A low, slow and small target detection method based on stepped clutter cancellation

Abstract

The application discloses a low, slow and small target detection method based on step-by-step ground clutter cancellation, and relates to the technical field of radar detection.The application establishes a node coordinate system and generates distance-Doppler two-dimensional data; then, current frame data and reference frame data are obtained, and the current frame data is subjected to ground clutter cancellation processing; then, a guide vector is calculated and generated, and the value is used for inter-element beam forming on the data after ground clutter cancellation, so that synthesized distance-Doppler data is obtained; target information and reference frame target information are obtained according to the synthesized distance-Doppler data, the target information is subjected to cancellation processing according to the reference frame target information, target angle measurement is further performed, and target positioning results are output.The application improves the detection probability of a radar for a low, slow and small target under the influence of a ground clutter signal, reduces the loss of a real target signal in the process of ground clutter cancellation processing, and improves the accuracy of ground clutter cancellation.

Description

Technical Field

[0001] This invention relates to the field of radar detection technology, and in particular to a method for detecting low-speed, small targets based on step-by-step ground clutter cancellation. Background Technology

[0002] Low-altitude, slow-moving, and small targets are characterized by their low flight altitude, slow speed, and small effective radar cross-section. Common examples include multi-rotor UAVs, fixed-wing UAVs, UAV swarms, and tethered balloons. These targets are easy to operate, carry, and difficult to detect and warn of, posing a serious threat to security operations in key areas and regions. Due to their unique characteristics, low-altitude, slow-moving, and small targets are significantly affected by ground clutter, making it difficult for radar to accurately locate them within this clutter. Therefore, a method for detecting low-altitude, slow-moving, and small targets that can eliminate ground clutter is urgently needed. Summary of the Invention

[0003] In view of this, this invention proposes a method for detecting low-speed, small targets based on stepped ground clutter cancellation. This method eliminates ground clutter signals, improving the radar's detection probability of low-speed, small targets under the influence of ground clutter signals. By employing a stepped reference frame selection rule, the loss of the real target signal during ground clutter cancellation is reduced, thus improving the accuracy of ground clutter cancellation.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for detecting small, slow-moving targets based on step-by-step ground clutter cancellation includes the following steps:

[0006] Step 1: Establish a node coordinate system for the detection radar to obtain the array element coordinates of the detection radar. Utilize the echo signals received by the detection radar from low, slow, and small targets to generate fast-time and slow-time two-dimensional data.

[0007] Step 2: Perform distance and velocity measurement on the fast-time-slow-time two-dimensional data obtained in Step 1 to generate distance-Doppler two-dimensional data, and store the data to obtain the current frame data;

[0008] Step 3: Set the reference frame data selection rules, selectively store the range-Doppler data obtained in Step 2, and obtain multiple sets of reference frame data;

[0009] Step 4: Perform ground clutter cancellation processing on the current frame data;

[0010] Step 5: Calculate and generate the steering vector, and use this value to perform inter-element beamforming on the data after ground clutter cancellation to obtain the synthesized range-Doppler data;

[0011] Step 6: Complete the threshold detection of the synthesized range-Doppler data in Step 5 to obtain the synthesized target information;

[0012] Step 7: Generate and store multiple sets of reference frame target information;

[0013] Step 8: Perform reference frame target information removal processing on the target information in Step 6;

[0014] Step 9: Based on the target information after the reference frame target information removal process, complete the target angle measurement and output the positioning result of the low, slow and small target.

[0015] Furthermore, the specific method of step 1 is as follows:

[0016] S11, establish the node coordinate system XYZ for the single-transmit, single-receive scenario of the detection radar, and further obtain the element coordinates (x, y, z) of the N array elements of the detection radar. n ,y n ,z n ), n = 1, 2, 3, ..., N;

[0017] S12, N array elements continuously perform spatial scanning and receive data. Each spatial scan consists of K wave positions. That is, each array element receives K frames of one-dimensional echo data after completing one spatial scan. The length of one frame of echo data is 1×PM, where P is the number of sampling points of the detection radar and M is the number of pulses of the detection radar.

[0018] S13, organize the echo data received by each array element during the current spatial domain scanning process to obtain K-frame P×M fast-time-slow-time two-dimensional data corresponding to each array element.

[0019] Furthermore, the specific method of step 2 is as follows:

[0020] S21, matched filtering and multi-pulse accumulation are performed on the K frames of P×M fast-time-slow-time two-dimensional data of N array elements respectively to realize target ranging and velocity measurement, and obtain N×K frames of range-Doppler two-dimensional data;

[0021] S22, allocate N sets of current frame data storage spaces, each set stores K-frame distance-Doppler two-dimensional data corresponding to one array element, denoted as the current frame data of the current array element. Use this storage space to store the N×K-frame distance-Doppler two-dimensional data obtained in S21, that is, the current frame data of N array elements; record the consecutive frame numbers for the K-frame distance-Doppler two-dimensional data obtained by each array element in the continuous spatial domain scanning.

[0022] After each N array elements perform a new spatial scan, the N sets of current frame data storage spaces are cleared, and the new N×K frame range-Doppler two-dimensional data are stored accordingly, resulting in new current frame data for N array elements.

[0023] Furthermore, the specific method of step 3 is as follows:

[0024] S31. For each array element, three sets of reference frame data storage spaces are allocated, each storing K frames of reference frame data. The initial value of the three sets of reference frame data storage spaces is 0. Initially, the K-frame range-Doppler two-dimensional data corresponding to the first spatial domain scan is recorded as a set of reference frame data and stored in the first set of reference frame data storage space. For each subsequent new set of reference frame data, it is stored sequentially in the three sets of reference frame data storage spaces. When all three sets of reference frame data storage spaces are full, the first set of reference frame data storage space is cleared, the second set of reference frame data is shifted to the first set of reference frame data storage space, the third set of reference frame data is shifted to the second set of reference frame data storage space, and the third set of reference frame data storage space is freed up to store new reference frame data.

[0025] S32, based on the frame number of the current frame data corresponding to each array element in the current frame data storage space, calculate the difference between the corresponding bit frame number and the latest set of reference frame data in the reference frame data storage space of the corresponding array element. If the difference between the corresponding bit frame numbers is pK, then record the current frame data as a new set of reference frame data and store it in the reference frame data storage space corresponding to the array element.

[0026] Furthermore, step 4 is specifically implemented as follows:

[0027] Based on the frame number of the current frame data corresponding to each array element in the current frame data storage space, calculate the difference between the corresponding bit frame number and the first group of reference frame data in the latest reference frame data storage space of the corresponding array element. If the difference between the corresponding bit frame numbers is greater than or equal to 2pK and less than 3pK, then subtract the corresponding bit of the current frame data corresponding to the array element from the first group of reference frame data in the latest reference frame data storage space of the array element, and record the result after subtraction as the K-frame ground clutter cancellation data corresponding to the array element.

[0028] Furthermore, step 5 is specifically implemented as follows:

[0029] S51, the wave position pointing coordinates (x, y, z) in the node coordinate system are calculated based on the received wave position pointing (azi, ele) of the echo signal. The specific calculation expression is: x = cos(azi)cos(ele), y = sin(ele), z = sin(azi)cos(ele); where azi is the azi angle of the echo signal, ele is the elevation angle of the echo signal, the elevation angle of the node coordinate system is defined as the angle between the echo signal and the XOZ plane, and the azi angle is defined as the angle between the projection of the echo signal on the XOZ plane and the X-axis;

[0030] S52, using the wave position pointing coordinates (x, y, z) and the coordinates of N array elements (x, y, z) n ,y n ,z n The guiding vectors corresponding to the N array elements are calculated, and the calculation expression is: Where λ is the wavelength of the echo signal;

[0031] S53, the guide vectors corresponding to the N array elements in 1 row and N columns are conjugately multiplied with the data after the N rows and K columns of ground clutter cancellation to complete the beamforming between array elements and obtain the K-frame P×M synthesized range-Doppler data.

[0032] Furthermore, step 6 is specifically implemented as follows:

[0033] S61, set the signal-to-noise ratio value for threshold detection, compare the P×M elements in the synthesized distance-Doppler data of each frame with the signal-to-noise ratio value, and record the elements that are greater than the signal-to-noise ratio value and their corresponding row number and column number;

[0034] S62, convert the row and column numbers recorded in S61 to obtain the distance and velocity information of the slow, small target. The conversion expression is:

[0035] Where row is the row number, col is the column number, c is the speed of light, and T is the column number. s The sampling interval of the detection radar is denoted by PRF, the pulse repetition frequency of the detection radar is denoted by range, the range is denoted by v, and the velocity of the low-speed, small target is denoted by v.

[0036] S63, allocate a target information storage space, which stores K-frame data; for the synthesized range-Doppler data of K-frame P×M, record all elements in each frame of synthesized range-Doppler data that are greater than the signal-to-noise ratio value, their corresponding row and column numbers, and the distance and velocity information of the corresponding low, slow and small targets as a frame of target information, thereby obtaining K-frame target information and storing it in the target information storage space;

[0037] Whenever new K-frame P×M synthesized range-Doppler data is obtained, the target information storage space is cleared, and the K-frame target information corresponding to the new K-frame P×M synthesized range-Doppler data is stored.

[0038] Furthermore, step 7 is specifically implemented as follows:

[0039] S71, allocate 3 sets of reference frame target information storage space, each set stores K frame data; the initial value of the 3 sets of reference frame target information storage space is 0, the first K frame target information obtained is recorded as a set of reference frame target information, and stored in the first set of reference frame target information storage space.

[0040] For each new set of reference frame target information, it is stored sequentially in the storage space of the three sets of reference frame target information. When all three sets of reference frame target information storage spaces are full, the storage space of the first set of reference frame target information is cleared, the second set of reference frame target information is moved to the storage space of the first set of reference frame target information, the third set of reference frame target information is moved to the storage space of the second set of reference frame target information, and the storage space of the third set of reference frame target information is freed up to store new reference frame target information.

[0041] S72: Based on the distance-Doppler data of the K-frame synthesized after K-frame target information in the target information storage space, calculate the difference between the corresponding bit frame number and the distance-Doppler data of the latest set of reference frame target information in the reference frame target information storage space. If the difference between the corresponding bit frame numbers is pK, then record the current K-frame target information as a new set of reference frame target information and store it in the corresponding reference frame target information storage space.

[0042] Furthermore, step 8 is specifically described as follows:

[0043] Based on the frame number of the distance-Doppler data synthesized from the K-frame target information in the target information storage space, calculate the difference between the corresponding bit frame number and the distance-Doppler data synthesized from the K-frame target information in the first group of reference frames in the latest reference frame target information storage space. If the difference between the corresponding bit frame numbers is greater than or equal to 2pK and less than 3pK, then compare the current K-frame target information with the corresponding frame of the first group of reference frames in the latest reference frame target information storage space. If the two contain the same row number and column number information in a certain corresponding frame, then remove the row number and column number related information from the target information of that frame to obtain the K-frame canceled target information data.

[0044] Furthermore, the specific method of step 9 is as follows:

[0045] Based on the dense beam angle measurement method, the angle measurement steering vectors under different azimuth and elevation conditions are used to calculate the signal-to-noise ratio of low, slow and small targets in each direction based on the canceled target information data. The peak position is the location of the low, slow and small target, thus completing the angle measurement of the low, slow and small target and outputting the positioning result of the low, slow and small target.

[0046] Due to the adoption of the above technical solution, the beneficial effects of this invention compared with the prior art are as follows:

[0047] 1. This invention performs ground clutter cancellation processing on range-Doppler two-dimensional data and multi-target detection information respectively, thereby eliminating ground clutter signals and improving the radar's detection probability of low, slow, and small targets under the influence of ground clutter signals.

[0048] 2. The present invention adopts a step-by-step reference frame selection rule, which reduces the loss of the real target signal during the ground clutter cancellation process and improves the accuracy of ground clutter cancellation. Attached Figure Description

[0049] Figure 1 This is an overall flowchart of a low-speed, small target detection method based on step-by-step ground clutter cancellation in an embodiment of the present invention.

[0050] Figure 2 This is a schematic diagram of the reference frame selection rules in an embodiment of the present invention.

[0051] Figure 3 , Figure 4 These are two-dimensional planar target positioning results corresponding to ground clutter cancellation and ground clutter cancellation in the embodiments of the present invention.

[0052] Figure 5 , Figure 6 The figures shown are the three-dimensional target positioning results corresponding to ground clutter cancellation and ground clutter cancellation in the embodiments of the present invention. Detailed Implementation

[0053] The invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0054] A method for detecting low-speed, small targets based on step-by-step ground clutter cancellation, such as... Figure 1 As shown, the specific steps include:

[0055] S1. The low-speed, small target is set as an unmanned aerial vehicle (UAV). A node coordinate system is established to obtain the array element coordinates. The received echo signals are then processed to generate fast-time and slow-time two-dimensional data. The specific steps include the following:

[0056] S11: Establish the node coordinate system in a single-transmitter, single-receiver scenario, and construct the coordinates (x, y, y) of the 16 array elements on the receiving node. n ,y n ,zn ), n=1,2,...,16, the pitch angle of the nodal coordinate system is defined as the angle with the XOZ plane, and the azimuth angle is defined as the angle between the projection on the XOZ plane and the X-axis;

[0057] S12: The 16 array elements perform spatial scanning and receive data respectively. One spatial scan consists of 5 wave positions, that is, each array element completes one spatial scan and receives 5 frames of one-dimensional echo data.

[0058] S13: The length of one frame of echo data is 1×3037500. The echo data (1×3037500) received by each array element is processed to obtain fast time-slow time two-dimensional data (486×6250).

[0059] S2. Perform distance and velocity measurement processing on the two-dimensional data obtained in S1 to generate distance-Doppler two-dimensional data, and store the data to obtain the current frame data. The specific steps include the following:

[0060] S21: Matched filtering and multi-pulse accumulation are performed on the two-dimensional data of the 16 array elements obtained in S1 to achieve target ranging and velocity measurement, and 16×5 frames of range-Doppler two-dimensional data are obtained.

[0061] S22: Allocate 16 groups of current frame data storage space, each group storing 5 frames of data. Use this storage space to store the 16×5 frames of distance-Doppler two-dimensional data obtained in S21 to obtain the current frame data.

[0062] S3, such as Figure 2 As shown, the range-Doppler data obtained in S2 is stored according to the reference frame data selection rules to generate multiple sets of reference frame data. The specific steps include the following:

[0063] S31: For each array element, allocate 3 sets of reference frame data storage spaces, each set storing 5 frames of data; the first set of space stores the distance-Doppler two-dimensional data of frames 1 to 5, and the remaining sets of data are initialized to 0;

[0064] S32: The step interval for each group of reference frames is 50 frames of data. Determine whether the frame number of the current frame differs from the frame number of the previous group of reference frames by 50. Group the 5 frames of data that meet the interval condition and store them in the storage space allocated in S31.

[0065] Specifically, in this embodiment, p = 10, therefore p × K = 50;

[0066] S33: Update the reference frame data according to the reference frame update rule. The update rule is: update the reference frame data once every 50 frames of data, that is, the second group of data is shifted to the first group, the third group of data is shifted to the second group, and so on, leaving the storage position of the third group empty to store the new reference frame.

[0067] S4. Complete the ground clutter cancellation processing of the current frame data in S2, which includes the following steps:

[0068] Ground clutter cancellation is performed on the current frame data obtained in S22 according to the ground clutter cancellation condition. The ground clutter cancellation condition is: 100 ≤ current frame number - first group reference frame number < 150. The ground clutter cancellation method is: subtract the first group reference frame data from the current frame data in S22. That is, in the cancellation process, the data from frame 101 to frame 150 is subtracted from the data from reference frames 1 to 5. The ground clutter cancellation process is completed in this way.

[0069] Specifically, the first set of reference frame numbers refers to the latest first set of reference frame numbers in the latest reference frame data storage space; 2×p×K=100, 3×p×K=150;

[0070] S5. Calculate and generate the steering vector, and use this value to perform inter-element beamforming on the data after ground clutter cancellation to obtain the synthesized range-Doppler data. The specific steps include the following:

[0071] S51: The wave position pointing coordinates (x, y, z) in the node coordinate system are calculated based on the received wave position pointing (azi, ele). The specific calculation expression is: x = cos(azi)cos(ele), y = sin(ele), z = sin(azi)cos(ele). The five wave positions are set as (-5.64, -19.35), (-23.14, -19.49), (0.06, -17.96), (-17.39, -14.92), and (-22.71, -17.40). The wave position pointing coordinates (x, y, z) can be obtained according to the above expression.

[0072] S52: Utilizing wave position pointing coordinates (x, y, z) and 16 element coordinates (x, y, z) n ,y n ,z n The guiding vectors corresponding to the 16 array elements are calculated, and the calculation expression is as follows: Where λ = 0.3m;

[0073] S53: Multiply the steering vector obtained in S51 and the canceled data obtained in S41 by conjugate to complete the inter-element beamforming and obtain the synthesized range-Doppler data.

[0074] Specifically, the steering vectors corresponding to the 16 array elements in 1 row and 16 columns are multiplied conjugately with the ground clutter cancellation data in 16 rows and 5 columns to complete inter-element beamforming, resulting in 5 frames of synthesized 486×6250 range-Doppler data. The 5 frames of synthesized range-Doppler data are recorded according to the frame number of the corresponding 5 frames of current frame data before ground clutter cancellation.

[0075] S6. Complete the threshold detection of the synthesized data in S5 to obtain the synthesized target information. This includes the following steps:

[0076] S61: Set the signal-to-noise ratio value for threshold detection, compare the synthesized range-Doppler data with this value, and the value exceeding the threshold is the target. Store the values ​​greater than the threshold and their corresponding row and column numbers.

[0077] S62: Convert the row and column numbers stored in S61 to obtain the target's distance and velocity information. The conversion expression is: Where c is the speed of light, and T s =16us, PRF=10000, M=6250.

[0078] S7. Generation and storage of target information for multiple sets of reference frames, specifically including the following steps:

[0079] S71: Allocate 3 sets of reference frame target information storage space, each set storing 5 frames of data; the first set of space stores the target information of frames 1 to 5, and the data of the remaining sets is initialized to 0;

[0080] S72: The step interval for each group of reference frames is 50 frames of data. Determine whether the frame number of the current frame differs from the frame number of the previous group of reference frames by 50. Group the 5 frames that meet the interval condition and store them in the storage space allocated by S71.

[0081] S8. Perform reference frame target removal processing on the target information in S6 and update the reference frame target information. This includes the following steps:

[0082] Referring to the ground clutter elimination conditions in S4, the target information of the first set of reference frames in S71 is subtracted from the target information obtained in S62 to complete the target removal process of the reference frames.

[0083] S9. Complete the target angle measurement and output the target positioning result, which includes the following steps:

[0084] Based on the dense beam angle measurement method, the signal-to-noise ratio of the target in each direction is calculated using the angle measurement steering vector under different azimuth and elevation positions. The peak position is the location of the target, thus completing the target angle measurement and outputting the target positioning result.

[0085] Specifically, this includes measuring the target's distance and angle to obtain the target localization result. For each frame of target information data after the reference frame target removal process, each frame contains a set of row and column number related information, corresponding to one target detected in that frame. Based on the number of detected targets, the corresponding number of signal-to-noise ratio peaks are calculated in S9, which represents the position of the corresponding target, thus completing the target angle measurement.

[0086] Two-dimensional planar target localization results are as follows Figure 3 , Figure 4 As shown. Among them Figure 3 This is the target location result under the condition of no ground clutter cancellation processing. Figure 4 This is the target location result after clutter cancellation processing according to the present invention. By comparison... Figure 3 , Figure 4 The two figures show that without ground clutter cancellation processing, the target localization result deviates greatly from the actual UAV trajectory, and they are almost impossible to match. This invention can significantly improve the detection probability of low, slow and small targets in complex ground clutter environments.

[0087] The three-dimensional coordinate target localization result is as follows Figure 5 , Figure 6 As shown. Among them Figure 5 This is the target location result under the condition of no ground clutter cancellation processing. Figure 6 This is the target location result after clutter cancellation processing according to the present invention. By comparison... Figure 5 , Figure 6 The two figures show that without ground clutter cancellation, the Z-coordinate positioning result is basically inaccurate and the three-dimensional positioning result appears intermittently. This invention can significantly improve the positioning accuracy and detection probability of low, slow and small targets in complex ground clutter environments. Figures 3-6 In this context, t(s) represents the observation time.

[0088] Those skilled in the art will recognize that the described embodiments are intended to help readers understand the principles of the invention and should be understood as not limiting the scope of protection of the invention to the described embodiments. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of the claims of the invention.

Claims

1. A method for detecting low-speed, small targets based on step-by-step ground clutter cancellation, characterized in that, Includes the following steps: Step 1: Establish a node coordinate system for the detection radar to obtain the array element coordinates of the detection radar. Utilize the echo signals received by the detection radar from low, slow, and small targets to generate fast-time and slow-time two-dimensional data. Step 2: Perform distance and velocity measurement on the fast-time-slow-time two-dimensional data obtained in Step 1 to generate distance-Doppler two-dimensional data, and store the distance-Doppler two-dimensional data to obtain the current frame data; Step 3: Set the reference frame data selection rules, selectively store the range-Doppler data obtained in Step 2, and obtain multiple sets of reference frame data; Step 4: Perform ground clutter cancellation processing on the current frame data; Step 5: Calculate and generate the steering vector, and use the steering vector to perform inter-element beamforming on the data after ground clutter cancellation to obtain the synthesized range-Doppler data; Step 6: Complete the threshold detection of the synthesized range-Doppler data in Step 5 to obtain the synthesized target information; Step 7: Generate and store multiple sets of reference frame target information; Step 8: Perform reference frame target information removal processing on the target information in Step 6; Step 9: Based on the target information after the reference frame target information removal process, complete the target angle measurement and output the positioning result of the low, slow and small target.

2. The method for detecting low-speed, small targets based on step-by-step ground clutter cancellation according to claim 1, characterized in that, The specific method of step 1 is as follows: S11, establish the node coordinate system XYZ for the single-transmit and single-receive scenario of the detection radar, and further obtain the element coordinates of the N array elements of the detection radar ( , ), ; S12, N array elements continuously perform spatial scanning and receive data. Each spatial scan consists of K wave positions, meaning each element receives K frames of one-dimensional echo data after completing one spatial scan. The length of one echo data frame is... P represents the number of sampling points of the detection radar, and M represents the number of pulses of the detection radar; S13, The echo data received by each array element during the current spatial domain scanning process are processed to obtain the K frames corresponding to each array element. Fast-time - slow-time two-dimensional data.

3. The method for detecting low-speed, small targets based on step-by-step ground clutter cancellation according to claim 2, characterized in that, The specific method for step 2 is as follows: S21, for each of the N array elements in K frames Matched filtering and multi-pulse accumulation are performed on fast-time and slow-time two-dimensional data to achieve target ranging and velocity measurement. Frame distance - Doppler two-dimensional data; S22, allocate N groups of current frame data storage spaces, each group storing K-frame distance-Doppler two-dimensional data corresponding to one array element, denoted as the current frame data of the current array element, and use this storage space to process the data obtained in S21. The frame distance-Doppler two-dimensional data is stored, i.e., the current frame data of N array elements; and the data obtained for each array element during continuous spatial scanning are stored separately. Frame distance-Doppler two-dimensional data is used for continuous frame number recording; After each new spatial scan by N array elements, the N sets of current frame data storage spaces are cleared, and the new data is stored in the array. The frame distance-Doppler two-dimensional data are stored accordingly to obtain new current frame data for N array elements.

4. The method for detecting low-speed, small targets based on step-by-step ground clutter cancellation according to claim 3, characterized in that, The specific method for step 3 is as follows: S31. For each array element, three sets of reference frame data storage spaces are allocated, each storing K frames of reference frame data. The initial value of the three sets of reference frame data storage spaces is 0. Initially, the K-frame range-Doppler two-dimensional data corresponding to the first spatial domain scan is recorded as a set of reference frame data and stored in the first set of reference frame data storage space. For each subsequent new set of reference frame data, it is stored sequentially in the three sets of reference frame data storage spaces. When all three sets of reference frame data storage spaces are full, the first set of reference frame data storage space is cleared, the second set of reference frame data is shifted to the first set of reference frame data storage space, the third set of reference frame data is shifted to the second set of reference frame data storage space, and the third set of reference frame data storage space is freed up to store new reference frame data. S32, based on the frame number of the current frame data corresponding to each array element in the current frame data storage space, calculate the difference between the corresponding bit frame number and the latest set of reference frame data in the reference frame data storage space of the corresponding array element. If the difference between the corresponding bit frame numbers is pK, then record the current frame data as a new set of reference frame data and store it in the reference frame data storage space corresponding to the array element.

5. The method for detecting low-speed, small targets based on step-by-step ground clutter cancellation according to claim 4, characterized in that, The specific method for step 4 is as follows: Based on the frame number of the current frame data corresponding to each array element in the current frame data storage space, calculate the difference between the corresponding bit frame number and the first group of reference frame data in the latest reference frame data storage space of the corresponding array element. If the difference between the corresponding bit frame numbers is greater than or equal to 2pK and less than 3pK, then subtract the corresponding bit of the current frame data corresponding to the array element from the first group of reference frame data in the latest reference frame data storage space of the array element, and record the result after subtraction as the K-frame ground clutter cancellation data corresponding to the array element.

6. The method for detecting low-speed, small targets based on step-by-step ground clutter cancellation according to claim 5, characterized in that, The specific method of step 5 is as follows: S51, the wave position pointing coordinates (x, y, z) in the node coordinate system are calculated based on the received wave position pointing (azi, ele) of the echo signal. The specific calculation expression is as follows: , , Where azi is the azimuth angle of the echo signal, ele is the elevation angle of the echo signal, the elevation angle of the nodal coordinate system is defined as the angle between the echo signal and the XOZ plane, and the azimuth angle is defined as the angle between the projection of the echo signal on the XOZ plane and the X-axis. S52, using the wave position pointing coordinates (x, y, z) and the coordinates of N array elements ( , The guiding vectors corresponding to the N array elements are calculated, and the calculation expression is: ,in The wavelength of the echo signal; S53, the guide vectors corresponding to the N array elements in row N columns are conjugately multiplied with the ground clutter cancellation data in row K columns to complete the inter-element beamforming and obtain K frames. The synthesized distance-Doppler data.

7. The method for detecting low-speed, small targets based on step-by-step ground clutter cancellation according to claim 6, characterized in that, The specific method for step 6 is as follows: S61, Set the signal-to-noise ratio value for threshold detection, and combine the range-Doppler data from each frame into a single frame. Each element is compared with the signal-to-noise ratio value, and the elements that are greater than the signal-to-noise ratio value, along with their corresponding row and column numbers, are recorded. S62, convert the row and column numbers recorded in S61 to obtain the distance and velocity information of the slow, small target. The conversion expression is: , ; Where row is the row number, col is the column number, and c is the speed of light. The sampling interval of the detection radar is denoted by PRF, the pulse repetition frequency of the detection radar is denoted by range, the range is denoted by v, and the velocity of the low-speed, small target is denoted by v. S63, allocate a target information storage space, the target information storage space stores K-frame data; for K-frames The synthesized range-Doppler data is used to record all elements in each frame of synthesized range-Doppler data that are greater than the signal-to-noise ratio value, their corresponding row and column numbers, and the distance and velocity information of the corresponding low, slow and small targets as a frame of target information, thereby obtaining K frames of target information, which are stored in the target information storage space. Whenever a new K-frame is obtained After synthesizing the range-Doppler data, the target information storage space is cleared, and a new K-frame is generated. The K-frame target information corresponding to the synthesized range-Doppler data is stored.

8. The method for detecting low-speed, small targets based on step-by-step ground clutter cancellation according to claim 7, characterized in that, The specific method for step 7 is as follows: S71, allocate 3 sets of reference frame target information storage space, each set stores K frame data; the initial value of the 3 sets of reference frame target information storage space is 0, the first K frame target information obtained is recorded as a set of reference frame target information, and stored in the first set of reference frame target information storage space. For each new set of reference frame target information, it is stored sequentially in the storage space of the three sets of reference frame target information. When all three sets of reference frame target information storage spaces are full, the storage space of the first set of reference frame target information is cleared, the second set of reference frame target information is moved to the storage space of the first set of reference frame target information, the third set of reference frame target information is moved to the storage space of the second set of reference frame target information, and the storage space of the third set of reference frame target information is freed up to store new reference frame target information. S72: Based on the distance-Doppler data of the K-frame synthesized after K-frame target information in the target information storage space, calculate the difference between the corresponding bit frame number and the distance-Doppler data of the latest set of reference frame target information in the reference frame target information storage space. If the difference between the corresponding bit frame numbers is pK, then record the current K-frame target information as a new set of reference frame target information and store it in the corresponding reference frame target information storage space.

9. A method for detecting low-speed, small targets based on step-by-step ground clutter cancellation according to claim 8, characterized in that, The specific method of step 8 is as follows: Based on the frame number of the distance-Doppler data synthesized from the K-frame target information in the target information storage space, calculate the difference between the corresponding bit frame number and the distance-Doppler data synthesized from the K-frame target information in the first group of reference frames in the latest reference frame target information storage space. If the difference between the corresponding bit frame numbers is greater than or equal to 2pK and less than 3pK, then compare the current K-frame target information with the corresponding frame of the first group of reference frames in the latest reference frame target information storage space. If the two contain the same row number and column number information in a certain corresponding frame, then remove the row number and column number related information from the target information of that frame to obtain the K-frame canceled target information data.

10. A method for detecting low-speed, small targets based on step-by-step ground clutter cancellation according to claim 9, characterized in that, The specific method for step 9 is as follows: Based on the dense beam angle measurement method, the angle measurement steering vectors under different azimuth and elevation conditions are used to calculate the signal-to-noise ratio of low, slow and small targets in each direction based on the canceled target information data. The peak position is the location of the low, slow and small target, thus completing the angle measurement of the low, slow and small target and outputting the positioning result of the low, slow and small target.

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