Real-time synchronization method of direct wave and echo for GNSS-InSAR deformation monitoring

Abstract

The present invention discloses a direct wave-echo real-time synchronization method for GNSS-InSAR deformation monitoring. The present invention directly obtains the Doppler frequency and CA code starting position through direct wave channel capture and tracking processing, directly calculates the echo compensation phase through a corresponding algorithm, and synchronously acts on the echo channel to perform compensation synchronization processing on the echo signal. The method does not require the storage of direct waves and echo signals. The direct waves and echo signals only need to undergo pulse compression processing once, which saves resources and can achieve real-time synchronous processing of direct waves and echoes. The GNSS-InSAR system echo signal BP imaging requires less time, has high processing efficiency, and is hardware-implementable. It can ensure that GNSS-InSAR system deformation monitoring can be carried out in a timely, efficient, and complete manner.

Description

Technical Field

[0001] The present invention relates to the field of radar and satellite navigation technology, and in particular to a direct wave-echo real-time synchronization method applied to GNSS-InSAR deformation monitoring. Background Art

[0002] Monitoring geological hazards primarily focuses on monitoring surface displacement and deformation. Obtaining three-dimensional surface deformation is crucial for monitoring and early warning. Existing differential navigation receivers can measure three-dimensional deformation with high precision. These receivers are deployed at monitoring points, receiving direct satellite signals and enabling deformation monitoring. However, since they only measure deformation at discrete points in space, this can lead to underreporting.

[0003] With the official launch of the BeiDou-3 system, my country became the third country to independently own a global satellite navigation system. The BeiDou system, with its unique constellation configuration, is more capable of achieving continuous spatial deformation monitoring based on scene reflection signals than systems like the Global Positioning System (GPS). Compared to traditional differential navigation receivers, BeiDou receivers for surface scene deformation measurement can achieve continuous spatial deformation monitoring of surface scenes, eliminating missed detections and significantly enhancing geological disaster monitoring and early warning capabilities. BeiDou-based surface scene deformation monitoring involves deploying receivers outside the monitoring area to simultaneously receive direct and reflected satellite signals. Deformation at any location within the monitoring area will result in changes in the reflected signal, enabling the monitoring of surface scene deformation.

[0004] Because the transmitting and receiving sources in a GNSS-InBSAR system are located on separate, moving platforms, frequency source deviations between the platforms can cause errors in time, frequency, and phase synchronization between the direct wave and the echo, leading to low resolution in BP imaging of three Beidou satellite frequency points. To address these time-frequency and phase synchronization errors, a method for echo time-frequency and phase synchronization based on the direct wave is proposed. Existing echo signal synchronization methods collect the direct wave and echo signals using a data logger and perform synchronization processing in MATLAB. The direct wave and echo require two pulse compression processes: the first pulse compression process obtains the starting position for echo reading. A second pulse compression process reads the direct wave and echo data from this starting position, then performs a second pulse compression process to obtain the echo compensation phase for synchronization compensation. Existing echo synchronization methods require storing the direct wave and echo data for post-processing, which is time-consuming, inefficient, and impractical in engineering. Summary of the Invention

[0005] In view of this, the present invention provides a direct wave-echo real-time synchronization method applied to GNSS-InSAR deformation monitoring, which only requires one pulse compression processing to achieve direct wave-echo real-time synchronization processing, requires few resources, is highly efficient, and is feasible in engineering.

[0006] The present invention provides a direct wave-echo real-time synchronization method for GNSS-InSAR deformation monitoring, comprising:

[0007] Step 1: Convert the direct wave and echo RF signals into intermediate frequency analog signals, and use the same clock to perform ADC sampling on the direct wave and echo intermediate frequency analog signals to convert them into digital signals;

[0008] The direct wave is captured and tracked to obtain the CA code phase and the starting position of the CA code. Starting from the starting position of the CA code in each cycle, the direct wave CA code and the echo are synchronously read to achieve time synchronization between the direct wave and the echo.

[0009] Step 2: Use the carrier loop of the direct wave channel to obtain the carrier Doppler frequency, and then synchronously strip the carrier of the direct wave and the echo to obtain the baseband signals of the direct wave and the echo signal, thereby achieving frequency synchronization and partial phase synchronization of the direct wave and the echo;

[0010] Step 3: Correlate the recovered local CA code with the direct wave baseband signal, despread the direct wave signal, and accumulate the despread signals to obtain the direct wave IQ signal after correlation accumulation. The phase compensation angle of the direct wave IQ signal after correlation accumulation is solved using the CORDIC algorithm.

[0011] Step 4: Synchronously read the echo signal and the recovered local CA code to perform pulse compression processing, and synchronously compensate the phase compensation angle obtained in step 3 to the pulse compression result of each PRT of the echo signal to achieve phase synchronization.

[0012] Preferably, in step 1, a PMF-FFT fast capture algorithm is used to achieve fast capture of the direct wave signal; and a 2FLL+3PLL, 2DLL loop tracking algorithm is used to achieve stable tracking of the direct wave signal.

[0013] Preferably, in step 3, the phase compensation angle is:

[0014] (1)

[0015] Qsum and Isum are the Q and I signals after correlation accumulation respectively.

[0016] The better one is to use Xilinx Cordic IP core of FPGA, the input is the Q and I signals after correlation accumulation, and the output is quantized The radian value is quantized to 11 bits. After the data is stored, pulse compression is performed on the echo signal in Matlab to extract the pulse compression peak point phase as the direct wave compensation phase.

[0017] Preferably, in step 4, in FPGA, based on the output of Xilinx Cordic IP core Calculate the sin and cos values ​​of the radian value and store the calculated sin and cos values ​​in RAM; then use The value of is used as the address to query the lookup table where the sin and cos values ​​are stored. The quantization value of the output of sin and cos is 8 bits. The queried sin and cos values ​​are conjugate multiplied by the pulse compression result of each PRT of the echo. The calculation formula is as follows

[0018] (2)

[0019] (3)

[0020] I and Q are the real and imaginary parts of the compressed 1ms echo pulse, respectively.

[0021] The present invention also provides a GNSS-InBSAR system imaging method, which uses the above-mentioned direct wave-echo real-time synchronization method to synchronize the time, frequency and phase of the direct wave sent by the transmitter and the echo signal received by the receiver; based on the synchronized echo signal pulse compression result and the direct wave solution, the satellite position, direct wave and echo antenna position, Beidou time, and satellite elevation and azimuth are obtained to perform dual-base BP imaging.

[0022] The imaging method specifically includes:

[0023] Step 1: Set the imaging grid area, the number of grids is , corresponding to the east-west and north-south sizes of the scene respectively;

[0024] Step 2: For each PRT moment, calculate The bistatic slant distance for each grid point of the grid is:

[0025]

[0026] in, is the PRT number, is the satellite position of the kth PRT, for The location of the coordinate point, is the echo antenna position;

[0027] Constructing phase compensation factors ; That is, La cycles are performed and the processing results are output for each PRT The phase compensation factor matrix of the point;

[0028] Step 3: Synchronize the time, frequency, and phase of the direct wave and echo signals using the direct wave-echo real-time synchronization method described above;

[0029] Step 4: For each PRT of the echo data after time, frequency, and phase synchronization, perform 8-fold interpolation processing on the range-dimensional data sequence. Specifically, extract the range dimension data of La PRTs one by one (perform L For loops), with each line length being Lr points; perform Lr-point FFT on the Lr-point vector, add Nr×7 zeros, and perform 8Nr-point IFFT processing to obtain a La×8Lr-point pulse pressure data matrix;

[0030] Step 5: For each PRT moment, find each The distance to the index position corresponding to the imaging grid point is Phase compensation factor Multiply; perform La cycles, and output each cycle Imaging data of size;

[0031] Step 6: For each PRT moment, The imaging data is added, i.e. La accumulation is performed to obtain the final Imaging results.

[0032] Beneficial effects:

[0033] The present invention directly acquires the Doppler frequency and CA code starting position through direct wave channel capture and tracking processing. Using a corresponding algorithm, the echo compensation phase is directly calculated and synchronously applied to the echo channel to perform compensation and synchronous processing on the echo signal. This method does not require storage of the direct wave and echo signals; instead, the direct wave and echo signals only require a single pulse compression process, saving resources and enabling real-time synchronous processing of the direct wave and echo. GNSS-InSAR system echo signal BP imaging requires minimal time, offers high processing efficiency, and is hardware-implementable. This ensures timely, efficient, and comprehensive deformation monitoring of the GNSS-InSAR system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Design schematics for RF circuits;

[0035] Figure 2 Schematic diagram for quick capture;

[0036] Figure 3 This is the principle block diagram of loop tracking;

[0037] Figure 4 This is the principle block diagram of the time-frequency synchronization of the direct wave and the echo signal;

[0038] Figure 5This is a block diagram of the principle of direct wave-echo signal phase synchronization;

[0039] Figure 6 This is the compensation phase comparison result diagram of the engineering prototype and the principle prototype;

[0040] Figure 7 This is the comparison result of 1s echo pulse compression amplitude and phase between the engineering prototype and the principle prototype;

[0041] Figure 8 This is the on-site deployment diagram of the engineering prototype in Chongqing;

[0042] Figure 9 The three-frequency imaging result diagram of the same Beidou satellite using the method of the present invention is shown in FIG; wherein, (a) B2a frequency point; (b) B2b frequency point; (c) B3 frequency point;

[0043] Figure 10 A comparison diagram of the imaging results using the method of the present invention and the optical geographic image;

[0044] Figure 11 Design a flow chart for BP imaging processing. DETAILED DESCRIPTION

[0045] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0046] The present invention provides a real-time direct wave-echo synchronization method for GNSS-InSAR deformation monitoring, comprising three components: time synchronization, frequency synchronization, and phase synchronization. This embodiment is implemented on an FPGA hardware platform. The method rapidly captures, loops, and performs position resolution on the direct wave signal to obtain the starting position of the direct wave signal's CA code period. The direct wave and echo signals are then synchronously read from this position. A relatively accurate Doppler frequency is obtained by processing the direct wave. This Doppler frequency is used to synchronously strip the carriers of the direct wave and echo received signals. During the direct wave processing, the echo compensation phase is calculated using a cordic algorithm and synchronously compensated for within the pulse compression result of each PRT of the echo. This method can obtain the pulse compression result after echo synchronization processing, and azimuth accumulation is performed to obtain a BP image. The Beidou three-frequency BP image obtained using this method has high resolution and a large number of strong feature points. The three-frequency imaging results for the same satellite are highly consistent in both contour and azimuth, facilitating image fusion and improving deformation monitoring accuracy.

[0047] The specific steps include:

[0048] S1. The RF module converts the direct wave and echo RF signals into intermediate frequency signals, samples them into digital signals through the ADC, and synchronously collects and reads the direct wave and echo digital signals to achieve direct wave-echo time synchronization. The specific steps include:

[0049] S11. The receiver receives the Beidou satellite signal and the echo signal reflected by the monitoring scene through the direct wave antenna and the echo antenna, and sends them to the RF module. The RF receiving channel uses a low noise amplifier 1 + SAW filter + 1-to-3 power splitter + low noise amplifier 2 + SAW filter + mixer structure circuit to convert the Beidou direct wave and echo RF signal into an intermediate frequency analog signal. The RF circuit design schematic diagram is shown below. Figure 1 As shown, it outputs the RF clock.

[0050] The direct wave and echo intermediate frequency analog signals are down-converted and sampled by the ADC under the control of the same RF clock, becoming digital signals. This enables the synchronous acquisition of the direct wave and echo signals. At the same time, the output ADC clock serves as the working clock for FPGA processing, ensuring the time synchronization of the direct wave and echo data.

[0051] S12. Rapid capture of direct wave signals is achieved through PMF-FFT rapid capture algorithm. The principle block diagram of FPGA for rapid capture is as follows: Figure 2 As shown. The 2FLL+3PLL and 2DLL loop tracking algorithm is used to achieve stable tracking of the direct wave signal. The principle of the tracking algorithm is shown in the figure. Figure 3 shown.

[0052] S13. The code phase obtained by stable tracking of the direct wave channel code loop is used to periodically divide the echo channel data. The starting position of the CA code 1ms can be obtained through the direct wave tracking loop, and the starting position of the CA code obtained is relatively accurate. Starting from the starting position of the CA code in each period, the direct wave CA code and the echo are read synchronously to achieve time synchronization of the direct wave and the echo.

[0053] S2. On the basis of achieving time synchronization, the Doppler frequency obtained from the direct wave channel is used to perform frequency synchronization processing on the echo. The specific steps are as follows:

[0054] After stably tracking the direct wave signal, a more accurate satellite Doppler frequency can be obtained through the carrier loop. The direct wave signal and the echo signal are synchronously orthogonally down-converted using this Doppler frequency, and the carrier waves in the direct wave signal and the echo signal are stripped off to obtain the baseband signals of the direct wave and the echo that are only modulated by CA code spread spectrum.

[0055] The Doppler frequency synchronization obtained by the carrier loop of the direct wave channel is used to perform carrier stripping on the direct wave signal and the echo signal, achieving frequency synchronization of the direct wave and echo signals, and also achieving partial phase synchronization of the direct wave and echo signals. This is because during the carrier stripping process, the locally generated sine and cosine signals both contain the influence of Doppler, while also maintaining the internal phase consistent with the input signal, that is, partial phase synchronization includes the synchronization of the ionosphere, troposphere, and noise phases. The principle block diagram of the direct wave-echo signal to achieve time-frequency synchronization is shown in the figure below. Figure 4 shown.

[0056] S3. Although carrier stripping has completed some phase synchronization, the phase accuracy of the phase-locked loop itself also introduces additional phase errors, and carrier stripping cannot eliminate the impact of message jumps. Therefore, it is necessary to perform phase compensation on each PRT in the acquired effective truncated pulse pressure data to eliminate the impact of phase errors, that is, to achieve phase synchronization. The principle block diagram of phase synchronization is shown in the figure below. Figure 5 As shown, specifically:

[0057] S31. Perform pulse compression processing on each PRT of the echo signal after time and frequency synchronization is completed, and use the direct wave CA signal as the matching signal of the echo signal to perform pulse compression processing on the echo signal.

[0058] Specifically, the direct wave signal and the echo signal are down-converted to baseband signals through frequency synchronization, and the echo signal and the locally recovered CA code are read through time synchronization to perform 1ms pulse compression processing.

[0059] S32. In the direct wave channel, carrier loop tracking is used to obtain a relatively accurate carrier signal. The locally recovered carrier signal is then used with the received direct wave signal for orthogonal down-conversion, removing the carrier and obtaining the direct wave baseband signal. Code loop tracking is used to obtain a local CA code that is phase-aligned with the direct wave CA code. The recovered local CA code is correlated with the direct wave baseband signal to despread the direct wave signal. The despread signal is then accumulated for 1 ms to obtain the correlated and accumulated direct wave IQ signal.

[0060] S33. The phase compensation angle of the IQ signal after correlation accumulation is solved by the CORDIC algorithm. The phase is the phase difference between the calculated echo and direct wave channels caused by atmospheric error, tropospheric error, etc. The calculation formula of this angle is:

[0061] (1)

[0062] Qsum and Isum are the Q and I signals after correlation accumulation respectively.

[0063] In this embodiment, the Xilinx Cordic IP core is directly called in the FPGA to implement the IQ branch accumulation and the output is the quantized The radian value is quantized to 11 bits. The compensation phase is solved by the existing principle prototype method for solving the compensation phase using the data actually collected by the data sampler, that is, after the data is stored, the pulse compression is performed on the direct wave and echo signal in Matlab to extract the pulse compression peak point phase as the direct wave compensation phase. For the same data, the compensation phase obtained by the engineering prototype through the direct wave-echo real-time processing method proposed in the present invention is compared with the compensation phase obtained by the principle prototype. The phase comparison results are shown as follows: Figure 6 As shown in the figure, the error between the two is within 0.2°, which meets the phase accuracy requirement.

[0064] S34. Synchronously compensate the direct wave peak phase calculated by the direct wave channel into the echo pulse compression result of the corresponding PRT, that is, compensate the phase angle calculated in step S33 into the echo pulse compression result.

[0065] In FPGA, according to the above calculation The radian value is used to calculate the sin and cos values. Here, the calculated sin and cos values ​​are first stored in RAM. The value of is used as the address to query the lookup table where sin and cos are stored. The quantization value of the output of sin and cos is 8 bits. The sine and cosine values ​​of the phase angle are obtained and conjugate multiplied with the pulse compression result of each PRT of the echo. The calculation formula is as follows

[0066] (2)

[0067] (3)

[0068] I and Q are the real and imaginary parts of the compressed 1ms echo pulse, respectively.

[0069] S35. Perform 1000PRT synthesis on 1000 1PRT echo pulse compression results to obtain the echo 1s pulse compression result.

[0070] The 1000 consecutive compensated PRT pulse compression results are coherently accumulated to synthesize the 1s echo pulse compression result.

[0071] The amplitude and phase comparison results of the echo pulse compression results of the principle prototype after phase compensation and the engineering prototype after phase compensation using the phase compensation method proposed in this invention are shown in the figure. Figure 7 The two signals are consistent in amplitude and have a phase difference within 0.2°, meeting the system monitoring requirements.

[0072] S4. The 1s echo pulse compression result and the satellite position and antenna position calculated by the direct wave channel are packaged according to the specified data protocol and uploaded through the network port according to the TCP protocol.

[0073] The echo channel outputs the 1s pulse compression result, the direct wave channel outputs the calculated satellite position and direct wave and echo antenna positions, and also outputs the calculated Beidou time and satellite elevation and azimuth angles. All data are packaged according to the agreed data protocol and the packaged data packets are uploaded through the gigabit network port according to the TCP protocol.

[0074] S5. Perform bistatic BP imaging on the uploaded pulse compression data and position data. The BP imaging processing design flow chart is as follows: Figure 11 As shown, the specific steps include:

[0075] Step 51: Convert the satellite positions and direct wave and echo antenna positions in the uploaded CGCS2000 coordinate system into the Northeast Sky coordinate system and divide the monitoring area into grids. The number of grids is , corresponding to the east-west and north-south sizes of the scene respectively;

[0076] Step 52, for each PRT moment, calculate The bistatic slant distance for each grid point of the grid is:

[0077]

[0078] in, is the PRT number, is the satellite position of the kth PRT, for The location of the coordinate point, is the echo antenna position;

[0079] Constructing phase compensation factors ; That is, La cycles are performed and the processing results are output for each PRT The phase compensation factor matrix of the point;

[0080] Step 53: For each PRT of the uploaded time, frequency, and phase synchronized echo data, perform an 8-fold interpolation process on the range-dimensional data sequence. Specifically, extract the range dimension data of La PRTs one by one (perform L For loops), with each line being Lr points long. Perform an Lr-point FFT on the Lr-point vector, add Nr×7 zeros, and perform an 8Nr-point IFFT process to obtain a La×8Lr-point pulse pressure data matrix.

[0081] Step 54: For each PRT moment, find each The distance to the index position corresponding to the imaging grid point is Phase compensation factor Multiply; perform La cycles, and output each cycle Imaging data of size;

[0082] Step 55: For each PRT moment, The imaging data is added, i.e. La accumulation is performed to obtain the final Imaging results.

[0083] The three-frequency imaging results were compared with the real optical physical images to verify the correctness of the three-frequency imaging results. The strong feature points were extracted to verify the validity of the imaging results.

[0084] At this point, all steps are completed.

[0085] Next, an implementation example is given based on the actual collected data.

[0086] This example is to deploy an engineering prototype in Jiuxianping, Yunyang, Chongqing. The engineering prototype adopts the direct wave-echo real-time synchronization method proposed in this invention for synchronization processing. Figure 8 As shown in the figure. Using the coordinates of the engineering prototype and the orientation of the experimental site, the imaging resolution and elevation angle of the corresponding satellite at each moment can be calculated. This allows us to select satellites that meet the resolution requirements. These satellites are then arranged and combined according to time to obtain the final experimental design results.

[0087] The satellites designed for the experiment were used to collect high-frequency data, with 12 groups of data collected every day for seven days. The imaging results of the three-frequency points of the same satellite are as follows: Figure 9 As shown in the figure, it can be seen that the contours of the multi-star imaging results are basically consistent, and the positions of some strong points are different due to different illumination angles, which shows the effectiveness of the imaging results.

[0088] Extract strong feature points, more than 400 can be extracted to meet the system requirements, verifying that the imaging result is correctly focused. The imaging result is consistent with the contour of the corresponding position of the optical geographic image, verifying that the image focus position is correct. The optical geographic image comparison chart is as follows Figure 10 As shown, Figure 10 In the image, the blue layer represents the imaging result, while the layer below the blue area represents the optical image. It can be seen that the contours and orientation of the imaging result are consistent with the actual geographical features. This demonstrates that the synchronized BP imaging results using the proposed method are accurate and effective. By extracting the interferometric phase using strong feature points and performing subsequent deformation inversion processing, the resulting deformation monitoring accuracy is shown in Table 1, enabling millimeter-level deformation monitoring.

[0089] Table 1

[0090]

[0091] According to the deformation measurement accuracy, it can also be explained that the phase of the echo imaging result after synchronous processing using the method proposed by the present invention is stable.

[0092] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A direct wave-echo real-time synchronization method for GNSS-InSAR deformation monitoring, characterized in that: include: Step 1: Convert the direct wave and echo RF signals into intermediate frequency analog signals, and use the same clock to perform ADC sampling on the direct wave and echo intermediate frequency analog signals to convert them into digital signals; The direct wave is captured and tracked to obtain the CA code phase and the starting position of the CA code. Starting from the starting position of the CA code in each cycle, the direct wave CA code and the echo are synchronously read to achieve time synchronization between the direct wave and the echo. Step 2: Use the carrier loop of the direct wave channel to obtain the carrier Doppler frequency, and then synchronously strip the carrier of the direct wave and the echo to obtain the baseband signals of the direct wave and the echo signal, thereby achieving frequency synchronization and partial phase synchronization of the direct wave and the echo; Step 3: Correlate the recovered local CA code with the direct wave baseband signal, despread the direct wave signal, and accumulate the despread signal to obtain a direct wave IQ signal after correlation accumulation. The phase compensation angle of the direct wave IQ signal after correlation accumulation is solved using the CORDIC algorithm. The phase compensation angle is: （1） Qsum and Isum are the Q and I signals after correlation accumulation respectively; Adopting Xilinx Cordic IP core of FPGA, the input is Q and I signals after correlation accumulation, and the output is quantized The radian value is quantized to 11 bits. After storing the data, the pulse compression is performed on the echo signal in Matlab to extract the pulse compression peak point phase as the direct wave compensation phase. Step 4: Synchronously read the echo signal and the recovered local CA code to perform pulse compression processing, and synchronously compensate the phase compensation angle obtained in step 3 to the pulse compression result of each PRT of the echo signal to achieve phase synchronization; In FPGA, based on Xilinx Cordic IP core output Calculate the sin and cos values ​​of the radian value and store the calculated sin and cos values ​​in RAM; then use The value of is used as the address to query the lookup table where the sin and cos values ​​are stored. The quantization value of the output of sin and cos is 8 bits. The queried sin and cos values ​​are conjugate multiplied by the pulse compression result of each PRT of the echo. The calculation formula is as follows （2） （3） I and Q are the real and imaginary parts of the compressed 1ms echo pulse, respectively.

2. The method according to claim 1, wherein In step 1, the PMF-FFT fast capture algorithm is used to achieve fast capture of the direct wave signal; and the 2FLL+3PLL and 2DLL loop tracking algorithms are used to achieve stable tracking of the direct wave signal.

3. A GNSS-InBSAR system imaging method, characterized in that: The direct wave-echo real-time synchronization method as described in any one of claims 1 to 2 is used to synchronize the time, frequency and phase of the direct wave sent by the transmitter and the echo signal received by the receiver; based on the synchronized echo signal pulse compression result and the direct wave solution, the satellite position, direct wave and echo antenna position, Beidou time, and satellite elevation and azimuth are obtained to perform bistatic BP imaging.

4. The method according to claim 3, wherein Specifically include: Step 1: Set the imaging grid area, the number of grids is , corresponding to the east-west and north-south sizes of the scene respectively; Step 2: For each PRT moment, calculate The bistatic slant distance for each grid point of the grid is: in, is the PRT number, is the satellite position of the kth PRT, for The location of the coordinate point, is the echo antenna position; Constructing phase compensation factors ; That is, La cycles are performed and the processing results are output for each PRT The phase compensation factor matrix of the point; Step 3, synchronizing the time, frequency, and phase of the direct wave and echo signals using the direct wave-echo real-time synchronization method as described in any one of claims 1 to 2; Step 4: For each PRT of the echo data after time, frequency, and phase synchronization, perform 8-fold interpolation processing on the range-dimensional data sequence. Specifically, extract the range dimension data of La PRTs one by one and perform L For loops, with each line of length Lr points; perform Lr-point FFT on the Lr-point vector, fill Nr×7 zeros, and perform 8Nr-point IFFT processing to obtain a La×8Lr-point pulse pressure data matrix; Step 5: For each PRT moment, find each The distance to the index position corresponding to the imaging grid point is Phase compensation factor Multiply; perform La cycles, and output each cycle Imaging data of size; Step 6: For each PRT moment, The imaging data is added, i.e. La accumulation is performed to obtain the final Imaging results.

Images