JP2008164545A - Moving target detection device, moving target detection method, and moving target detection program - Google Patents

Abstract

An object of the present invention is to reduce stationary detection of a moving target by removing stationary targets other than the moving target having a high signal level in the moving target detection processing for an SAR image.
A moving target detecting apparatus includes a moving target detecting unit including a suppression ratio calculating unit. The image difference processing unit 140 uses the amplitude difference between the SAR image A indicating the amplitude value of the received signal observed by the radar at time t and the SAR image B indicating the amplitude value of the received signal observed at the time t + Δt as a target distribution map. calculate. The suppression ratio calculation unit 152 calculates a suppression ratio obtained by dividing the target distribution map by either the SAR image A or the SAR image B. The target identifying unit 153 detects the movement target by comparing the suppression ratio with a threshold value. The moving target detection apparatus 100 can detect the moving target more easily than comparing the target distribution chart with the threshold by comparing the suppression ratio with the threshold, and can reduce the erroneous detection of the moving target.
[Selection] Figure 1

Description

  The present invention relates to a moving target detecting device, a moving target detecting method, and a moving target that detect a moving target from an image obtained by a sensor that is mounted on a platform such as an aircraft, an unmanned aircraft, or a satellite and captures a high-resolution image of the ground surface or the sea surface. It relates to a target detection program.

  In radars that use aircraft, unmanned aircraft, artificial satellites, etc. as a platform, arrange two or more antennas (antennas) in the direction of movement of the onboard machine, and receive the signal received by the first antenna according to the speed of the aircraft. If adjustment is made so that signals received by the second and subsequent antennas after several pulses have the same phase, clutter can be suppressed by the difference between these received signals, and a moving target can be detected (for example, Non-Patent Document 1). This function is called DPCA (Displaced Phase Center Antenna) or STAP (Space Time Adaptive Processing), and is a moving target detection function used in aircraft radars in recent years.

An example of such a system performs synthetic aperture radar processing on each of the signals received by each of the two antennas, and obtains two complex SAR (Synthetic Aperture Radar) images. The system then superimposes these two complex SAR images to obtain a phase difference, and obtains the amplitude of the phase difference for each pixel. By such processing, the system can obtain a moving target distribution map in which a signal appears only in a pixel where the moving target exists. This is because the phase of the two complex images is the same for the stationary target, whereas the phase of the two complex images is different for the moving target due to the Doppler effect. Therefore, by taking the phase difference between the two complex images, the stationary target is canceled out, and only the moving target having a different phase remains as an image (see, for example, Patent Document 1).
JP-A-10-232282 "RADAR HANDBOOK SECOND EDITION" by MERRILL SKOLNIK, McGRAW-HILL, 1990, p16.8-p16.31

  However, when processing using field data is performed in the conventional moving target detection processing, the remaining non-moving target (clutter etc.) other than the moving target with a high signal level occurs in the original image, and the remaining clutter etc. It was falsely detected as a moving target.

  It is an object of the present invention to suppress this erroneous detection.

  The moving target detection apparatus of the present invention irradiates an electromagnetic wave, observes the amplitude of the reflected wave from each place in the irradiation direction at the first time and the second time, and the amplitude of the reflected wave at each place at the first time Is a moving target detection device that detects a moving object whose reflected wave amplitude difference at a different time is larger than a stationary body based on the amplitude of the reflected wave at each point at the second time and the reflected wave at each point at the first time A difference calculating unit that calculates the absolute value of the difference between the amplitude of the reflected wave and the amplitude of the reflected wave at each point at the second time using a CPU (Central Processing Unit), and the amplitude of the reflected wave at each point calculated by the difference calculating unit A division unit that uses a CPU to calculate a division value obtained by dividing the difference by the amplitude of the reflected wave at each location at either the first time or the second time, and the division value calculated by the division unit Threshold of C A comparison is made using a PU, and when the division value is larger than the threshold value, a moving body detection unit that detects that a moving body exists at the position and detects the moving body is provided.

According to the present invention, the division unit calculates a division value as the suppression ratio, and the moving body detection unit detects the moving body by comparing the suppression ratio with the threshold value, so that erroneous detection can be suppressed.
In the present invention, attention is paid to the fact that the clutter (stationary object) is suppressed and the moving target is not suppressed in the conventional moving target detection process, and the suppression ratio is compared with the threshold value for the detected target. In the present invention, if the suppression ratio is lower than the threshold value, the target is made unerased by the clutter, and if the suppression ratio is high, the target is determined to be a moving target so that erroneous detection can be suppressed. The present invention is particularly useful when a moving target is detected after imaging rather than when a moving target is detected in parallel with radar observation.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram of a moving target detection apparatus 100 according to the first embodiment.
The configuration of the moving target detection apparatus 100 according to Embodiment 1 will be described below with reference to FIG.
As shown in FIG. 1, the moving target detection device 100 includes a SAR sensor 110, a motion sensor 120, an image reproduction processing unit 130, an image difference processing unit 140, a moving target detection unit 150, a received signal A storage device 191, and a received signal B storage. A device 192, an exercise data storage device 193, a SAR image A storage device 194, a SAR image B storage device 195, and a target distribution map storage device 196;

  The SAR sensor 110 (SAR: Synthetic Aperture Radar [Synthetic Aperture Radar]) is composed of an antenna, a transmitter, a receiver, and the like that can generate two images, and generates a high-frequency pulse signal (an example of an electromagnetic wave [radio wave, light wave]). The received signal is obtained by transmitting and receiving this. The SAR sensor 110 is an example of a radar that irradiates a high-frequency pulse signal in a certain direction, receives a high-frequency pulse signal (echo signal, reflected wave) reflected at various places in the irradiation direction, and observes the amplitude of the received signal. The SAR sensor 110 may be another radar such as a real aperture radar or a reverse synthetic aperture radar. Specifically, the SAR sensor 110 generates a high-frequency pulse signal, radiates the high-frequency pulse signal from the antenna to the space, and receives an echo signal reflected in some way by the antenna. Further, the SAR sensor 110 amplifies the received echo signal, converts the frequency of the amplified echo signal to an intermediate frequency, and converts the echo signal of the intermediate frequency into a digital signal (digital data) to obtain a received signal. The amplitude of the received signal observed by the SAR sensor 110 indicates the power and intensity of the echo signal, and the received signal is used for imaging at various places. The magnitude of the amplitude of the echo signal corresponds to the brightness of the image. The SAR sensor 110 according to the first embodiment receives an echo signal by each of two receiving antennas arranged at different positions, or performs two observations, thereby obtaining a first time (first time zone). ), The amplitude and phase of the echo signal reflected at each place and the amplitude and phase of the echo signal reflected at each place at the second time (second time zone) are observed.

In the received signal A storage device 191, data indicating the amplitude value and phase of the echo signal from each place at the first time observed by the SAR sensor 110 is stored as the received signal A.
In the received signal B storage device 192, data indicating the amplitude value and phase of the echo signal from each place at the second time observed by the SAR sensor 110 is stored as the received signal B.

  The motion sensor 120 measures the motion of the platform on which the SAR sensor 110 is mounted by using a gyro or the like, and outputs the instantaneous position / posture of the platform when the SAR sensor 110 transmits / receives a high-frequency pulse signal. The instantaneous position / posture of the platform output from the motion sensor 120 corresponds to the position / posture of the SAR sensor 110 when transmitting / receiving a high-frequency pulse signal. By calculating the positional relationship between the SAR sensor 110 and each location where the high-frequency pulse signal is reflected based on the calculated position / orientation of the SAR sensor 110, each location can be represented at an accurate position in imaging.

  The movement data storage device 193 stores the position / posture of the SAR sensor 110 calculated by the movement sensor 120 as movement data.

The image reproduction processing unit 130 performs image reproduction processing for imaging each part based on the amplitude value and phase of the echo signal from each part indicated by the received signal. There are various image reproduction methods such as a polar format method, a range Doppler method, and a chirp scaling method, and the image reproduction processing unit 130 performs signal processing of the received signal using any one of the image reproduction methods to perform a two-dimensional process. Play high-resolution SAR images. The SAR image is represented by complex data.
The image reproduction processing unit 130 includes an image reproduction processing unit A 131 and an image reproduction processing unit B 132, and the image reproduction processing unit A 131 is stored in the received signal A and motion data storage device 193 stored in the received signal A storage device 191. SAR image data representing each location at the first time is generated based on the position and orientation of the SAR sensor 110, and the image reproduction processing unit B132 stores the received signal B and the motion data stored in the received signal B storage device 192. Based on the position and orientation of the SAR sensor 110 stored in the device 193, SAR image data representing each place at the second time is generated.

In the SAR image A storage device 194, the SAR image data at the first time generated by the image reproduction processing unit A131 is stored as the SAR image A.
In the SAR image B storage device 195, the SAR image data at the second time generated by the image reproduction processing unit B132 is stored as the SAR image B.

  An image difference processing unit 140 (an example of a difference calculation unit) performs image difference processing for calculating an image difference from two images. In the image difference processing, the image difference processing unit 140 applies two SAR images to the SAR image A stored in the SAR image A storage device 194 and the SAR image B stored in the SAR image B storage device 195. The phase difference is obtained by superposition, and the amplitude of the difference is obtained for each pixel. The amplitude difference of each pixel in the two SAR images calculated by the image difference processing is a feature moving to the ground surface corresponding to the pixel (moving body, hereinafter referred to as a moving target) or a stationary feature (stationary body). , Hereinafter referred to as a stationary target).

  The target distribution chart storage device 196 stores data indicating the amplitude difference of each pixel between the SAR image A and the SAR image B calculated by the image difference processing unit 140 as a target distribution chart indicating the distribution between the moving target and the stationary target. The

The movement target detection unit 150 calculates an amplitude suppression ratio between the original image and the difference-detected image, and detects the movement target based on the calculated suppression ratio. At this time, the moving target detection unit 150 calculates the amplitude difference between the pixels of the SAR image A and the SAR image B indicated by the target distribution map stored in the target distribution map storage device 196, and stores the SAR stored in the SAR image A storage device 194. A value obtained by dividing the amplitude of each pixel indicated by the SAR image B stored in the image A or SAR image B storage device 195 is calculated as the suppression ratio of the amplitude difference in the target distribution map based on the SAR image. Next, the movement target detection unit 150 compares the calculated suppression ratio with a specific threshold value, and when the suppression ratio is larger than the threshold value, it is determined that the movement target is present on the surface portion corresponding to the pixel. Then, the movement target detection unit 150 generates movement target data indicating the position and time at which the movement target exists based on the determination result.
The movement target detection unit 150 includes a CFAR processing unit 151, a suppression ratio calculation unit 152, and a target identification unit 153.
The CFAR processing unit 151 selects a target to be identified as a moving target or a stationary target by removing noise from the target distribution map by performing CFAR (Constant False Alarm Rate) processing on the target distribution map. To do.
The suppression ratio calculation unit 152 (dividing unit) calculates the amplitude difference of each pixel between the SAR image A and the SAR image B indicated by the target distribution diagram for the target selected by the CFAR processing unit 151, as the SAR image A or the SAR image B. The suppression ratio divided by the amplitude of each pixel indicated by is calculated.
The target identification unit 153 (target identification unit) compares the suppression ratio calculated by the suppression ratio calculation unit 152 with a specific threshold, and identifies whether the target to be identified is a moving target or a stationary target based on the comparison result. Movement target data is generated based on the identification result.

The moving target detection apparatus 100 according to the first embodiment is a synthetic aperture radar apparatus that is mounted on a moving platform such as an aircraft, an unmanned aerial vehicle, or a satellite to obtain a high resolution image of the ground surface or the sea surface. An image reproduction processing unit 130, an image difference processing unit 140, and a movement target detection unit 150 are provided.
The moving target detection apparatus 100 according to Embodiment 1 is particularly characterized by including a moving target detection unit 150.

FIG. 2 is a diagram illustrating an example of hardware resources of the moving target detection apparatus 100 according to the first embodiment.
In FIG. 2, the moving target detection apparatus 100 includes a CPU 911 (also referred to as a central processing unit, a central processing unit, a processing unit, a processing unit, a microprocessor, a microcomputer, or a processor) that executes a program. The CPU 911 is connected to the ROM 913, the RAM 914, the communication board 915, and the magnetic disk device 920 via the bus 912, and controls these hardware devices.
The RAM 914 is an example of a volatile memory. The storage medium of the ROM 913 and the magnetic disk device 920 is an example of a nonvolatile memory. These are examples of a storage device, a storage device, or a storage unit.
The communication board 915 is an example of an input / output device, an input / output device, or an input / output unit. The storage device in which the input / output data is stored is an example of an input / output device, an input / output device, or an input / output unit.

  The communication board 915 is connected to the SAR sensor 110 and receives a reception signal received by the SAR sensor 110.

  The magnetic disk device 920 stores an OS 921 (operating system), a program group 923, and a file group 924. The programs in the program group 923 are executed by the CPU 911 and the OS 921.

  The program group 923 stores a program for executing a function described as “˜unit” in the embodiment. The program is read and executed by the CPU 911.

In the file group 924, in the embodiment, result data such as “determination result”, “calculation result of”, “processing result of” when executing the function of “to part”, “to part” The data to be passed between programs that execute the function “,” other information, data, signal values, variable values, and parameters are stored as items “˜file” and “˜database”. Received signals, motion data, SAR images, target distribution maps, movement target data, and the like are examples of what is included in the file group 924.
The “˜file” and “˜database” are stored in a recording medium such as a disk or a memory. Information, data, signal values, variable values, and parameters stored in a storage medium such as a disk or memory are read out to the main memory or cache memory by the CPU 911 via a read / write circuit, and extracted, searched, referenced, compared, and calculated. Used for CPU operations such as calculation, processing, output, printing, and display. Information, data, signal values, variable values, and parameters are temporarily stored in the main memory, cache memory, and buffer memory during the CPU operations of extraction, search, reference, comparison, operation, calculation, processing, output, printing, and display. Is remembered.
In addition, arrows in the flowcharts described in the embodiments mainly indicate input / output of data and signals, and the data and signal values are recorded in the memory of the RAM 914, the magnetic disk of the magnetic disk device 920, and other recording media. . Data and signal values are transmitted online via a bus 912, signal lines, cables, or other transmission media.

  In addition, what is described as “˜unit” in the embodiment may be “˜circuit”, “˜device”, “˜device”, “˜means”, and “˜step”, “˜”. “Procedure” and “˜Process” may be used. That is, what is described as “˜unit” may be realized by firmware stored in the ROM 913. Alternatively, it may be implemented only by software, or only by hardware such as elements, devices, substrates, and wirings, by a combination of software and hardware, or by a combination of firmware. Firmware and software are stored as programs on a magnetic disk or other recording medium. The program is read by the CPU 911 and executed by the CPU 911. In other words, the moving target detection program causes the computer to function as “to part”. Alternatively, the procedure or method of “to part” is executed by a computer.

FIG. 3 is a flowchart illustrating the moving target detection method according to the first embodiment.
A movement target detection process executed by the movement target detection device 100 as a movement target detection method in the first embodiment will be described below with reference to FIG.
Each “˜ unit” executes a movement target detection process described below using a CPU.
The moving target detection program causes the computer to execute a moving target detection process described below.

<S101: Radar observation processing (first time)>
First, the SAR sensor 110 performs the first radar observation.
At this time, the SAR sensor 110 generates a high-frequency pulse signal and radiates the high-frequency pulse signal from the antenna to the space. Next, the SAR sensor 110 receives an echo signal, which is a reflection of some high-frequency pulse signal at each location, by an antenna. When the SAR sensor 110 receives an echo signal, the SAR sensor 110 amplifies the received echo signal, converts the frequency of the amplified echo signal into an intermediate frequency, and converts the echo signal converted into the intermediate frequency into a digital signal (digital data). To obtain a received signal A. Then, the SAR sensor 110 stores the reception signal A obtained by the first radar observation in the reception signal A storage device 191. The amplitude of the echo signal observed by the SAR sensor 110 indicates the power and intensity of the echo signal, and the received signal based on the echo signal is used for imaging at various places. The magnitude of the amplitude of the echo signal corresponds to the brightness of the image.

<S102: Image Reproduction Process (First Time)>
Next, the image reproduction processing unit A131 images the first radar observation result.
At this time, the image reproduction processing unit A131 acquires the reception signal A that is the first radar observation result from the reception signal A storage device 191. Next, the image reproduction processing unit A131 images each part based on the amplitude value of the echo signal from each part indicated by the received signal A. There are various image reproduction methods such as a polar format method, a range Doppler method, and a chirp scaling method, and the image reproduction processing unit 130 performs two-dimensional processing on the received signal A using any one of the image reproduction methods. A high-resolution SAR image A is generated. The SAR image A is represented by complex data. Then, the image reproduction processing unit 130 stores the generated SAR image A in the SAR image A storage device 194.

<S103: Radar observation processing (second time)>
The SAR sensor 110 performs the second radar observation.
At this time, the SAR sensor 110 stores the received signal B, which is the second radar observation result, in the received signal B storage device 192, as in S101.

<S104: Image Reproduction Process (Second Time)>
Next, the image reproduction processing unit B132 images the second radar observation result.
At this time, the image reproduction processing unit B132 generates the SAR image B based on the received signal B, and stores the SAR image B in the SAR image B storage device 195, similarly to the image reproduction processing unit A131 in S102.

<S105: Image Difference Processing>
Next, the image difference processing unit 140 generates a target distribution map in which the difference between the SAR image A and the SAR image B is taken.
At this time, the image difference processing unit 140 acquires the SAR image A from the SAR image A storage device 194 and acquires the SAR image B from the SAR image B storage device 195. Next, the image difference processing unit 140 superimposes the SAR image A and the SAR image B to obtain a phase difference, and obtains the amplitude of the difference for each pixel. Then, the image difference processing unit 140 stores data indicating the amplitude difference of each pixel between the SAR image A and the SAR image B in the target distribution map storage device 196 as a target distribution map. The target distribution diagram indicates that a moving target or a stationary target exists on the ground surface corresponding to a pixel indicating a specific amplitude difference value.

<S106: Moving target detection process>
Then, the moving target detection unit 150 detects the moving target based on the suppression ratio obtained by dividing the value of the target distribution map by the value of the SAR image.
At this time, the moving target detection unit 150 acquires the target distribution map from the target distribution map storage device 196, and acquires the SAR image A from the SAR image A storage device 194 or the SAR image B from the SAR image B storage device 195. . Next, the moving target detection unit 150 divides the amplitude difference of each pixel between the SAR image A and the SAR image B indicated by the target distribution map by the amplitude of each pixel indicated by the SAR image A or the SAR image B. The value divided by the moving target detection unit 150 is set as the suppression ratio of the amplitude difference in the target distribution map based on the SAR image. Next, the movement target detection unit 150 compares the calculated suppression ratio with a specific threshold value, and when the suppression ratio is larger than the threshold value, it is determined that the movement target is present on the surface portion corresponding to the pixel. Next, the movement target detection unit 150 generates movement target data indicating the position and time at which the movement target exists based on the determination result. Then, the movement target detection unit 150 outputs the generated movement target data to the output device. For example, the movement target detection unit 150 outputs movement target data to a communication device and transmits it to a ground server device. Further, for example, the movement target detection unit 150 outputs movement target data to a display device or a printer device.

When the moving target detection apparatus 100 according to the first embodiment detects a moving target, the moving target detection unit 150 sets the amplitude difference of each pixel between the SAR image A and the SAR image B indicated by the target distribution map as a specific threshold value. Rather than a comparison, the suppression ratio obtained by dividing the amplitude difference of each pixel between the SAR image A and the SAR image B indicated by the target distribution map by the amplitude of each pixel indicated by the SAR image A or the SAR image B is compared with a specific threshold value. It is characterized by
Thereby, the movement target detection apparatus 100 in Embodiment 1 can suppress the erroneous detection of a moving body.

Next, details of the movement target detection process of the movement target detection unit 150 in S106 will be described.
FIG. 4 is a flowchart showing the movement target detection process of the movement target detection unit 150 in the first embodiment.

<S201: CFAR processing>
First, the CFAR processing unit 151 performs CFAR processing on the target distribution map and selects a target to be identified from the target distribution map.
At this time, the CFAR processing unit 151 acquires a target distribution map from the target distribution map storage device 196. The CFAR processing unit 151 performs two-dimensional CFAR processing on the target distribution map. The result of the two-dimensional CFAR process indicates a target to be identified for identifying whether it is a moving target or a stationary target in the target distribution map.

FIG. 5 is a relationship diagram of each cell in the two-dimensional CFAR process.
In the two-dimensional CFAR process, a reference cell and a guard cell are set as shown in FIG. Next, in the two-dimensional CFAR process, the threshold value for the cell of interest is set based on the average value of the luminance of the reference cell area (the amplitude difference between the SAR image A and the SAR image B indicated by the target distribution map) and the CFAR (threshold) coefficient. decide. In the two-dimensional CFAR process, a threshold value is determined for all pixels, and a target portion having a higher luminance than the surroundings is extracted by comparing the threshold value with the threshold value. Thereby, in the two-dimensional CFAR process, a noise portion having a lower luminance than the surroundings can be removed.
6 and 7 are diagrams illustrating an example of noise removal by the two-dimensional CFAR process.
FIG. 8 is a diagram illustrating an example of identifying a movement target.
Here, it is assumed that FIG. 6 shows a target distribution diagram in which the image difference processing unit 140 calculates the amplitude difference between the SAR image A and the SAR image B in S105 (see FIG. 3). FIG. 6 shows pixels in which the amplitude difference is generated between the SAR image A and the SAR image B in black. Represents.
In the two-dimensional CFAR process, for example, target e to target q, which are noise portions, are removed from the target distribution diagram shown in FIG.
In S202 to S203 (see FIG. 4), for example, with respect to the target distribution diagram from which noise is removed by the two-dimensional CFAR process shown in FIG. 7, each target is a moving target or a stationary target as shown in FIG. Determine if it exists.

<S202: Suppression Ratio Calculation Processing>
Next, the suppression ratio calculation unit 152 calculates a suppression ratio obtained by dividing the target distribution map by the SAR image for the target to be identified. Alternatively, the suppression ratio calculation unit 152 calculates a suppression ratio obtained by dividing one SAR image by the other SAR image for the target to be identified.
At this time, the suppression ratio calculation unit 152 acquires the target distribution map from the target distribution map storage device 196, and acquires the SAR image A from the SAR image A storage device 194 or the SAR image B from the SAR image B storage device 195. . Then, the suppression ratio calculation unit 152 calculates the amplitude difference of each pixel between the SAR image A and the SAR image B indicated by the target distribution map for the target pixel portion selected by the CFAR processing unit 151, as the SAR image A or the SAR image. The suppression ratio divided by the amplitude of each pixel indicated by B is calculated.
Alternatively, the suppression ratio calculation unit 152 acquires the SAR image A from the SAR image A storage device 194, acquires the SAR image B from the SAR image B storage device 195, and targets the target pixel portion selected by the CFAR processing unit 151. Then, a suppression ratio is calculated by dividing the amplitude of each pixel indicated by one SAR image (for example, SAR image A) by the amplitude of each pixel indicated by the other SAR image (for example, SAR image B).
A specific example of the suppression ratio calculation process (S202) will be described later.

<S203: Target identification process>
Then, the target identifying unit 153 compares the suppression ratio with the threshold, identifies whether the target to be identified is a moving target or a stationary target, and detects the moving target.
At this time, the target identification unit 153 compares the suppression ratio calculated by the suppression ratio calculation unit 152 with a specific threshold value. Then, the target identification unit 153 determines a target having a suppression ratio larger than the threshold as a moving target, and determines a target having a suppression ratio smaller than the threshold as a stationary target.

In the moving target detection apparatus 100 according to the first embodiment, when the moving target detection unit 150 detects a moving target, the target identification unit 153 detects the amplitude difference of each pixel between the SAR image A and the SAR image B indicated by the target distribution map. Is not compared with a specific threshold value, and a suppression ratio obtained by dividing the amplitude difference of each pixel between the SAR image A and the SAR image B indicated by the target distribution map by the amplitude of each pixel indicated by the SAR image A or the SAR image B is obtained. It is characterized by being compared with a specific threshold. Alternatively, in the moving target detection apparatus 100 according to the first embodiment, the target identification unit 153 indicates the amplitude of each pixel indicated by one SAR image (for example, SAR image A) by the other SAR image (for example, SAR image B). The suppression ratio divided by the amplitude of each pixel is compared with a specific threshold value.
Here, the moving target has different pixel positions appearing in the SAR image A and the SAR image B obtained by radar observation at different times, and in the SAR image A before the movement, the pixel position of the movement target indicated by the SAR image B after the movement. The amplitude value at is small. In the SAR image B after movement, the amplitude value at the pixel position of the movement target indicated by the SAR image A before movement is small. Therefore, the suppression ratio of the moving target calculated by the suppression ratio calculation unit 152 by dividing the target distribution map or the SAR image A (or SAR image B) by the SAR image B (or SAR image A) indicating a small amplitude value is large. Indicates the value.
Further, since the stationary target usually has a larger amplitude of the received signal observed than the moving target, the amplitude value of each pixel indicated by the SAR image A and the SAR image B shows a large value. For this reason, the suppression ratio calculation unit 152 has a small target target suppression ratio calculated by dividing the target distribution map or the SAR image A (or SAR image B) by the SAR image B (or SAR image A) indicating a large amplitude value. Indicates the value.
That is, the suppression ratio indicates a moving target with a large value and a stationary target with a small value.
For this reason, the target identifying unit 153 detects the moving target by comparing the suppression ratio with a specific threshold value, thereby making it easier than detecting the moving target by comparing the value of the target distribution map with the specific threshold value. A threshold can be set, a moving target can be easily detected, and erroneous detection of the moving target can be reduced.

  Next, specific examples of the suppression ratio calculation process (S202) and the target identification process (S203) will be described with reference to FIGS.

FIG. 9 is a diagram illustrating specific examples of (1) SAR image A and (2) SAR image B.
As a specific example, FIG. 9 shows (1) SAR image A obtained by radar observation at time t and (2) SAR image B obtained by radar observation at time t + Δt after Δt.
In FIG. 9, each cell represents a pixel on the screen. In the SAR image, the amplitude value of the received signal is represented in a pixel group indicating two targets, a moving target and a stationary target. It shows that the vehicle has moved to the right from time t + Δt.
FIG. 10 is a diagram showing a target distribution diagram for (1) SAR image A and (2) SAR image B, and a suppression ratio with (1) SAR image A as a divisor.
For example, in the image difference process (S105), the image difference processing unit 140 calculates the absolute value of the difference in amplitude between the SAR image A and the SAR image B and generates a target distribution map. A target distribution diagram generated by calculating the absolute value of the difference between (1) SAR image A and (2) SAR image B is shown on the left side of FIG.
Further, for example, in the suppression ratio calculation process (S202), the suppression ratio calculation unit 152 calculates the suppression ratio by dividing the amplitude difference between the SAR image A and the SAR image B indicated by the target distribution map by the SAR image A. The suppression ratio calculated by dividing the target distribution diagram indicating the absolute value of the difference between (1) SAR image A and (2) SAR image B by SAR image A is shown on the right side of FIG.

Here, a case where a movement target is detected by comparing the SAR image with a threshold value instead of the suppression ratio will be described.
FIG. 11 is a diagram illustrating the detection result of the moving target when (2) the SAR image B is compared with a threshold value.
For example, when (2) the SAR image B shown on the left side of FIG. 11 is compared with the threshold value “1”, the value of the moving target portion and the value of the stationary target portion are both larger than the threshold value “1”. A moving target and a stationary target cannot be separated.

Next, a case will be described in which a moving target is detected by comparing a target distribution diagram with a threshold value instead of a suppression ratio.
FIG. 12 is a diagram showing the detection result of the moving target when the target distribution diagrams of (1) SAR image A and (2) SAR image B are compared with threshold values.
For example, when the target distribution map of (1) SAR image A and (2) SAR image B shown on the left side of FIG. 12 is compared with the threshold “1”, (1) movement before movement at time t appearing in SAR image A The value of the target portion is also (2) the value of the movement target portion after movement at time t + Δt appearing in the SAR image B is also larger than the threshold value “1”, so that one movement target is moved before movement at time t as shown on the right side of FIG. Are detected separately as two movement targets, that is, the movement target after the movement at time t + Δt.

Next, a case where a movement target is detected by comparison with a threshold for the suppression ratio will be described.
FIG. 13 is a diagram illustrating the detection result of the moving target when the suppression ratio (divisor: SAR image A) between (1) SAR image A and (2) SAR image B is compared with a threshold value.
For example, when the suppression ratio (divisor: SAR image A) between (1) SAR image A and (2) SAR image B shown on the left side of FIG. 13 is compared with the threshold “1”, the value of the stationary target portion is (1) The value of the movement target portion before the movement at the time t appearing in the SAR image A is equal to or less than the threshold “1”, and (2) the value of the movement target portion after the movement at the time t + Δt appearing in the SAR image B is the threshold “1”. Therefore, the moving target at time t + Δt can be detected separately from the stationary target and the moving target at time t, as shown on the right side of FIG.

  9 to 13, the target identification unit 153 detects the movement target by comparing the suppression ratio with the threshold “1”.

In FIGS. 9 to 13, the stationary target is described as having no difference in amplitude between the SAR image A at time t and the SAR image B at time t + Δt.
Next, based on FIGS. 14 to 17, it is assumed that the stationary target has a difference in amplitude between the SAR image A at the time t and the SAR image B at the time t + Δt due to the observation error.

FIG. 14 is a diagram illustrating specific examples of (3) SAR image A and (4) SAR image B.
FIG. 14 corresponds to FIG. 9 and is different from FIG. 9 in that there is a difference in the amplitude of the stationary target between (3) SAR image A at time t and (4) SAR image B at time t + Δt.
FIG. 15 is a diagram illustrating a target distribution diagram for (3) SAR image A and (4) SAR image B, and a suppression ratio with (3) SAR image A as a divisor. FIG. 15 corresponds to FIG.
FIG. 16 is a diagram showing the detection result of the moving target when the target distribution diagrams of (3) SAR image A and (4) SAR image B are compared with threshold values.
FIG. 16 corresponds to FIG. 12, and when the target distribution chart is compared with the threshold value, the stationary target and the moving target are separated and detected if the threshold value is “0.2” or more and less than “2.0”. However, it is shown that one movement target is detected separately as two movement targets: a movement target at time t and a movement target at time t + Δt.
FIG. 17 is a diagram illustrating a detection result of a moving target when the suppression ratio (divisor: SAR image A) between (3) SAR image A and (4) SAR image B is compared with a threshold value.
FIG. 17 corresponds to FIG. 13 and shows that when the suppression ratio is compared with the threshold value, the movement target at time t + Δt can be detected if the threshold value is greater than or equal to “1”.

  14 to 17, the target identifying unit 153 detects the moving target by comparing the suppression ratio with a threshold “1”.

9 to 17, the case where the absolute value of the amplitude difference between the SAR image A and the SAR image B is used as the target distribution map has been described.
Next, a case where the amplitude difference calculated by subtracting the SAR image B from the SAR image A is used as a target distribution map will be described with reference to FIGS.

FIG. 18 is a diagram showing a target distribution diagram for (3) SAR image A and (4) SAR image B, and a suppression ratio with (3) SAR image A as a divisor.
FIG. 18 is a diagram corresponding to FIG. 15, and the target distribution chart is not the absolute value of the amplitude difference between (3) SAR image A and (4) SAR image B, but (3) from SAR image A to (4 ) A point obtained by subtracting the SAR image B is different from FIG.
FIG. 19 is a diagram illustrating a detection result of a moving target when a target distribution diagram obtained by subtracting (4) SAR image B from (3) SAR image A is compared with a threshold value.
FIG. 19 corresponds to FIG. 16 and shows that when the target distribution diagram is compared with the threshold value, the moving target at time t + Δt can be detected if the threshold value is between “0.2” and “2.0”. Yes.
FIG. 20 is a diagram illustrating the detection result of the moving target when the suppression ratio (divisor: SAR image A) between (3) SAR image A and (4) SAR image B is compared with a threshold value.
FIG. 20 corresponds to FIG. 17 and shows that when the suppression ratio is compared with the threshold value, the movement target at time t + Δt can be detected if the threshold value is “0.05” or more.
In FIG. 19 and FIG. 20, the range of the threshold for detecting the moving target at time t + Δt is the range “0.2 to 2.0” when compared with the target distribution diagram and the range “when comparing with the suppression ratio”. "0.05 ~" is wider. That is, in the moving target detection method that compares the suppression ratio with the threshold value, it is easy to set the threshold value, and it is easy to detect the moving target.

9 to 20, the detection of the movement target at time t + Δt based on the suppression ratio with the SAR image A at time t as a divisor has been described.
Next, based on FIGS. 21 to 22, detection of a moving target at time t based on a suppression ratio obtained by dividing SAR image B at time t + Δt will be described.

FIG. 21 is a diagram showing a target distribution diagram for (3) SAR image A and (4) SAR image B, and a suppression ratio with (4) SAR image B as a divisor.
FIG. 21 is a diagram corresponding to FIG. 15, and is different from FIG. 15 in that the target distribution chart is obtained by dividing the target distribution chart by (4) SAR image B instead of (3) SAR image A.
FIG. 22 is a diagram illustrating the detection result of the moving target when the suppression ratio (divisor: SAR image B) between (3) SAR image A and (4) SAR image B is compared with a threshold value.
FIG. 22 corresponds to FIG. 17 and shows that when the suppression ratio in which the divisor is the SAR image B at time t + Δt is compared with the threshold value, the moving target at time t can be detected if the threshold value is “1” or more. ing.

21 to 22, the detection of the movement target based on the suppression ratio obtained by dividing the target distribution diagram indicating the absolute value of the amplitude difference between the SAR image A and the SAR image B by the SAR image B has been described.
Next, based on FIGS. 23 to 24, the movement target is detected based on the suppression ratio obtained by dividing the target distribution diagram indicating the amplitude difference calculated by subtracting the SAR image A from the SAR image B by the SAR image B. Will be described.

FIG. 23 is a diagram illustrating a target distribution diagram for (3) SAR image A and (4) SAR image B, and a suppression ratio with (4) SAR image B as a divisor.
FIG. 23 is a diagram corresponding to FIG. 21, and the target distribution diagram is not the absolute value of the amplitude difference between (3) SAR image A and (4) SAR image B, but (4) from SAR image B to (3 ) A point obtained by subtracting the SAR image A is different from FIG.
FIG. 24 is a diagram illustrating the detection result of the moving target when the suppression ratio (divisor: SAR image B) between (3) SAR image A and (4) SAR image B is compared with a threshold value.
FIG. 24 corresponds to FIG. 22 and shows that when the suppression ratio is compared with the threshold value, the moving target at time t can be detected if the threshold value is “−0.02” or more.

23 to 24, the amplitude difference obtained by subtracting the SAR image A from the SAR image B is used as the target distribution map. However, the amplitude difference obtained by subtracting the SAR image B from the SAR image A may be used as the target distribution chart.
In this case, if the threshold value is “0.02” or less, the moving target at time t can be detected.

9 to 24, the value obtained by dividing the target distribution map by the SAR image is described as the suppression ratio.
Next, a value obtained by dividing one SAR image by the other SAR image will be described as a suppression ratio based on FIGS.

FIG. 25 is a diagram illustrating the detection result of the moving target when the suppression ratio calculated by dividing (4) SAR image B by (3) SAR image A is compared with a threshold value.
FIG. 25 corresponds to FIG. 13 and the like, and when the suppression ratio calculated by dividing (4) SAR image B by (3) SAR image A is compared with the threshold value, the threshold value is set to “1.05” or more. This indicates that the moving target at time t + Δt can be detected.
FIG. 26 is a diagram illustrating a moving target detection result when the suppression ratio calculated by dividing (3) SAR image A by (4) SAR image B is compared with a threshold value.
FIG. 26 corresponds to FIG. 13 and the like, and when the suppression ratio calculated by dividing (3) SAR image A by (4) SAR image B is compared with the threshold value, the threshold value is equal to or greater than “0.98”. This shows that the movement target at time t can be detected.

  25 to 26, the target identification unit 153 compares the suppression ratio with a threshold value “2 (when rounded up after the decimal point)” to detect a moving target.

  9 to 26, the target identification unit 153 determines that the amplitude indicated by either the SAR image A or the SAR image B is at least between the moving target and the stationary target by the CFAR processing (S201) of the CFAR processing unit 151. It is characterized in that it is determined whether or not there is a moving target for a cell (pixel) having a predetermined amplitude or greater indicating any of them.

9 to 26, the case where two targets (moving target and stationary target) are set as identification targets by the CFAR process has been described.
27 to 30, a case will be described in which CFAR processing is not performed and all targets (pixels) are targeted for identification.

FIG. 27 is a diagram illustrating specific examples of (5) SAR image A and (6) SAR image B.
FIG. 27 corresponds to FIG. 14 and shows a specific example of (5) SAR image A at time t and (6) SAR image B at time t + Δt.
FIG. 28 is a diagram illustrating a target distribution diagram for (5) SAR image A and (6) SAR image B, and a suppression ratio with (5) SAR image A as a divisor. FIG. 28 corresponds to FIG.
FIG. 29 is a diagram illustrating the detection result of the moving target when the target distribution diagrams of (5) SAR image A and (6) SAR image B are compared with threshold values.
FIG. 29 corresponds to FIG. 16, and when the target distribution chart is compared with the threshold value, the stationary target and the moving target are detected separately if the threshold value is “0.2” or more and less than “1.8”. However, it is shown that one movement target is detected separately as two movement targets: a movement target at time t and a movement target at time t + Δt.
FIG. 30 is a diagram illustrating the detection result of the moving target when the suppression ratio (divisor: SAR image A) of (5) SAR image A and (6) SAR image B is compared with a threshold value.
FIG. 30 corresponds to FIG. 17 and shows that when the suppression ratio is compared with the threshold value, the movement target at time t + Δt can be detected if the threshold value is greater than or equal to “2.00” and less than “19.00”. .

  9 to 30, the target identification unit 153 calculates the suppression ratio between the first time (t) of the SAR image A and the second time (t + Δt) of the SAR image B. It is determined that a moving target exists at the pixel position at the time when the SAR image is not taken as a divisor. The first time (t) and the second time (t + Δt) may be interchanged.

  9 to 30, the suppression ratio calculation unit 152 determines the SAR at the second time (t + Δt) when the target identification unit 153 determines the position of the moving target at the first time (t) of the SAR image A. The suppression ratio is calculated using the image B as a divisor, and when the target identification unit 153 determines the position of the moving target at the second time (t + Δt) of the SAR image B, the SAR image A at the first time (t) is a divisor. The suppression ratio is calculated as follows.

  As described above, in the first embodiment, by comparing the suppression ratio with the threshold value, it is possible to easily identify the moving target and the stationary target, improve the identification accuracy, and suppress erroneous detection of the moving target. .

  In the first embodiment, the movement target detection device 100 includes the SAR sensor 110, the motion sensor 120, and the image reproduction processing unit 130, but the movement target detection device 100 may not include these. For example, the moving target detection device 100 may be a server device on the ground that detects a moving target reflected in a SAR image using SAR images acquired by a radar in the sky as input data.

1 is a configuration diagram of a movement target detection device 100 according to Embodiment 1. FIG. FIG. 3 is a diagram illustrating an example of hardware resources of the movement target detection device 100 according to the first embodiment. 3 is a flowchart showing a moving target detection method in the first embodiment. 6 is a flowchart showing a movement target detection process of the movement target detection unit 150 according to the first embodiment. The relationship diagram of each cell in a two-dimensional CFAR process. The figure which shows the example of noise removal by a two-dimensional CFAR process. The figure which shows the example of noise removal by a two-dimensional CFAR process. The figure which shows the example of identification of a movement target. The figure which shows the specific example of (1) SAR image A and (2) SAR image B. FIG. The figure which shows the target distribution figure with respect to (1) SAR image A and (2) SAR image B, and the suppression ratio which makes the divisor (1) SAR image A. (2) The figure which shows the detection result of the movement target at the time of comparing SAR image B with a threshold value. The figure which shows the detection result of the movement target at the time of comparing the target distribution map of (1) SAR image A and (2) SAR image B with a threshold value. The figure which shows the detection result of the movement target at the time of comparing the suppression ratio (divisor: SAR image A) of (1) SAR image A and (2) SAR image B with a threshold value. The figure which shows the specific example of (3) SAR image A and (4) SAR image B. FIG. The figure which shows the target distribution figure with respect to (3) SAR image A and (4) SAR image B, and the suppression ratio which makes the divisor (3) SAR image A. The figure which shows the detection result of the movement target at the time of comparing the target distribution map of (3) SAR image A and (4) SAR image B with a threshold value. The figure which shows the detection result of the movement target at the time of comparing the suppression ratio (divisor: SAR image A) of (3) SAR image A and (4) SAR image B with a threshold value. The figure which shows the target distribution figure with respect to (3) SAR image A and (4) SAR image B, and the suppression ratio which makes the divisor (3) SAR image A. (3) The figure which shows the detection result of the movement target at the time of comparing the target distribution figure which subtracted (4) SAR image B from SAR image A with a threshold value. The figure which shows the detection result of the movement target at the time of comparing the suppression ratio (divisor: SAR image A) of (3) SAR image A and (4) SAR image B with a threshold value. The figure which shows the target distribution map with respect to (3) SAR image A and (4) SAR image B, and the suppression ratio which makes the divisor (4) SAR image B. The figure which shows the detection result of the movement target at the time of comparing the suppression ratio (divisor: SAR image B) of (3) SAR image A and (4) SAR image B with a threshold value. The figure which shows the target distribution map with respect to (3) SAR image A and (4) SAR image B, and the suppression ratio which makes the divisor (4) SAR image B. The figure which shows the detection result of the movement target at the time of comparing the suppression ratio (divisor: SAR image B) of (3) SAR image A and (4) SAR image B with a threshold value. (4) The figure which shows the detection result of the movement target at the time of comparing the suppression ratio calculated by dividing SAR image B by (3) SAR image A with a threshold value. (3) The figure which shows the detection result of the movement target at the time of comparing the suppression ratio computed by dividing SAR image A by (4) SAR image B with a threshold value. The figure which shows the specific example of (5) SAR image A and (6) SAR image B. FIG. The figure which shows the target distribution map with respect to (5) SAR image A and (6) SAR image B, and the suppression ratio which makes the divisor (5) SAR image A. The figure which shows the detection result of the movement target at the time of comparing the target distribution map of (5) SAR image A and (6) SAR image B with a threshold value. The figure which shows the detection result of the movement target at the time of comparing the suppression ratio (divisor: SAR image A) of (5) SAR image A and (6) SAR image B with a threshold value.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 Moving target detection apparatus, 110 SAR sensor, 120 Motion sensor, 130 Image reproduction processing part, 131 Image reproduction processing part A, 132 Image reproduction processing part B, 140 Image difference processing part, 150 Moving target detection part, 151 CFAR processing part , 152 suppression ratio calculation unit, 153 target identification unit, 191 received signal A storage device, 192 received signal B storage device, 193 motion data storage device, 194 SAR image A storage device, 195 SAR image B storage device, 196 target distribution diagram Storage device, 911 CPU, 912 bus, 913 ROM, 914 RAM, 915 communication board, 920 magnetic disk device, 921 OS, 923 program group, 924 file group.

Claims (10)

Irradiate an electromagnetic wave and observe the amplitude of the reflected wave from each place in the irradiation direction at the first time and the second time. The amplitude of the reflected wave at each place at the first time and the reflection at each place at the second time A moving target detection device that detects a moving body in which an amplitude difference of reflected waves at different times is larger than a stationary body based on the amplitude of the wave,
A difference calculating unit that calculates the absolute value of the difference between the amplitude of the reflected wave at each place at the first time and the amplitude of the reflected wave at each place at the second time using a CPU (Central Processing Unit);
Division by which the CPU calculates a division value obtained by dividing the amplitude difference of the reflected wave at each place calculated by the difference calculation unit by the amplitude of the reflected wave at each place at any one of the first time and the second time. And
A moving body that compares the division value calculated by the division unit with a specific threshold value using a CPU and determines that a moving body exists at the position when the division value is larger than the specific threshold value, and detects the moving body. A moving target detection apparatus comprising: a detection unit.   The said moving body detection part sets the said specific threshold value to 1, The moving target detection apparatus of Claim 1 characterized by the above-mentioned. Irradiate an electromagnetic wave and observe the amplitude of the reflected wave from each place in the irradiation direction at the first time and the second time. The amplitude of the reflected wave at each place at the first time and the reflection at each place at the second time A moving target detection device that detects a moving body in which an amplitude difference of reflected waves at different times is larger than a stationary body based on the amplitude of the wave,
The CPU divides a value obtained by dividing the amplitude of the reflected wave at each place at one time between the first time and the second time by the amplitude of the reflected wave at each place at the other time between the first time and the second time. A division unit calculated using (Central Processing Unit);
A moving body that compares the division value calculated by the division unit with a specific threshold value using a CPU and determines that a moving body exists at the position when the division value is larger than the specific threshold value, and detects the moving body. A moving target detection apparatus comprising: a detection unit.   The said moving body detection part sets the said specific threshold value to 2, The moving target detection apparatus of Claim 3 characterized by the above-mentioned. The moving body detection unit is configured such that one of the amplitude of the reflected wave at the first time and the amplitude of the reflected wave at the second time is greater than or equal to a predetermined amplitude indicating at least one of the moving body and the stationary body. 5. The moving target detection apparatus according to claim 1, wherein it is determined whether a moving body exists at a certain position. The mobile body detection unit is located at the position at the time of the first time and the second time when the division unit calculates the division value and the amplitude of the reflected wave at each place is not a divisor. 6. The moving target detection apparatus according to claim 1, wherein it is determined that a moving body exists. The division unit calculates the division value by using the amplitude of the reflected wave at each point as a divisor when the mobile unit detection unit determines the position of the mobile unit at the first time, and detects the mobile unit. 6. The division value according to claim 1, wherein when the unit determines the position of the moving body at the second time, the division value is calculated by using the amplitude of the reflected wave at each place at the first time as a divisor. The moving target detection apparatus described in 1. Irradiate an electromagnetic wave and observe the amplitude of the reflected wave from each place in the irradiation direction at the first time and the second time. The amplitude of the reflected wave at each place at the first time and the reflection at each place at the second time It is a moving target detection method for detecting a moving object whose amplitude difference between reflected waves at different times is larger than a stationary object based on the amplitude of the wave,
The difference calculation unit performs a difference calculation process in which the absolute value of the difference between the amplitude of the reflected wave at each place at the first time and the amplitude of the reflected wave at each place at the second time is calculated using a CPU (Central Processing Unit). ,
Using a CPU, the division unit divides the amplitude difference of the reflected waves at each location calculated by the difference calculation unit by the amplitude of the reflected waves at each location at either the first time or the second time. Perform the division process to calculate,
The moving object detection unit compares the division value calculated by the division unit with a specific threshold value using a CPU, and when the division value is larger than the threshold value, determines that the moving object exists at the position and detects the moving object. A moving target detection method characterized by performing a moving object detection process. Irradiate an electromagnetic wave and observe the amplitude of the reflected wave from each place in the irradiation direction at the first time and the second time. The amplitude of the reflected wave at each place at the first time and the reflection at each place at the second time It is a moving target detection method for detecting a moving object whose amplitude difference between reflected waves at different times is larger than a stationary object based on the amplitude of the wave,
The division unit divides the amplitude of the reflected wave at each place at one time between the first time and the second time by the amplitude of the reflected wave at each place at the other time between the first time and the second time. Performs division processing to calculate a value using a CPU (Central Processing Unit),
The moving object detection unit compares the division value calculated by the division unit with a specific threshold value using a CPU, and when the division value is larger than the threshold value, determines that the moving object exists at the position and detects the moving object. A moving target detection method characterized by performing a moving object detection process.   A moving target detection program for causing a computer to execute the moving target detection method according to claim 8.

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