Wideband Frequency Division Full Polarization SAR Imaging Method and System
By continuously transmitting H and V polarization signals during the pulse repetition period, and performing frequency division multiplexing and filtering processing at the receiving end, the problems of increasing pulse repetition frequency and decreasing observation of observation amplitude in traditional fully polarized SAR systems are solved, and wide-range fully polarized observation is achieved.
Patent Information
- Application Number
- CN202210692401.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-06-17
- Publication Date
- 2025-07-11
- Estimated Expiration
- 2042-06-17
AI Technical Summary
When traditional fully polarized SAR systems emit different polarization pulses, the pulse repetition frequency increases and the observation width decreases, making it impossible to achieve efficient fully polarized observations.
The H polarization signal and the V polarization signal are continuously transmitted in one pulse repetition period, and the echo signal is separated by frequency division multiplexing and bandpass filter at the receiving end, and the delay processing is performed to obtain a fully polarized ground SAR image.
It effectively solves the problems of increasing pulse repetition frequency and decreasing observation width in traditional fully polarized SAR systems, and achieves the improvement of wide-scale fully polarized observation capabilities.
Smart Images
Figure CN115184931B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical fields of microwave remote sensing and radar signal processing, and in particular to a wide-swath frequency-division full-polarization SAR imaging method and system. Background Art
[0002] Synthetic Aperture Radar (SAR) is a ground exploration device that can achieve two-dimensional imaging. Compared with optics, SAR has the advantages of all-weather and all-time detection, and also has significant advantages such as vegetation penetration, deformation monitoring, and internal structure detection of ground objects. It can be widely applied in many fields such as military reconnaissance, terrain and geological monitoring, agricultural and forest remote sensing. With the development of radar technology, the application of multi-polarization SAR makes various information such as the dielectric constant, physical characteristics, geometric size, and orientation of targets more abundant, providing a basis for revealing the target scattering mechanism and retrieving the physical and structural characteristics of targets, and greatly promoting the application of SAR in ground object classification and high-resolution imaging. At the same time, the resolvability of adjacent targets caused by polarization characteristic differences promotes the improvement of radar resolution ability. All these characteristics make polarimetric SAR an emerging and popular research direction internationally.
[0003] The full-polarization spaceborne SAR system in orbit mainly realizes full-polarization imaging observation of the ground by alternately transmitting different polarization pulses and then receiving echo signals with a dual-polarization channel. Its drawback is that this polarization method needs to increase the Pulse Repetition Frequence (PRF) to avoid the aggravation of azimuth ambiguity, resulting in the reduction of the coverage band width to half of the single-polarization working mode, thus causing problems such as the reduction of the observation swath width and the reduction of the revisit observation frequency, seriously restricting the effectiveness of the full-polarization SAR system.
[0004] In view of the above problems, the international academic community has been looking for a new system that does not lose the observation bandwidth in recent years. In 2012, the Indian Space Research Organization first used the "compact polarization" mode on the RISAT-1 satellite to solve the above problems. This mode transmits a hybrid polarization wave and uses a complex non-linear algorithm to reconstruct the full-polarization information of the echo signal. However, the pseudo full-polarization information obtained by the compact polarization reconstruction method is not comprehensive and also faces information loss during the calculation process. Therefore, this mode still cannot replace the traditional full-polarization SAR mode. Summary of the Invention
[0005] In order to solve the above technical problems existing in the prior art, the present invention provides a wide-swath frequency-division full-polarization SAR imaging method and system, which realizes full-polarization observation without losing resolution and swath width.
[0006] To achieve the above invention purpose, the technical solution of the present invention is:
[0007] The present invention provides a wide - band frequency - division full - polarization SAR imaging method, including:
[0008] S1. Continuously transmit H - polarization signals and V - polarization signals in a frequency - division multiplexing manner within one pulse repetition period;
[0009] S2. Receive the polarization echo signals formed by the scattering of the H - polarization signals and the V - polarization signals by the ground objects;
[0010] S3. Use a band - pass filter to separate the polarization echo signals to obtain full - polarization echo signals;
[0011] S4. Perform echo time - delay processing on the filtered full - polarization echo signals to obtain a full - polarization ground object SAR image.
[0012] According to one aspect of the present invention, the step S1 includes: within one pulse repetition period, first transmit the H - polarization signal, and then, after rapid switching, transmit the V - polarization signal. The carrier frequencies of the H - polarization signal and the V - polarization signal are divided into a lower carrier frequency and an upper carrier frequency for continuous transmission.
[0013] According to one aspect of the present invention, in the step S1, the transmission time of the H - polarization signal and the V - polarization signal is 15 μs, the switching time is 5 μs, and finally the transmitter emits a chirp signal with a duration of 35 μs.
[0014] According to one aspect of the present invention, the step S2 includes: the transmitted H - polarization signal and V - polarization signal form polarization echo signals after being scattered by the ground objects. The receiving end uses a large sampling rate covering the upper carrier frequency and the lower carrier frequency to perform AD acquisition and reception of the polarization echo signals in both the H - channel and the V - channel simultaneously.
[0015] According to one aspect of the present invention, the step S3 includes: using a band - pass filter to separate the polarization echo signals. In the H - channel, use a low - pass filter to form an HH - polarization signal and a high - pass filter to form an HV - polarization signal; in the V - channel, use a low - pass filter to form a VH - polarization signal and a high - pass filter to form a VV - polarization signal, thereby obtaining full - polarization echo signals.
[0016] According to one aspect of the present invention, the step S4 includes: performing echo time - delay processing on the HH - polarization signal, the HV - polarization signal, the VH - polarization signal, and the VV - polarization signal, and imaging them respectively, and finally obtaining a full - polarization ground object SAR image.
[0017] The present invention also provides a wide-swath frequency-division full-polarization SAR imaging system using the wide-swath frequency-division full-polarization SAR imaging method, including: a signal transmitter at the transmitting end, a signal receiver at the receiving end, and a duplexer.
[0018] The signal transmitter is used to continuously transmit H-polarization signals and V-polarization signals in a frequency-division multiplexing manner within one pulse repetition period.
[0019] The signal receiver is used to receive, separate, perform echo time-delay processing, and image the polarization echo signals formed by the scattering of the H-polarization signals and the V-polarization signals by the ground objects, so as to obtain a full-polarization ground object SAR image.
[0020] The duplexer is used to isolate the signals of the signal transmitter and the signal receiver, so that the signal transmitter and the signal receiver can work properly simultaneously.
[0021] According to another aspect of the present invention, the signal transmitter includes an H-channel antenna, a V-channel antenna, and a signal switching switch.
[0022] The H-channel antenna is used to transmit the H-polarization signal using the downlink frequency.
[0023] The V-channel antenna is used to transmit the V-polarization signal using the uplink frequency.
[0024] The signal switching switch is used to quickly switch the H-polarization signal to the V-polarization signal.
[0025] According to another aspect of the present invention, the signal receiver includes: an AD module, a band-pass filter, and an SAR imaging module.
[0026] The AD module is used to collect and receive the polarization echo signals in both the H-channel and the V-channel simultaneously using a large sampling rate covering the uplink frequency and the downlink frequency.
[0027] The band-pass filter is used to separate the polarization echo signals to form a full-polarization echo signal including HH-polarization signals and HV-polarization signals in the H-channel, and VH-polarization signals and VV-polarization signals in the V-channel.
[0028] The SAR imaging module is used to perform echo time-delay processing on the HH-polarization signal, the HV-polarization signal, the VH-polarization signal, and the VV-polarization signal, and image them respectively, and finally obtain a full-polarization ground object SAR image.
[0029] According to another aspect of the present invention, the transmission time of the H-polarization signal and the V-polarization signal is 15 μs, the switching time is 5 μs, and finally the signal transmitter emits a chirp signal with a duration of 35 μs.
[0030] Compared with the prior art, the present invention has the following advantages:
[0031] According to the solution of the present invention, by continuously transmitting H-polarized signals and V-polarized signals within one pulse repetition period, the ground echo signals are simultaneously received by two channels at the receiving end, and imaging is performed after filtering in the frequency domain. The technical solution effectively separates the aliasing of different polarized pulse echo signals in time sequence, and obtains a full-polarization ground image. The present invention effectively solves the problems of increased system PRF and decreased observation swath width caused by separately transmitting H and V polarized signals in traditional full-polarization SAR, and ensures the wide-swath full-polarization observation ability. BRIEF DESCRIPTION OF THE DRAWINGS
[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the embodiments. Obviously, the drawings in the following description are only 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.
[0033] Figure 1 Schematically showing the flowchart of a wide-swath frequency-division full-polarization SAR imaging method disclosed in an embodiment of the present invention;
[0034] Figure 2 Schematically showing the hardware design diagram of a wide-swath frequency-division full-polarization SAR imaging system disclosed in an embodiment of the present invention;
[0035] Figure 3 Schematically showing the pulse signal transmission diagram disclosed in an embodiment of the present invention;
[0036] Figure 4 Schematically showing the signal time-sequence dual-channel receiving and transmitting diagram disclosed in an embodiment of the present invention;
[0037] Figure 5 Schematically showing the signal frequency-domain dual-channel receiving and transmitting diagram disclosed in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0038] The description of the embodiments of this specification should be combined with the corresponding drawings, and the drawings should be regarded as a part of the complete specification. In the drawings, the shape or thickness of the embodiments can be enlarged, and simplified or conveniently marked. Furthermore, each part of the structure in the drawings will be described separately. It should be noted that the elements not shown or not described in words in the drawings are in the forms known to those of ordinary skill in the art.
[0039] In the description of the embodiments herein, any reference to directions and orientations is for convenience of description only and should not be construed as any limitation on the scope of protection of the present invention. The following description of the preferred embodiments involves combinations of features, which may exist independently or in combination. The present invention is not particularly limited to the preferred embodiments. The scope of the present invention is defined by the claims.
[0040] See Figure 1 , a wideband frequency-division full-polarization SAR imaging method provided by an embodiment of the present invention includes the following steps: S1. Continuously transmit H-polarized signals and V-polarized signals in a frequency-division multiplexing manner within a pulse repetition period; S2. Receive the polarization echo signals formed by the scattering of the H-polarized signals and V-polarized signals by the ground objects; S3. Use a band-pass filter to separate the polarization echo signals to obtain full-polarization echo signals; S4. Perform echo time-delay processing on the filtered full-polarization echo signals to obtain a full-polarization ground object SAR image. This method effectively solves the problems of increased system PRF and decreased observation swath caused by separately transmitting H and V polarization signals in traditional full-polarization SAR, and ensures the wideband full-polarization observation ability.
[0041] Among them, step S1 specifically includes: within a pulse repetition period, first transmit an H-polarized signal, and then, after rapid switching, transmit a V-polarized signal. The carrier frequencies of the H-polarized signal and the V-polarized signal are divided into a lower carrier frequency and an upper carrier frequency for continuous transmission.
[0042] Preferably, see Figure 3 , in step S1, the transmission time of the H-polarized signal and the V-polarized signal is 15 μs, the switching time is 5 μs, and finally the transmitter transmits a chirp signal of 35 μs.
[0043] Step S2 specifically includes: the transmitted H-polarized signal and V-polarized signal form polarization echo signals after being scattered by the ground objects. In an echo reception interval, the receiver simultaneously performs AD acquisition and reception of the polarization echo signals in the H channel and the V channel at a large sampling rate covering the upper carrier frequency and the lower carrier frequency.
[0044] Step S3 specifically includes: designing a reasonable band-pass filter and using the band-pass filter to separate the polarization echo signals. In the H channel, use a low-pass filter to form an HH polarization signal and a high-pass filter to form an HV polarization signal; in the V channel, use a low-pass filter to form a VH polarization signal and a high-pass filter to form a VV polarization signal, thereby obtaining full-polarization echo signals. The time-sequence dual-channel reception and transmission of the signals are as shown in Figure 4 shown, and the frequency-domain dual-channel reception and transmission are as shown in Figure 5 shown. Obtaining full-polarization echo signals through frequency-domain band-pass filtering effectively separates the aliasing of different polarization pulse echo signals in time sequence and obtains a full-polarization ground object image.
[0045] Step S4 specifically includes: performing echo time delay processing on HH polarization signals, HV polarization signals, VH polarization signals, and VV polarization signals, and imaging them respectively, and finally obtaining a full-polarization ground object SAR image.
[0046] See Figure 2 , an embodiment of the present invention also discloses a hardware structure of a wide-swath frequency-division full-polarization SAR imaging system using the above wide-swath frequency-division full-polarization SAR imaging method. The system includes: a signal transmitter at the transmitting end, a signal receiver at the receiving end, and a duplexer. Among them, the signal transmitter is used to continuously transmit H polarization signals and V polarization signals in a frequency-division multiplexing manner within one pulse repetition period. The signal receiver is used to receive, separate, perform echo time delay processing on, and image the polarization echo signals formed by the scattering of the H polarization signals and V polarization signals by the ground object, and obtain a full-polarization ground object SAR image. The duplexer is used to isolate the signals of the signal transmitter and the signal receiver, so that the signal transmitter and the signal receiver can work properly at the same time.
[0047] Among them, the signal transmitter includes an H-channel antenna, a V-channel antenna, and a signal switching switch. The H-channel antenna is used to transmit H polarization signals using the downlink frequency. The V-channel antenna is used to transmit V polarization signals using the uplink frequency. The signal switching switch is used to quickly switch the H polarization signal to the V polarization signal.
[0048] Preferably, see Figure 3 , the transmission time of the H polarization signal and the V polarization signal is 15 μs, and the switching time is 5 μs. Finally, the signal transmitter transmits a chirp signal of 35 μs outward.
[0049] The signal receiver includes: an AD module, a band-pass filter, and an SAR imaging module. The AD module is used to simultaneously collect and receive polarization echo signals in the H channel and the V channel using a large sampling rate covering the uplink frequency and the downlink frequency. A band-pass filter with reasonable design is used to separate the polarization echo signals to form a full-polarization echo signal including the HH polarization signal and the HV polarization signal of the H channel, and the VH polarization signal and the VV polarization signal of the V channel. See Figure 4 and Figure 5 . The SAR imaging module is used to perform echo time delay processing on the above HH polarization signals, HV polarization signals, VH polarization signals, and VV polarization signals, and image them respectively, and finally obtain a full-polarization ground object SAR image.
[0050] For the serial numbers of the above various steps involved in the method of the present invention, it does not mean the sequence of execution of the method. The execution sequence of each step should be determined according to its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.
[0051] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.
Claims
1. A wideband frequency division full polarization SAR imaging method, comprising: S1. Continuously transmit H polarization signals and V polarization signals in a frequency division multiplexing manner within one pulse repetition period; Step S1 includes: within one pulse repetition period, first transmit the H polarization signal, and then, after rapid switching, transmit the V polarization signal. Divide the carrier frequencies of the H polarization signal and the V polarization signal into a lower carrier frequency and an upper carrier frequency for continuous transmission; There is an isolation zone between the upper carrier frequency and the lower carrier frequency; S2. Receive the polarization echo signals formed by the scattering of the H polarization signal and the V polarization signal by the ground object; Step S2 includes: the transmitted H polarization signal and V polarization signal form polarization echo signals after being scattered by the ground object. The receiving end uses a large sampling rate covering the upper carrier frequency and the lower carrier frequency to perform AD acquisition and reception of the polarization echo signals in both the H channel and the V channel; S3. Use a band-pass filter to separate the polarization echo signals to obtain full polarization echo signals; S4. Perform echo time delay processing on the filtered full polarization echo signals to obtain a full polarization ground object SAR image.
2. The method according to claim 1, wherein In step S1, the transmission time of the H polarization signal and the V polarization signal is 15 μs, the switching time is 5 μs, and finally the transmitter transmits a chirp signal of 35 μs.
3. The method according to claim 1, characterized in that Step S3 includes: using a band-pass filter to separate the polarization echo signals. In the H channel, use a low-pass filter to form HH polarization signals and a high-pass filter to form HV polarization signals; in the V channel, use a low-pass filter to form VH polarization signals and a high-pass filter to form VV polarization signals, thereby obtaining full polarization echo signals.
4. The method according to claim 3, characterized in that, Step S4 includes: performing echo time delay processing on the HH polarization signal, the HV polarization signal, the VH polarization signal, and the VV polarization signal, and imaging them respectively, and finally obtaining a full polarization ground object SAR image.
5. A wide-swath frequency-division full-polarization SAR imaging system using the wide-swath frequency-division full-polarization SAR imaging method according to any one of claims 1-4, characterized in that, Comprising: A signal transmitter located at the transmitting end, a signal receiver located at the receiving end, and a duplexer, The signal transmitter is used to continuously transmit H polarization signals and V polarization signals in a frequency division multiplexing manner within one pulse repetition period; The signal receiver is used to receive, separate, perform echo time delay processing and imaging on the polarization echo signals formed by the scattering of the H polarization signal and the V polarization signal by the ground object to obtain a full polarization ground object SAR image; The duplexer is used to isolate the signals of the signal transmitter and the signal receiver, so that the signal transmitter and the signal receiver can work properly simultaneously; The signal transmitter includes an H channel antenna, a V channel antenna, and a signal switching switch, The H channel antenna is used to transmit the H polarization signal using the lower carrier frequency; The V channel antenna is used to transmit the V polarization signal using the upper carrier frequency; The signal switching switch is used to quickly switch the H polarization signal to the V polarization signal; The signal receiver includes: an AD module, a band-pass filter, and an SAR imaging module, The AD module is used to collect and receive the polarization echo signals in both the H channel and the V channel using a large sampling rate covering the upper carrier frequency and the lower carrier frequency; The bandpass filter is used to separate the polarization echo signal to form a full polarization echo signal including an HH polarization signal and an HV polarization signal of the H channel, and a VH polarization signal and a VV polarization signal of the V channel; The SAR imaging module is used to perform echo time delay processing on the HH polarization signal, the HV polarization signal, the VH polarization signal and the VV polarization signal, and to image them respectively, and finally obtain a fully polarized ground object SAR image.
6. The system according to claim 5, wherein The transmission time of the H polarization signal and the V polarization signal is 15 μs, the switching time is 5 μs, and finally the signal transmitter transmits a 35 μs linear frequency modulation signal.