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 scan correlation of low-speed targets is higher than that of clutter. Therefore, in this disclosure, the scan correlation between past radar scans and current radar scans is calculated for each target cell within each cluster, and when the scan correlation of each target cell within each cluster shows no temporal correlation, 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. 1. 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 (centroid 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 scan correlation of low-speed targets is higher than that of clutter. To solve the above problem, the scan correlation between past radar scans and current radar scans is calculated for each target cell within each cluster. When the scan correlation of each target cell within each cluster shows no temporal correlation, 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 scan correlation calculation unit calculates the scan correlation between past radar scans and current radar scans for each target cell within each cluster. A cluster separation unit that separates each target cell within each cluster from the respective cluster when the scan correlation of each target cell within each cluster indicates that there is no temporal correlation, and maintains each target cell within each cluster within the respective cluster when the scan correlation of each target cell within each cluster indicates that there is a temporal correlation, This is a target image processing device characterized by having the following features.

[0009] 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.

[0010] Furthermore, this disclosure states that the cluster extraction unit lowers the scan correlation of clutter while maintaining a high scan correlation of targets by increasing the received power threshold. This is a target image processing device characterized by the following features.

[0011] With this configuration, even if the scan correlation of the clutter is somewhat high, by 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.

[0012] Furthermore, this disclosure is a target image processing program that causes a computer to execute each processing step performed by each processing unit of the target image processing apparatus described above.

[0013] This configuration makes it possible to provide a program that has the effects described above.

[0014] Furthermore, the inventions disclosed above can be combined as much as possible. [Effects of the Invention]

[0015] Thus, this disclosure enables the detection of small targets not only by using a radar device, but also by clustering cells where the radar received power exceeds a "small received power threshold" in order to detect small targets. This allows for the detection of small targets separately from clutter, even when the small targets are in close proximity to clutter. [Brief explanation of the drawing]

[0016] [Figure 1] This figure shows the problems that conventional cluster extraction methods have failed to solve. [Figure 2] This figure shows the configuration of the target image processing system disclosed herein. [Figure 3] This figure shows the solution for the cluster extraction process described herein. [Figure 4]This is a diagram showing the configuration of the target image processing system of the present embodiment. [Figure 5] This is a diagram showing the content of the scan correlation processing of the present embodiment. [Figure 6] This is a diagram showing the content of the received power threshold processing of the present embodiment. [Figure 7] This is a diagram showing the results of the cluster extraction processing of the prior art and the present embodiment.

Embodiments for Carrying Out the Invention

[0017] Embodiments of the present disclosure will be described with reference to the accompanying drawings. The embodiments described below are examples of the implementation of the present disclosure, and the present disclosure is not limited to the following embodiments.

[0018] (Configuration of the Target Image Processing System of the Present Disclosure) The configuration of the target image processing system of the present disclosure is shown in FIG. 2. The target image processing system S includes 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 includes 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 install and implement a target image processing program for executing the processing shown in FIGS. 5 and 6 of the present embodiment on a computer. The radar display device 3 displays the position, speed, and tracking result of the target.

[0019] The solution means for the cluster extraction processing of the present disclosure is shown in FIG. 3. In the present disclosure as well, 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 whose radar received power exceeds a "small received power threshold". 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.

[0020] Here, the scan correlation of low-speed small vessels V or targets such as buoys is higher than the scan correlation of clutter such as waves W. Therefore, in this disclosure, the scan correlation between past radar scans and current radar scans is calculated for each target cell (low-speed target or clutter) within each cluster, and when the scan correlation of each target cell (clutter) within each cluster shows no temporal correlation, each target cell (clutter) within each cluster is separated from each cluster (low-speed target).

[0021] 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.

[0022] 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.

[0023] (Configuration of the target image processing system of this embodiment) Figure 4 shows the configuration of the target image processing system of this 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 radar received power storage unit 231 and a scan correlation calculation unit 232. The cluster separation unit 24 includes a coordinate information extraction unit 241 and a clustering unit 242.

[0024] Figure 5 shows the scan correlation processing of this embodiment. Figure 6 shows the received power threshold processing of this 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 and DBSCAN (Density-Based Spatial Clustering of Applications with Noise) processing, etc., and extracts the clusters.

[0025] The radar received power storage unit 231 stores past radar scans after the output of the received power threshold calculation unit 222. The scan correlation calculation unit 232 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.

[0026] As a variation, the radar received power storage unit 231 stores past radar scans prior to the input of the received power threshold calculation unit 222. The scan correlation calculation unit 232 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.

[0027] The scan correlation calculation unit 232 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 Z-axis coordinate of each target cell within each cluster (see Figure 5).

[0028] On the other hand, the scan correlation calculation unit 232 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 Z-axis coordinate of each target cell within each cluster (see Figure 5).

[0029] 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 upper left column of Figure 6), and clutter such as rainfall has spread and therefore has some scan correlation (see lower left column of Figure 6).

[0030] 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 6), and removes clutter such as rainfall overall and lowers the scan correlation (see the lower right column of Figure 6).

[0031] 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 target) when the Z-axis coordinate of each target cell within each cluster is 0. On the other hand, the clustering unit 242 maintains each target cell (part of the low-speed target) within each cluster (low-speed target) when the Z-axis coordinate of each target cell within each cluster is 1.

[0032] Figure 7 shows the results of the cluster extraction process of the prior art and this embodiment. The upper left column of Figure 7 shows the XY plane coordinate information of the radar received power, in which a small, low-speed target is observed together with the clutter. The upper right column of Figure 7 shows the XY plane coordinate information of the scan correlation, in which a small, low-speed target is observed separately from the clutter. The lower left column of Figure 7 shows the results of the cluster extraction process of the prior art (Patent Document 1), in which the clutter is not separated from the small, low-speed target. The lower right column of Figure 7 shows the results of the cluster extraction process of this embodiment, in which the clutter is separated from the small, low-speed target.

[0033] 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.

[0034] Furthermore, by taking into account that the scan correlation of the 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. [Industrial applicability]

[0035] 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]

[0036] 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: Radar receiving power storage unit 232: Scan Correlation Calculation Unit 241: Coordinate information extraction unit 242: Clustering section

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 scan correlation calculation unit calculates the scan correlation between past radar scans and current radar scans for each target cell within each cluster. A cluster separation unit that separates each target cell within each cluster from the respective cluster when the scan correlation of each target cell within each cluster indicates that there is no temporal correlation, and maintains each target cell within each cluster within the respective cluster when the scan correlation of each target cell within each cluster indicates that there is a temporal correlation, A target image processing apparatus characterized by comprising:

2. The cluster extraction unit lowers the scan correlation of clutter while maintaining a high scan correlation of targets by increasing the received power threshold. The target image processing apparatus according to claim 1, characterized in that

3. 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 claim 1 or 2.

Images