beam.

[0010] In some embodiments, the encoding process of the H-polarized pulse signal and the V-polarized pulse signal includes: Determine the center carrier frequency, the first frequency modulation slope, and the second frequency modulation slope of the polarized pulse signal, where the first frequency modulation slope and the second frequency modulation slope are opposite to each other; Perform positive frequency modulation slope encoding on the H-polarized pulse signal according to the center carrier frequency and the first frequency modulation slope, and perform negative frequency modulation slope encoding on the V-polarized pulse signal according to the center carrier frequency and the second frequency modulation slope.

[0011] In some embodiments, the imaging metrics include a spatial resolution metric and an imaging width metric. After determining the second spatial resolution and the second imaging width in the spaceborne SAR scanning mode according to the number of mapping sub-bands, the method further includes: When the second spatial resolution is worse than the spatial resolution index or the second imaging width is less than the imaging width index, the following iterative process is executed: Based on the preset SAR satellite parameters, re-determine the first spatial resolution and the first imaging width of the SAR satellite system in the spaceborne SAR full polarization strip mode, and based on the re-determined first spatial resolution and the re-determined first imaging width, determine the new second spatial resolution and the new second imaging width in the spaceborne SAR scanning mode; When the new second spatial resolution is better than the spatial resolution index and the new second imaging width is greater than the imaging width index, end the iteration.

[0012] The present invention also provides a device for implementing the spaceborne SAR full polarization scanning mode based on time division coding, including: A first determination module, configured to determine the first spatial resolution and the first imaging width of the SAR satellite system in the spaceborne SAR full polarization strip mode based on the preset SAR satellite parameters; A second determination module, configured to determine the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode according to the first spatial resolution and the first imaging width; An observation module, configured to determine the second spatial resolution and the second imaging width in the spaceborne SAR scanning mode according to the number of mapping sub-bands, and when the second spatial resolution and the second imaging width meet the preset imaging index, enable the SAR satellite system to execute the observation process in the spaceborne SAR scanning mode by means of time division coding; An imaging module, configured to perform imaging processing on the full polarization SAR echo data scanned by each mapping sub-band after the observation process is completed to obtain the corresponding full polarization SAR image; A splicing module, configured to splice the full polarization SAR images corresponding to each mapping sub-band to obtain a full polarization SAR scanning image.

[0013] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the method for implementing the spaceborne SAR full polarization scanning mode based on time division coding as described in any one of the above is implemented.

[0014] The present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the method for implementing the spaceborne SAR full polarization scanning mode based on time division coding as described in any one of the above is implemented.

[0015] The present invention also provides a computer program product, including a computer program, which when executed by a processor, implements the method for implementing the full-polarization scanning mode of spaceborne SAR based on time-division coding as described in any one of the above.

[0016] The method for implementing the full-polarization scanning mode of spaceborne SAR based on time-division coding provided by the present invention combines the full-polarization strip mode of spaceborne SAR and the scanning mode of spaceborne SAR, overcomes the defects that the observation swath of the full-polarization strip mode of spaceborne SAR is limited and the scanning mode of spaceborne SAR is limited to single polarization or dual polarization, improves the observation amplitude and observation efficiency of the full-polarization SAR mode of the SAR satellite system, and ensures stable acquisition of full-polarization scattering information. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art one by one. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0018] Figure 1 It is a schematic flowchart of the method for implementing the full-polarization scanning mode of spaceborne SAR based on time-division coding provided by the present invention.

[0019] Figure 2 It is a schematic working principle diagram of the SAR satellite system provided by the present invention in the full-polarization strip mode of spaceborne SAR.

[0020] Figure 3 It is a schematic working principle diagram of the SAR satellite system provided by the present invention in the scanning mode of spaceborne SAR.

[0021] Figure 4 It is a schematic principle diagram of the method for implementing the full-polarization scanning mode of spaceborne SAR based on time-division coding provided by the present invention.

[0022] Figure 5 It is a schematic principle diagram of the transmission signal coding in the method for implementing the full-polarization scanning mode of spaceborne SAR based on time-division coding provided by the present invention.

[0023] Figure 6 It is a schematic structural diagram of the device for implementing the full-polarization scanning mode of spaceborne SAR based on time-division coding provided by the present invention.

[0024] Figure 7 It is a schematic structural diagram of the electronic device provided by the present invention. Detailed Embodiments

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] The method for implementing the full-polarization scanning mode of spaceborne SAR based on time-division coding in the present invention will be described below with reference to the accompanying drawings. Figure 1 It is a schematic flowchart of the method for implementing the full-polarization scanning mode of spaceborne SAR based on time-division coding provided by the present invention. As Figure 1 shown, the method includes the following steps 101 to 105, which will be specifically described below.

[0027] Step 101: Determine the first spatial resolution and the first imaging swath of the SAR satellite system in the full-polarization strip mode of spaceborne SAR based on preset SAR satellite parameters.

[0028] In the embodiment of the present invention, the full-polarization strip mode of spaceborne SAR is first designed by the SAR satellite system for observing the target. The preset SAR satellite parameters include the satellite orbit and the satellite SAR payload parameters. As Figure 2 shown, the full-polarization strip mode of spaceborne SAR adopts the working principle of time-division full-polarization SAR. When the radar signal is transmitted, the H-polarization channel and the V-polarization channel alternately transmit chirp pulse signals at different pulse repetition times (PRTs), and then during the gap after the signal transmission within each PRT, the H-polarization channel and the V-polarization channel simultaneously receive and acquire the SAR echo data, specifically the HH, HV, VH, and VV four-polarization echo data. PRF represents the frequency of the pulse signal transmitted during the imaging observation of the SAR satellite system, and this parameter has a constraint relationship with multiple indicators of the imaging performance of the SAR satellite system, including the swath, azimuth ambiguity, and range ambiguity, etc. It should be noted that there is a mutual restriction relationship between PRF and the first imaging swath. It can be simply understood that the higher the PRF, the greater the limitation on the first imaging swath, and the smaller the achievable maximum value.

[0029] In specific operations, the SAR satellite parameters are used as input information to design an on-board SAR full-polarization strip mode to perform the observation process, and the first spatial resolution and the first imaging swath are calculated after the observation process. The first spatial resolution is divided into two parts: the first azimuth resolution and the range resolution. Among them, the half-power width of the point target impulse response in the azimuth direction of the main lobe in the SAR image can be used as the first azimuth resolution, while the half-power width of the main lobe in the range direction can be used as the range resolution. The first spatial resolution can reflect the resolution ability of the SAR satellite system for targets. In the on-board SAR full-polarization strip mode, the first azimuth resolution is calculated as follows: (1) In the above formula (1), is the antenna azimuth dimension of the SAR satellite system, is the broadening factor of the azimuth resolution, and this broadening factor is affected by factors such as imaging windowing processing, antenna pattern characteristics, and space-ground improvement coefficient.

[0030] The range resolution is calculated as follows: (2) In the above formula (2), c represents the speed of light, represents the signal bandwidth, represents the incident angle, represents the broadening factor of the range resolution, and this broadening factor is affected by factors such as imaging windowing processing, amplitude-frequency and phase-frequency of the SAR system.

[0031] The first imaging swath can be denoted as , which is an important indicator to measure the ground coverage ability of the SAR satellite system. It can be defined as the effective image width that can be obtained by processing all range data and can characterize the observation efficiency of the SAR satellite system. After the observation process is completed and the imaging image is obtained, the corresponding first imaging swath can be easily determined according to the PRF.

[0032] Step 102: Determine the number of mapping sub-bands of the SAR satellite system in the on-board SAR scanning mode according to the first spatial resolution and the first imaging swath.

[0033] Next, according to the first spatial resolution and the first imaging swath calculated in the on-board SAR full-polarization strip mode in step 101, determine the number of mapping sub-bands of the SAR satellite system in the on-board SAR scanning mode.

[0034] Here, it is still necessary to design the on-board SAR scanning mode through the SAR satellite system for observing the target, and it is still designed according to the preset SAR satellite parameters, including the satellite orbit and the satellite SAR payload parameters. Refer to Figure 3 , Figure 3 which shows the working principle of the SAR satellite system in the on-board SAR scanning mode. The on-board SAR scanning mode can be implemented by ScanSAR or TOPS. In this embodiment of the present invention, the ScanSAR method is taken as an example to illustrate the on-board SAR scanning mode. As Figure 3 shown, the observation in the on-board SAR scanning mode is realized by stitching N mapping sub-bands. is the beam dwell time of the Nth mapping sub-band, is the sub-band scan return time, is the synthetic aperture time, and the three satisfy the following relationship: (3) During the observation process in the on-board SAR scanning mode, the antenna range-direction beam of the SAR satellite system first points to mapping sub-band 1, and signals are transmitted and received according to predetermined parameters, specifically, linear frequency modulation pulse signals are transmitted and received. After the observation time passes , the antenna range-direction beam switches to mapping sub-band 2, and the observation time is , then switches to mapping sub-band 3, and so on. After observing mapping sub-band N, it switches back to mapping sub-band 1 for observation again. In this way, cyclic observation is performed between mapping sub-band 1 and mapping sub-band N to obtain wide-swath data. Finally, the imaging data of each mapping sub-band are stitched together to obtain the image finally observed by the SAR satellite system.

[0035] Therefore, the most important thing in the on-board SAR scanning mode is to determine the number N of mapping sub-bands. In this embodiment of the present invention, the number N of mapping sub-bands is determined according to the first spatial resolution and the first imaging swath calculated in the on-board SAR full-polarization strip mode. There are various ways to determine it here. First, obtain the azimuth resolution index and the observation amplitude index in the on-board SAR scanning mode. The first method is to calculate the ratio of the azimuth resolution index to the first azimuth resolution included in the first spatial resolution. Subtracting 1 from this ratio can determine the number N of mapping sub-bands. The second method is to establish an equation according to the first imaging swath and the observation amplitude index. Specifically, calculate the product of the number N of mapping sub-bands and the first imaging swath , then determine the overlapping swath of adjacent mapping sub-bands, and calculate the product of N - 1 and the overlapping swath. The difference between these two products is equal to the observation amplitude index. The equation constructed in this way has only one unknown, the number N of mapping sub-bands. Solving the equation can determine the number N of mapping sub-bands.

[0036] Step 103: Determine the second spatial resolution and the second imaging swath in the spaceborne SAR scanning mode according to the number of mapping sub-bands. When the second spatial resolution and the second imaging swath meet the preset imaging indicators, enable the SAR satellite system to perform the observation process in the spaceborne SAR scanning mode by means of time-division coding.

[0037] After determining the number N of mapping sub-bands in the spaceborne SAR scanning mode through Step 102, further determine the second spatial resolution and the second imaging swath in the spaceborne SAR scanning mode according to the number of mapping sub-bands. Here, according to the number N of mapping sub-bands, the beam dwell time of the mapping sub-bands can be re-determined , and the sub-band scanning regression time , and further adjust the spatial resolution and the imaging swath, so that the second spatial resolution and the second imaging swath in the spaceborne SAR scanning mode can be determined.

[0038] Next, it is necessary to ensure that the subsequent imaging meets the index requirements. Here, it is judged whether the second spatial resolution and the second imaging swath meet the preset imaging indicators. Here, the imaging indicators can be the spatial resolution indicator and the imaging swath indicator in the spaceborne SAR scanning mode. When the second spatial resolution is better than the spatial resolution indicator and the second imaging swath is greater than the imaging swath indicator, it means that the imaging indicators are met. In the SAR satellite system, the smaller the spatial resolution, the better the effect. Therefore, the second spatial resolution being better than the spatial resolution indicator means that the second spatial resolution is less than the spatial resolution indicator.

[0039] When the second spatial resolution and the second imaging swath meet the preset imaging indicators, the SAR satellite system can be enabled to perform the observation process in the spaceborne SAR scanning mode by means of time-division coding, that is, while observing using the mapping sub-bands in the spaceborne SAR scanning mode, time-division transmitting polarization pulse signals in the spaceborne SAR full polarization strip mode and acquiring HH, HV, VH, and VV four-polarization echo data on each mapping sub-band to complete the observation process. When sending the pulse signals, the positive frequency modulation slope coding method is used for the H polarization pulse signal, and the negative frequency modulation slope coding method is used for the V polarization pulse signal for coding. Of course, in actual implementation, the coding methods of the two can also be interchanged.

[0040] Step 104: After the observation process is completed, perform imaging processing on the full polarization SAR echo data scanned from each mapping sub-band to obtain the corresponding full polarization SAR image.

[0041] During the observation process of step 103, polarization pulse signals can be transmitted in time division in each mapping sub-band and corresponding quad-polarization echo data can be received. After the observation process is completed, imaging processing is performed on the fully polarized SAR echo data obtained by scanning each mapping sub-band to obtain a corresponding fully polarized SAR image. The imaging processing can be implemented by various SAR imaging algorithms, such as a back-projection algorithm, a range Doppler algorithm, and an NCP algorithm, etc., which are not limited in the embodiment of the present invention.

[0042] Step 105: stitching the full-polarization SAR images corresponding to each mapping sub-band to obtain a full-polarization SAR scanning image.

[0043] Finally, referring to the imaging processing process in the spaceborne SAR scanning mode, the full-polarization SAR images corresponding to each mapping sub-band are spliced ​​to obtain the full-polarization SAR scanning image.

[0044] The embodiment of the present invention combines the spaceborne SAR full-polarization strip mode and the spaceborne SAR scanning mode to perform the observation process, thereby overcoming the observation limitations of the spaceborne SAR full-polarization strip mode and the limitation of the spaceborne SAR scanning mode to single polarization or dual polarization. Not only the observation amplitude and observation efficiency of the SAR satellite system are improved, but also the polarization information acquisition capability is improved, ensuring that the full-polarization scattering information is stably acquired.

[0045] In some embodiments, determining the number of mapping subbands of the SAR satellite system in the spaceborne SAR scanning mode according to the first spatial resolution and the first imaging width can also be achieved through the following process, which is described in detail below.

[0046] First, the observation width and second azimuth resolution of the SAR satellite system in the spaceborne SAR scanning mode are obtained, which are respectively denoted as and The observation width and the second azimuth resolution here are the resolution and width that need to be satisfied by imaging. Of course, in some embodiments, the observation width and the second azimuth resolution may also be preset according to actual needs, not limited to the spaceborne SAR scanning mode.

[0047] Then, according to the first azimuthal resolution included in the first spatial resolution And the second azimuth resolution , determine the beam dwell time of the mapping sub-band in the spaceborne SAR scanning mode Synthetic Aperture Time The ratio of is as follows: (4) In the above formula (4), N represents the number of mapping sub-bands. From formula (4), it can be seen that the beam dwell time through the mapping sub-band is Synthetic Aperture Time Ratio , the number of surveying and mapping sub-zones N can be determined.

[0048] Although N can be calculated according to formula (4), the subsequent imaging still needs to meet the width requirement. Therefore, the embodiment of the present invention further determines the number of mapping sub-bands N according to the width. First, determine the overlapping width of the mapping sub-bands in the spaceborne SAR scanning mode. , the overlapping width is the overlapping part of the width between two adjacent surveying sub-bands, which needs to be removed when calculating the total width. , Observation width And the first imaging width , construct the width relationship equation based on the number of surveying sub-bands, expressed as the following formula: (5) Finally, the number of sub-bands for mapping in the spaceborne SAR scanning mode is determined based on the ratio and the width relationship equation. N can be calculated, and the above formula (5) has only one unknown number, N, which can also be calculated.

[0049] Next, the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode can be comprehensively determined based on the N calculated by formula (4) and formula (5). When the N calculated by formula (4) and formula (5) are the same, this N can be used as the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode. When the N calculated by formula (4) and formula (5) are different, it is necessary to re-deploy the SAR satellite system, and then perform an iterative process. The iterative process includes executing the above steps 101 and 102, and recalculating the number of mapping sub-bands N using formula (4) and formula (5) in step 102 until the N calculated by formula (4) and formula (5) are the same, and then the iterative process ends.

[0050] In the embodiment of the present invention, the number of mapping sub-bands in the spaceborne SAR scanning mode is determined by the first spatial resolution and the first imaging width of the SAR satellite system in the spaceborne SAR full-polarization strip mode, thereby realizing the combination of the two modes. When calculating the number of mapping sub-bands, the spatial resolution and the width are comprehensively considered to ensure that subsequent imaging can have better spatial resolution and width.

[0051] The following describes the observation process of the SAR satellite system using time-division coding in the spaceborne SAR scanning mode. In some embodiments, when the second spatial resolution and the second imaging swath width in the spaceborne SAR scanning mode meet the preset imaging metrics, the observation in the spaceborne SAR scanning mode can be performed using time-division coding. Specifically, as Figure 4 shown, this observation process is still completed through N survey sub-bands. During the observation, each survey sub-band is cyclically observed in the spaceborne SAR scanning mode. Here, the range-direction beam of the SAR satellite system's transmitting antenna is pointed at the survey sub-band to perform the observation.

[0052] Within each survey sub-band, the encoded H-polarization pulse signal and the encoded V-polarization pulse signal are alternately transmitted in time through the H-polarization channel and the V-polarization channel, and four full-polarization SAR echo data are received during the gap time of the transmitted signal.

[0053] The time-division alternate transmission method here can refer to the signal transmission mode in the spaceborne SAR full-polarization strip mode. Finally, HH, HV, VH, and VV four-polarization echo data are received. Of course, the transmitted signal and the received signal still need to be within the pulse repetition time (PRT).

[0054] And during the observation process, it is necessary to adjust the beam pointing of the antenna range-direction beam to switch the survey sub-band. During the scanning return time of one survey sub-band , the range-direction beam of the SAR satellite system's antenna first points to survey sub-band 1, and the H and V polarization pulse signals are transmitted according to the predetermined parameters and four full-polarization SAR echo data are received. After the observation time passes , the range-direction beam of the antenna switches to survey sub-band 2, and the observation time is . Then it switches to survey sub-band 3, and so on. After observing survey sub-band N, that is, the observation process of one sub-band scanning return time is completed. Then the range-direction beam of the antenna switches back to survey sub-band 1 again to perform the observation process of the next sub-band scanning return time . In this way, cyclic observation is performed between survey sub-band 1 and survey sub-band N.

[0055] In addition, before transmitting the H-polarization pulse signal and the V-polarization pulse signal, it is necessary to encode the pulse signals using different coding methods, that is, perform the "code division" process in the H-polarization channel and the V-polarization channel. The H-polarization pulse signal is encoded using the positive frequency modulation slope coding method, and the V-polarization pulse signal is encoded using the negative frequency modulation slope coding method before transmission.

[0056] In the embodiment of the present invention, the SAR satellite system uses a time-sharing coding method to perform the observation process in the spaceborne SAR scanning mode. It can effectively apply the method of time-sharing transmitting polarization pulse signals and receiving full-polarization SAR echo data in the spaceborne SAR full-polarization strip mode to the spaceborne SAR scanning mode, overcome the limitation of the spaceborne SAR scanning mode to single polarization or dual polarization defects, improve the polarization information acquisition ability of the ScanSAR mode, and ensure stable acquisition of full-polarization scattering information.

[0057] Further, when cyclically observing each mapping sub-band in the spaceborne SAR scanning mode, it includes: First, determine the beam direction of the antenna range-direction beam of the SAR satellite system according to the number of mapping sub-bands and the second imaging width. Then, within the sub-band scan return time, switch the mapping sub-band pointed by the antenna range-direction beam according to the beam direction. Finally, perform observations on the switched mapping sub-band.

[0058] Specifically, first, the beam direction of the antenna range-direction beam of the SAR satellite system can be determined one by one according to the number of mapping sub-bands and the second imaging width, so as to transmit H and V polarization pulse signals when the antenna range-direction beam points to the corresponding mapping sub-band.

[0059] As Figure 4 shown, after determining the beam direction, within the sub-band scan return time , switch the mapping sub-band pointed by the antenna range-direction beam according to the beam direction. Each mapping sub-band has a corresponding observation time. First, the beam direction of the antenna range-direction beam will point to mapping sub-band 1. At this time, observations are performed on mapping sub-band 1. During the observation process, H and V polarization pulse signals are transmitted according to predetermined parameters and four kinds of full-polarization SAR echo data are received. After the observation time of mapping sub-band 1 passes , according to the wave velocity direction, the pointing of the antenna range-direction beam will switch to mapping sub-band 2, and then observations are performed on mapping sub-band 2. Still, H and V polarization pulse signals are transmitted according to predetermined parameters and four kinds of full-polarization SAR echo data are received. The observation time is . Next, switch to mapping sub-band 3, and so on, until the beam direction switches to the last mapping sub-band N. After the observation time passes, the observation process of the sub-band scan return time is completed.

[0060] Next, continue to execute the observation process of the next sub-band scan return time . According to the beam direction, the mapping sub-band N pointed by the antenna range-direction beam will switch back to mapping sub-band 1, and repeat the above switching process and scanning process. In this way, multiple observations of N mapping sub-bands are completed in a cycle, and the spaceborne SAR scanning mode is realized.

[0061] In an embodiment of the present invention, N mapping sub-bands are set in the spaceborne SAR scanning mode, and on each mapping sub-band, polarization pulse signals are transmitted and four full-polarization SAR echo data are received according to the spaceborne SAR full-polarization strip mode, so that the SAR satellite system can also stably obtain full-polarization scattering information in the spaceborne SAR scanning mode, improving the polarization information acquisition ability.

[0062] In some embodiments, considering that the transmitted polarization pulse signals are for obtaining full-polarization SAR echo data to obtain the imaging of the observed target, to ensure stable and high-quality imaging, in the embodiment of the present invention, "code division" of the polarization pulse signals is realized in the spaceborne SAR scanning mode, that is, when transmitting the polarization pulse signals, encoding processing is performed on the polarization pulse signals. The encoding processes of the H polarization pulse signal and the V polarization pulse signal are specifically described below.

[0063] As Figure 5 shown, the encoding method of the polarization pulse signal is frequency modulation encoding based on the slope. First, in the frequency f of the polarization pulse signal, the center carrier frequency 、the first frequency modulation slope and the second frequency modulation slope of the polarization pulse signal are determined. Among them, the first frequency modulation slope is for the H polarization pulse signal and takes a positive number, while the second frequency modulation slope is for the V polarization pulse signal and takes a negative number, and the first frequency modulation slope and the second frequency modulation slope are opposite to each other.

[0064] When observing through the mapping sub-band, within the azimuth time t, the H polarization channel transmits the H polarization pulse signal. At this time, according to the center carrier frequency and the first frequency modulation slope, positive frequency modulation slope encoding is performed on the H polarization pulse signal. In this way, the frequency of the encoded H polarization pulse signal gradually increases with the azimuth time t. The first frequency modulation slope represents the trend of frequency increase, and it is ensured that the average of the maximum frequency and the minimum frequency of the encoded H polarization pulse signal is the center carrier frequency .

[0065] And within the azimuth time t, the V polarization channel transmits the V polarization pulse signal. At this time, according to the center carrier frequency and the second frequency modulation slope, negative frequency modulation slope encoding is performed on the V polarization pulse signal. In this way, the frequency of the encoded V polarization pulse signal gradually decreases with the azimuth time t. The second frequency modulation slope represents the trend of frequency decrease, and it is also ensured that the average of the maximum frequency and the minimum frequency of the encoded V polarization pulse signal is the center carrier frequency .

[0066] In the embodiments of the present invention, "code division" of polarization pulse signals is achieved in the spaceborne SAR scanning mode. Different slope frequency modulation coding methods are respectively used to encode the transmitted polarization pulse signals, so as to effectively suppress the blurring of cross-polarization images and improve the image quality of subsequent imaging.

[0067] In some embodiments, to ensure that the SAR satellite system can combine the advantages of the spaceborne SAR full polarization strip mode and the spaceborne SAR scanning mode during observation, preset imaging indexes are also set. In step 103 above, only when the second spatial resolution and the second imaging swath meet the preset imaging indexes can the SAR satellite system be triggered to perform the observation process in the spaceborne SAR scanning mode by means of time-sharing coding. The preset imaging indexes include a spatial resolution index and an imaging swath index, so as to ensure that the obtained imaging after observation can meet the spatial resolution requirement and the swath requirement.

[0068] However, in the actual scenario, after determining the second spatial resolution and the second imaging swath in the spaceborne SAR scanning mode according to the number of mapping sub-bands, there may still be a situation where the preset imaging indexes are not met. In view of this situation, the embodiments of the present invention adopt an iterative process, that is, when the situation where the preset imaging indexes are not met occurs in step 103 above, the SAR satellite system is not triggered to perform the observation process in the spaceborne SAR scanning mode by means of time-sharing coding, but steps 101 to 103 above are continuously repeated until the preset imaging indexes are met.

[0069] Specifically, when the second spatial resolution is worse than the spatial resolution index or the second imaging swath is smaller than the imaging swath index, it means that the second spatial resolution is greater than the spatial resolution index, that is, step 103 does not meet the preset imaging indexes in the spaceborne SAR scanning mode. Therefore, the iterative process of the following steps 201 to 202 is executed.

[0070] Step 201, based on the preset SAR satellite parameters, re-determine the first spatial resolution and the first imaging swath of the SAR satellite system in the spaceborne SAR full polarization strip mode.

[0071] Here, when the preset imaging indexes are not met in the spaceborne SAR scanning mode, the first spatial resolution and the first imaging swath of the SAR satellite system in the spaceborne SAR full polarization strip mode are re-determined based on the preset SAR satellite parameters, that is, step 101 above is re-executed. The specific determination process can refer to step 101 and will not be elaborated here.

[0072] Step 202, based on the re-determined first spatial resolution and the re-determined first imaging swath, determine the new second spatial resolution and the new second imaging swath in the spaceborne SAR scanning mode.

[0073] Based on the re-determined first spatial resolution and the re-determined first imaging swath in step 201, the new second spatial resolution and the new second imaging swath in the spaceborne SAR scanning mode are continuously determined, that is, steps 102 and 103 are continuously executed above, so as to determine the new second spatial resolution and the new second imaging swath. The determination process can refer to steps 102 and 103 above and will not be elaborated here.

[0074] Next, it is continued to determine whether the preset imaging index is satisfied accordingly, that is, it is necessary to determine whether there is still a situation where the new second spatial resolution is worse than the spatial resolution index or the new second imaging swath is less than the imaging swath index. Here, both the spatial resolution index and the imaging swath index need to be satisfied, and neither can be missing.

[0075] When the new second spatial resolution is better than the spatial resolution index and the new second imaging swath is greater than the imaging swath index, it indicates that after the above iteration, the preset imaging index has been satisfied, and the iteration is ended, triggering the SAR satellite system to execute the observation process in the spaceborne SAR scanning mode by means of time-sharing coding.

[0076] When the new second spatial resolution is still worse than the spatial resolution index or the new second imaging swath is still less than the imaging swath index, it indicates that after one iteration, the preset imaging index is still not satisfied, and the iteration process is continued, that is, steps 201 to 202 above are continuously executed until the preset imaging index is satisfied, and then the iteration can be ended.

[0077] In the embodiment of the present invention, in order to ensure that the SAR satellite system can meet the preset imaging index by combining the spaceborne SAR full polarization strip mode and the spaceborne SAR scanning mode, an iteration process is designed. Through the iteration process, the influencing factors and errors that may appear in the two observation modes can be effectively removed, so that the two modes can be effectively combined to ensure that the subsequent imaging meets the requirements of spatial resolution and imaging swath.

[0078] Next, the spaceborne SAR full polarization scanning mode implementation device based on time-sharing coding provided by the present invention is described. The spaceborne SAR full polarization scanning mode implementation device described below can be correspondingly referred to the spaceborne SAR full polarization scanning mode implementation method described above.

[0079] Such as Figure 6As shown in the figure, an on-board SAR full-polarization scanning mode implementation device based on time-division coding includes: a first determination module 601, a second determination module 602, an observation module 603, an imaging module 604, and a splicing module 605. Among them, the first determination module 601 is used to determine the first spatial resolution and the first imaging swath of the SAR satellite system in the on-board SAR full-polarization strip mode based on preset SAR satellite parameters; the second determination module 602 is used to determine the number of mapping sub-bands of the SAR satellite system in the on-board SAR scanning mode according to the first spatial resolution and the first imaging swath; the observation module 603 is used to determine the second spatial resolution and the second imaging swath in the on-board SAR scanning mode according to the number of mapping sub-bands. When the second spatial resolution and the second imaging swath meet the preset imaging indicators, the SAR satellite system is enabled to perform the observation process in the on-board SAR scanning mode by means of time-division coding; the imaging module 604 is used to perform imaging processing on the full-polarization SAR echo data obtained by scanning each mapping sub-band after the observation process is completed to obtain the corresponding full-polarization SAR image; the splicing module 605 is used to splice the full-polarization SAR images corresponding to each mapping sub-band to obtain a full-polarization SAR scanning image.

[0080] It should be noted that the beneficial effects of the on-board SAR full-polarization scanning mode implementation device based on time-division coding here can correspond to those of the on-board SAR full-polarization scanning mode implementation method in the above text. Therefore, the beneficial effects of the on-board SAR full-polarization scanning mode implementation device based on time-division coding will not be elaborated here.

[0081] Figure 7 An example of the physical structure diagram of an electronic device is shown in Figure 7As shown in the figure, the electronic device may include: a processor 710, a communications interface 720, a memory 730, and a communication bus 740. Among them, the processor 710, the communications interface 720, and the memory 730 complete communication with each other through the communication bus 740. The processor 710 may call the logical instructions in the memory 730 to execute a method for implementing the full-polarization scanning mode of spaceborne SAR based on time-division coding. The method includes: determining the first spatial resolution and the first imaging swath of the SAR satellite system in the full-polarization strip mode of spaceborne SAR based on preset SAR satellite parameters; determining the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode according to the first spatial resolution and the first imaging swath; determining the second spatial resolution and the second imaging swath in the spaceborne SAR scanning mode according to the number of mapping sub-bands. When the second spatial resolution and the second imaging swath meet the preset imaging indexes, enabling the SAR satellite system to execute the observation process in the spaceborne SAR scanning mode by means of time-division coding; after the observation process is completed, performing imaging processing on the full-polarization SAR echo data scanned for each mapping sub-band to obtain the corresponding full-polarization SAR image; and splicing the full-polarization SAR images corresponding to each mapping sub-band to obtain a full-polarization SAR scanning image.

[0082] In addition, when the logical instructions in the above-mentioned memory 730 are implemented in the form of software functional units and sold or used as independent products, they may be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of this technical solution, may be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs that can store program codes.

[0083] On the other hand, the present invention also provides a computer program product, which includes a computer program. The computer program can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the method for realizing the full-polarization scanning mode of spaceborne SAR based on time-division coding provided by the above-mentioned various methods. The method includes: determining the first spatial resolution and the first imaging swath of the SAR satellite system in the full-polarization strip mode of spaceborne SAR based on preset SAR satellite parameters; determining the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode according to the first spatial resolution and the first imaging swath; determining the second spatial resolution and the second imaging swath of the spaceborne SAR scanning mode according to the number of mapping sub-bands. When the second spatial resolution and the second imaging swath meet the preset imaging indexes, enabling the SAR satellite system to execute the observation process in the spaceborne SAR scanning mode by means of time-division coding; after the observation process is completed, performing imaging processing on the full-polarization SAR echo data scanned by each mapping sub-band to obtain the corresponding full-polarization SAR image; and performing stitching processing on the full-polarization SAR images corresponding to each mapping sub-band to obtain a full-polarization SAR scanning image.

[0084] On another aspect, the present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it realizes the method for realizing the full-polarization scanning mode of spaceborne SAR based on time-division coding provided by the above-mentioned various methods. The method includes: determining the first spatial resolution and the first imaging swath of the SAR satellite system in the full-polarization strip mode of spaceborne SAR based on preset SAR satellite parameters; determining the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode according to the first spatial resolution and the first imaging swath; determining the second spatial resolution and the second imaging swath of the spaceborne SAR scanning mode according to the number of mapping sub-bands. When the second spatial resolution and the second imaging swath meet the preset imaging indexes, enabling the SAR satellite system to execute the observation process in the spaceborne SAR scanning mode by means of time-division coding; after the observation process is completed, performing imaging processing on the full-polarization SAR echo data scanned by each mapping sub-band to obtain the corresponding full-polarization SAR image; and performing stitching processing on the full-polarization SAR images corresponding to each mapping sub-band to obtain a full-polarization SAR scanning image.

[0085] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative work.

[0086] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment 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 essence of the above technical solution, or the part that contributes to the prior art, can be embodied in the form of a software product. The computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions for causing 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.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for implementing a spaceborne SAR full polarization scanning mode based on time-sharing coding, characterized in that: include: Determine a first spatial resolution and a first imaging width of the SAR satellite system in a spaceborne SAR full-polarization strip mode based on preset SAR satellite parameters; Determining the number of mapping subbands of the SAR satellite system in a spaceborne SAR scanning mode according to the first spatial resolution and the first imaging width; Determine a second spatial resolution and a second imaging width in the spaceborne SAR scanning mode according to the number of the mapping sub-bands, and when the second spatial resolution and the second imaging width meet preset imaging indicators, enable the SAR satellite system to perform an observation process in the spaceborne SAR scanning mode by using a time-sharing coding method; After the observation process is completed, the full-polarization SAR echo data obtained by scanning each mapping sub-band is imaged and processed to obtain the corresponding full-polarization SAR image; The full-polarization SAR images corresponding to each mapping sub-band are spliced ​​to obtain a full-polarization SAR scanning image.

2. The method for implementing the spaceborne SAR full polarization scanning mode based on time-sharing coding according to claim 1, characterized in that: The determining, according to the first spatial resolution and the first imaging width, the number of mapping subbands of the SAR satellite system in the spaceborne SAR scanning mode comprises: Obtain the observation width and second azimuth resolution of the SAR satellite system in the spaceborne SAR scanning mode; Determine, according to the first azimuth resolution and the second azimuth resolution included in the first spatial resolution, a ratio of a beam dwell time to a synthetic aperture time of a mapping sub-band in a spaceborne SAR scanning mode; Determine the overlapping width of the mapping sub-bands in the spaceborne SAR scanning mode, and construct a width relationship equation based on the number of mapping sub-bands according to the overlapping width, the observation width and the first imaging width; The number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode is determined based on the ratio and the width relationship equation.

3. The method for realizing the spaceborne SAR full polarization scanning mode based on time-division coding according to claim 1, characterized in that: The SAR satellite system uses a time-sharing coding method to perform an observation process in a spaceborne SAR scanning mode, including: Observe each mapping sub-band cyclically in the spaceborne SAR scanning mode; In each mapping sub-band, the coded H-polarization pulse signal and the coded V-polarization pulse signal are transmitted alternately through the H-polarization channel and the V-polarization channel in a time-sharing manner, and four types of fully polarized SAR echo data are received in the interval time of the transmitted signals.

4. The method for realizing the spaceborne SAR full polarization scanning mode based on time-sharing coding according to claim 3 is characterized in that: The step of cyclically observing each mapping sub-band in the spaceborne SAR scanning mode includes: Determine the beam direction of the antenna distance beam of the SAR satellite system according to the number of surveying sub-bands and the second imaging width; During the sub-band scanning regression time, switching the antenna distance to the mapping sub-band pointed by the beam according to the beam direction; Observations are made for the mapping sub-bands in which the antenna range and beam are pointed.

5. The method for implementing the spaceborne SAR full polarization scanning mode based on time-sharing coding according to claim 3 is characterized in that: The encoding process of the H polarization pulse signal and the V polarization pulse signal includes: Determine a center carrier frequency, a first frequency modulation slope, and a second frequency modulation slope of a polarization pulse signal, wherein the first frequency modulation slope and the second frequency modulation slope are inverse numbers of each other; The H-polarized pulse signal is encoded with a positive frequency modulation slope according to the center carrier frequency and the first frequency modulation slope, and the V-polarized pulse signal is encoded with a negative frequency modulation slope according to the center carrier frequency and the second frequency modulation slope.

6. The method for implementing the spaceborne SAR full polarization scanning mode based on time-sharing coding according to claim 1, characterized in that: The imaging index includes a spatial resolution index and an imaging width index. After determining the second spatial resolution and the second imaging width in the spaceborne SAR scanning mode according to the number of mapping sub-bands, the method further includes: When the second spatial resolution is worse than the spatial resolution index or the second imaging width is smaller than the imaging width index, the following iterative process is performed: re-determining a first spatial resolution and a first imaging width of the SAR satellite system in the spaceborne SAR full-polarization strip mode based on preset SAR satellite parameters, and determining a new second spatial resolution and a new second imaging width in the spaceborne SAR scanning mode based on the re-determined first spatial resolution and the re-determined first imaging width; When the new second spatial resolution is better than the spatial resolution indicator and the new second imaging width is greater than the imaging width indicator, the iteration ends.

7. A device for implementing a spaceborne SAR full polarization scanning mode based on time-sharing coding, characterized in that: include: A first determination module is used to determine a first spatial resolution and a first imaging width of the SAR satellite system in a spaceborne SAR full-polarization strip mode based on preset SAR satellite parameters; A second determination module is used to determine the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode according to the first spatial resolution and the first imaging width; An observation module is used to determine a second spatial resolution and a second imaging width in the spaceborne SAR scanning mode according to the number of the mapping sub-bands, and when the second spatial resolution and the second imaging width meet the preset imaging index, the SAR satellite system performs the observation process in the spaceborne SAR scanning mode by using a time-sharing coding method; An imaging module is used to perform imaging processing on the full-polarization SAR echo data obtained by scanning each mapping sub-band after the observation process is completed to obtain the corresponding full-polarization SAR image; The splicing module is used to splice the full-polarization SAR images corresponding to each mapping sub-band to obtain a full-polarization SAR scanning image.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that: When the processor executes the computer program, the method for realizing the spaceborne SAR full polarization scanning mode based on time-sharing coding as claimed in any one of claims 1 to 6 is implemented.

9. 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 method for realizing the spaceborne SAR full polarization scanning mode based on time-sharing coding as claimed in any one of claims 1 to 6 is implemented.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the method for realizing the spaceborne SAR full polarization scanning mode based on time-sharing coding as claimed in any one of claims 1 to 6 is implemented.

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