JP5520035B2 - Signal processing apparatus, radar apparatus, and signal processing program - Google Patents

Description

  The present invention mainly relates to a signal processing device included in a radar device. Specifically, the present invention relates to a configuration for suppressing a false image included in a radar echo in the signal processing device.

  When a false image appears on the display screen of the radar, there are problems that an operator misrecognizes a target that does not exist originally, or a target with low signal intensity is hidden by the false image. A false image is an unnecessary image that is generated when a reflected wave of a beam other than the main beam of a radar wave is received by the antenna, or when a radar wave is received by the antenna after multiple reflection.

  For this reason, various configurations for removing a false image have been proposed.

  For example, a radar apparatus disclosed in Patent Document 1 is configured to detect a level of a false image due to multiple reflection caused by a structure of a moving body on which the radar apparatus is mounted, and perform level adjustment according to the detected level of the false image. It is. In addition, the radar device disclosed in Patent Document 2 determines that the image at the shortest distance is a real image when there are a plurality of images regarded as targets in a preset false image processing area, The image is determined to be a false image due to multiple reflections and removed. The radar device disclosed in Patent Document 3 is configured to increase the correction threshold level by determining that a false image has occurred when the variance of the center of gravity position of the target is larger than a reference value.

JP 2004-170165 A JP-A-8-82671 JP-A-8-75841

  However, in the configurations of Patent Documents 1 and 2, a false image due to multiple reflection can be removed, but a false image due to side lobes cannot be removed.

  On the other hand, in the configuration of Patent Document 3, when a false image is temporarily generated, the dispersion of the center of gravity position of the target is increased, so that the generation of the false image can be detected, but the false image is always generated. Cannot be detected. Therefore, in such a case, the false image cannot be suppressed. In Patent Document 3, since the false image is removed by raising the threshold level, there is a possibility that even a necessary signal may be removed.

  The present invention has been made in view of the above circumstances, and a main object thereof is to provide a signal processing device capable of appropriately suppressing a false image due to a side lobe.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

  According to a first aspect of the present invention, a signal processing device having the following configuration is provided. That is, this signal processing device includes a target presence area detection unit, a radar echo acquisition unit, and a false image suppression unit. The target presence area detection unit detects an area where the target is present. The radar echo acquisition unit acquires a radar echo continuous in the azimuth direction. The false image suppression unit performs a process of suppressing a false image included in the radar echo based on information obtained from a radar echo continuous in the azimuth direction. Then, the false image suppression unit performs a process different from the process for the radar echo in the other area for the radar echo in the area where the target exists. In this specification, “continuous in the azimuth direction” means continuous on a circle or arc centered on the device itself.

  That is, the false image due to the side lobe appears to spread at the same distance as the target. Therefore, it is possible to appropriately suppress the false image due to the side lobe based on the radar echo continuous in the azimuth direction. In addition, after detecting the area where the target is present in advance, the area where the target is present can be prevented from suppressing even the echo of the target by changing the false image suppression processing. be able to.

  In the above signal processing device, it is preferable that the false image suppression unit performs processing differently for a radar echo in a region where the target is present and a radar echo in a region around the target region.

  That is, the false image due to the side lobe tends to appear in the area around the target. Therefore, by configuring as described above, the processing for the radar echo of the target and the processing for the false image by the side lobe can be made different. Thereby, it is possible to prevent even the echo of the target from being suppressed while appropriately suppressing the false image due to the side lobe.

  In the above signal processing device, the false image suppression unit determines a threshold value of a region where no target exists based on a moving average of radar echoes continuous in the azimuth direction, and suppresses the false image based on the threshold value. It is preferable.

  That is, it is preferable to remove the false image in an area other than the area where the target exists (area where a true echo image is detected). Therefore, by determining a threshold value for such an area based on a moving average of radar echoes continuous in the azimuth direction, processing equivalent to high-pass filter processing can be performed on the radar echoes continuous in the azimuth direction. it can. By this high-pass filter processing, it is possible to remove a false image spreading in the azimuth direction (false image due to side lobes).

The signal processing apparatus is preferably configured as follows. That is, the false image suppression unit determines a threshold based on a moving average of signal levels of radar echoes that are continuous in the azimuth direction, and suppresses the false image by subtracting the threshold from the signal level. . Then, the false image suppression unit changes at least one of the number of data points for the moving average and the offset coefficient by which the moving average is multiplied between the area where the target is present and the other areas.

  Thereby, the effect of the high-pass filter process can be made different between the area where the target exists and the other area. Thereby, a false image can be suppressed more appropriately.

  The signal processing apparatus is preferably configured as follows. That is, the signal processing device includes a map information acquisition unit that acquires map information. And the said target presence area detection part detects the area | region where a target exists based on the said map information.

  Thereby, the area | region where the target (specifically land) exists can be specified.

  The signal processing apparatus is preferably configured as follows. That is, the signal processing apparatus includes an AIS information acquisition unit that acquires AIS information. And the said target presence area | region detection part detects the area | region where a target exists based on the said AIS information.

  Thereby, the area | region where the target (specifically, the ship carrying AIS) exists can be specified.

  In the above signal processing device, the false image suppression unit may be configured not to suppress the false image in a region that is a predetermined distance or more away from the region where the target exists in the azimuth direction.

  That is, the false image due to the side lobe appears around the area where the target exists. Therefore, by configuring as described above, since the processing for suppressing the false image is not performed for the region where the false image does not occur, the signal level of the radar echo can be prevented from being unintentionally suppressed. . In addition, since processing is performed only for portions that require suppression of false images, the calculation load can be reduced.

  In the above signal processing device, the false image suppression unit may be configured to suppress the false image only in a region where the distance from the own device is less than a predetermined distance.

  That is, since a false image is likely to appear at a short distance where strong reflection is likely to return, the configuration as described above makes it possible to perform processing only in a region where a false image is likely to occur. Thereby, calculation load can be reduced.

  According to a second aspect of the present invention, there is provided a radar apparatus including the signal processing apparatus described above and a radar antenna that outputs a radar echo to the signal processing apparatus.

  This radar apparatus can suppress false images due to side lobes by a signal processing apparatus.

  According to the third aspect of the present invention, the following signal processing program is provided. That is, this signal processing program is a program that causes the signal processing device to execute processing including a target presence area detection step, a radar echo acquisition step, and a false image suppression step. In the target presence region detection step, a region where the target is present is detected. In the radar echo acquisition step, radar echoes continuous in the azimuth direction are acquired. In the false image suppression step, processing for suppressing the false image included in the radar echo is performed based on information obtained from the radar echo continuous in the azimuth direction. In the false image suppression step, processing different from processing for radar echoes in other regions is executed for radar echoes in the region where the target is present.

  That is, the false image due to the side lobe appears to spread at the same distance as the target. Therefore, it is possible to appropriately suppress the false image due to the side lobe based on the radar echo continuous in the azimuth direction. In addition, after detecting the area where the target is present in advance, the area where the target is present can be prevented from suppressing even the echo of the target by changing the false image suppression processing. be able to.

1 is a block diagram showing an overall configuration of a marine radar apparatus according to an embodiment of the present invention. (A) The schematic diagram which shows the example of the radar image | video displayed on a display part. (B) The schematic diagram which shows the example of the radar image | video at the time of not performing a false image suppression process. (A) The graph which shows the high-pass filter process threshold value calculated | required with constant offset coefficient. (B) The graph which shows a mode that the target echo was suppressed by the high pass filter process. (A) The graph which shows the high-pass filter process threshold value calculated | required in consideration of the detection result of the target presence area | region detection part. (B) The graph which shows the result of the false image suppression process in this embodiment. (A) The graph which shows the high-pass filter process threshold value calculated | required in the modification. (B) The graph which shows the result of the false image suppression process in the said modification. The block diagram which shows the structure of the radar apparatus for ships concerning another modification.

  Next, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a marine radar apparatus 1 according to an embodiment of the present invention. As shown in FIG. 1, the marine radar apparatus 1 includes an antenna unit 2 and a radar indicator 3.

  The antenna unit 2 includes a radar antenna 11 and a transmission / reception unit 12. The marine radar apparatus of this embodiment is configured as a so-called pulse radar apparatus. That is, a pulsed radio wave with high directivity is transmitted from the radar antenna 11, and the echo source (target such as a ship or land) is based on the time until the radar antenna 11 receives an echo (reflected wave). To obtain a distance r. Further, the azimuth θ in which the echo source is present can be determined by the direction of the radar antenna 11 (radio wave transmission / reception direction) when the echo is received. That is, the position of the echo source on the horizontal plane can be acquired in polar coordinates (r, θ). The radar antenna 11 is configured to rotate in a horizontal plane while repeating transmission and reception of the radio wave. Thereby, the state of the target around the ship can be scanned over 360 °.

  In the following description, the operation of transmitting a pulsed radio wave once and receiving the echo is called “sweep”. The operation of rotating the radar antenna 11 once while repeating the sweep is called “scan”.

  The transmission / reception unit 12 is configured to sample the signal (radar echo) received by the radar antenna 11 and output the digitized radar echo to the radar indicator 3. In the following description, each sample value of the digitized radar echo may be referred to as “received data”. The value of each received data represents the radar echo signal level. In the following description, the position of the echo source (target) corresponding to each received data on the horizontal plane (the position acquired by the polar coordinates) may be simply referred to as “received data position”.

  The radar indicator (signal processing device) 3 includes a control unit 14, a display memory 15, and a display unit 16. In addition, the control unit 14 includes a sweep memory 13.

  The sweep memory 13 is a buffer memory capable of storing received data sequentially input from the transmission / reception unit 12 for one sweep. The received data temporarily stored in the sweep memory 13 is sequentially read out by the control unit 14. The received data for one sweep is stored sequentially from the top address of the sweep memory 13. Therefore, the timing at which the received data is sampled (the timing at which the echo is received by the radar antenna 11) can be determined based on the read address when the received data is read from the sweep memory 13.

  The control unit 14 performs appropriate processing such as processing for suppressing false images on the received data read from the sweep memory 13 and outputs the processed data to the display memory 15. The process for suppressing the false image will be described later.

  The display memory 15 is configured to be able to store a radar image in a raster image format. The radar image is generated based on reception data (reception data that has been subjected to false image suppression) output from the control unit 14. A method of generating a radar image is well known, but a brief description is as follows.

  As described above, the position of the echo source (the position of the received data) can be obtained in polar coordinates. On the other hand, the address of each pixel of the raster image is expressed by orthogonal coordinates. When outputting the received data to the display memory 15, the control unit 14 converts the position of the received data from the polar coordinates to the orthogonal coordinates, and designates the address of the pixel corresponding to the position of the orthogonal coordinates. As a result, the value of the received data is stored in an appropriate pixel of the raster image stored in the image memory. Then, by repeating the above processing, the values of the received data are plotted one after another on the raster image. As a result, a radar image showing the state of the echo source (target) around the ship can be generated. it can.

  The display unit 16 is a liquid crystal display capable of color display, for example, and is configured to read and display the radar image from the display memory 15. The operator of the marine radar apparatus 1 can confirm the state of the target around the ship by confirming the radar image displayed on the display unit 16.

  Here, the example of the radar image | video displayed on the display part 16 of the radar apparatus of this embodiment is shown in the schematic diagram of Fig.2 (a). For comparison with this, an example of a radar image (a radar image when the false image suppression processing of the present invention is not performed) in a conventional radar apparatus is shown in the schematic diagram of FIG.

  As shown in FIG. 2B, in the conventional radar apparatus, a false image due to side lobes is displayed around an echo image indicating a target having a large effective reflection cross-sectional area (such as a large ship or land). It was. For this reason, in the conventional radar apparatus, the operator of the radar apparatus may erroneously recognize the position of the target, the size of the target, and the like.

  In this regard, in the marine radar device 1 of the present embodiment, the control unit 14 performs a process of suppressing the false image due to the side lobe. Thereby, as shown to Fig.2 (a), it can prevent that the false image by a side lobe is displayed, and can display only the echo image which shows a target (land or ship). Therefore, the operator of the marine radar apparatus 1 of the present embodiment can accurately grasp the state of the target around the ship without being confused by the false image due to the side lobe.

  Next, processing for suppressing a false image due to side lobes will be described in detail. The control unit 14 that performs the processing includes hardware (not shown) such as a CPU, ROM, and RAM, and software such as a signal processing program stored in the ROM.

  The signal processing program is a program for causing the control unit 14 to perform a process of removing a false image from a radar echo, and includes a target presence area detection step, a radar echo acquisition step, and a false image suppression step. It is out. When the hardware and the software operate in cooperation, the control unit 14 is changed to a target presence area detection unit 21, a past sweep accumulation unit (radar echo acquisition unit) 22, a false image suppression unit 23, and the like. Can function as.

  The received data read from the sweep memory 13 is output to the target presence area detection unit 21 and the past sweep accumulation unit 22. The target presence area detection unit 21 and the past sweep accumulation unit 22 will be described later.

  The false image suppression unit 23 performs a process of suppressing the false image included in the radar echo. The processing content in the false image suppression unit 23 corresponds to the false image suppression step of the signal processing program.

  Here, the feature of the false image based on the side lobe will be briefly described. As shown in FIG. 2B, the false image based on the side lobe appears around a region where a target (such as a large ship or land) having a large effective reflection cross-sectional area exists. This is because a target having a large effective reflection cross-sectional area strongly reflects the beam due to the side lobe.

  Here, “around the area where the target exists” is the same distance as the area where the target exists and the area where the target exists when viewed in polar coordinates around the device itself. On the other hand, it refers to a region adjacent in the azimuth direction.

  The reason why the false image due to the side lobe easily appears around the area where the target exists will be briefly described below. That is, the side lobe is radiated in a different direction from the main lobe at the same timing as the main lobe. Accordingly, the false image due to the side lobe appears at the same distance as the true target echo image (echo image due to the main lobe) and in a different direction from the true target echo image, as shown in FIG. . Moreover, since the side lobe is reflected by a target having a large effective reflection cross-sectional area, the false image due to the side lobe has a certain extent. In other words, the false image due to the side lobe appears adjacent to the true target echo image and spreads in the azimuth direction from the target echo image (so as to spread on an arc centered on the ship).

  Focusing on this point, the false image suppression unit 23 of the present embodiment performs high-pass filter processing on radar echoes that continue in the azimuth direction (radar echoes that continue on an arc centered on the ship). It is configured. Thereby, the false image (a false image by a side lobe) spreading in the azimuth direction can be removed.

  However, when the high-pass filter processing is uniformly performed on the entire radar echo, there is a problem in that all echoes spreading in the azimuth direction are suppressed regardless of whether the false image is caused by side lobes. For example, a large target (land, large ship, etc.) has a large true echo image by the main lobe and a large width in the azimuth direction. Therefore, it is considered that such a true echo image is also suppressed by the high-pass filter process. Then, the echo image of the land and the ship is not displayed on the radar image, and the operator of the ship radar device 1 may not be able to accurately determine the situation around the ship.

  Considering the above points, the false image suppression unit 23 of the present embodiment is configured to vary the processing depending on whether or not the target area exists. In order to realize this configuration, the control unit 14 of the present embodiment includes a target presence area detection unit 21.

  The target presence area detection unit 21 is configured to detect an area where the target exists. More specifically, the target presence area detection unit 21 sends an echo from the area where the target (specifically, land or ship) exists for each of the received data read from the sweep memory 13. The received data is configured to be identified. The processing contents in the target presence area detection unit 21 correspond to the target presence area detection step of the signal processing program.

  In order to enable detection of a region where a ship is present as described above, an AIS receiver 25, a GPS receiver 27, and a magnetic direction sensor 28 are connected to the radar indicator 3 of the present embodiment. ing.

  The AIS receiver 25 is configured to receive an AIS signal transmitted from another ship. The AIS (Universal Shipborn Automatic Identification System) is a system that transmits the position information, navigation information, etc. of the ship to the surroundings by wireless communication, and receives the information from the other ship. Information (AIS information) such as the ship's position can be acquired.

  The AIS information acquired by the AIS receiver 25 is output to the AIS information acquisition unit 29 provided in the radar indicator 3. The AIS information acquisition unit 29 is an external interface (for example, a connection connector) for taking AIS information from the AIS receiver 25 into the radar indicator 3.

  The GPS receiver 27 is configured to receive GPS signals from GPS satellites and acquire information related to the position of the ship (absolute position with respect to the earth reference). The GPS information acquired by the GPS receiver 27 is output to the GPS information acquisition unit 30 provided in the radar indicator 3.

  The magnetic direction sensor 28 is configured to acquire the bow direction (absolute direction of the earth reference) of the ship. Information on the bow direction of the ship acquired by the magnetic direction sensor 28 is output to the direction information acquisition unit 31 provided in the radar indicator 3.

  In addition, an HD signal indicating the azimuth θ that the radar antenna 11 faces is input to the target presence area detection unit 21. On the other hand, as described above, the timing at which an echo corresponding to the received data is received by the radar antenna 11 can be acquired based on the read address of the received data from the sweep memory 13. If the timing of receiving the echo is known, the distance r to the echo source can be obtained. Therefore, the target presence area detection unit 21 can acquire the position of the received data that is the identification target in polar coordinates (r, θ).

  And the target presence area | region detection part 21 compares the ship position of the other ship acquired by AIS, and the position of the received data which is identification object, and the said receiving data has the ship carrying AIS. It is configured to identify whether or not the received data indicates an echo from the area.

  Note that the position of the reception data (echo source position) acquired by the radar apparatus is relative position information about the ship itself. On the other hand, the ship position of the other ship acquired based on the AIS information is absolute position information based on the earth. Accordingly, the target presence area detection unit 21 converts the absolute ship position information of the other ship acquired based on the AIS information into relative position information using the GPS information and the direction information, and then the identification target. It is comprised so that it may collate with the relative positional information of the received data which is.

  Further, in order to enable detection of an area where land exists, the radar indicator 3 of the present embodiment includes a map information acquisition unit 26 that acquires map information (such as an electronic chart or coastline data). As a means for acquiring the map information, an appropriate one can be used. For example, the map information acquisition unit 26 may be configured to acquire the map information by reading a recording medium in which the map information is recorded, or communicate with an external device connected to the radar indicator 3. Thus, the map information held by the external device may be acquired.

  The target presence area detection unit 21 compares the information on the shape and position of the land included in the map information with the position of the reception data that is the identification target, so that the received data is an area where the land exists. It is configured to identify whether or not the received data indicates an echo from.

  Note that the information included in the map information is expressed in absolute coordinates based on the earth. Therefore, the target presence area detection unit 21 converts the information on the shape and position of the land acquired based on the map information into relative information centered on the ship, and then receives the received data that is the identification target. It is configured to collate with location information.

  As described above, the target presence area detection unit 21 can detect an area where a target (land or ship equipped with an AIS) exists. The detection result of the target presence area in the target presence area detection unit 21 is output to the false image suppression unit 23.

  Next, the high-pass filter process performed by the false image suppression unit 23 will be described.

  The high-pass filter processing in this embodiment is as follows. First, a moving average of received data continuous in the azimuth direction is obtained. Subsequently, a high-pass filter processing threshold value is obtained by multiplying the moving average by a predetermined offset coefficient. Then, the high-pass filter processing threshold is subtracted from the original signal. That is, since the low frequency component can be extracted by the moving average, the low frequency component can be removed and the high frequency component can be left by subtracting the high pass filter processing threshold obtained from the moving average from the original signal. It is.

  More specifically, it is as follows. First, the received data read from the sweep memory 13 is temporarily stored in the past sweep storage unit 22. The past sweep accumulation unit 22 is configured as a ring-shaped buffer memory capable of storing received data for several past sweeps. The reason why the past sweep storage unit 22 is configured in this way is to acquire reception data continuous in the azimuth direction.

  That is, it is possible to acquire reception data continuous in the distance direction (reception data continuous on a straight line starting from the ship) that can be acquired in one sweep. Accordingly, in order to acquire reception data continuous in the azimuth direction (reception data continuous on an arc centered on the ship), reception data for a plurality of sweeps is required. Thus, since the past sweep accumulation unit 22 can acquire radar echoes continuous in the azimuth direction, the past sweep accumulation unit 22 can be called a radar echo acquisition unit. The processing content in the past sweep accumulation unit 22 corresponds to the radar echo acquisition step of the signal processing program.

  The false image suppression unit 23 selects one reception data (processing target reception data) to be subjected to high-pass filter processing from the reception data stored in the past sweep accumulation unit 22. Subsequently, the false image suppression unit 23 extracts a predetermined number of reception data continuous in the azimuth direction with respect to the reception data to be processed from the reception data stored in the past sweep accumulation unit 22. Thereby, the reception data group which is continuing on the circular arc centering on the own ship can be acquired.

  Then, the false image suppression unit 23 calculates an average value for the received data group acquired from the past sweep accumulation unit 22 as described above. As a result, the moving average at the position of the reception data to be processed is obtained for the reception data series continuous in the azimuth direction.

  Next, the false image suppression unit 23 refers to the detection result of the target presence region input from the target presence region detection unit 21, and the received data to be processed is an echo from the region where the target exists. It is determined whether or not the received data indicates. The false image suppression unit 23 employs one of the first coefficient and the second coefficient as an offset coefficient based on the determination result.

  Specifically, it is as follows. When the reception data to be processed is reception data indicating an echo from a region where the target exists, the false image suppression unit 23 multiplies the moving average value by a predetermined first coefficient, A high-pass filter processing threshold is set. On the other hand, when the reception data to be processed is not reception data indicating an echo from the area where the target exists, the false image suppression unit 23 multiplies the moving average value by a predetermined second coefficient. Is a high-pass filter processing threshold value. Here, the second coefficient> the first coefficient. That is, the false image suppression unit 23 according to the present embodiment is configured to make the offset coefficient smaller in the region where the target is present than in the region where the target is not present. The first coefficient is always a value of 1 or less, but the second coefficient may be a value of 1 or more as long as it is a positive value.

  Then, the false image suppression unit 23 subtracts the high-pass filter processing threshold from the value of the reception data to be processed. By sequentially performing the above processing on all received data, low frequency components can be removed, so that false images due to side lobes can be suppressed.

  Next, the effect of reducing the offset coefficient in the region where the target exists will be described in detail. As described above, when the high-pass filter processing is uniformly performed on all radar echoes, there is a problem that even echoes from the target are suppressed. Here, “performs high-pass filter processing uniformly for all radar echoes” corresponds to the case where the offset coefficient is constant for all radar echoes, corresponding to the above embodiment. .

A case where the offset coefficient is constant will be described with reference to FIG. FIG. 3 (a) shows that the distance from the ship is r ₁ , r ₂ , r ₃ when the target surrounding the ship is like the radar image shown in FIG. 2 (b). It is a graph of the azimuth | direction echo cross section in the case of. The azimuth-direction echo section refers to a reception data sequence in which reception data continuous in the azimuth direction (reception data having the same distance from the ship) is arranged according to the azimuth (antenna angle) θ. The vertical axis of the graph indicates the signal level, and the horizontal axis indicates the direction θ. Further, a high-pass filter processing threshold value obtained by calculating a moving average for the received data series and multiplying the moving average by a certain offset coefficient is shown by a two-dot chain line in FIG.

  When the high-pass filter processing threshold is obtained with the offset coefficient being constant, the high-pass filter processing threshold fluctuates in proportion to the moving average of the reception data series continuous in the azimuth direction. Therefore, in this case, as shown in FIG. 3A, in a region where a target having a large effective reflection cross-sectional area (land or large ship) exists, or in a region where a false image due to a side lobe appears, The high-pass filter processing threshold is larger than that in the region.

  FIG. 3B shows the result of subtracting the high-pass filter processing threshold obtained with the offset coefficient constant from the received data (result when the high-pass filter processing is uniformly performed). If the offset coefficient is an appropriate value, low frequency components can be removed by performing the high-pass filter process. Thereby, as shown in FIG.3 (b), the false image (fake image by a side lobe) which appears around the target can be suppressed. However, if the offset coefficient is constant, even echoes in areas where large ships or land exist are greatly suppressed, as shown in FIG. This is because, as described above, when the offset coefficient is constant, the high-pass filter processing threshold increases in a region where a target having a large effective reflection cross-sectional area exists.

  Next, an example of the high-pass filter processing threshold (high-pass filter processing threshold obtained by changing the offset coefficient in the region where the target exists) obtained in the configuration of the present embodiment is shown by a two-dot chain line in FIG. Show. Further, FIG. 4B shows the result of subtracting the high-pass filter processing threshold obtained in the configuration of the present embodiment from the received data (result of the false image suppression processing of the present embodiment).

  By setting the first coefficient to a sufficiently small value, as shown in FIG. 4A, the high-pass filtering threshold value in the area where the target (land or large ship) exists is set to a sufficiently small value. Can do. Therefore, even if the high-pass filter processing threshold is subtracted from the received data, the value of the received data in the area where the target is present is not excessively reduced. As a result, as shown in FIG. 4B, the radar echo of the target can be prevented from being suppressed by the false image suppression process. In order to set the high-pass filter processing threshold to a sufficiently small value in this way, the first coefficient is preferably set to a value of at least 1 or less, and more preferably set to zero or a value close to zero.

  In addition, by setting the second coefficient to an appropriate value, it is possible to appropriately remove the low frequency component in the region other than the region where the target exists. Here, the “region other than the region where the target exists” includes “the periphery of the region where the target exists (a region where a false image due to a side lobe easily appears)”. Therefore, as shown in FIG. 4B, it is possible to appropriately suppress a false image (a false image due to a side lobe) that appears around the area where the target exists.

  That is, according to the configuration of the present embodiment, it is possible to suppress only false images due to side lobes without suppressing radar echoes from land or large ships.

  The AIS is required to be mounted on a large ship, but is not always mounted on a small ship. Therefore, in the configuration of the present embodiment, the target presence area detection unit 21 may not be able to identify the radar echo from the small vessel as a radar echo from the area where the target exists. In this case, the high-pass filter processing threshold obtained by multiplying the moving average value by the second coefficient is applied to the region where the small ship is present. That is, the same processing as the high-pass filter processing for suppressing the false image is applied to the radar echo from the small ship.

  However, since a small ship has a small echo image and a narrow signal width when viewed in the azimuth direction, it is hardly suppressed even when high-pass filter processing is performed (see FIGS. 3 and 4). Therefore, even if it is not possible to detect a region where a small ship exists, there is little possibility that the radar echo from the small ship is suppressed by the false image suppression processing of the present embodiment. That is, according to the configuration of the present embodiment, it is possible to suppress only the false image due to the side lobes while leaving substantially all the target echoes.

  As described above, the marine radar apparatus 1 according to the present embodiment includes the radar indicator 3 and the radar antenna 11 that outputs a radar echo to the radar indicator 3. The radar indicator 3 includes a target presence area detection unit 21, a past sweep accumulation unit 22, and a false image suppression unit 23. The target presence area detection unit 21 detects an area where the target exists. The past sweep accumulation unit 22 can acquire radar echoes that are continuous in the azimuth direction. The false image suppression unit 23 can perform processing to suppress the false image included in the radar echo based on information obtained from the radar echo continuous in the azimuth direction. Then, the false image suppression unit 23 performs a process different from the process for the radar echo in the other area for the radar echo in the area where the target exists. Specifically, the offset coefficients are made different.

  In addition, the signal processing program of the present embodiment is a program that causes the signal processing device to execute processing including a target presence area detection step, a radar echo acquisition step, and a false image suppression step. In the target presence area detection step, an area where the target is present is detected. In the radar echo acquisition step, radar echoes continuous in the azimuth direction are acquired. In the false image suppression step, processing for suppressing the false image included in the radar echo is performed based on information obtained from the radar echo continuous in the azimuth direction. In the false image suppression step, processing different from processing for radar echoes in other regions is executed for the radar echoes in the region where the target exists.

  That is, the false image due to the side lobe appears to spread at the same distance as the target. Therefore, it is possible to appropriately suppress the false image due to the side lobe based on the radar echo continuous in the azimuth direction. In addition, after detecting the area where the target is present in advance, the area where the target is present can be prevented from suppressing even the echo of the target by changing the false image suppression processing. be able to.

  Further, in the radar indicator 3 of the present embodiment, the false image suppression unit 23 makes the offset coefficient different between the radar echo in the area where the target is present and the radar echo in the surrounding area.

  That is, the false image due to the side lobe tends to appear in the area around the target. Therefore, by configuring as described above, the processing for the radar echo of the target and the processing for the false image by the side lobe can be made different. Thereby, it is possible to prevent even the echo of the target from being suppressed while appropriately suppressing the false image due to the side lobe.

  In the radar indicator 3 of the present embodiment, the false image suppression unit 23 determines a high-pass filter processing threshold based on a moving average of radar echoes that are continuous in the azimuth direction, and the false image based on the high-pass filter processing threshold. Can be suppressed.

  That is, by determining the high-pass filter processing threshold based on the moving average of radar echoes continuous in the azimuth direction, processing equivalent to the high-pass filter processing can be performed on the radar echoes continuous in the azimuth direction. By this high-pass filter processing, it is possible to remove a false image spreading in the azimuth direction (a false image due to side lobes).

  Further, in the radar indicator 3 of the present embodiment, the false image suppression unit 23 determines a threshold based on the moving average of radar echoes continuous in the azimuth direction, and suppresses the false image based on the threshold. is there. The false image suppression unit 23 varies the offset coefficient to be multiplied by the moving average between the area where the target is present and the other area.

  Thereby, the effect of the high-pass filter process can be made different between the area where the target exists and the other area. Thereby, a false image can be suppressed more appropriately.

  In addition, the radar indicator 3 of the present embodiment includes a map information acquisition unit 26 that acquires map information. And the target presence area | region detection part 21 detects the area | region where a target exists based on the said map information.

  Thereby, the area | region where the target (specifically land) exists can be specified.

  Further, the radar indicator 3 of the present embodiment includes an AIS information acquisition unit 29 that acquires AIS information. And the target presence area | region detection part 21 detects the area | region where a target exists based on the said AIS information.

  Thereby, the area | region where the target (specifically, the ship carrying AIS) exists can be specified.

  Next, a second embodiment of the present invention will be described. In the following description, the same or similar configurations as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and description thereof is omitted.

  In the region where the target exists, the false image suppression unit 23 of the present embodiment does not calculate the high-pass filter processing threshold by multiplying the moving average by the offset coefficient, but sets the high-pass filter processing threshold to a predetermined value (fixed). Value).

  That is, in the area where the target is present, it is not necessary to suppress the false image by the high-pass filter processing, so that the high-pass filter processing threshold value does not need to be obtained based on the moving average and can be a fixed value. Then, if a sufficiently small value is set in advance as the high-pass filtering threshold value applied to the area where the target exists, it is possible to prevent the echo of the target from being suppressed. The substantially same effect as the embodiment can be obtained. Further, according to this configuration, in the area where the target exists, processing for calculating the high-pass filter processing threshold (calculation of the moving average, processing for multiplying the moving average by the offset coefficient, etc.) can be omitted. .

  As described above, in the radar indicator 3 of the present embodiment, the false image suppression unit 23 sets the high-pass filter processing threshold of the area where the target is present as a predetermined threshold.

  That is, since it is not necessary to remove the radar echo in the area where the target exists, a fixed threshold can be used. Thereby, the calculation load for calculating the threshold value can be reduced.

  Next, a third embodiment of the present invention will be described. In the following description, the same or similar configurations as those of the first and second embodiments are denoted by the same reference numerals as those of the first and second embodiments, and description thereof is omitted.

  As shown in FIG. 2B, the false image based on the side lobe appears around the area where the target exists. In other words, the false image based on the side lobe does not appear in a region separated by a predetermined distance or more in the azimuth direction from the region where the target exists. And it is not necessary to perform a high-pass filter process about the area | region previously known that a false image does not appear.

  Therefore, the false image suppression unit 23 according to the present embodiment is configured not to perform the high-pass filter processing on a region that is a predetermined distance or more away from the region where the target exists in the azimuth direction. As a result, the calculation load can be reduced because the high-pass filter process is not performed for the region where the false image based on the side lobe is unlikely to appear. Further, since unnecessary processing is not performed, it is possible to prevent an echo other than a false image from being unintentionally suppressed.

  Whether or not to perform high-pass filter processing is determined for each received data. That is, in the azimuth direction echo section, the reception data within the range of the predetermined data points counted from the reception data indicating the area where the target exists is the reception data indicating the radar echo around the area where the target exists. . Therefore, since it is highly possible that such received data indicates a false image based on the side lobe, high-pass filter processing is performed.

  On the other hand, in the azimuth echo section, the received data that is outside the range of the predetermined data points counted from the received data indicating the area where the target is present is the radar in the area that is more than the predetermined distance from the area where the target is present. Received data indicating echo. Therefore, since it is considered that such received data does not show a false image based on the side lobe, high-pass filter processing is not performed.

  As described above, in the radar indicator 3 of the present embodiment, the false image suppression unit 23 performs false image suppression in a region that is a predetermined distance or more away from the region where the target exists in the azimuth direction. Is configured to not.

  That is, the false image due to the side lobe appears around the area where the target exists. Therefore, by configuring as described above, since the processing for suppressing the false image is not performed for the region where the false image does not occur, the signal level of the radar echo can be prevented from being unintentionally suppressed. . In addition, since processing is performed only for portions that require suppression of false images, the calculation load can be reduced.

  Next, a fourth embodiment of the present invention will be described. In the following description, the same or similar configurations as those of the first to third embodiments are denoted by the same reference numerals as those of the first to third embodiments, and description thereof is omitted.

  In the present embodiment, the false image suppression unit 23 is configured to switch the presence or absence of the high-pass filter process according to the distance from the ship. That is, the false image due to the side lobe tends to appear in the vicinity of a target that is close to the ship, and hardly appears in the vicinity of a target that is far away from the ship. This is because a target closer to the ship returns stronger reflection.

  Focusing on this point, in the present embodiment, the false image suppression unit 23 performs high-pass filter processing only on received data indicating echoes from a position where the distance from the ship is less than the predetermined distance, and the predetermined distance from the ship. High-pass filter processing is not performed on received data indicating echoes from positions farther away. As a result, the high-pass filter process is performed only in the region where the false image is likely to occur, so that the calculation load can be reduced.

  As described above, in the present embodiment, the false image suppression unit 23 can be configured to perform the high-pass filter process only on the region where the distance from the own device is less than the predetermined distance. That is, since a false image is likely to appear at a short distance where strong reflection is likely to return, the configuration as described above makes it possible to perform processing only in a region where a false image is likely to occur. Thereby, calculation load can be reduced.

  The preferred embodiment of the present invention has been described above, but the above configuration can be modified as follows, for example.

  Although the processing for suppressing the false image is the high-pass filter processing, it is not limited to this. The configuration of the present invention can be applied as long as signal processing is performed on echoes from the same distance (echoes continuous in the azimuth direction) to suppress false images. That is, the main points of the present invention are that a false image due to side lobes is suppressed based on radar echoes continuous in the azimuth direction, and a target existence area is detected in advance in order to prevent echoes from the target from being suppressed. The point is that the processing is different between the target existence area and the other areas. Therefore, the content of the process for suppressing the false image is not particularly limited, and is not limited to the high-pass filter process.

  The control unit 14 has been described as being configured with hardware such as a CPU, ROM, and RAM, and software such as a program, but is not limited thereto, and may be configured with dedicated hardware.

  The radar apparatus of the present invention can be applied not only to a marine radar apparatus but also to a radar apparatus for other purposes. The radar apparatus of the present invention is not limited to the pulse radar apparatus, and can be applied to other types of radar apparatuses such as FMCW radar.

  The method for detecting the region where the target exists in the target presence region detection unit is not limited to the above method, and an appropriate method can be used. For example, when reception data having a signal level equal to or higher than a predetermined value is detected, it can be configured to determine that a target exists at the position of the reception data.

  The signal processing apparatus of the present invention is not limited to the radar indicator 3 provided with the display unit 16. For example, a signal processing apparatus that does not include a display unit itself, only generates a radar image in which a false image is suppressed, and outputs data of the radar image to an external display. good.

  Further, the received data in which the false image is suppressed may be used for purposes other than generating the radar image. For example, if TT (Target Tracking) processing is performed based on received data in which a false image is suppressed, the echo of a target can be accurately tracked.

  In the above embodiment, the high-pass filter processing threshold is configured to be a small value in the area where the target exists, thereby weakening the effect of the high-pass filter processing and suppressing echoes from the target having a large effective reflection cross-sectional area. It was prevented from being done. However, since it is not necessary to perform the high-pass filter process in the area where the target exists, the high-pass filter process may not be performed in the area.

  In the above embodiment, the false image can be suppressed by the high-pass filter process, but it is difficult to completely erase the false image (for example, as shown in FIG. 4B, the false image may remain a little. is there). Of course, if the high-pass filter processing threshold is set to a sufficiently large value, the false image can be completely removed, but there is a risk that even the necessary radar echo is unintentionally suppressed. Therefore, a configuration in which the offset coefficient is increased only around the target existence area (an area where a false image due to side lobes is likely to occur) is conceivable.

  For example, in the example of FIG. 5A, the offset coefficient is gradually increased to 1.1, 1.2, 1.3... As the target presence area is approached around the target presence area. It is getting bigger. As a result, the high-pass filter processing threshold can be increased only around the target presence area, so that the side lobes can be completely eliminated as shown in FIG. Further, according to this configuration, the high-pass filter threshold value does not become an unnecessarily large value in a region where the possibility of appearance of side lobes is low, so that necessary radar echo is suppressed unintentionally. Can be prevented.

  Moreover, in the said embodiment, it is set as the structure which changes the intensity | strength of a high-pass filter process by changing the coefficient (offset coefficient) by which a moving average is multiplied. Instead of this, or in addition to this, it is also possible to change the number of points of data for which a moving average is taken for each region. Here, the smaller the number of data points for which the moving average is taken, the better the followability of the high-pass filter processing threshold with respect to signal level fluctuations. Therefore, for example, by reducing the number of data points that take a moving average around the target presence area (area where the side lobe is generated), it is possible to completely suppress the false image due to the side lobe. Thereby, it is possible to prevent a fine peak as shown in FIG. 4B from remaining, and to more appropriately suppress a false image due to a side lobe. In addition, for example, by increasing the number of data points that take a moving average in the target presence area, it is possible to reduce the followability of the high-pass filter processing threshold. Thereby, the radar echo of the target can be made difficult to be suppressed.

  Note that in the case of the configuration in which the number of data points for which the moving average is taken as described above, the offset coefficient may be constant in all regions. Even if the offset coefficient is constant in the entire area, it is possible to change the method of applying the high-pass filter process between the target existence area and the other areas by changing the number of data points for which the moving average is taken. Furthermore, in this case, the process of multiplying the moving average by the offset coefficient may be omitted, and the moving average value may be adopted as it is as the high-pass filter processing threshold (corresponding to the case where the offset coefficient = 1).

  In addition, for example, in each case of an area where land exists, an area where land exists, an area where ships equipped with AIS exist, an area where ships equipped with AIS exist, and other areas, The offset coefficient (and / or the number of data points taking a moving average) may be varied. Thereby, a false image can be suppressed more appropriately.

  In the above embodiment, the false image suppression process is performed before the reception data is output to the display memory 15. Instead, the reception data is output to the display memory 15 without performing the false image suppression process. In addition, the false image suppression process may be performed on the reception data stored in the display memory 15. A diagram of a radar apparatus according to this modification is shown in FIG.

  The display memory 15 stores a radar image generated based on reception data for one rotation of the antenna (one scan). Therefore, continuous reception data in the azimuth direction can be acquired from the display memory 15. In this case, the display memory 15 functions as an echo data acquisition unit. In this modification, the past sweep accumulation unit 22 provided in the radar indicator 3 of the above embodiment can be omitted.

  However, if the position of the received data is expressed in polar coordinates, it is easy to extract data that continues in the azimuth direction (data that continues on an arc centered on the ship), but data that continues in the azimuth direction If an attempt is made to extract from a radar image in a raster image format, an operation such as coordinate conversion is required. Therefore, as in the above-described embodiment, it is preferable to perform high-pass filtering before storing the received data in the image memory (while the position of the received data is expressed in polar coordinates).

  In the above embodiment, the radar indicator 3 performs the false image suppression process. Instead, the false image suppression process is performed in the antenna unit, and the false image suppressed radar image is output to the radar indicator. You may comprise so that it may do. In this case, the signal processing apparatus of the present invention is provided in the antenna unit.

1 Marine radar equipment (radar equipment)
3 Radar indicator (signal processing device)
21 target area detection unit 22 past sweep storage unit (radar echo acquisition unit)
23 False Image Suppression Unit 26 Map Information Acquisition Unit 29 AIS Information Acquisition Unit

Claims (9)

A target area detection unit for detecting an area where the target exists;
A radar echo acquisition unit for acquiring a radar echo continuous in the azimuth direction;
A false image suppression unit that determines a threshold based on a moving average of signal levels of radar echoes continuous in the azimuth direction, and performs a process of suppressing a false image by subtracting the threshold from the signal level ;
With
The artifacts reduction unit, at least one of the offset coefficient multiplying the data points or the moving average takes the moving average, and wherein at different Selle be said target object is present area and other areas Signal processing device. The signal processing device according to claim 1,
The artifacts reduction unit, a realm in which the target object is present, in the realm of the surrounding, the signal processing apparatus characterized by varying at least one of the data points or the offset coefficient. The signal processing device according to claim 1 or 2,
The false image suppression unit determines a threshold value of a region where no target exists based on a moving average of signal levels of radar echoes continuous in the azimuth direction, and subtracts the threshold value from the signal level to thereby detect a false image. A signal processing device that suppresses the noise. A signal processing device according to any one of claims 1 to 3 ,
It has a map information acquisition unit that acquires map information,
The signal processing apparatus according to claim 1, wherein the target presence area detection unit detects an area where the target exists based on the map information. The signal processing device according to any one of claims 1 to 4 , wherein
An AIS information acquisition unit that acquires AIS information is provided.
The signal processing apparatus according to claim 1, wherein the target presence area detecting unit detects an area where the target exists based on the AIS information. A signal processing device according to any one of claims 1 to 5 ,
The signal processing apparatus, wherein the false image suppression unit does not suppress the false image in a region that is a predetermined distance or more away from the region where the target exists in the azimuth direction. The signal processing device according to any one of claims 1 to 6 ,
The signal processing apparatus, wherein the false image suppression unit suppresses the false image only in a region where the distance from the own apparatus is less than a predetermined distance. A signal processing device according to any one of claims 1 to 7 ,
A radar antenna that outputs a radar echo to the signal processing device;
A radar apparatus comprising: A target presence region detecting step for detecting a region where the target is present; and
A radar echo acquisition step for acquiring a radar echo continuous in the azimuth direction;
A false image suppression step of determining a threshold based on a moving average of signal levels of radar echoes continuous in the azimuth direction, and performing a process of suppressing a false image by subtracting the threshold from the signal level ;
The signal processing device to execute processing including
Wherein in the above artifacts reduction step, at least one of the offset coefficient multiplying the data points or the moving average takes the moving average, said target object different in a region where there is the other regions Selle A signal processing program.

Images