Target image processing device and target image processing program

Abstract

This disclosure aims to detect small targets separately from clutter, even when the small targets are in close proximity to clutter, when clustering cells in which the radar received power exceeds a "small received power threshold" in order to detect not only large targets but also small targets using a radar device. [Solution] The Doppler velocity of an object is independent of and often different from the Doppler velocity of clutter, and is rarely close. Therefore, in this disclosure, the Doppler velocity deviation of each target cell within each cluster is calculated relative to the average Doppler velocity of surrounding cells outside each cluster. When the Doppler velocity deviation of each target cell within each cluster falls below a Doppler velocity deviation threshold, each target cell within each cluster is separated from the cluster.

Description

Technical Field

[0001] The present disclosure relates to a technique for separating and detecting a target from clutter using a radar device.

Background Art

[0002] Techniques for separating and detecting targets such as ships from clutter such as waves using a radar device are disclosed in Patent Document 1 and the like. In Patent Document 1, in a target image acquired from a radar device, cells in which the radar reception power exceeds a reception power threshold value are clustered using DBSCAN (Density-Based Spatial Clustering of Applications with Noise) or the like, and clusters are extracted.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The problems to be solved by the conventional cluster extraction process are shown in FIG. In Patent Document 1, in order to detect not only targets such as large ships but also targets such as small ships V or buoys, it is necessary to cluster cells in which the radar reception power exceeds a "small reception power threshold value". However, when a target such as a small ship V or a buoy is close to clutter such as a wave W, the target such as a small ship V or a buoy cannot be separated from the clutter such as a wave W and detected.

[0005] Then, when tracking a target such as a small ship V or a buoy, the target such as a small ship V or a buoy is integrated with clutter such as a wave W, and the feature amounts (center of gravity position, irradiated area, maximum reception power, average Doppler speed, etc.) of the tracked target are shifted, resulting in low accuracy of target tracking.

[0006] Therefore, in order to solve the aforementioned problems, this disclosure aims to detect small targets separately from clutter when clustering cells in which the radar received power exceeds a "small received power threshold" in order to detect not only large targets but also small targets using a radar device, even when the small targets are in close proximity to the clutter. [Means for solving the problem]

[0007] The Doppler velocity of an object is independent of and often different from the Doppler velocity of clutter, and is rarely close. To solve the above problem, the Doppler velocity deviation of each target cell within each cluster is calculated relative to the average Doppler velocity of surrounding cells outside each cluster. When the Doppler velocity deviation of each target cell within each cluster falls below a Doppler velocity deviation threshold, each target cell within each cluster is separated from the cluster.

[0008] Specifically, this disclosure relates to a target image acquisition unit that acquires a target image from a radar device, In the aforementioned target image, a cluster extraction unit clusters cells in which the radar received power exceeds the received power threshold and extracts the clusters. A Doppler velocity deviation calculation unit calculates the Doppler velocity deviation of each target cell within each cluster relative to the average Doppler velocity of surrounding cells outside each cluster. A cluster separation unit separates each target cell within each cluster from the cluster when the Doppler velocity deviation of each target cell within each cluster falls below a Doppler velocity deviation threshold, and maintains each target cell within each cluster within the cluster when the Doppler velocity deviation of each target cell within each cluster is equal to or greater than the Doppler velocity deviation threshold. This is a target image processing device characterized by having the following features.

[0009] With this configuration, considering that the Doppler velocity of a target is independent of and often different from that of clutter, and rarely close, it is possible to detect small targets separately from clutter even when they are in close proximity.

[0010] Furthermore, this disclosure further comprises a Doppler velocity variance calculation unit that calculates (1) the Doppler velocity variance of each target cell within each cluster and the average Doppler velocity variance of surrounding cells outside each cluster, or (2) the Doppler velocity variance deviation of each target cell within each cluster with respect to the average Doppler velocity variance of surrounding cells outside each cluster. The cluster separation unit determines whether to separate or maintain each target cell within each cluster from each cluster based on (1) the Doppler velocity variance of each target cell within each cluster and the average Doppler velocity variance of surrounding cells outside each cluster, or (2) the Doppler velocity variance deviation of each target cell within each cluster from each cluster. This is a target image processing device characterized by the following features.

[0011] With this configuration, considering that the Doppler velocity dispersion of the target is small compared to the Doppler velocity dispersion of the system noise, it is possible to detect small, low-speed targets separately from the system noise, even when the small, low-speed targets are in close proximity to the system noise.

[0012] Furthermore, the present disclosure states that the cluster separation unit determines whether to separate or maintain each target cell within each cluster from each cluster based on the Doppler velocity deviation of each target cell within each cluster when the average Doppler velocity variance of surrounding cells outside each cluster is below the average Doppler velocity variance threshold, and determines whether to separate or maintain each target cell within each cluster from each cluster based on the Doppler velocity variance of each target cell within each cluster when the average Doppler velocity variance of surrounding cells outside each cluster is equal to or greater than the average Doppler velocity variance threshold. This is a target image processing device characterized by the following features.

[0013] With this configuration, when the average Doppler velocity variance of surrounding cells is small, like that of clutter, small targets can be detected separately from clutter based on the Doppler velocity deviation of the target cell. On the other hand, when the average Doppler velocity variance of surrounding cells is large, like that of system noise, small, low-velocity targets can be detected separately from system noise based on the Doppler velocity variance of the target cell.

[0014] Furthermore, this disclosure further comprises a scan correlation calculation unit that calculates the scan correlation between past radar scans and current radar scans at each target cell within each cluster, The cluster separation unit determines, based on the scan correlation of each target cell within each cluster, whether to separate or maintain each target cell within each cluster relative to the respective cluster. This is a target image processing device characterized by the following features.

[0015] With this configuration, considering that the scan correlation of low-speed targets is higher than that of clutter, even when low-speed, small targets are in close proximity to clutter, low-speed, small targets can be detected separately from the clutter.

[0016] Furthermore, the present disclosure states that the cluster separation unit determines whether to separate or maintain each target cell within each cluster based on the scan correlation of each target cell within each cluster when the Doppler velocity deviation of each target cell within each cluster is below the Doppler velocity deviation threshold, and determines whether to maintain each target cell within each cluster based on the Doppler velocity deviation of each target cell within each cluster when the Doppler velocity deviation of each target cell within each cluster is equal to or greater than the Doppler velocity deviation threshold. This is a target image processing device characterized by the following features.

[0017] With this configuration, when the Doppler velocity deviation of the target cell is small, such as the deviation between a low-speed target and clutter, small, low-speed targets can be detected separately from clutter based on the scan correlation of the target cell. On the other hand, when the Doppler velocity deviation of the target cell is large, such as the deviation between a high-speed target and clutter, small, high-speed targets can be detected separately from clutter based on the Doppler velocity deviation of the target cell.

[0018] Furthermore, this disclosure includes a Doppler velocity variance calculation unit that calculates (1) the Doppler velocity variance of each target cell within each cluster and the average Doppler velocity variance of surrounding cells outside each cluster, or (2) the Doppler velocity variance deviation of each target cell within each cluster with respect to the average Doppler velocity variance of surrounding cells outside each cluster. The system further comprises a scan correlation calculation unit that calculates the scan correlation between past radar scans and current radar scans for each target cell within each cluster, The cluster separation unit determines whether to separate or maintain each target cell within each cluster relative to each cluster based on (1) the Doppler velocity variance of each target cell within each cluster, the average Doppler velocity variance of surrounding cells outside each cluster, and the scan correlation of each target cell within each cluster, or (2) the Doppler velocity variance deviation of each target cell within each cluster relative to each cluster, and the scan correlation of each target cell within each cluster. This is a target image processing device characterized by the following features.

[0019] With this configuration, even when small targets are in close proximity to clutter and system noise, small targets can be detected separately from clutter and system noise, taking into account Doppler velocity deviation, Doppler velocity dispersion, and scan correlation.

[0020] The present disclosure is also a target image processing program for causing a computer to execute each processing step executed by each processing unit included in the target image processing apparatus described above.

[0021] According to this configuration, it is possible to provide a program having the effects described above.

[0022] Note that the inventions of the above disclosures can be combined as much as possible.

Effects of the Invention

[0023] As described above, the present disclosure uses a radar device not only to detect large targets but also to detect small targets. When clustering cells in which the radar reception power exceeds a "small reception power threshold value" to detect small targets, even when a small target is close to clutter, the small target can be separated from the clutter and detected.

Brief Description of the Drawings

[0024] [Figure 1] It is a diagram showing problems to be solved in the conventional cluster extraction process. [[ID=​​​​​​​​​​​​​​​​​​​​​​​​This is a diagram showing the configuration of the target image processing system according to the second embodiment. [Figure 11] This figure shows the principle of cluster isolation processing in the second embodiment. [Figure 12] This figure shows the principle of cluster isolation processing in the second embodiment. [Figure 13] This figure shows the configuration of the rate dispersion threshold processing unit in the second embodiment. [Figure 14] This figure shows the contents of the Z-axis coordinate extraction process in the second embodiment. [Figure 15] This figure shows a specific example of the Z-axis coordinate extraction process of the second embodiment. [Figure 16] This figure shows the results of the cluster extraction process in the first and second embodiments. [Figure 17] This figure shows the challenges of the cluster isolation process in the first embodiment. [Figure 18] This is a diagram showing the configuration of the target image processing system according to the third embodiment. [Figure 19] This figure shows the contents of the scan correlation processing in the third embodiment. [Figure 20] This figure shows the contents of the received power threshold processing in the third embodiment. [Figure 21] This figure shows the contents of the Z-axis coordinate extraction process in the third embodiment. [Figure 22] This figure shows a specific example of the Z-axis coordinate extraction process of the third embodiment. [Figure 23] This figure shows the results of the cluster extraction process in the first and third embodiments. [Figure 24] This is a diagram showing the configuration of the target image processing system according to the fourth embodiment. [Figure 25] This figure shows the contents of the Z-axis coordinate extraction process in the fourth embodiment. [Modes for carrying out the invention]

[0025] Embodiments of the present disclosure will be described with reference to the attached drawings. The embodiments described below are examples of the implementation of the present disclosure, and the present disclosure is not limited to these embodiments.

[0026] (Configuration of the target image processing system in this disclosure) Figure 2 shows the configuration of the target image processing system of this disclosure. The target image processing system S comprises a radar device 1, a target image processing device 2, and a radar display device 3. The radar device 1 transmits a radar irradiation signal and receives a radar reflection signal. The target image processing device 2 comprises a target image acquisition unit 21, a cluster extraction unit 22, a radar characteristic calculation unit 23, and a cluster separation unit 24. The target image processing device 2 can be implemented by installing a target image processing program for performing the processing shown in Figures 6, 13, 14, 19-21, and 25 of the first to fourth embodiments on a computer. The radar display device 3 displays the position, velocity, and tracking results of the target.

[0027] Figure 3 shows the solution for the cluster extraction process in this disclosure. In this disclosure as well, it is necessary to cluster cells in which the radar received power exceeds a "small received power threshold" in order to detect not only large targets such as ships, but also small targets such as ships V or buoys. However, when small targets such as ships V or buoys are in close proximity to clutter such as waves W, it is not possible to detect the small targets such as ships V or buoys separately from the clutter such as waves W.

[0028] Here, the Doppler velocity of a small vessel V or target such as a buoy is independent of and often different from the Doppler velocity of clutter such as waves W, and is rarely close. Therefore, in this disclosure, the Doppler velocity deviation of each target cell (target or clutter) within each cluster is calculated relative to the average Doppler velocity of surrounding cells (clutter) outside each cluster. When the Doppler velocity deviation of each target cell within each cluster falls below a Doppler velocity deviation threshold, each target cell (clutter) within each cluster is separated from each cluster (target).

[0029] As a result, when tracking a small vessel V or buoy or other target, the target is not integrated with clutter such as waves W, and the characteristic quantities of the tracked target (center of gravity position, illumination area, maximum received power, or average Doppler velocity, etc.) are not distorted, thus improving the accuracy of target tracking.

[0030] In Figure 3, small vessels V or buoys are detected separately from clutter such as waves W. However, as a modified example, small helicopters (whose rotor rotation can be detected) or aircraft may be detected separately from clutter such as rain clouds.

[0031] (Configuration of the target image processing system in the first embodiment) Figure 4 shows the configuration of the target image processing system according to the first embodiment. The cluster extraction unit 22 includes a radar received power calculation unit 221 and a received power threshold processing unit 222. The radar characteristic calculation unit 23 includes a Doppler velocity deviation calculation unit 231 and a velocity deviation threshold processing unit 232. The cluster separation unit 24 includes a coordinate information extraction unit 241 and a clustering unit 242.

[0032] The principle of the cluster separation process in the first embodiment is shown in Figure 5. The left column of Figure 5 shows the XY plane coordinate information of the radar received power, and it is not possible to separate and detect the target from the clutter when the target is in close proximity to the clutter. The right column of Figure 5 shows the XY plane coordinate information of the Doppler velocity, and it is not uncommon for the Doppler velocity of the target to be independent of and different from that of the clutter, and rarely close. Based on the right column of Figure 5, it is considered that even when a small target is in close proximity to the clutter, the small target can be separated and detected from the clutter.

[0033] Figure 6 shows the configuration of the velocity deviation threshold processing unit of the first embodiment. The target image acquisition unit 21 acquires a target image from the radar device 1. The radar received power calculation unit 221 calculates the radar received power in the target image. The received power threshold processing unit 222 clusters cells in the target image where the radar received power exceeds the received power threshold using CFAR (Constant False Alarm Rate) processing (see Figure 6) and DBSCAN (Density-Based Spatial Clustering of Applications with Noise) processing, and extracts the clusters.

[0034] The Doppler velocity deviation calculation unit 231 and the velocity deviation threshold processing unit 232 can reduce computational costs by arranging the CFAR processing. The Doppler velocity deviation calculation unit 231 calculates the Doppler velocity of each target cell TC within each cluster relative to the average Doppler velocity (calculated by the average Doppler velocity calculation unit AD) of the surrounding cells PC outside each cluster (cells outside the guard cells GC adjacent to the target cell TC).

[0035] The velocity deviation threshold processing unit 232 outputs 0 as the Z-axis coordinate of each target cell TC in each cluster when the Doppler velocity deviation of each target cell TC in each cluster falls below the Doppler velocity deviation threshold. On the other hand, the velocity deviation threshold processing unit 232 outputs 1 as the Z-axis coordinate of each target cell TC in each cluster when the Doppler velocity deviation of each target cell TC in each cluster is equal to or greater than the Doppler velocity deviation threshold. The velocity deviation threshold processing unit 232 may also set the Doppler velocity deviation threshold to a constant multiple (1 or more) of the Doppler velocity resolution.

[0036] The coordinate information extraction unit 241 adds the Z-axis coordinate information of each target cell TC within each cluster to the XY plane coordinate information of the radar received power, thereby pseudo-expanding the coordinate information. The clustering unit 242 separates each target cell TC (clutter) within each cluster from each cluster (target) when the Z-axis coordinate of each target cell TC within each cluster is 0. On the other hand, the clustering unit 242 maintains each target cell TC (part of the target) within each cluster (target) when the Z-axis coordinate of each target cell TC within each cluster is 1.

[0037] A specific example of the Z-axis coordinate extraction process of the first embodiment is shown in Figure 7. The left column of Figure 7 shows the XY plane coordinate information of the Doppler velocity, and the middle column of Figure 7 shows the XY plane coordinate information of the Doppler velocity deviation, where a small target is clearly observed in the clutter. The right column of Figure 7 shows the XY plane coordinate information of the Z-axis coordinate information, where the small target is observed even more clearly in the clutter.

[0038] Figure 8 shows the results of the cluster extraction process of the prior art and the first embodiment. The upper left column of Figure 8 shows the XY plane coordinate information of the radar received power, where small targets are observed together with clutter. The upper right column of Figure 8 shows the XY plane coordinate information of the Doppler velocity, where small targets are observed separately from clutter. The lower left column of Figure 8 shows the results of the cluster extraction process of the prior art (Patent Document 1), where clutter is not separated from small targets. The lower right column of Figure 8 shows the results of the cluster extraction process of the first embodiment, where clutter is separated from small targets.

[0039] Thus, considering that the Doppler velocity of a target is independent of and often different from that of clutter, and is rarely similar, it is possible to detect small targets separately from clutter even when they are in close proximity.

[0040] (Configuration of the target image processing system in the second embodiment) The problems with the cluster separation process in the first embodiment are shown in Figure 9. In the left column of Figure 9, the XY plane coordinate information of the Doppler velocity is shown, and small targets appear to be observed separately from the system noise. In the middle column of Figure 9, the XY plane coordinate information of the Doppler velocity deviation is shown, and small targets appear not to be observed separately from the system noise. In the right column of Figure 9, the XY plane coordinate information of the Z axis coordinate information is shown, and small targets are excessively separated from the system noise.

[0041] Here, the Doppler velocity of the system noise is random. Therefore, if the number of peripheral cell PCs outside each cluster is insufficient, the average Doppler velocity of the peripheral cell PCs outside each cluster becomes unstable, and small targets are excessively separated from the system noise. On the other hand, if the number of peripheral cell PCs outside each cluster is sufficient, the average Doppler velocity of the peripheral cell PCs outside each cluster becomes close to 0, and small targets with low velocity are not separated from the system noise.

[0042] Figure 10 shows the configuration of the target image processing system according to the second embodiment. The cluster extraction unit 22 includes a radar received power calculation unit 221 and a received power threshold processing unit 222. The radar characteristic calculation unit 23 includes a Doppler velocity deviation calculation unit 231, a velocity deviation threshold processing unit 232, a Doppler velocity dispersion calculation unit 233 and a velocity dispersion threshold processing unit 234. The cluster separation unit 24 includes a coordinate information extraction unit 241, a clustering unit 242 and a Z-axis coordinate information extraction unit 243.

[0043] Figure 11 shows the principle of cluster separation processing in the second embodiment. The left column of Figure 11 shows the XY plane coordinate information of radar received power, and it is not possible to separate and detect a small, low-speed target when it is close to system noise. The middle column of Figure 11 shows the XY plane coordinate information of Doppler velocity, and it is not possible to separate and detect a small, low-speed target when it is close to system noise. The right column of Figure 11 shows the XY plane coordinate information of Doppler velocity dispersion, and it is not possible to separate and detect a small, low-speed target when it is close to system noise.

[0044] The principle of the cluster separation process in the second embodiment is also shown in Figure 12. The left column of Figure 12 shows the XY plane coordinate information of the radar received power, and it is not possible to separate and detect the small target when it is close to the clutter. The right column of Figure 12 shows the XY plane coordinate information of the Doppler velocity dispersion, and it is not possible to separate and detect the small target when it is close to the clutter because the Doppler velocity of the clutter is not sufficiently random. The middle column of Figure 12 shows the XY plane coordinate information of the Doppler velocity, and it is not possible to separate and detect the small target when it is close to the clutter.

[0045] Figure 13 shows the configuration of the velocity dispersion threshold processing unit in the second embodiment. Figure 14 shows the contents of the Z-axis coordinate extraction process in the second embodiment. In embodiment 2, compared to embodiment 1, the target image acquisition unit 21, radar received power calculation unit 221, received power threshold processing unit 222, Doppler velocity deviation calculation unit 231, and velocity deviation threshold processing unit 232 perform similar processing.

[0046] In Embodiment 2, the Doppler velocity variance calculation unit 233 and the velocity variance threshold processing unit 234 can reduce computational costs by arranging the CFAR processing. The Doppler velocity variance calculation unit 233 calculates the Doppler velocity variance of each target cell TC within each cluster and the average Doppler velocity variance of surrounding cells PC outside each cluster (outer cells of guard cells GC adjacent to the target cell TC) (calculated by the average Doppler velocity variance calculation unit AV).

[0047] The velocity dispersion thresholding unit 234 outputs 0 as the processing result (not the Z-axis coordinate) for each target cell TC in each cluster when the Doppler velocity dispersion of each target cell TC in each cluster falls below the Doppler velocity dispersion threshold. On the other hand, the velocity dispersion thresholding unit 234 outputs 1 as the processing result (not the Z-axis coordinate) for each target cell TC in each cluster when the Doppler velocity dispersion of each target cell TC in each cluster is equal to or greater than the Doppler velocity dispersion threshold. The velocity dispersion thresholding unit 234 may set the Doppler velocity dispersion threshold to approximately half of the Nyquist velocity used in the Fourier transform for calculating the Doppler velocity.

[0048] The velocity dispersion thresholding unit 234 outputs 0 as the processing result (not the Z-axis coordinate) for each peripheral cell PC outside the cluster when the average Doppler velocity dispersion of each peripheral cell PC outside the cluster falls below the average Doppler velocity dispersion threshold. On the other hand, the velocity dispersion thresholding unit 234 outputs 1 as the processing result (not the Z-axis coordinate) for each peripheral cell PC outside the cluster when the average Doppler velocity dispersion of each peripheral cell PC outside the cluster is equal to or greater than the average Doppler velocity dispersion threshold. The velocity dispersion thresholding unit 234 may set the average Doppler velocity dispersion threshold to about half of the Nyquist velocity used in the Fourier transform for calculating Doppler velocity, and it may be set to the same value or a different value compared to the Doppler velocity dispersion threshold.

[0049] The Z-axis coordinate information extraction unit 243 outputs the Z-axis coordinate of each target cell TC within each cluster based on the threshold processing result of the Doppler velocity deviation of each target cell TC within each cluster when the threshold processing result of the average Doppler velocity variance of surrounding cells PC (clutter) outside each cluster is 0. In other words, the Z-axis coordinate information extraction unit 243 outputs 0 as the Z-axis coordinate of each target cell TC (clutter) within each cluster when the threshold processing result of the Doppler velocity deviation of each target cell TC (clutter) within each cluster is 0. On the other hand, the Z-axis coordinate information extraction unit 243 outputs 1 as the Z-axis coordinate of each target cell TC (part of the target) within each cluster when the threshold processing result of the Doppler velocity deviation of each target cell TC (part of the target) within each cluster is 1.

[0050] The Z-axis coordinate information extraction unit 243 outputs the Z-axis coordinate of each target cell TC within each cluster based on the threshold processing result of the Doppler velocity variance of each target cell TC within each cluster when the threshold processing result of the average Doppler velocity variance of the surrounding cells PC (system noise) outside each cluster is 1. In other words, the Z-axis coordinate information extraction unit 243 outputs 1 as the Z-axis coordinate of each target cell TC (part of the target) within each cluster when the threshold processing result of the Doppler velocity variance of each target cell TC (part of the target) within each cluster is 0 (it inverts 0 to 1 and outputs it). On the other hand, the Z-axis coordinate information extraction unit 243 outputs 0 as the Z-axis coordinate of each target cell TC (system noise) within each cluster when the threshold processing result of the Doppler velocity variance of each target cell TC (system noise) within each cluster is 1 (it inverts 1 to 0 and outputs it).

[0051] The coordinate information extraction unit 241 adds the Z-axis coordinate information of each target cell TC within each cluster to the XY plane coordinate information of the radar received power, thereby pseudo-expanding the coordinate information. The clustering unit 242 separates each target cell TC (clutter or system noise) within each cluster from each cluster (target) when the Z-axis coordinate of each target cell TC within each cluster is 0 (an indicator of low target likelihood). On the other hand, the clustering unit 242 maintains each target cell TC (part of the target) within each cluster (target) when the Z-axis coordinate of each target cell TC within each cluster is 1 (an indicator of high target likelihood).

[0052] Figure 15 shows a specific example of the Z-axis coordinate extraction process of the second embodiment. The upper left column of Figure 15 shows the XY plane coordinate information of the Doppler velocity dispersion, where a small, low-velocity target is clearly observed amid system noise. The upper middle and lower left columns of Figure 15 show the XY plane coordinate information of the peripheral velocity dispersion processing result, where system noise is observed. The upper right and lower two columns of Figure 15 show the XY plane coordinate information of the target velocity dispersion processing result, where a small, low-velocity target is clearly observed amid system noise. The lower three columns of Figure 15 show the XY plane coordinate information of the velocity deviation processing result, where a small, low-velocity target is observed buried in system noise. The lower right column of Figure 15 shows the XY plane coordinate information of the Z-axis coordinate information, where a small, low-velocity target is clearly observed amid clutter.

[0053] Figure 16 shows the results of the cluster extraction process in the first and second embodiments. The upper left column of Figure 16 shows the XY plane coordinate information of the radar received power, where small targets are observed somewhat together with the system noise. The upper middle column of Figure 16 shows the XY plane coordinate information of the Doppler velocity, where small targets are observed somewhat together with the system noise. The upper right column of Figure 16 shows the XY plane coordinate information of the Doppler velocity dispersion, where small targets are observed separately from the system noise. The lower left column of Figure 16 shows the cluster extraction process results of the first embodiment, where small targets are excessively separated from the system noise. The lower right column of Figure 16 shows the cluster extraction process results of the second embodiment, where small targets are not excessively separated from the system noise.

[0054] Thus, considering that the Doppler velocity dispersion of the target is smaller than that of the system noise, it is possible to detect small, low-speed targets separately from the system noise, even when they are in close proximity to it.

[0055] Furthermore, when the average Doppler velocity variance of surrounding cells is small, like that of clutter, small targets can be detected separately from clutter based on the Doppler velocity deviation of the target cell. On the other hand, when the average Doppler velocity variance of surrounding cells is large, like that of system noise, small, low-velocity targets can be detected separately from system noise based on the Doppler velocity variance of the target cell.

[0056] As a modification of the second embodiment, the Doppler velocity variance calculation unit 233 may calculate the Doppler velocity variance deviation of each target cell TC within each cluster with respect to the average Doppler velocity variance of surrounding cells PC outside each cluster (outer cells of guard cells GC adjacent to the target cell TC) (calculated by the average Doppler velocity variance calculation unit AV).

[0057] Furthermore, the clustering unit 242 may separate each target cell TC (system noise) within each cluster from each cluster (target) when the Doppler velocity dispersion deviation of each target cell TC (system noise) within each cluster falls below the Doppler velocity dispersion deviation threshold. On the other hand, the clustering unit 242 may maintain each target cell TC (part of the target) within each cluster within each cluster (target) when the Doppler velocity dispersion deviation of each target cell TC (part of the target) within each cluster is equal to or greater than the Doppler velocity dispersion deviation threshold.

[0058] In the second embodiment, thresholding can be performed on the Doppler velocity variance of each target cell TC within each cluster and on the average Doppler velocity variance of surrounding cells PC outside each cluster, according to their respective characteristics. On the other hand, in a modified version of the second embodiment, a single, simplified thresholding can be performed on the Doppler velocity variance deviation between these Doppler velocity variances.

[0059] Clutter can have a larger Doppler velocity dispersion than targets, though not to the same extent as system noise. In the second embodiment, targets, clutter, and system noise can be distinguished by performing thresholding with different values ​​as thresholding according to each characteristic. On the other hand, in a modified version of the second embodiment, if the resolution of the Doppler velocity is sufficiently high in a single simplified thresholding process, targets can be distinguished from clutter and system noise.

[0060] (Configuration of the target image processing system in the third embodiment) The challenges of the cluster separation process in the first embodiment are shown in Figure 17. In the left column of Figure 17, the XY plane coordinate information of the Doppler velocity is shown, and a small, low-velocity target is observed together with the clutter. In the middle column of Figure 17, the XY plane coordinate information of the Doppler velocity deviation is shown, and a small, low-velocity target is observed together with the clutter. In the right column of Figure 17, the XY plane coordinate information of the Z-axis coordinate information is shown, and a small, low-velocity target is not observed and is not separated from the clutter.

[0061] Here, if the wind speed is low, the clutter velocity will be low in all directions, and the velocity of small, slow-moving targets will match the clutter velocity. On the other hand, if the wind speed is high, the clutter velocity will be high in one direction but low in other directions, and the velocity of small, slow-moving targets will match the velocity of clutter in other directions. Therefore, by lowering the Doppler velocity deviation threshold, it is possible to separate the clutter from small, slow-moving targets, but this can also lead to excessive separation.

[0062] Figure 18 shows the configuration of the target image processing system according to the third embodiment. The cluster extraction unit 22 includes a radar received power calculation unit 221 and a received power threshold processing unit 222. The radar characteristic calculation unit 23 includes a Doppler velocity deviation calculation unit 231, a velocity deviation threshold processing unit 232, a radar received power storage unit 235 and a scan correlation calculation unit 236. The cluster separation unit 24 includes a coordinate information extraction unit 241, a clustering unit 242 and a Z-axis coordinate information extraction unit 243.

[0063] Figure 19 shows the scan correlation processing of the third embodiment. Figure 20 shows the received power threshold processing of the third embodiment. Figure 21 shows the Z-axis coordinate extraction processing of the third embodiment. In Embodiment 3, compared to Embodiment 1, the target image acquisition unit 21, radar received power calculation unit 221, Doppler velocity deviation calculation unit 231, and velocity deviation threshold processing unit 232 perform similar processing, while the received power threshold processing unit 222 performs slightly different processing.

[0064] In Embodiment 3, the radar received power storage unit 235 stores past radar scans after the output of the received power threshold calculation unit 222. The scan correlation calculation unit 236 calculates the scan correlation between past radar scans after the output of the received power threshold calculation unit 222 and the current radar scan after the output of the received power threshold calculation unit 222 for each target cell within each cluster.

[0065] As a variation, the radar received power storage unit 235 stores past radar scans prior to the input of the received power threshold calculation unit 222. The scan correlation calculation unit 236 calculates the scan correlation between the past radar scans prior to the input of the received power threshold calculation unit 222 and the current radar scan prior to the input of the received power threshold calculation unit 222 for each target cell within each cluster.

[0066] The scan correlation calculation unit 236 then determines that there is no temporal correlation when the radar reception intensity of each target cell within each cluster falls below a predetermined threshold in either a past radar scan or the current radar scan, and outputs 0 as the processing result (not the Z-axis coordinate) for each target cell within each cluster (see Figure 19).

[0067] On the other hand, the scan correlation calculation unit 236 determines that there is a temporal correlation when the radar reception intensity of each target cell within each cluster is above a predetermined threshold for both past and current radar scans, and outputs 1 as the processing result (not the Z-axis coordinate) for each target cell within each cluster (see Figure 19).

[0068] Here, system noise has almost no scan correlation, while clutter has some scan correlation, though not as much as target correlation. For example, clutter such as wind waves is irregular and therefore has little scan correlation, but clutter such as swells is regular and therefore has some scan correlation (see the upper left column of Figure 20), and clutter such as rainfall has spread and therefore has some scan correlation (see the lower left column of Figure 20).

[0069] Therefore, the received power threshold calculation unit 222 lowers the scan correlation of clutter by increasing the received power threshold, while maintaining a high scan correlation of targets. In other words, by increasing the received power threshold, the received power threshold calculation unit 222 fragments clutter such as swells and lowers the scan correlation (see the upper right column of Figure 20), and removes clutter such as rainfall overall and lowers the scan correlation (see the lower right column of Figure 20).

[0070] The Z-axis coordinate information extraction unit 243 outputs the Z-axis coordinate of each target cell in each cluster based on the calculation result of the scan correlation of each target cell in each cluster when the threshold processing result of the Doppler velocity deviation of each target cell (part of a low-velocity target or clutter) in each cluster is 0. In other words, the Z-axis coordinate information extraction unit 243 outputs 0 as the Z-axis coordinate of each target cell (clutter) in each cluster when the calculation result of the scan correlation of each target cell (clutter) in each cluster is 0. On the other hand, the Z-axis coordinate information extraction unit 243 outputs 1 as the Z-axis coordinate of each target cell (part of a low-velocity target) in each cluster when the calculation result of the scan correlation of each target cell (part of a low-velocity target) in each cluster is 1.

[0071] The Z-axis coordinate information extraction unit 243 outputs the Z-axis coordinate of each target cell in each cluster (without using scan correlation) based on the threshold processing result of the Doppler velocity deviation of each target cell in each cluster (a portion of the high-speed targets) when the threshold processing result of the Doppler velocity deviation of each target cell in each cluster is 1. In other words, the Z-axis coordinate information extraction unit 243 outputs 1 as the Z-axis coordinate of each target cell in each cluster (a portion of the high-speed targets) when the threshold processing result of the Doppler velocity deviation of each target cell in each cluster (a portion of the high-speed targets) is 1.

[0072] The coordinate information extraction unit 241 adds the Z-axis coordinate information of each target cell within each cluster to the XY plane coordinate information of the radar received power, thereby pseudo-expanding the coordinate information. The clustering unit 242 separates each target cell (clutter) within each cluster from each cluster (low-speed and high-speed targets) when the Z-axis coordinate of each target cell within each cluster is 0 (an indicator of low target likelihood). On the other hand, the clustering unit 242 maintains each target cell (a part of the low-speed and high-speed targets) within each cluster (low-speed and high-speed targets) when the Z-axis coordinate of each target cell within each cluster is 1 (an indicator of high target likelihood).

[0073] A specific example of the Z-axis coordinate extraction process of the third embodiment is shown in Figure 22. The upper left column of Figure 22 shows the XY plane coordinate information of past radar scans, the upper middle column of Figure 22 shows the XY plane coordinate information of the current radar scan, the upper right and lower middle columns of Figure 22 show the XY plane coordinate information of the scan correlation calculation results, the lower left column of Figure 22 shows the XY plane coordinate information of the velocity deviation processing results, and the lower right column of Figure 22 shows the XY plane coordinate information of the Z-axis coordinate information.

[0074] Figure 23 shows the results of the cluster extraction process in the first and third embodiments. The upper left column of Figure 23 shows the XY plane coordinate information of the radar received power, where a small, low-speed target is observed together with the clutter. The upper right column of Figure 23 shows the XY plane coordinate information of the Doppler velocity, where a small, low-speed target is observed together with the clutter. The lower left column of Figure 23 shows the cluster extraction process result of the first embodiment, where the clutter is not separated from the small, low-speed target. The lower right column of Figure 23 shows the cluster extraction process result of the third embodiment (the scan correlation calculation results are the same as in the upper right and middle lower columns of Figure 22), where the clutter is separated from the small, low-speed target.

[0075] Thus, considering that the scan correlation of low-velocity targets is higher than that of clutter, it is possible to detect small, low-velocity targets separately from clutter even when they are in close proximity.

[0076] Furthermore, when the Doppler velocity deviation of the target cell is small, like the deviation between a low-speed target and clutter, small, low-speed targets can be detected separately from clutter based on the scan correlation of the target cell. On the other hand, when the Doppler velocity deviation of the target cell is large, like the deviation between a high-speed target and clutter, small, high-speed targets can be detected separately from clutter based on the Doppler velocity deviation of the target cell.

[0077] Furthermore, by considering that the scan correlation of clutter is somewhat high and using received power thresholding to keep it low, it is possible to detect small, low-speed targets separately from clutter even when they are in close proximity.

[0078] As a modification of the third embodiment, the Z-axis coordinate information extraction unit 243 may output the Z-axis coordinate of each target cell in each cluster based not only on the threshold processing result of the Doppler velocity deviation of each target cell in each cluster, but also on the calculation result of the scan correlation of each target cell in each cluster, when the threshold processing result of the Doppler velocity deviation of each target cell in each cluster is 1.

[0079] In the third embodiment, when parts of low-speed targets overlap in past radar scans and current radar scans, the low-speed targets can be prevented from being excessively separated. Furthermore, in the third embodiment, when a high-speed target approaches a location where noise was present in a past radar scan during the current radar scan, the high-speed targets can be prevented from being excessively separated. On the other hand, in a modified version of the third embodiment, when a high-speed target approaches a location where a low-speed target was present in a past radar scan during the current radar scan, the high-speed targets can be separated from the low-speed targets.

[0080] (Configuration of the target image processing system in the fourth embodiment) Figure 24 shows the configuration of the target image processing system of the fourth embodiment (combining the first to third embodiments). The cluster extraction unit 22 includes a radar received power calculation unit 221 and a received power threshold processing unit 222. The radar characteristic calculation unit 23 includes a Doppler velocity deviation calculation unit 231, a velocity deviation threshold processing unit 232, a Doppler velocity dispersion calculation unit 233, a velocity dispersion threshold processing unit 234, a radar received power storage unit 235 and a scan correlation calculation unit 236. The cluster separation unit 24 includes a coordinate information extraction unit 241, a clustering unit 242 and a Z-axis coordinate information extraction unit 243.

[0081] Figure 25 shows the contents of the Z-axis coordinate extraction process of the fourth embodiment (combining the first to third embodiments). The Z-axis coordinate information extraction unit 243 outputs the Z-axis coordinate based on the threshold processing result of the Doppler velocity deviation of the target cell, the threshold processing result of the Doppler velocity dispersion of the target cell, the threshold processing result of the average Doppler velocity dispersion of surrounding cells, and the calculation processing result of the scan correlation of the target cell. Specifically, the Z-axis coordinate information extraction unit 243 outputs the Z-axis coordinate in the following priority order: threshold processing result of the average Doppler velocity dispersion of surrounding cells → (threshold processing result of the Doppler velocity dispersion of the target cell or threshold processing result of the Doppler velocity deviation of the target cell) → calculation processing result of the scan correlation of the target cell.

[0082] In this way, by considering Doppler velocity deviation, Doppler velocity dispersion, and scan correlation, small targets can be detected separately from clutter and system noise, even when they are in close proximity to them. [Industrial applicability]

[0083] The target image processing apparatus and target image processing program of this disclosure, when clustering cells in which the radar received power exceeds a "small received power threshold" in order to detect not only large targets but also small targets using a radar apparatus, can detect small targets separately from clutter even when the small targets are in close proximity to clutter. [Explanation of Symbols]

[0084] V: Ship W:Wave S: Target image processing system 1: Radar equipment 2: Target Image Processing Device 3: Radar display device 21: Target image acquisition unit 22: Cluster extraction unit 23: Radar characteristic calculation unit 24: Cluster Isolation Unit 221: Radar reception power calculation unit 222: Received power threshold processing unit 231: Doppler velocity deviation calculation unit 232: Speed ​​deviation threshold processing unit 233: Doppler velocity dispersion calculation section 234: Velocity distribution threshold processing unit 235: Radar receiving power storage unit 236: Scan Correlation Calculation Unit 241: Coordinate information extraction unit 242: Clustering section 243:Z-axis coordinate information extraction part TC: Target cell GC: Guard Cell PC: Peripheral Cells AD: Average Doppler velocity calculation unit AV: Average Doppler velocity dispersion calculation unit

Claims

1. A target image acquisition unit that acquires target images from a radar device, In the aforementioned target image, a cluster extraction unit clusters cells in which the radar received power exceeds the received power threshold and extracts the clusters. A Doppler velocity deviation calculation unit calculates the Doppler velocity deviation of each target cell within each cluster relative to the average Doppler velocity of surrounding cells outside each cluster. A cluster separation unit separates each target cell within each cluster from the cluster when the Doppler velocity deviation of each target cell within each cluster falls below a Doppler velocity deviation threshold, and maintains each target cell within each cluster within the cluster when the Doppler velocity deviation of each target cell within each cluster is equal to or greater than the Doppler velocity deviation threshold. A target image processing apparatus characterized by comprising:

2. (1) A Doppler velocity variance calculation unit that calculates the Doppler velocity variance of each target cell within each cluster and the average Doppler velocity variance of surrounding cells outside each cluster, or (2) a Doppler velocity variance calculation unit that calculates the Doppler velocity variance deviation of each target cell within each cluster with respect to the average Doppler velocity variance of surrounding cells outside each cluster. The cluster separation unit determines whether to separate or maintain each target cell within each cluster from each cluster based on (1) the Doppler velocity variance of each target cell within each cluster and the average Doppler velocity variance of surrounding cells outside each cluster, or (2) the Doppler velocity variance deviation of each target cell within each cluster from each cluster. The target image processing apparatus according to claim 1, characterized in that

3. The cluster separation unit determines whether to separate or maintain each target cell within each cluster from each cluster based on the Doppler velocity deviation of each target cell within each cluster when the average Doppler velocity variance of surrounding cells outside each cluster falls below the average Doppler velocity variance threshold, and determines whether to separate or maintain each target cell within each cluster from each cluster based on the Doppler velocity variance of each target cell within each cluster when the average Doppler velocity variance of surrounding cells outside each cluster is equal to or greater than the average Doppler velocity variance threshold. The target image processing apparatus according to claim 2, characterized in that

4. The system further comprises a scan correlation calculation unit that calculates the scan correlation between past radar scans and current radar scans for each target cell within each cluster, The cluster isolation unit determines, based on the scan correlation of each target cell within each cluster, whether to separate or maintain each target cell within each cluster relative to the respective cluster. The target image processing apparatus according to claim 1, characterized in that

5. The cluster separation unit determines whether to separate or maintain each target cell within each cluster based on the scan correlation of each target cell within each cluster when the Doppler velocity deviation of each target cell within each cluster falls below the Doppler velocity deviation threshold, and determines whether to maintain each target cell within each cluster based on the Doppler velocity deviation of each target cell within each cluster when the Doppler velocity deviation of each target cell within each cluster is equal to or greater than the Doppler velocity deviation threshold. The target image processing apparatus according to claim 4, characterized in that

6. (1) A Doppler velocity variance calculation unit that calculates the Doppler velocity variance of each target cell within each cluster and the average Doppler velocity variance of surrounding cells outside each cluster, or (2) a Doppler velocity variance calculation unit that calculates the Doppler velocity variance deviation of each target cell within each cluster with respect to the average Doppler velocity variance of surrounding cells outside each cluster. The system further comprises a scan correlation calculation unit that calculates the scan correlation between past radar scans and current radar scans for each target cell within each cluster, The cluster separation unit determines whether to separate or maintain each target cell within each cluster relative to each cluster based on (1) the Doppler velocity variance of each target cell within each cluster, the average Doppler velocity variance of surrounding cells outside each cluster, and the scan correlation of each target cell within each cluster, or (2) the Doppler velocity variance deviation of each target cell within each cluster relative to each cluster, and the scan correlation of each target cell within each cluster. The target image processing apparatus according to claim 1, characterized in that

7. A target image processing program for causing a computer to perform each processing step performed by each processing unit of the target image processing apparatus according to any one of claims 1 to 6.

Images