A shipborne ground wave radar target azimuth ambiguity discrimination and correction method based on target azimuth statistical characteristics

Abstract

The application discloses a ship-borne ground wave radar target azimuth ambiguity discrimination and correction method based on target azimuth statistical characteristics, and belongs to the technical field of ship-borne ground wave radar target direction finding. The method comprises the following steps: acquiring target track data and ship-borne platform attitude data; calculating statistical characteristics of target geographical azimuth angles before and after eliminating the influence of platform yaw on the target geographical azimuth angles based on the target geographical azimuth angles and the platform heading change amount; discriminating whether the target is a mirror image target or a non-mirror image target by using the calculated statistical characteristics; and correcting the azimuth of the mirror image target according to the symmetry characteristics of the mirror image target and the real target with respect to the platform heading. The application realizes effective discrimination and accurate correction of target azimuth ambiguity by analyzing the differences in the changes of the left and right target azimuth angles, and significantly improves the positioning accuracy of the target.

Description

Technical Field

[0001] This invention relates to a method for precise target localization using shipborne ground wave radar, specifically a method for ambiguity discrimination and correction of target azimuth based on the statistical characteristics of target azimuth in shipborne ground wave radar. Background Technology

[0002] High-Frequency Surface Wave Radar (HFSWR) utilizes the mechanism of vertically polarized electromagnetic waves in the 3-30MHz high-frequency band diffracting and propagating along the sea surface to achieve wide-range, over-the-horizon continuous detection of ships and low-flying targets at sea. In addition to the above advantages, shipborne HFSWR also has extremely high mobility and flexibility.

[0003] In shipborne ground wave radar target detection, azimuth is an essential parameter for determining target location. Regarding the problem of target azimuth estimation using shipborne HFSWR, numerous scholars both domestically and internationally have advanced research in this field from different perspectives. Early research mainly focused on analyzing the platform's motion characteristics and the resulting Doppler frequency shift in target echoes. It also involved accurately modeling the instantaneous disturbances of the array geometry caused by the platform's six-degree-of-freedom motion to reconstruct the array manifold and correct the direction-finding reference. To overcome array amplitude and phase errors in the shipborne environment, researchers established more accurate error models and developed online self-calibration and robust adaptive beamforming techniques. Currently, research has shifted towards comprehensively utilizing the spatiotemporal characteristics and polarization information of target signals. Through joint space-time-frequency analysis, complex moving targets can be separated and clutter suppressed, and the detection capability for low-observable targets can be improved by utilizing polarization feature differences. Furthermore, cutting-edge explorations are beginning to attempt to transform platform motion into an advantage, utilizing synthetic aperture technology to increase the virtual aperture and actively introducing data-driven methods such as deep learning to learn the nonlinear mapping from complex echoes to target azimuth in an end-to-end manner.

[0004] However, existing shipborne ground-wave radar direction-finding methods all rely on the assumption that the target signal originates from only one side, and perform direction-of-arrival estimation, making it impossible to determine whether the target is located to the left or right of the platform, resulting in target ambiguity. Currently, in ship target direction finding using ground-wave radar, only a few researchers have conducted studies on the discrimination of targets with ambiguity. For example, Wang Xinling used the distance from the target azimuth angle to the ideal left and right target straight lines under conditions of significant platform yaw to eliminate azimuth ambiguity. However, this method is based on the premise of significant platform yaw, making it difficult to guarantee the real-time and continuous nature of target positioning and tracking, and it does not correct for the target azimuth.

[0005] This invention combines the characteristics of current shipborne ground wave radar direction finding methods and makes full use of the differences in the azimuth characteristics of left and right targets when the platform's heading changes. It proposes a method for judging and correcting target azimuth ambiguity suitable for shipborne ground wave radar, which effectively solves the target azimuth ambiguity problem and improves the target positioning accuracy. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] The purpose of this invention is to provide a method for target azimuth ambiguity discrimination and correction based on the statistical characteristics of target azimuth in shipborne ground wave radar, so as to achieve correct discrimination of targets on both sides of the platform and improve the positioning accuracy of the target.

[0008] (II) Technical Solution

[0009] This invention includes the following steps:

[0010] Step 1: Data Reading.

[0011] Read the target point data and platform attitude data corresponding to each target point in the target trajectory; then obtain the relevant parameters of the target from the target point data, including radial distance, geographical azimuth, target longitude, and target latitude; then obtain the relevant parameters of the platform from the platform attitude data, including heading, platform longitude, and platform latitude.

[0012] Step 2: Calculation of the statistical characteristics of the target geographic azimuth.

[0013] The statistical characteristics of the target geographic azimuth are calculated using the obtained target geographic azimuth. Then, the change in platform heading at each moment relative to the initial moment is calculated using the obtained platform heading. Based on this data, the target geographic azimuth error caused by platform heading is eliminated, and the statistical characteristics of the target geographic azimuth after eliminating the influence are calculated.

[0014] Step 3: Target location ambiguity determination.

[0015] Based on the calculated relationship between the statistical characteristics of the target's geographic azimuth before and after removing the influence of platform bow roll, determine whether the target is a mirror target or a non-mirror target;

[0016] Step 4: Correct the orientation of the mirrored target.

[0017] Targets identified as non-mirror targets do not require azimuth correction; for targets identified as mirror targets, the geographic azimuth of the mirror target is corrected by utilizing the symmetry between the mirror target and its symmetrical target about the platform's heading axis at each moment, and finally converted into the target's latitude and longitude.

[0018] (III) Beneficial Effects

[0019] The advantages of this invention are as follows:

[0020] This invention innovatively utilizes the statistical differences in the left and right target azimuth angles, and integrates the relationship between the platform's heading and the change in the target azimuth angle, to determine whether a target is a mirror image target, and greatly improves the positioning accuracy of targets with ambiguous azimuth, providing effective technical support for the precise positioning of maritime targets. Attached Figure Description

[0021] Figure 1 This is a flowchart of the target azimuth ambiguity discrimination and correction method for shipborne ground wave radar based on the target azimuth statistical characteristics proposed in this invention.

[0022] Figure 2 This is a schematic diagram showing the change in the left and right target azimuth angles when the platform's heading changes, under the geographic coordinate system of this invention.

[0023] Figure 3 This is a schematic diagram showing the change in the left and right target azimuth angles when the platform's heading changes, within the radar coordinate system of this invention.

[0024] Figure 4 This is a schematic diagram of the trajectory information of the simulated right target in this invention.

[0025] Figure 5 This is a schematic diagram of the trajectory information of the simulated left target in this invention. Detailed Implementation

[0026] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings:

[0027] Reference Figure 1 The specific implementation steps of the present invention are as follows:

[0028] Step 1: Data Reading.

[0029] Set the start time of the target trajectory as T. 1， The end time is T n Using shipborne observation equipment and platform inertial navigation system, data from T1 to T2 are acquired synchronously in time sequence. n Every moment T i Target point data (i=1,2,...,n) and shipborne platform attitude data.

[0030] For each time T i The acquired target point data includes the target geographic azimuth angle θ. i Radial distance R i Target longitude Tlon i Target latitude Tlat iThe target geographic azimuth is represented by the angle obtained by rotating clockwise from due north to the line connecting the target and the platform.

[0031] For each time T i The acquired platform attitude data includes the platform's bow α. i Platform Longitude Plon i Platform Dimensions i The platform heading indicates the angle traversed by rotating clockwise from due north to the platform's bow direction.

[0032] Step 2: Calculation of the statistical characteristics of the target geographic azimuth.

[0033] Figure 2 In the diagram, time T1 represents the platform's state before the bow rolls. The orange-filled area represents the desired detection area, located on the right side of the platform. Targets within this area are right targets, such as right target B1. The dashed orange area represents the undesired detection area, located on the left side of the platform. Targets within this area are left targets, such as left target A1. Because the radar assumes that all received target echoes originate from the desired detection area for direction finding, it becomes impossible to determine whether a target is on the left or right, resulting in azimuth ambiguity, which requires further discrimination.

[0034] First, calculate the statistical characteristic value of the target's geographic azimuth angle throughout the entire flight path period. The specific formula is as follows:

[0035] ,

[0036] Where STD1 is the standard deviation of the target geographic azimuth sequence, and MAD1 is the average absolute error of the target geographic azimuth sequence. The formulas for calculating STD1 and MAD1 are as follows:

[0037] ,

[0038] ,

[0039] Where n represents the total number of frames of the target waypoints, θ i T represents i The target geographic azimuth at that moment This represents the average value of the target geographic azimuth sequence.

[0040] Then, the change in platform heading relative to the initial time is calculated using the following formula:

[0041] ,

[0042] Where α1 represents the platform heading at the start of the trajectory, Δα i T represents iChange in the forward direction of the platform at any given moment.

[0043] Then calculate the target geographic azimuth after removing the bow roll effect:

[0044] ,

[0045] Where, θ i To eliminate the impact of platform bow roll, T i The geographic azimuth of the target is mirrored at all times.

[0046] Finally, the statistical characteristics of the target's geographic azimuth after removing the effect of bow roll were calculated:

[0047] ,

[0048] Where STD2 and MAD2 are the standard deviation and average absolute error of the target geographic azimuth sequence after removing the bow roll effect, respectively. The formulas for calculating STD2 and MAD2 are as follows:

[0049] ,

[0050] ,

[0051] in, This represents the average value of the target geographic azimuth sequence after removing the effects of bow roll.

[0052] Step 3: Target location ambiguity determination.

[0053] Based on the target azimuth statistics before and after removing the platform bow roll effect calculated in step two, target azimuth ambiguity is determined. When S2 > S1, the target is determined to be a non-mirror target. Figure 2 As shown in targets B1 and B2, the orientation of non-mirror targets does not need to be corrected; when S1 > S2, the target is determined to be a mirror target, as shown in the image. Figure 2 As shown in targets A1' and A2', the orientation of the mirrored targets needs to be corrected.

[0054] Step 4: Correct the orientation of the mirrored target.

[0055] Because radar assumes that the received target echoes originate from the desired detection area when performing target direction finding, the left target A1 is treated as its mirror image A1', symmetrical about the platform's heading axis, for direction finding. Time T2 represents the platform's state after a heading change. The blue area represents the desired detection area; at this time, the right target has moved from position B1 to B2. The dashed blue area represents the undesired detection area; at this time, the left target has moved from position A1 to A2, and its mirror image has moved from A1' to A2'. This significant positional change means a large change in the mirror image's geographical azimuth, which is caused by the platform's bow roll. Since the platform's bow roll introduces an azimuth error to the mirror image's geographical azimuth that is twice the amount of the platform's heading change, based on this relationship, the azimuth error caused by the platform's bow roll is corrected using the following formula:

[0056] ;

[0057] After correcting the geographic azimuth of the mirrored targets, it is necessary to relocate their true counterparts, i.e., calculate the geographic azimuth of A1 and A2. Since the true targets A1 and A2 and their mirrored targets A1' and A2' are symmetrically distributed about the platform's heading, to utilize this symmetry, it is necessary to first transform the geographic coordinate system to the radar coordinate system, such as... Figure 3 As shown. The radar azimuth angle is defined as the geographical azimuth angle θ, obtained by rotating clockwise from the radar's main axis to the point where the line connecting the platform and the target passes, and correcting for the target's azimuth. i 'Converted to its radar azimuth angle φ' i The formula is as follows:

[0058] ;

[0059] Then, by utilizing the symmetry between the mirror target and the real target about the platform's heading axis, the radar azimuth angle φ of the real target is obtained by repositioning the real target. i The calculation formula is:

[0060] ;

[0061] Finally, the latitude and longitude information of the target point is updated based on the corrected azimuth angle. The update formula is as follows:

[0062] ,

[0063] ,

[0064] Among them, R i Tlon i Tlat i T respectively i Radial distance, longitude, and latitude of the target at any given time; Plon iPlat i These represent the platform's longitude and latitude, respectively; ARC represents the Earth's radius.

[0065] Example

[0066] The effects of the present invention will be further illustrated by the following data:

[0067] The ground wave radar data was obtained from a shipborne ground wave radar experiment conducted on October 24, 2021. The receiving array was positioned on the starboard side of the platform. Therefore, in this experiment, the right side of the platform was the desired detection area, meaning the mirrored target was actually the left target. Two targets were added to the data: one left target and one right target. The simulated left target had a velocity of 3 m / s, a radial distance of 30 km, and an azimuth of 320°; the simulated right target had a velocity of 3 m / s, a radial distance of 40 km, and an azimuth of 40°. The platform velocity was 2 m / s, exhibiting a sinusoidal periodic variation in the bow direction with a peak value of 3°. Figure 4 To simulate the trajectory information of the right target, where the blue trajectory represents the trajectory drawn using the direction finding results and the green trajectory represents the theoretical trajectory, the statistical characteristics of the target's geographical azimuth before and after removing the influence of platform bow roll, calculated using the formula, are 1.1934 and 4.3521, respectively. The statistical characteristic value after removing the influence is larger, indicating that the target is a non-mirror target, i.e., a right target, and there is no need to correct its azimuth. Figure 5 To simulate the trajectory information of the left target, where the blue trajectory represents the trajectory drawn using direction finding results and the green trajectory represents the theoretical trajectory, the statistical characteristics of the target's geographical azimuth before and after removing the influence of platform bow roll, calculated using formulas, are 3.5735 and 1.6329, respectively. The statistical characteristic value after removing the influence is smaller, indicating that the target is a mirror target, i.e., the left target, and its azimuth needs to be corrected. Figure 5 It can be seen that the track drawn using actual orientation measurement results differs significantly from the theoretical track, located on both sides of the platform. Figure 5 The black track in the image is the track after the orientation correction of the mirror target. It can be seen that the corrected track information is close to the theoretical track, proving that the method can effectively distinguish between left and right targets and improve the positioning accuracy of mirror targets.

[0068] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

[0069] The innovation of this invention is reflected in the following aspects:

[0070] This invention leverages the difference in target azimuth angle changes between the left and right sides during platform bow roll. Starting from target point data and platform attitude data, it utilizes the statistical differences in the left and right target azimuth angles to achieve target azimuth ambiguity discrimination. Based on the discrimination results, it corrects the mirror azimuth by utilizing the relationship between the platform's bow change angle and the target's geographic azimuth angle change, as well as the symmetry between the ambiguously oriented target and its mirror image target about the platform's heading axis. The target azimuth ambiguity discrimination method proposed in this invention is based on the inherent statistical characteristics of the target azimuth angle, overcoming the shortcomings of traditional methods that rely on large-scale platform bow adjustments, and has high practicality.

Claims

1. A method for target azimuth ambiguity discrimination and correction based on target azimuth statistical characteristics of shipborne ground wave radar, characterized in that, include: (1) Data reading: Read the target point track data and platform attitude data corresponding to each target point in the target track; Then, relevant parameters of the target are obtained from the target point data, including radial distance, geographic azimuth, target longitude, and target latitude; and relevant parameters of the platform are obtained from the platform attitude data, including heading, platform longitude, and platform latitude. (2) Calculation of statistical characteristics of the target geographic azimuth: First, calculate the statistical characteristics of the target's geographic azimuth throughout the entire flight path period. The specific formula is as follows: ， Where STD1 is the standard deviation of the target geographic azimuth sequence, and MAD1 is the average absolute error of the target geographic azimuth sequence. The formulas for calculating STD1 and MAD1 are as follows: ， ， Where n represents the total number of frames of the target waypoints, θ i T represents i The target geographic azimuth at that moment This represents the average value of the target geographic azimuth sequence; Then, the change in platform heading relative to the initial time is calculated using the following formula: ， Where α1 represents the platform heading at the start of the trajectory, Δα i T represents i The platform's heading change at any given time; then, the target's geographic azimuth angle after removing the influence of bow roll is calculated: ， Where, θ i To eliminate the impact of platform bow roll, T i The target's geographic azimuth is mirrored at all times, and finally, the statistical characteristics of the target's geographic azimuth after removing the bow roll effect are calculated: ， Where STD2 and MAD2 are the standard deviation and average absolute error of the target geographic azimuth sequence after removing the bow roll effect, respectively. The formulas for calculating STD2 and MAD2 are as follows: ， ， in, This represents the average value of the target geographic azimuth sequence after removing the effects of bow roll; (3) Target azimuth fuzzy discrimination: Based on the calculated statistical characteristics of the target azimuth angle before and after removing the influence of platform bow roll, the target azimuth fuzzy discrimination is performed. When S2>S1, the target is judged to be a non-mirror target, and the azimuth of the non-mirror target does not need to be corrected; when S1>S2, the target is judged to be a mirror target, and the azimuth of the mirror target needs to be corrected. (4) Correction of the target orientation in mirror image: Since changes in platform bow roll introduce twice the change in platform bow angle into the geographic azimuth of the mirrored target, based on this relationship, the azimuth error caused by platform bow roll is eliminated, and the correction formula is as follows: ； Since the symmetry relationship is reflected in the radar coordinate system, it is necessary to first convert the corrected geographic azimuth of the mirrored target into its radar azimuth. The radar azimuth is defined as the angle traversed by rotating clockwise around the radar principal axis to the line connecting the platform and the target. The corrected geographic azimuth θ of the mirrored target is... i 'Converted to its radar azimuth angle φ' i The formula is as follows: ； Then, by utilizing the symmetry between the mirror target and the real target about the platform's heading axis, the radar azimuth angle φ of the real target is obtained through repositioning. i The calculation formula is: ； Finally, the latitude and longitude information of the target point is updated based on the corrected azimuth angle. The update formula is as follows: ， ， Among them, R i Tlon i Tlat i T respectively i Radial distance, longitude, and latitude of the target at any given time; Plon i Plat i These represent the platform's longitude and latitude, respectively; ARC represents the Earth's radius.

2. The method for target azimuth ambiguity discrimination and correction based on target azimuth statistical characteristics of shipborne ground wave radar according to claim 1, characterized in that, Data reading includes: Set the start time of the target trajectory as T1 and the end time as T. n Using shipborne observation equipment and platform inertial navigation system, data from T1 to T2 are acquired synchronously in time sequence. n Every moment T i Target point data, shipborne platform attitude data; For each time T i The acquired target point data includes the target geographic azimuth angle θ. i Radial distance R i Target longitude Tlon i Target latitude Tlat i The target azimuth angle refers to the angle taken by rotating clockwise from due north to the line connecting the observation point and the target. For each time T i The acquired platform attitude data includes the platform's bow α. i Platform Longitude Plon i Platform Dimensions i The platform heading indicates the angle taken when rotating clockwise from due north to the platform's bow direction.

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