A Method for Correcting Pattern Errors of Shipborne Ground Wave Radar Array Based on Multiple AIS Information and Target Time-Frequency Characteristics

Abstract

This invention relates to a method for calibrating the radiation pattern error of a shipborne ground wave radar array based on multiple AIS information and target time-frequency characteristics. The method includes: selecting multiple reference signal sources that meet requirements in the time-frequency dimension from radar time-domain data, AIS information, and shipborne platform attitude information acquired during the bow change time; extracting the time-frequency information of each reference signal source to estimate the error matrix within a single azimuth range; constructing an error matrix within the radar detection range by combining multiple azimuth ranges; and compensating the array output signal to calibrate the array radiation pattern. This invention utilizes AIS information from multiple ship targets, combined with target azimuth changes caused by the bow roll characteristics of the shipborne platform and time-frequency analysis of the targets, to extract target time-frequency data for radiation pattern error estimation, thereby achieving radiation pattern error calibration and improving the direction-finding performance of targets.

Description

Technical Field

[0001] This invention relates to a method for calibrating the pattern error of a shipborne ground wave radar, specifically a method for calibrating the pattern error of a shipborne ground wave radar array based on multiple AIS information and target time-frequency characteristics. Background Technology

[0002] High-Frequency Surface Wave Radar (HFSWR) utilizes the diffraction of high-frequency (3~30MHz) vertically polarized electromagnetic waves along the coastal plane to detect and track targets such as ships and low-altitude aircraft at sea. It offers advantages such as wide coverage, beyond-line-of-sight capability, and continuous detection. Compared to shore-based ground wave radar, shipborne HFSWR has its transmitting and receiving stations mounted on mobile platforms, leveraging the platform's mobility and flexibility for a wider detection range. However, when estimating the Direction of Arrival (DOA) of a target, shipborne HFSWR is affected by the surrounding environment and platform motion, leading to distortion in the array radiation pattern and a decrease in DOA estimation accuracy. Therefore, to improve the direction-finding performance of shipborne HFSWR, it is necessary to consider the impact of the surrounding environment and platform motion on the radiation pattern, develop a radiation pattern error calibration method suitable for shipborne systems, correct errors, ensure data accuracy, and thus improve direction-finding precision.

[0003] Current research on pattern error calibration for shipborne ground-wave radar is relatively limited, with most studies focusing on shore-based ground-wave radar. One existing method utilizes Automatic Identification System (AIS) information as an auxiliary source for pattern error calibration. This involves accumulating AIS information from various azimuths and ship echo signals to estimate and calibrate the error. However, this method requires accumulating AIS information from all azimuths of interest to obtain the true azimuth of the ship echoes, resulting in a long implementation cycle and high cost. In reality, shipborne ground-wave radar often has limited AIS information in some detection areas, making it difficult to acquire a large number of high signal-to-noise ratio ship echoes. Furthermore, due to the motion characteristics of shipborne radar, the surrounding environment is constantly changing, causing the error value to vary over time, thus requiring real-time calibration. Therefore, traditional shore-based calibration methods are not suitable for shipborne systems. This invention utilizes AIS information from multiple ship targets, combined with the azimuth changes of the targets in the radar coordinate system caused by the yaw characteristics of the shipborne platform, and the time-frequency analysis and processing of the targets, to extract the broadened time-frequency data of the targets to estimate the radiation pattern error, thereby achieving the calibration of the radiation pattern error and improving the direction finding performance of the targets. Summary of the Invention

[0004] (a) The technical problems to be solved.

[0005] The present invention aims to provide a method for calibrating the radiation pattern of a shipborne ground wave radar array based on multiple AIS information and target time-frequency characteristics, so as to improve the direction finding accuracy of ship targets.

[0006] (ii) Technical solution.

[0007] This invention includes the following steps:

[0008] Step 1: Acquisition of data within the heading change.

[0009] The radar time-domain data, AIS information, and shipboard platform attitude information are acquired during the heading change time. The time-domain data is transformed to the time-frequency domain to obtain the radar time-frequency (TF). Then, the target latitude, longitude, speed, and other information provided by the platform's attitude information and AIS information are projected onto the time-frequency and matched with the target information.

[0010] Step 2: Screening of multiple reference signal sources and extraction of time and frequency information.

[0011] For the matched target, the precise azimuth information of each sampling point within the accumulation time is calculated based on the platform's attitude information and the latitude and longitude provided by AIS information. ;according to N targets meeting the following requirements are selected: the combined azimuth range of each target should cover as much of the radar detection area as possible (-60°~60°). Then, the time-frequency information of each target is extracted: based on the energy intensity of each time unit, the entire time unit is divided into several levels, and different frequency cells are extracted for each level. This method is used to extract the target time-frequency information for each channel.

[0012] Step 3: Estimation of the error matrix within a single azimuth range.

[0013] Based on the target's time-frequency information obtained in step 2, a covariance matrix is ​​constructed for the time-frequency information at each time point, and eigenvalue decomposition is performed to obtain the signal subspace; simultaneously, the azimuth information obtained in step 2 is used... Construct an ideal guidance vector; combine the signal subspace and orientation information. Calculate the error value at each time point (i.e., different orientations) to construct an error matrix. ;

[0014] Step 4: Construct the error matrix across multiple azimuth ranges.

[0015] Step 3 processes the time-frequency information of each target obtained in step 2 to obtain the information within each azimuth range. This constitutes the overall error matrix. .

[0016] To address the potential overlap between two azimuth ranges, the average error value within the overlapping range is used to represent the overlapping portion. This process is repeated for all overlapping portions to obtain the updated error matrix. .

[0017] Step 5: Array data compensation.

[0018] Using the error matrix obtained in step 4, the array output data is compensated to obtain the calibrated radiation pattern.

[0019] (iii) Beneficial effects.

[0020] The advantages of this invention are as follows:

[0021] This invention utilizes AIS information from multiple ship targets, combined with the azimuth changes of the targets in the radar coordinate system caused by the yaw characteristics of the shipborne platform, and the time-frequency analysis and processing of the targets, to extract the broadened time-frequency data of the targets to estimate the radiation pattern error, thereby achieving the calibration of the radiation pattern error and improving the direction finding performance of the targets. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the basic process of the present invention.

[0023] Figure 2 This refers to the range of azimuth angle changes for multiple targets under varying heading conditions according to the present invention.

[0024] Figure 3 The time-frequency spectrum diagrams of target channels 1 to 4 of this invention are shown.

[0025] Figure 4 The time-frequency spectrum of the target channels 5-8 of this invention is shown.

[0026] Figure 5 This is a comparison of the radiation patterns before and after calibration in this invention. Detailed Implementation

[0027] To make the objectives, contents, and advantages of the present invention clearer, the following description is provided in conjunction with the appendix. Figure 1 The specific embodiments of the present invention will be described in further detail below.

[0028] Step 1: Acquisition of data within the heading change.

[0029] Changes in azimuth of multiple targets under changing heading conditions, such as Figure 2 As shown, the bow direction of the shipborne platform has changed. Then the azimuth angles of multiple targets within the detection range also change in the radar coordinate system. There may be cases where the ranges of change for two targets overlap. The radar time-domain data for the bow change time is obtained. The data includes AIS information and the attitude information of the shipborne platform, where M is the number of array elements. The time-domain data is transformed to the time-frequency domain using the Short-time Fourier Transform (STFT) method to obtain the radar time-frequency (TF). It is assumed that the target signal of the shipborne ground wave radar is a single-component signal.

[0030] ,

[0031] In the formula, It is time. For instantaneous amplitude, This is the instantaneous phase. Therefore... The STFT time spectrum is:

[0032] ,

[0033] In the formula, For frequency, To analyze the signal, To move the window.

[0034] Figure 3 The time-frequency spectrum of a certain target in channels 1-4. Figure 4 The time-frequency spectra are for channels 5 to 8.

[0035] Simultaneously, the platform's attitude information and the target's latitude, longitude, speed, and other information provided by AIS are projected onto the time spectrum and matched with the target information:

[0036] ,

[0037] in This represents the target's velocity calculated from AIS information and platform attitude information. This represents the velocity of a target in the radar time spectrum, when the absolute value of the difference between the two is less than a certain threshold. When the time is right, it means the match is successful. It is related to the current radar velocity resolution.

[0038] Step 2: Screening of multiple reference signal sources and extraction of time and frequency information.

[0039] For the matched target, the precise azimuth information of each sampling point within the accumulation time is calculated based on the platform's attitude information and the latitude and longitude provided by AIS information. Where T is the accumulation time; according to Select N targets that meet the following requirements: Each target The combined range should cover as much of the radar detection area as possible (-60°~60°). Then, the time-frequency information of each target is extracted: based on the energy intensity of each time unit, the entire time unit is divided into several levels, and different frequency cells are extracted from each level. This method is used to extract the target time-frequency information for each channel. Let the energy of the entire time dimension be... Calculate the 25th, 50th, and 75th percentiles. The entire time dimension is divided into four levels based on quantiles, and each level of the time dimension is labeled according to its energy intensity:

[0040] ,

[0041] Extracting based on the frequency dimension By widening the grid cells, the target widening information was fully utilized, and the time-frequency data of each corresponding channel was extracted. .

[0042] Step 3: Estimation of the error matrix within a single azimuth range.

[0043] Based on the time-frequency information of the target obtained in step 2, a covariance matrix is ​​constructed for the time-frequency information at each time point, and eigenvalue decomposition is performed:

[0044] ,

[0045] ,

[0046] In the formula, The eigenvector corresponding to the largest eigenvalue after constructing the covariance matrix and eigenvalue decomposition of the target time-frequency data represents the signal subspace of the signal.

[0047] Simultaneously utilize the orientation information obtained in step 2. Construct the ideal guide vector in each direction:

[0048] ,

[0049] in,

[0050] ,

[0051] In the above formula, For carrier frequency, , The distance between array elements.

[0052] joint and location information Calculate the error value at each time point (i.e., different orientations). This constitutes the error matrix. They satisfy the following relationship:

[0053] ,

[0054] in, Therefore, the error value can be expressed as:

[0055] ,

[0056] The error matrix is: .

[0057] Step 4: Construct the error matrix across multiple azimuth ranges.

[0058] Step 3 processes the time-frequency information of each target obtained in step 2 to obtain the information within each azimuth range. This constitutes the overall error matrix. .

[0059] Regarding the potential overlap between two directional ranges, i.e., the two targets... The ranges may overlap, resulting in the error matrix. There will also be overlapping parts, for two The overlapping part is defined as and ,right and Taking the average yields:

[0060] ,

[0061] use To replace two The overlapping portions are then processed as described above. This process is applied to all overlapping portions to obtain the updated error matrix. .

[0062] Step 5: Array data compensation.

[0063] Using the error matrix obtained in step 4, the array output data is compensated to obtain the calibrated radiation pattern, such as... Figure 5 As shown, the diagram illustrates the comparison of radiation patterns before and after calibration within a certain azimuth range. It can be seen from the diagram that after adding the estimated error matrix to the ideal radiation pattern, it closely matches the uncalibrated radiation pattern. Similarly, after compensating the array data with the estimated error, it closely matches the ideal radiation pattern.

Claims

1. A shipboard ground wave radar array pattern error calibration method based on multi-AIS information and target time-frequency features, characterized in that, Comprise: (1) the acquisition of data within the change of heading, the acquisition of radar time domain data, AIS information and the attitude information of the shipboard platform within the change of heading time; the radar time domain data is transformed to time-frequency domain, and radar time-frequency spectrum (Time-frequency, TF) is obtained; then the target latitude and longitude, speed information provided by the platform attitude information and AIS information are processed and projected into the time-frequency spectrum, and matched with the target information; (2) Screening of multiple reference signal sources and extraction of time-frequency information. For the matched target, the accurate bearing information of each sampling point in the accumulation time is calculated according to the attitude information of the platform and the latitude and longitude provided by the AIS information ; according to , N targets meeting the following requirements are screened: the joint of the bearing range of each target should cover the bearing range of interest in the radar detection area (-60°~60°); then the time-frequency information of each target is extracted: according to the energy intensity of each time unit, the entire time unit is divided into several levels, and different frequency cells are extracted for each level. The target time-frequency information of each channel is extracted by this method; (3) Error matrix estimation in single azimuth range, according to the obtained time-frequency information of the target, a covariance matrix is constructed for the time-frequency information of each time point, and eigenvalue decomposition is performed to obtain a signal subspace; at the same time, an ideal steering vector is constructed by using the azimuth information ; the signal subspace and the azimuth information are combined ; the error value of each time point corresponding to different azimuths is calculated to form an error matrix ; (4) Error matrix construction in multiple azimuth ranges, the time-frequency information of each target is estimated in a single azimuth range to obtain the error matrix in each azimuth range , and the error matrix of the whole ; for the problem of possible overlap of two azimuth ranges, the average of the error values in the overlapping range is taken to replace the overlapping part, and all overlapping parts are processed to obtain the updated error matrix ; (5) array data compensation, using the obtained error matrix, the array output data is compensated, and the calibrated directional diagram can be obtained.

2. The shipborne ground wave radar array pattern error calibration method based on multi-AIS information and target time-frequency characteristics according to claim 1, characterized in that, The acquisition of data within the change of heading comprises: If the bow direction of the ship's platform changes Then the azimuth angles of multiple targets within the detection range also change in the radar coordinate system. There may be cases where the range of change of two targets overlaps; obtain radar time-domain data within the time of heading change. The data includes AIS information and the attitude information of the shipborne platform, where M is the number of array elements. The time-domain data is transformed to the time-frequency domain to obtain the radar time-frequency (TF). It is assumed that the target signal of the shipborne ground wave radar is a single-component signal. ， wherein is time, is the instantaneous amplitude, is the instantaneous phase, then the STFT time-frequency spectrum of ， wherein is the frequency, is the analysis signal, is the moving window; At the same time, the target latitude and longitude, speed and other information provided by the platform attitude information and AIS information are projected into the time-frequency spectrum, and matched with the target information: ， wherein represents the velocity of the target calculated from the AIS information and the platform attitude information, represents the velocity of the target in the radar time-frequency spectrum, when the absolute value of the difference between the two is less than a certain threshold represents a match success, is related to the current radar velocity resolution.

3. The shipboard ground wave radar array pattern error calibration method based on multi-AIS information and target time-frequency characteristics according to claim 1, characterized in that, The screening and time-frequency information extraction of multiple reference signal sources comprise: For the matched targets, the accurate azimuth information of each sampling point in the accumulation time is calculated according to the attitude information of the platform and the latitude and longitude provided by the AIS information , wherein T is the accumulation time; according to , N targets meeting the following requirements are screened out: each target The joint range should cover the azimuth range of interest in the radar detection area (-60°~60°); then the time-frequency information of each target is extracted: according to the energy intensity of each time unit, the entire time unit is divided into several levels, and different frequency cells are extracted for each level. The target time-frequency information corresponding to each channel is extracted by this method. Let the energy of the entire time dimension be The 25%, 50%, and 75% quantiles are calculated The entire time dimension is divided into four levels according to the quantiles, and each time dimension level is marked according to the energy intensity: ， According to the level, the frequency dimension is extracted A spread lattice is extracted, so that the spread target information is fully utilized, and the time-frequency data corresponding to each channel is extracted .

4. The shipboard ground wave radar array pattern error calibration method based on multi-AIS information and target time-frequency characteristics according to claim 1, characterized in that, Single azimuth range error matrix estimation comprises: According to the obtained time-frequency information of the target, the covariance matrix of the time-frequency information of each time point is constructed, and eigenvalue decomposition is performed: ， ， In the formula, The eigenvector corresponding to the maximum eigenvalue after the covariance matrix construction and eigenvalue decomposition of the target time-frequency data, which represents the signal subspace of the signal. Simultaneous use of orientation information constructing an ideal steering vector in each orientation direction: ， Wherein, ， In the above formula, is the carrier frequency, , is the array element spacing; joint and orientation information , calculate the error value of different orientations corresponding to each time point , constitute an error matrix , which satisfy the following relationship: ， wherein So the error value can be expressed as: ， The error matrix is: .

5. The shipboard ground wave radar array pattern error calibration method based on multi-AIS information and target time-frequency characteristics according to claim 1, characterized in that, Multiple azimuth range error matrix construction comprises: The time-frequency information of each target is subjected to error matrix estimation in a single azimuth range to obtain an error matrix in each azimuth range , which constitutes an overall error matrix ; For the problem that there may be overlap in the two azimuth ranges, i.e. the two targets may overlap, the resulting error matrix will also have overlapping parts, for the two overlapping parts, define them as and , for and take the average: ， Instead of two overlapping parts, use the overlapping parts; for all overlapping parts, do the above, to get an updated error matrix .

6. The shipboard ground wave radar array pattern error calibration method based on multi-AIS information and target time-frequency characteristics according to claim 1, characterized in that, Array data compensation comprises: Using the obtained error matrix, the array output data is compensated, and the calibrated directional diagram can be obtained.

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