Interferometric SAR synchronization method combining radar inter-satellite link with cross-correction of Ka band link

Abstract

The application discloses an interferometric SAR synchronization method of radar inter-satellite link combined with Ka-band link cross correction, and aims at the problems of interrupting normal SAR imaging or existing initial phase winding in the existing synchronization link method, and proposes a cross correction scheme of X-band radar inter-satellite link combined with Ka-band high-precision synchronization link. The system adopts a common reference source to ensure the phase correlation, and different synchronization time sequences are designed, that is, the X-band link is synchronized at a low frequency to eliminate the initial phase winding, and the Ka-band link is synchronized at a high frequency same as the SAR pulse repetition frequency (PRF) to realize high-precision phase measurement. During ground processing, the initial phase error of the Ka-band compensation function is corrected by using the X-band synchronization data, so that a high-precision phase synchronization compensation function is obtained, and the echo of the secondary satellite is compensated. The application solves the problem of initial phase winding under the premise of not interrupting the normal SAR imaging time sequence, and significantly improves the phase synchronization precision, image quality and absolute height measurement reliability of the dual-satellite interferometric SAR system.

Description

Technical Field

[0001] This invention belongs to the field of space microwave remote sensing technology, specifically relating to an interferometric SAR synchronization method that combines radar inter-satellite links with Ka-band link cross-correction. Background Technology

[0002] Dual-satellite interferometric synthetic aperture radar (InSAR) employs a "one transmit, two receive" operating mode, enabling the acquisition of high-precision elevation information. However, because the primary and secondary satellites use independent frequency sources, their echo signals exhibit phase errors, severely impacting the coherence of bistatic SAR imaging and the accuracy of subsequent interferometric processing.

[0003] In existing technologies, phase synchronization methods mainly include independent frequency source synchronization, data-based self-synchronization, and synchronization link methods. Among these, on-orbit dual-satellite SAR systems often employ the synchronization link method, which involves transmitting synchronization signals between satellites to measure and compensate for phase errors. For example, the TanDEM-X mission used an X-band inter-satellite bidirectional synchronization pulse scheme. However, this scheme has a significant drawback: the transmission of synchronization pulses periodically interrupts normal SAR data acquisition, introducing paired echoes into the images and degrading image quality. Lowering the synchronization frequency to avoid interruption may lead to ambiguity in the extracted phase, failing to meet the requirements of high-precision interferometric measurements.

[0004] Furthermore, even if the inter-satellite synchronization system and the SAR system share a crystal oscillator, the initial phase of the system's local oscillator changes randomly (0~360°) each time it is powered on. After interferometry, a random fixed phase offset (i.e., the initial phase winding problem) will be generated, which makes it impossible to obtain accurate absolute elevation measurements. Summary of the Invention

[0005] To address the aforementioned problems, the purpose of this invention is to provide an interferometric SAR synchronization method that combines radar inter-satellite links with Ka-band link cross-correction, in order to solve the problems of interrupted imaging during synchronization, the contradiction between synchronization accuracy and image quality, and the impact of initial phase entanglement on absolute measurement accuracy in the prior art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention includes:

[0007] An interferometric SAR synchronization method combining radar inter-satellite links with Ka-band link cross-correction includes the following steps:

[0008] S1. Construct a dual-satellite interferometric SAR system operating in the X-band. The dual-satellite interferometric SAR system includes a primary satellite and a secondary satellite. Each satellite is equipped with an X-band inter-satellite measurement system and a Ka-band inter-satellite measurement system. The X-band inter-satellite measurement system and the Ka-band inter-satellite measurement system share the same reference frequency source with the SAR payload.

[0009] S2. During SAR payload operation, the following operations are performed synchronously: S2.1 Using the X-band inter-satellite measurement system, synchronization pulse signals are transmitted between the primary satellite and the auxiliary satellite at a first synchronization frequency, wherein the first synchronization frequency is set to not cause phase ambiguity and not significantly affect SAR image quality; S2.2 Using the Ka-band inter-satellite measurement system, synchronization carrier signals are transmitted between the primary satellite and the auxiliary satellite at a second synchronization frequency, wherein the second synchronization frequency is the same as the pulse repetition frequency (PRF) of the current SAR payload operation.

[0010] S3. Synchronously collect and transmit the following data: primary satellite SAR echo data and secondary satellite SAR echo data, primary and secondary satellite X-band synchronization signal data, and primary and secondary satellite Ka-band synchronization signal data.

[0011] S4. Based on the X-band synchronization signal data of the primary and secondary satellites obtained in S3, calculate the X-band inter-satellite synchronization compensation function. Based on the Ka-band synchronization signal data of the primary and secondary satellites obtained from S3, the Ka-band inter-satellite synchronization compensation function is calculated. ;

[0012] S5. Using the X-band inter-satellite synchronization compensation function obtained in S4 Ka-band inter-satellite synchronization compensation function obtained from S4 Initial phase correction is performed to obtain the corrected high-precision phase synchronization compensation function. ;

[0013] S6. High-precision phase synchronization compensation function obtained from S5 Phase compensation is performed on the secondary satellite SAR echo data obtained from S3 to obtain the compensated secondary satellite SAR echo data.

[0014] Preferably, in S5, the initial phase correction specifically involves: calculating the initial phase difference between the X-band compensation function and the Ka-band compensation function, and using this initial phase difference to adjust the Ka-band inter-satellite synchronization compensation function. Perform initial phase correction.

[0015] Preferably, the Ka-band inter-satellite measurement system includes an inter-satellite synchronization antenna, a low-noise amplifier, and an inter-satellite measurement synchronization processing terminal connected in series, as well as a waveguide network interconnected with the inter-satellite measurement synchronization processing terminal, and an inter-satellite synchronization high-performance antenna interconnected with the waveguide network; the inter-satellite measurement synchronization processing terminal includes a processing unit, a transceiver channel, and a radio frequency front-end connected in sequence, and a frequency source is also connected between the processing unit and the transceiver channel, the low-noise amplifier is connected in series with the processing unit, and the waveguide network is interconnected with the radio frequency front-end.

[0016] A computer-readable storage medium storing a computer program, which, when executed by a processor, implements the interferometric SAR synchronization method disclosed in this application, which combines radar inter-satellite links with Ka-band link cross-correction.

[0017] A computer program product includes a computer program / instructions that, when executed by a processor, implement the interferometric SAR synchronization method disclosed in this application, which combines radar inter-satellite links with Ka-band link cross-correction.

[0018] Compared with the prior art, the advantages of the present invention are:

[0019] (1) The interferometric SAR synchronization method of the present invention, which combines radar inter-satellite link with Ka-band link cross-correction, avoids the periodic interruption of SAR data acquisition by the traditional pulse synchronization scheme by using Ka-band continuous wave synchronization with the same frequency as PRF, solves the imaging interruption problem, eliminates paired echoes, and significantly improves SAR image quality.

[0020] (2) The interferometric SAR synchronization method of the present invention, which combines radar inter-satellite links with Ka-band link cross-correction, solves the initial phase winding problem through the same X-band low-frequency synchronization link, realizes accurate measurement and cancellation of the random initial phase of the system, and ensures the accuracy of absolute elevation measurement.

[0021] (3) The interferometric SAR synchronization method of the present invention, which combines radar inter-satellite links with Ka-band link cross-correction, provides dense phase sampling through high-frequency synchronization in the Ka-band. Combined with the initial phase reference of the X-band, a phase compensation function with both high accuracy and reliability is obtained through cross-correction, which greatly improves the coherence of the primary and secondary satellite images and the accuracy of interferometric measurement.

[0022] (4) The interferometric SAR synchronization method of the present invention, which combines radar inter-satellite links with Ka-band link cross-correction, can be extended to multi-satellite formation InSAR systems and has important value in fields such as high-precision topographic mapping, urban 3D modeling, geological disaster monitoring, and military reconnaissance. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0024] Figure 1 This is a block diagram of the dual-satellite Ka-band high-precision inter-satellite measurement subsystem in an embodiment of the present invention.

[0025] Figure 2This is a schematic diagram illustrating the principle of the synchronization method described in this invention, which combines radar inter-satellite links with Ka-band high-precision synchronization links for cross-correction.

[0026] Figure 3 This is a schematic diagram of the transmission timing of the X-band and Ka-band synchronization pulses in an embodiment of the present invention. Detailed Implementation

[0027] The invention is not limited to the specific embodiments described below. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of this invention. Unless otherwise specified, all components and devices in this invention utilize components and devices known in the prior art.

[0028] Example

[0029] This embodiment discloses an interferometric SAR synchronization method combining radar inter-satellite links with Ka-band link cross-correction, characterized by the following steps:

[0030] S1. Construct a dual-satellite interferometric SAR system, which includes a primary satellite and a secondary satellite. Each satellite is equipped with an X-band inter-satellite measurement system and a Ka-band inter-satellite measurement system. Both the X-band and Ka-band inter-satellite measurement systems share the same reference frequency source with the SAR payload.

[0031] like Figure 1 As shown, the Ka-band inter-satellite measurement system of this embodiment includes an inter-satellite synchronization antenna (including four high-frequency antennas and one low-frequency antenna), a low-noise amplifier, and an inter-satellite measurement synchronization processing terminal connected in series. It also includes a waveguide network interconnected with the inter-satellite measurement synchronization processing terminal and an inter-satellite synchronization high-performance antenna interconnected with the waveguide network. The inter-satellite measurement synchronization processing terminal includes a processing unit, a transceiver channel, and a radio frequency front-end connected in sequence. A frequency source is also connected between the processing unit and the transceiver channel. The low-noise amplifier is connected in series with the processing unit, and the waveguide network is interconnected with the radio frequency front-end.

[0032] In this embodiment, the X-band inter-satellite measurement system uses a synchronization signal generated by coupling from a SAR transmitter and a dedicated antenna for inter-satellite transmission and reception.

[0033] S2. During SAR payload operation, perform the following operations synchronously:

[0034] S2.1 Using the X-band inter-satellite measurement system, synchronization pulse signals are transmitted between the primary and secondary satellites at a first synchronization frequency. This first synchronization frequency is set to not cause phase ambiguity and not significantly affect SAR image quality. The synchronization pulse signal of the X-band inter-satellite measurement system is generated by coupling from the SAR payload transmitter, originates from the same source as the SAR transmitted signal, and is transmitted and received via the inter-satellite synchronization transmission antenna. (See attached...) Figure 3As shown in the upper part, satellites A and B alternately transmit synchronization pulses at a lower frequency, which is determined based on the stability of the binary frequency sources and the acceptable pulse loss rate.

[0035] S2.2 Using the Ka-band inter-satellite measurement system, synchronization carrier signals are transmitted between the primary and secondary satellites at a second synchronization frequency. The second synchronization frequency is the same as the pulse repetition frequency (PRF) of the current SAR payload. A complete Ka-band bidirectional synchronization is completed within one SAR pulse repetition cycle.

[0036] S3. Synchronously collect and transmit the following data: primary satellite SAR echo data and secondary satellite SAR echo data, primary and secondary satellite X-band synchronization signal data, and primary and secondary satellite Ka-band synchronization signal data.

[0037] S4. Based on the X-band synchronization signal data of the primary and secondary satellites obtained in S3, calculate the X-band inter-satellite synchronization compensation function. Based on the Ka-band synchronization signal data of the primary and secondary satellites obtained from S3, the Ka-band inter-satellite synchronization compensation function is calculated. ;

[0038] The primary star is imaged using a three-calibration signal (a known technique) to obtain a composite image of the primary star. Then, the synchronization data is processed separately.

[0039] For a Ka-band link, taking the signal transmitted by satellite A and received by satellite B as an example, a signal model is established. Let the signal transmitted by satellite A at time t have a spatial time delay. Afterwards, B-star at t+ It receives and demodulates data in real time.

[0040] Received signal phase:

[0041] (1)

[0042] in, For the load frequency, Add phase to the transmission channel. For the initial phase, For phase noise, Add phase to the receive channel. The phase difference is added to the antenna, where A represents the relevant parameters of satellite A, and B represents the relevant parameters of satellite B.

[0043] Local oscillator phase at echo arrival time:

[0044] (2)

[0045] Demodulation phase It can be represented as:

[0046] (3)

[0047] in, For the initial phase, Add phase to the transmit and receive channels. Add a phase difference to the antenna. For phase noise, The load frequency.

[0048] Similarly, the demodulation phase transmitted by satellite B and received by satellite A can be obtained. .

[0049] By eliminating common error terms (such as partial channel and antenna errors) through bidirectional measurements, the Ka-band inter-satellite synchronization compensation function reflecting the relative phase drift between the two satellites can be extracted. As shown in equation (4). Similarly, by processing the X-band bidirectional synchronization data, the X-band inter-satellite synchronization compensation function is obtained. , as in equation (5).

[0050] (4)

[0051] (5)

[0052] For Ka-link frequencies, Add phase to the Ka-link transmit channel. This is the initial phase of the Ka link. For Ka-link phase noise, Add phase to the Ka link receive channel. Add a phase difference to the Ka-link antenna.

[0053] For SAR payload frequency, Add phase to the SAR payload transmission channel. The initial phase of the SAR payload. For SAR payload phase noise, Add phase to the SAR payload receiving channel. Add a phase difference to the radar inter-satellite link antenna.

[0054] S5. Using the X-band inter-satellite synchronization compensation function obtained in S4 Ka-band inter-satellite synchronization compensation function obtained from S4 Initial phase correction is performed to obtain the corrected high-precision phase synchronization compensation function. ;

[0055] Since the X-band synchronization system and the SAR payload are completely from the same source, their compensation function The initial phase error term included ( ) and the initial phase error of the SAR system itself ( - (Cancellation can be achieved during interference processing), therefore It can be used directly to eliminate initial phase winding.

[0056] However, the X-band has a low synchronization frequency and sparse time sampling. The Ka-band has a high synchronization frequency and dense sampling, and its accuracy potential is higher, but its independent system has an unknown initial phase that differs from that of the SAR system.

[0057] Therefore, cross-correction is performed: calculation and The phase difference at the initial moment or a certain reference moment is used to perform initial phase calibration on the Ka-band compensation function, resulting in a corrected high-precision phase synchronization compensation function. This function inherits the advantages of high sampling rate and high precision of the Ka band, and eliminates initial phase uncertainty through the X band reference.

[0058] S6. High-precision phase synchronization compensation function obtained from S5 Phase compensation is performed on the secondary satellite SAR echo data obtained from S3 to obtain compensated secondary satellite SAR echo data, so that the primary satellite SAR echo data and the compensated secondary satellite SAR echo data are accurately phase synchronized.

[0059] This embodiment performs imaging processing on the compensated SAR echo data of the secondary star to obtain a phase-synchronized composite image of the secondary star. At this point, the primary star image and the secondary star image have high phase coherence, and can be directly subjected to interferometry to generate a high-precision interferogram for elevation inversion or deformation monitoring.

[0060] This embodiment also discloses a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, it implements the interferometric SAR synchronization method of radar inter-satellite link combined with Ka-band link cross-correction disclosed in this invention.

[0061] This embodiment also discloses a computer program product, including a computer program / instruction, which, when executed by a processor, implements the interferometric SAR synchronization method of radar inter-satellite link combined with Ka-band link cross-correction disclosed in this invention.

[0062] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0063] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0064] Furthermore, the various implementation methods disclosed in this solution can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content invented by this disclosure.

Claims

1. An interferometric SAR synchronization method combining radar inter-satellite links with Ka-band link cross-correction, characterized in that, Includes the following steps: S1. Construct a dual-satellite interferometric SAR system operating in the X-band. The dual-satellite interferometric SAR system includes a primary satellite and a secondary satellite. Each satellite is equipped with an X-band inter-satellite measurement system and a Ka-band inter-satellite measurement system. Both the X-band inter-satellite measurement system and the Ka-band inter-satellite measurement system share the same reference frequency source with the SAR payload; S2. During SAR payload operation, perform the following operations synchronously: S2.1 Using the X-band inter-satellite measurement system, synchronization pulse signals are transmitted between the primary satellite and the auxiliary satellite at a first synchronization frequency. The first synchronization frequency is set to not cause phase ambiguity and not significantly affect the SAR image quality. S2.2 Using the Ka-band inter-satellite measurement system, synchronization carrier signals are transmitted between the primary satellite and the auxiliary satellite at a second synchronization frequency, which is the same as the pulse repetition frequency (PRF) of the current SAR payload. S3. Synchronously collect and transmit the following data: primary satellite SAR echo data and secondary satellite SAR echo data, primary and secondary satellite X-band synchronization signal data, and primary and secondary satellite Ka-band synchronization signal data. S4. Based on the X-band synchronization signal data of the primary and secondary satellites obtained in S3, calculate the X-band inter-satellite synchronization compensation function. ; Based on the Ka-band synchronization signal data of the primary and secondary satellites obtained from S3, the Ka-band inter-satellite synchronization compensation function is calculated. ; S5. Using the X-band inter-satellite synchronization compensation function obtained in S4 Ka-band inter-satellite synchronization compensation function obtained from S4 Initial phase correction is performed to obtain the corrected high-precision phase synchronization compensation function. ; S6. High-precision phase synchronization compensation function obtained from S5 Phase compensation is performed on the secondary satellite SAR echo data obtained from S3 to obtain the compensated secondary satellite SAR echo data.

2. The interferometric SAR synchronization method combining radar inter-satellite links with Ka-band link cross-correction as described in claim 1, characterized in that, In S5, the initial phase correction specifically involves: calculating the initial phase difference between the X-band compensation function and the Ka-band compensation function, and using this initial phase difference to adjust the Ka-band inter-satellite synchronization compensation function. Perform initial phase correction.

3. The interferometric SAR synchronization method combining radar inter-satellite links with Ka-band link cross-correction as described in any one of claims 1-2, characterized in that, The Ka-band inter-satellite measurement system includes an inter-satellite synchronization antenna, a low-noise amplifier, and an inter-satellite measurement synchronization processing terminal connected in series. It also includes a waveguide network interconnected with the inter-satellite measurement synchronization processing terminal and an inter-satellite synchronization high-performance antenna interconnected with the waveguide network. The inter-satellite measurement synchronization processing terminal includes a processing unit, a transceiver channel, and a radio frequency front-end that are interconnected in sequence. A frequency source is also connected between the processing unit and the transceiver channel. The low-noise amplifier is connected in series with the processing unit, and the waveguide network is interconnected with the radio frequency front-end.

4. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the interferometric SAR synchronization method of radar inter-satellite links combined with Ka-band link cross-correction as described in any one of claims 1-3.

5. A computer program product, characterized in that, Includes a computer program / instruction, which, when executed by a processor, implements the interferometric SAR synchronization method of radar inter-satellite link combined with Ka-band link cross-correction as described in any one of claims 1-3.

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