Method and device for realizing full polarization scanning mode of spaceborne SAR based on time-sharing coding

Abstract

The present invention provides a method and device for implementing a spaceborne SAR full-polarization scanning mode based on time-sharing coding, relating to the field of radar imaging technology. The method comprises: first determining a first spatial resolution and a first imaging width of a SAR satellite system in a spaceborne SAR full-polarization strip mode to determine the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode; further determining a second spatial resolution and a second imaging width in the spaceborne SAR scanning mode; when imaging indicators are met, causing the SAR satellite system to perform an observation process in the spaceborne SAR scanning mode using a time-sharing coding method; after the observation process is completed, imaging is performed on the full-polarization SAR echo data scanned for each mapping sub-band, and ultimately splicing them into a full-polarization SAR scanning image. Through this application, the defects of the limited observation width of the spaceborne SAR full-polarization strip mode and the spaceborne SAR scanning mode only supporting single or dual polarization are overcome.

Description

Technical Field

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

[0002] Spaceborne Synthetic Aperture Radar (SAR) is an active microwave remote sensing radar capable of high-resolution Earth observations, unaffected by sunlight or weather, and capable of operating around the clock and in all weather conditions. In this field, spaceborne SAR is developing towards high resolution, wide bandwidth, and multi-polarization capabilities. Polarimetric SAR utilizes the transmission and reception of horizontal (H) and vertical (V) polarized waves to acquire the different polarization scattering characteristics of ground targets. Fully polarimetric SAR, in particular, can acquire information in four polarizations: HH, HV, VH, and VV. This significantly expands the information dimensions available to spaceborne SAR and offers significant application value and significance in target identification and classification, forest resource monitoring, crop growth assessment, and disaster monitoring.

[0003] Traditional full-polarimetric SAR implementations include time division, code division, and frequency division. These require two transmit and receive channels, one transmitting H-polarized and the other receiving V-polarized signals, respectively, to acquire full-polarimetric signals. Time-division full-polarimetric SAR acquires four-polarimetric information by alternating between H-polarized and V-polarized signals, but this requires a pulse repetition frequency (PRF) nearly double that of single-polarimetric SAR, limiting the imaging bandwidth. Frequency-division full-polarimetric SAR simultaneously transmits H-polarized and V-polarized signals with different carrier frequencies. While this does not require a high PRF, filtering the received signals is difficult, hindering effective separation of the different polarization signals and resulting in unstable full-polarimetric scattering performance. Similar to frequency-division full-polarimetric SAR, code-division full-polarimetric SAR simultaneously transmits orthogonally coded H-polarized and V-polarized signals. However, in practice, completely orthogonal coded signals cannot be obtained. The coded signals are subject to certain cross-correlated noise, resulting in insufficient cross-polarization suppression and poor imaging quality.

[0004] To address these issues, existing technologies have proposed full-polarimetric methods for SAR satellites. These methods utilize a "time division + code division" full-polarimetric implementation, suppressing cross-polarization range ambiguity while simultaneously acquiring stable full-polarimetric scattering information. However, these SAR satellite full-polarimetric methods still have some drawbacks. Spaceborne full-polarimetric SAR all utilizes a stripe observation mode, resulting in a small observation width and low efficiency, making it inadequate for observing large areas such as oceans and forests. Spaceborne SAR scanning mode enables wide-area observations through range-directed beam scanning. Scanning mode can be implemented using Scanner Synthetic Aperture Radar (ScanSAR) and Terrain Observation by Progressive (TOPS) radars. However, current spaceborne SAR scanning modes only support single- or dual-polarization operation, failing to acquire full-polarimetric scattering information from a target. Summary of the Invention

[0005] The present invention provides a method and device for realizing a spaceborne SAR full-polarization scanning mode based on time-sharing coding, so as to solve the defects of the prior art SAR satellite full-polarization working method.

[0006] The present invention provides a method for realizing a spaceborne SAR full polarization scanning mode based on time-sharing coding, comprising:

[0007] Determining 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;

[0008] determining, according to the first spatial resolution and the first imaging width, the number of mapping subbands of the SAR satellite system in a spaceborne SAR scanning mode;

[0009] determining a second spatial resolution and a second imaging width in a spaceborne SAR scanning mode according to the number of mapping subbands, and causing the SAR satellite system to perform an observation process in the spaceborne SAR scanning mode using a time-sharing coding method when the second spatial resolution and the second imaging width meet preset imaging indicators;

[0010] 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;

[0011] The full-polarimetric SAR images corresponding to each mapping sub-band are stitched together to obtain a full-polarimetric SAR scanning image.

[0012] In some embodiments, 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 width includes:

[0013] Obtain the observation width and second azimuth resolution of the SAR satellite system in the spaceborne SAR scanning mode;

[0014] determining, according to a first azimuth resolution and a 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;

[0015] Determining the overlapping width of the mapping sub-bands in the spaceborne SAR scanning mode, and constructing 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;

[0016] The number of mapping sub-bands of the SAR satellite system in a spaceborne SAR scanning mode is determined based on the ratio and the width relationship equation.

[0017] In some embodiments, the SAR satellite system uses a time-sharing coding method to perform an observation process in a spaceborne SAR scanning mode, including:

[0018] Observe each mapping sub-band cyclically in the spaceborne SAR scanning mode;

[0019] 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 between the transmitted signals.

[0020] In some embodiments, the cyclically observing each mapping sub-band in the spaceborne SAR scanning mode includes:

[0021] Determining the beam direction of the antenna distance beam of the SAR satellite system according to the number of mapping sub-bands and the second imaging width;

[0022] Switching the antenna distance to the mapping sub-band pointed by the beam according to the beam direction within the sub-band scanning regression time;

[0023] Observe the mapping sub-band pointed by the antenna range beam.

[0024] In some embodiments, the encoding process of the H-polarized pulse signal and the V-polarized pulse signal includes:

[0025] Determining 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 reciprocal numbers of each other;

[0026] 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.

[0027] In some embodiments, 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:

[0028] 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:

[0029] re-determining a first spatial resolution and a first imaging swath 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 swath width in the spaceborne SAR scanning mode based on the re-determined first spatial resolution and the re-determined first imaging swath width;

[0030] 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.

[0031] The present invention also provides a device for implementing a spaceborne SAR full polarization scanning mode based on time-sharing coding, comprising:

[0032] A first determining module is configured 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;

[0033] A second determining module is configured to determine the number of mapping sub-bands of the SAR satellite system in a spaceborne SAR scanning mode according to the first spatial resolution and the first imaging width;

[0034] an observation module, configured to determine a second spatial resolution and a second imaging width in a spaceborne SAR scanning mode according to the number of 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 using a time-sharing coding method;

[0035] The imaging module is used to perform imaging processing on the fully polarimetric SAR echo data obtained by scanning each mapping sub-band after the observation process is completed to obtain the corresponding fully polarimetric SAR image;

[0036] 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.

[0037] The present invention also provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the method for implementing the spaceborne SAR full polarization scanning mode based on time-sharing coding as described in any one of the above is implemented.

[0038] The present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the method for implementing the spaceborne SAR full polarization scanning mode based on time-sharing coding as described in any of the above is implemented.

[0039] The present invention also provides a computer program product, comprising a computer program, wherein when the computer program is executed by a processor, the computer program implements any of the above-mentioned methods for implementing a spaceborne SAR full polarization scanning mode based on time-sharing coding.

[0040] The method and device for realizing the spaceborne SAR full-polarization scanning mode based on time-sharing coding provided by the present invention overcome the defects of the spaceborne SAR full-polarization strip mode being limited in observation width and the spaceborne SAR scanning mode being limited to single polarization or dual polarization by combining the spaceborne SAR full-polarization strip mode and the spaceborne SAR scanning mode, thereby improving the observation amplitude and observation efficiency of the full-polarization SAR mode of the SAR satellite system and ensuring the stable acquisition of full-polarization scattering information. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced one by one below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 The present invention provides a flow chart of a method for realizing a spaceborne SAR full polarization scanning mode based on time-sharing coding.

[0043] Figure 2 This is a diagram showing the working principle of the SAR satellite system provided by the present invention in the spaceborne SAR full-polarization strip mode.

[0044] Figure 3 This is a diagram of the working principle of the SAR satellite system provided by the present invention in the spaceborne SAR scanning mode.

[0045] Figure 4The diagram is a schematic diagram of the principle of the method for realizing the full polarization scanning mode of spaceborne SAR based on time-sharing coding provided by the present invention.

[0046] Figure 5 It is a schematic diagram of the principle of transmitting signal coding in the method for realizing the full polarization scanning mode of spaceborne SAR based on time-sharing coding provided by the present invention.

[0047] Figure 6 The present invention provides a schematic structural diagram of a device for realizing a spaceborne SAR full polarization scanning mode based on time-sharing coding.

[0048] Figure 7 It is a structural schematic diagram of the electronic device provided by the present invention. DETAILED DESCRIPTION

[0049] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0050] The following describes the method for implementing the spaceborne SAR full polarization scanning mode based on time-sharing coding in conjunction with the accompanying drawings. Figure 1 FIG. 1 is a flow chart of a method for realizing a spaceborne SAR full polarization scanning mode based on time-sharing coding provided by the present invention, as shown in FIG. Figure 1 As shown, the method includes the following steps 101 to 105, which are described in detail below.

[0051] Step 101: Determine a first spatial resolution and a first imaging width of a SAR satellite system in a spaceborne SAR full-polarization strip mode based on preset SAR satellite parameters.

[0052] The embodiment of the present invention first designs a spaceborne SAR full polarization strip pattern through a SAR satellite system to observe the target. The preset SAR satellite parameters include satellite orbit and satellite SAR payload parameters. Figure 2As shown in the figure, the spaceborne SAR full-polarimetric swath mode operates based on the principle of time-division full-polarimetric SAR. During radar signal transmission, the H and V polarization channels alternately transmit linear frequency-modulated pulse signals at different pulse repetition times (PRTs). Then, during the intervals between signal transmissions within each PRT, the H and V polarization channels simultaneously receive and acquire SAR echo data, specifically, four polarization echoes: HH, HV, VH, and VV. The PRF represents the frequency of the pulse signals transmitted during imaging observations by the SAR satellite system. This parameter constrains multiple SAR satellite system imaging performance indicators, including swath width, azimuth ambiguity, and range ambiguity. It is important to note that the PRF and the first imaging swath width are mutually constrained. Simply put, the higher the PRF, the greater the constraint on the first imaging swath width, and the smaller the achievable maximum value.

[0053] During the specific operation, the SAR satellite parameters are used as input information, and the spaceborne SAR full polarization strip mode is designed to perform the observation process, and the first spatial resolution and the first imaging width 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 main lobe along the azimuth direction of the point target impulse response in the SAR image can be used as the first azimuth resolution, and the half-power width of the main lobe along the range direction can be used as the range resolution. The first spatial resolution can reflect the SAR satellite system's ability to resolve targets. In the spaceborne SAR full polarization strip mode, the first azimuth resolution The calculation formula is as follows:

[0054] (1)

[0055] In the above formula (1), is the antenna azimuth size of the SAR satellite system, is the broadening factor of the azimuth resolution, which is affected by factors such as imaging windowing processing, antenna pattern characteristics, and satellite-to-ground improvement coefficient.

[0056] Distance resolution The calculation formula is as follows:

[0057] (2)

[0058] In the above formula (2), c represents the speed of light, represents the signal bandwidth, represents the angle of incidence, It represents the broadening factor of the range resolution. This broadening factor is affected by factors such as imaging windowing processing, the amplitude frequency and phase frequency of the SAR system.

[0059] The first imaging width can be recorded as , a key indicator of a SAR satellite system's ground coverage capability, can be defined as the effective image width obtained by processing all range data. It characterizes the observation efficiency of a SAR satellite system. After the observation is complete and the image is acquired, the corresponding first imaging width can be easily determined based on the PRF.

[0060] Step 102: 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.

[0061] Next, according to the first spatial resolution and the first imaging width calculated in step 101 in the spaceborne SAR full polarization strip mode, the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode is determined.

[0062] Here, it is still necessary to design a spaceborne SAR scanning mode through the SAR satellite system to observe the target, and it is still designed based on the preset SAR satellite parameters, including satellite orbit and satellite SAR payload parameters. Figure 3 , Figure 3 The working principle of the SAR satellite system in the spaceborne SAR scanning mode is demonstrated. The spaceborne SAR scanning mode can be implemented by ScanSAR or TOPS. The embodiment of the present invention takes the ScanSAR mode as an example to illustrate the spaceborne SAR scanning mode. Figure 3 As shown in Figure 2, the observation in the spaceborne SAR scanning mode is achieved by splicing N mapping sub-bands. is the beam dwell time of the Nth mapping subband, is the sub-band scan regression time, is the synthetic aperture time, and the three satisfy the following relationship:

[0063] (3)

[0064] During the observation process in the spaceborne SAR scanning mode, the antenna range beam of the SAR satellite system is first pointed to the mapping sub-band 1, and the signal is transmitted and received according to the predetermined parameters, specifically the linear frequency modulation pulse signal is transmitted and received. After that, the antenna range beam is switched to mapping sub-band 2, and the observation time is , then switch to mapping sub-band 3, and so on. After observing mapping sub-band N, switch back to mapping sub-band 1 for observation. In this way, observations are cyclically performed between mapping sub-bands 1 to N to achieve wide-band data acquisition. Finally, the imaging data of each mapping sub-band are spliced ​​to obtain the final image observed by the SAR satellite system.

[0065] Therefore, in the spaceborne SAR scanning mode, the most important thing is to determine the number N of mapping sub-bands. In the embodiment of the present invention, the number N of mapping sub-bands is determined based on the first spatial resolution and the first imaging width calculated in the spaceborne SAR full polarization strip mode. There are multiple ways to determine this. First, the azimuth resolution index and the observation amplitude index in the spaceborne SAR scanning mode are obtained. The first way is to calculate the first azimuth resolution included in the azimuth resolution index and the first spatial resolution. The ratio of the first imaging width is calculated by subtracting 1 from the ratio. The equation is established with the observation amplitude index, specifically to calculate the number of mapping sub-bands N and the first imaging width The product of N-1 and N-1 is then used to determine the overlap width of adjacent mapping sub-bands. The difference between these two products is the observed amplitude index. The equation constructed in this way has only one unknown variable, N, the number of mapping sub-bands. Solving this equation determines the number of mapping sub-bands N.

[0066] Step 103: Determine a second spatial resolution and a second imaging width in the spaceborne SAR scanning mode based on the number of mapping subbands. When the second spatial resolution and the second imaging width meet preset imaging indicators, enable the SAR satellite system to perform the observation process in the spaceborne SAR scanning mode using a time-sharing coding method.

[0067] After determining the number N of mapping sub-bands in the spaceborne SAR scanning mode in step 102, the second spatial resolution and the second imaging width in the spaceborne SAR scanning mode are further determined based on the number of mapping sub-bands. Here, the beam dwell time of the mapping sub-band can be re-determined based on the number N of mapping sub-bands. , and subband scan regression time , and further adjust the spatial resolution and imaging width, so that the second spatial resolution and the second imaging width in the spaceborne SAR scanning mode can be determined.

[0068] Next, we need to ensure that subsequent imaging meets the required imaging performance. This involves determining whether the second spatial resolution and second imaging width meet the preset imaging performance requirements. These imaging performance requirements can be the spatial resolution and imaging width requirements in the spaceborne SAR scanning mode. If the second spatial resolution exceeds the spatial resolution requirement and the second imaging width exceeds the imaging width requirement, the imaging performance requirements are met. In SAR satellite systems, smaller spatial resolutions produce better results. Therefore, if the second spatial resolution exceeds the spatial resolution requirement, the second spatial resolution also exceeds the spatial resolution requirement.

[0069] When the second spatial resolution and the second imaging width meet the preset imaging indicators, the SAR satellite system can use time-sharing coding to perform the observation process in the spaceborne SAR scanning mode. That is, while using the mapping sub-band in the spaceborne SAR scanning mode for observation, the spaceborne SAR full-polarization strip mode is used to transmit polarization pulse signals in each mapping sub-band and obtain HH, HV, VH and VV four-polarization echo data to complete the observation process. When sending the pulse signal, the H-polarized pulse signal is encoded using a positive frequency modulation slope encoding method, and the V-polarized pulse signal is encoded using a negative frequency modulation slope encoding method. Of course, the two encoding methods can also be interchanged in actual implementation.

[0070] Step 104: After the observation process is completed, imaging processing is performed on the fully polarimetric SAR echo data obtained by scanning each mapping sub-band to obtain a corresponding fully polarimetric SAR image.

[0071] During the observation process in step 103, polarized pulse signals can be transmitted in a time-sharing manner within each mapping sub-band, and corresponding quad-polarized 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 the corresponding fully polarized SAR image. Imaging processing can be implemented using various SAR imaging algorithms, such as backprojection, range Doppler, and NCP algorithms, and is not limited in this embodiment of the present invention.

[0072] Step 105: stitching the full-polarization SAR images corresponding to each mapping sub-band to obtain a full-polarization SAR scanning image.

[0073] Finally, referring to the imaging processing process in the spaceborne SAR scanning mode, the full-polarimetric SAR images corresponding to each mapping sub-band are spliced ​​to obtain the full-polarimetric SAR scanning image.

[0074] The embodiments of the present invention combine 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 or dual polarization. This not only increases the observation amplitude and observation efficiency of the SAR satellite system, but also improves the polarization information acquisition capability, ensuring stable acquisition of fully polarized scattering information.

[0075] 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.

[0076] First, the observation width and second azimuth resolution of the SAR satellite system in the spaceborne SAR scanning mode are obtained, respectively and The observation width and second azimuth resolution here are the resolution and width that need to be met by imaging. Of course, in some embodiments, the observation width and second azimuth resolution can also be preset according to actual needs, and are not limited to the spaceborne SAR scanning mode.

[0077] 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 is as follows:

[0078] (4)

[0079] 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.

[0080] Although N can be calculated according to formula (4), 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 based on 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 between the widths of two adjacent mapping 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 mapping sub-bands, which is expressed as the following formula:

[0081] (5)

[0082] Finally, the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode is determined based on the ratio and width relationship equation. N can be calculated, and the above formula (5) has only one unknown number N, which can also be calculated.

[0083] 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.

[0084] In an embodiment of the present invention, the number of mapping sub-bands in a spaceborne SAR scanning mode is determined by using the first spatial resolution and the first imaging width of the SAR satellite system in the spaceborne SAR full-polarization strip mode, thereby achieving a combination of the two modes. In addition, when calculating the number of mapping sub-bands, the spatial resolution and the width are comprehensively considered to ensure that subsequent imaging can have a better spatial resolution and width.

[0085] The following describes the observation process of the SAR satellite system in the spaceborne SAR scanning mode using the time-sharing coding method. In some embodiments, when the second spatial resolution and the second imaging width in the spaceborne SAR scanning mode meet the preset imaging indicators, the spaceborne SAR scanning mode observation can be performed using the time-sharing coding method, which can be specifically as follows: Figure 4 As shown in Figure 1, this observation process is still completed through N mapping sub-bands. During observation, each mapping sub-band is observed cyclically in the spaceborne SAR scanning mode. Here, the SAR satellite system transmits the antenna range beam, pointing to the mapping sub-band for observation.

[0086] 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 between the transmitted signals.

[0087] The time-sharing alternating transmission method here can refer to the signal transmission mode in the full-polarization strip mode of the spaceborne SAR, and ultimately receive the HH, HV, VH and VV four-polarization echo data. Of course, the transmission signal and the reception signal still need to be within the pulse repetition time (PRT).

[0088] During the observation process, it is necessary to adjust the antenna distance to the beam direction to switch the mapping sub-band. The antenna range beam of the SAR satellite system is first pointed to the mapping sub-band 1, and the H and V polarization pulse signals are transmitted according to the predetermined parameters and the four types of fully polarized SAR echo data are received. The observation time is After that, the antenna range beam is switched to mapping sub-band 2, and the observation time is , then switch to mapping sub-band 3, and so on. After observing mapping sub-band N, a sub-band scanning regression time is completed. Then the antenna range beam switches back to the mapping sub-band 1 and executes the next sub-band scan regression time. The observation process is carried out in this way, and the observation is performed cyclically between the mapping sub-band 1 to the mapping sub-band N.

[0089] In addition, before transmitting the H-polarized pulse signal and the V-polarized pulse signal, the pulse signals need to be encoded using different coding methods, that is, the "code division" process is performed in the H-polarized channel and the V-polarized channel, and the H-polarized pulse signal is encoded using a positive frequency modulation slope coding method, and the V-polarized pulse signal is encoded using a negative frequency modulation slope coding method. After encoding, they are transmitted.

[0090] In an embodiment of the present invention, a SAR satellite system utilizes a time-sharing coding method to execute an observation process in a spaceborne SAR scanning mode. This method can effectively apply the time-sharing transmission of polarized pulse signals and the reception of fully polarized SAR echo data in a spaceborne SAR fully polarized stripe mode to the spaceborne SAR scanning mode. This overcomes the defect that the spaceborne SAR scanning mode is limited to single polarization or dual polarization, improves the polarization information acquisition capability of the ScanSAR mode, and ensures stable acquisition of fully polarized scattering information.

[0091] Furthermore, each mapping sub-band is observed cyclically in the spaceborne SAR scanning mode, including:

[0092] First, the beam direction of the antenna distance beam of the SAR satellite system is determined according to the number of mapping sub-bands and the second imaging width. Then, within the sub-band scanning regression time, the mapping sub-band pointed by the antenna distance beam is switched according to the beam direction. Finally, observations are performed on the switched mapping sub-band.

[0093] Specifically, first, according to the number of mapping sub-bands and the second imaging width, the beam direction of the antenna distance beam of the SAR satellite system in each mapping sub-band can be determined one by one, so as to transmit H and V polarized pulse signals when the antenna distance beam points to the corresponding mapping sub-band.

[0094] like Figure 4 As shown, after determining the beam direction, the sub-band scanning regression time The mapping sub-band pointed by the antenna range beam is switched according to the beam direction. Each mapping sub-band has a corresponding observation time. First, the antenna range beam will point to mapping sub-band 1. At this time, the mapping sub-band 1 is observed. During the observation process, H and V polarization pulse signals are transmitted and four types of fully polarized SAR echo data are received according to the preset parameters. The observation time of mapping sub-band 1 is After that, according to the direction of the wave velocity, the direction of the antenna range beam will switch to the mapping sub-band 2, and then observe the mapping sub-band 2, still according to the predetermined parameters to transmit H, V polarization pulse signals and receive four kinds of fully polarized SAR echo data, the observation time is , the next step is to 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 After that, the sub-band scan return time is completed Observation process.

[0095] Next, continue to execute the next sub-band scan return time During the observation process, according to the beam direction, the antenna distance to the mapping sub-band N pointed by the 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 to realize the spaceborne SAR scanning mode.

[0096] In an embodiment of the present invention, N mapping sub-bands are set in a spaceborne SAR scanning mode, and polarization pulse signals are transmitted and four types of fully polarized SAR echo data are received in each mapping sub-band according to a spaceborne SAR fully polarized strip pattern. This enables the SAR satellite system to stably acquire fully polarized scattering information even in the spaceborne SAR scanning mode, thereby improving the polarization information acquisition capability.

[0097] In some embodiments, considering that the transmitted polarization pulse signal is to obtain full-polarization SAR echo data to obtain imaging of the observed target, in order to ensure the stability and high quality of the imaging, the embodiments of the present invention implement "code division" of the polarization pulse signal in the spaceborne SAR scanning mode, that is, when the polarization pulse signal is transmitted, the polarization pulse signal is encoded and processed. The encoding process of the H-polarization pulse signal and the V-polarization pulse signal is specifically described below.

[0098] like Figure 5 As shown, the encoding method of the polarization pulse signal is based on slope frequency modulation coding. First, the center carrier frequency of the polarization pulse signal is determined in the frequency f of the polarization pulse signal. , a first frequency modulation slope and a second frequency modulation slope, wherein the first frequency modulation slope is for the H-polarized pulse signal and takes a positive number, while the second frequency modulation slope is for the V-polarized pulse signal and takes a negative number, and the first frequency modulation slope and the second frequency modulation slope are opposite numbers to each other.

[0099] When observing through the surveying sub-band, the H polarization channel transmits the H polarization pulse signal within the azimuth time t. At this time, according to the center carrier frequency And the first frequency modulation slope, the H polarization pulse signal is encoded with a positive frequency modulation slope. 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 ensures that the average of the maximum frequency and the minimum frequency of the encoded H polarization pulse signal is the center carrier frequency. .

[0100] During the azimuth time t, the V polarization channel transmits a V polarization pulse signal. And the second frequency modulation slope, the V polarization pulse signal is encoded with a negative frequency modulation slope. 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 reduction and also ensures that the average of the maximum frequency and the minimum frequency of the V polarization pulse signal after encoding is the center carrier frequency. .

[0101] In an embodiment of the present invention, "code division" of polarization pulse signals is implemented in a spaceborne SAR scanning mode. Frequency modulation coding methods with different slopes are used to encode the transmitted polarization pulse signals. This can effectively suppress the blurring of cross-polarization images and improve the image quality of subsequent imaging.

[0102] In some embodiments, in order 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 indicators are also set. In the above step 103, only when the second spatial resolution and the second imaging width meet the preset imaging indicators can the SAR satellite system be triggered to perform the observation process in the spaceborne SAR scanning mode using time-sharing coding. The preset imaging indicators include spatial resolution indicators and imaging width indicators, thereby ensuring that the imaging obtained after observation can meet the spatial resolution requirements and width requirements.

[0103] However, in actual scenarios, even after determining the second spatial resolution and second imaging width in the spaceborne SAR scanning mode based on the number of mapping subbands, there may still be situations where the preset imaging indicators are not met. To address this situation, the embodiment of the present invention adopts an iterative process. Specifically, if the preset imaging indicators are not met in step 103, the SAR satellite system is not triggered to perform the observation process in the spaceborne SAR scanning mode using a time-sharing coding method. Instead, steps 101 to 103 are repeatedly performed until the preset imaging indicators are met.

[0104] Specifically, when the second spatial resolution is worse than the spatial resolution index or the second imaging width is smaller than the imaging width 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 index in the spaceborne SAR scanning mode, and then the iterative process of the following steps 201 to 202 is executed.

[0105] Step 201 : re-determine a first spatial resolution and a first imaging width of a SAR satellite system in a spaceborne SAR full-polarization strip mode based on preset SAR satellite parameters.

[0106] Here, when the preset imaging indicators are not met in the spaceborne SAR scanning mode, the first spatial resolution and the first imaging width 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, the above-mentioned step 101 is re-executed. The specific determination process can be referred to step 101 and will not be repeated here.

[0107] Step 202 : Based on the re-determined first spatial resolution and the re-determined first imaging width, a new second spatial resolution and a new second imaging width are determined in a spaceborne SAR scanning mode.

[0108] Here, based on the first spatial resolution and the first imaging width re-determined in step 201, a new second spatial resolution and a new second imaging width are further determined in the spaceborne SAR scanning mode, that is, the above steps 102 and 103 are continued to be executed, so as to determine the new second spatial resolution and the new second imaging width. The determination process can refer to the above steps 102 and 103 and is not repeated here.

[0109] Next, we continue to judge whether the preset imaging indicators are met, that is, we need to judge whether there is still a new second spatial resolution that is worse than the spatial resolution indicator or a new second imaging width that is smaller than the imaging width indicator. Here, both the spatial resolution indicator and the imaging width indicator need to be met, and neither can be missing.

[0110] 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, it means that after the above iteration, the preset imaging index has been met, then the iteration ends and the SAR satellite system is triggered to perform the observation process in the spaceborne SAR scanning mode using time-sharing coding.

[0111] When the new second spatial resolution is still worse than the spatial resolution index or the new second imaging width is still smaller than the imaging width index, it means that after one iteration, the preset imaging index is still not met. Then the iterative process is continued, that is, the above steps 201 to 202 are continued until the preset imaging index is met, and then the iteration is ended.

[0112] In an embodiment of the present invention, an iterative process is designed to ensure that the SAR satellite system, in combination with the spaceborne SAR full-polarization strip mode and the spaceborne SAR scanning mode, can meet preset imaging indicators. Through this iterative process, the influencing factors and errors that may occur in the two observation modes can be effectively removed, so that the two modes can be effectively combined to ensure that subsequent imaging meets the requirements of spatial resolution and imaging width.

[0113] The following describes a device for implementing a spaceborne SAR full-polarization scanning mode based on time-sharing coding provided by the present invention. The device for implementing a spaceborne SAR full-polarization scanning mode based on time-sharing coding described below and the method for implementing a spaceborne SAR full-polarization scanning mode based on time-sharing coding described above can be referenced to each other.

[0114] like Figure 6 As shown, the device for implementing the full polarization scanning mode of spaceborne SAR based on time-sharing coding includes: a first determination module 601, a second determination module 602, an observation module 603, an imaging module 604, and a stitching module 605. The first determination module 601 is configured to determine a first spatial resolution and a first imaging swath width of the SAR satellite system in the spaceborne SAR full-polarization strip mode based on preset SAR satellite parameters. The second determination module 602 is configured to determine the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode based on the first spatial resolution and the first imaging swath width. The observation module 603 is configured to determine a second spatial resolution and a second imaging swath width in the spaceborne SAR scanning mode based on the number of mapping sub-bands. When the second spatial resolution and the second imaging swath width meet preset imaging indicators, the SAR satellite system is configured to perform an observation process in the spaceborne SAR scanning mode using a time-sharing coding method. The imaging module 604 is configured to, after the observation process is completed, perform imaging processing on the fully-polarization SAR echo data obtained by scanning each mapping sub-band to obtain a corresponding fully-polarization SAR image. The stitching module 605 is configured to stitch the fully-polarization SAR images corresponding to each mapping sub-band to obtain a fully-polarization SAR scanning image.

[0115] It should be noted that the beneficial effects of the device for implementing the full polarization scanning mode of spaceborne SAR based on time-sharing coding here and the method for implementing the full polarization scanning mode of spaceborne SAR based on time-sharing coding mentioned above can correspond to each other, so the beneficial effects of the device for implementing the full polarization scanning mode of spaceborne SAR based on time-sharing coding will not be repeated here.

[0116] Figure 7 An example of a physical structure diagram of an electronic device is shown below. Figure 7As shown, the electronic device may include: a processor (processor) 710 , a communication interface (Communications Interface) 720 , a memory (memory) 730 and a communication bus 740 , wherein the processor 710 , the communication interface 720 and the memory 730 communicate with each other via the communication bus 740 . The processor 710 can call logic instructions in the memory 730 to execute a method for implementing a spaceborne SAR full-polarimetric scanning mode based on time-sharing coding. The method includes: determining a first spatial resolution and a first imaging width of the SAR satellite system in the spaceborne SAR full-polarimetric 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 based on the first spatial resolution and the first imaging width; determining a second spatial resolution and a second imaging width in the spaceborne SAR scanning mode based on the number of mapping sub-bands; when the second spatial resolution and the second imaging width meet preset imaging indicators, causing the SAR satellite system to perform an observation process in the spaceborne SAR scanning mode using a time-sharing coding method; after the observation process is completed, performing imaging processing on the full-polarimetric SAR echo data obtained by scanning each mapping sub-band to obtain a corresponding full-polarimetric SAR image; and performing splicing processing on the full-polarimetric SAR images corresponding to each mapping sub-band to obtain a full-polarimetric SAR scanning image.

[0117] Furthermore, the logic instructions in the aforementioned memory 730 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product, stored in a storage medium, includes instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0118] On the other hand, the present invention also provides a computer program product, comprising a computer program, which 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 time-sharing coding-based spaceborne SAR full-polarization scanning mode implementation method provided by the above methods, the method comprising: 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; determining the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode based on the first spatial resolution and the first imaging width; determining a second spatial resolution and a second imaging width in the spaceborne SAR scanning mode based on the number of mapping sub-bands; when the second spatial resolution and the second imaging width meet preset imaging indicators, causing the SAR satellite system to perform an observation process in the spaceborne SAR scanning mode using a time-sharing coding method; after the observation process is completed, performing imaging processing on the full-polarization SAR echo data obtained by scanning each mapping sub-band to obtain a corresponding full-polarization SAR image; and performing splicing processing on the full-polarization SAR images corresponding to each mapping sub-band to obtain a full-polarization SAR scanning image.

[0119] On the other hand, the present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method for implementing the spaceborne SAR full-polarization scanning mode based on time-sharing coding provided by the above methods, the method comprising: 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; determining the number of mapping sub-bands of the SAR satellite system in the spaceborne SAR scanning mode based on the first spatial resolution and the first imaging width; determining a second spatial resolution and a second imaging width in the spaceborne SAR scanning mode based on the number of mapping sub-bands; when the second spatial resolution and the second imaging width meet preset imaging indicators, causing the SAR satellite system to perform an observation process in the spaceborne SAR scanning mode using a time-sharing coding method; after the observation process is completed, performing imaging processing on the full-polarization SAR echo data obtained by scanning each mapping sub-band to obtain a corresponding full-polarization SAR image; and performing splicing processing on the full-polarization SAR images corresponding to each mapping sub-band to obtain a full-polarization SAR scanning image.

[0120] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e., they may be located in one location or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of the present embodiment. Persons of ordinary skill in the art will be able to understand and implement the present invention without inventive effort.

[0121] Through the above description of the embodiments, those skilled in the art will clearly understand that each embodiment can be implemented using software plus a necessary general-purpose hardware platform, or of course, hardware. Based on this understanding, the essence of the above technical solution, or the portion that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a magnetic disk, or an optical disk, and includes a number of instructions for causing a computer device (such as a personal computer, server, or network device) to execute the methods described in each embodiment or certain portions of the embodiments.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for implementing a spaceborne SAR full polarimetric scanning mode based on time-sharing coding, characterized in that: include: Determining 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, according to the first spatial resolution and the first imaging width, the number of mapping subbands of the SAR satellite system in a spaceborne SAR scanning mode; determining a second spatial resolution and a second imaging width in a spaceborne SAR scanning mode according to the number of mapping subbands, and causing the SAR satellite system to perform an observation process in the spaceborne SAR scanning mode using a time-sharing coding method when the second spatial resolution and the second imaging width meet preset imaging indicators; 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-polarimetric SAR images corresponding to each mapping sub-band are stitched together to obtain a full-polarimetric 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 sub-bands of the SAR satellite system in the spaceborne SAR scanning mode includes: Obtain the observation width and second azimuth resolution of the SAR satellite system in the spaceborne SAR scanning mode; determining, according to a first azimuth resolution and a 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; Determining the overlapping width of the mapping sub-bands in the spaceborne SAR scanning mode, and constructing 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 a spaceborne SAR scanning mode is determined based on the ratio and the width relationship equation.

3. The method for implementing the spaceborne SAR full polarization scanning mode based on time-sharing 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 between the transmitted signals.

4. The method for realizing the full polarization scanning mode of spaceborne SAR based on time-sharing coding according to claim 3, characterized in that: The cyclic observation of each mapping sub-band in the spaceborne SAR scanning mode includes: Determining the beam direction of the antenna distance beam of the SAR satellite system according to the number of mapping sub-bands and the second imaging width; Switching the antenna distance to the mapping sub-band pointed by the beam according to the beam direction within the sub-band scanning regression time; Observe the mapping sub-band pointed by the antenna range beam.

5. The method for realizing the full polarization scanning mode of spaceborne SAR based on time-sharing coding according to claim 3, characterized in that: The encoding process of the H-polarized pulse signal and the V-polarized pulse signal includes: Determining 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 reciprocal 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 realizing the full polarization scanning mode of spaceborne SAR 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 swath 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 swath width in the spaceborne SAR scanning mode based on the re-determined first spatial resolution and the re-determined first imaging swath 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 determining module is configured 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 determining module is configured to determine the number of mapping sub-bands of the SAR satellite system in a spaceborne SAR scanning mode according to the first spatial resolution and the first imaging width; an observation module, configured to determine a second spatial resolution and a second imaging width in a spaceborne SAR scanning mode according to the number of 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 using a time-sharing coding method; The imaging module is used to perform imaging processing on the fully polarimetric SAR echo data obtained by scanning each mapping sub-band after the observation process is completed to obtain the corresponding fully polarimetric 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 implementing the spaceborne SAR full-polarization scanning mode based on time-sharing coding as described 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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