JP2011191141A - False image reducing device, radar device, false image reducing method, and false image reducing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a false image reducing device for reducing a beam sub false image by image processing. <P>SOLUTION: A beam sub false image detecting part 154 calculates the number of consecutive pixels showing a predetermined level or more in the sweep direction with respect to polar coordinate image data at each distance and extracts the polar coordinate image data as a false image candidate when the number is a threshold value Th or more. The beam sub false image detecting part 154 detects a beam sub false image based on a width in the azimuthal direction of the false image candidate and a width in a distance direction of the same. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a false image reduction device that reduces false images (beam sub-false images) generated by side lobes.

  An antenna such as a radar device generates a certain level of side lobes in addition to the direction in which electromagnetic waves are emitted (the direction of the main lobe). When the side lobe is reflected on the target and received as an echo, it is assumed that the echo has been received from the direction of the main lobe, and a false image (hereinafter referred to as a beam sub-false image) is generated in the direction where the target does not exist. Displayed (see Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 3-138583 JP-A-3-138484

  Since the beam sub-false image is unnecessary in the radar image, it needs to be removed. Therefore, an object of the present invention is to provide a false image reduction device that reduces a beam sub false image by image processing.

  The false image reduction device of the present invention includes image data generation means, false image candidate extraction means, and false image extraction means. The measuring means receives an echo signal of the electromagnetic wave transmitted from the antenna, and generates image data based on the echo signal. Since electromagnetic waves are transmitted in pulses from the antenna every predetermined direction, the image data is generated as polar coordinate system data consisting of distance and direction.

  The false image candidate extraction means extracts a false image candidate in which the echo image exists in a azimuth direction with a predetermined width or more from echo images having a level of the echo signal equal to or higher than a predetermined level. For example, among pixels of image data, a pixel having a predetermined level or higher is binarized with a maximum value, and a pixel having a level lower than the predetermined level is binarized, and the maximum value is continuous to some extent in the azimuth direction (for example, 1000 sweeps in all directions) Echo images that continue for about 600 sweeps) are extracted as false image candidates. Alternatively, the pixels showing values of a predetermined level or more for each direction are frequency-distributed in the distance direction, and an echo image corresponding to the frequency peak is extracted as a false image candidate.

  It is desirable that the image data is averaged in the azimuth direction to perform processing for eliminating short breaks in the echo image.

  Then, the false image extraction means calculates the distance direction width in each azimuth among the extracted false image candidates, and extracts the false image echo image based on the distance direction width and the azimuth direction width. To do. Specifically, from the false image candidates, the azimuth whose width in the distance direction is equal to or greater than the predetermined width is extracted, the false image area width from the extracted azimuth to the end of the false image candidate in the azimuth direction is calculated, If the false image area width with respect to the width in the azimuth direction of the image candidate is equal to or greater than a predetermined ratio, the false image candidate is set as a false image echo image.

  Further, an echo signal level control means is provided to perform level control (reduction processing) of the extracted false image echo image. The level control of the echo signal is performed by interpolating between pixels adjacent to the false echo image among the pixels in each direction of the image data. Moreover, it is desirable that the interpolation between pixels is linear interpolation.

  As described above, by performing image processing that reflects the shape characteristics of the beam sub-false image, only the beam sub-false image can be accurately reduced.

  According to the false image reduction device of the present invention, the beam sub-false image can be reduced by image processing.

It is a block diagram which shows the structure of the radar apparatus of this embodiment. FIG. 2A is a schematic diagram when the image data before performing the false image reduction process is displayed on the display 18, and FIG. 2B shows the sweep data including the beam sub-false image expressed in polar coordinates. FIG. FIG. 3A is a diagram showing polar coordinate image data after low-pass filter processing, and FIG. 3B is a diagram showing polar coordinate image data after binarization. It is a figure which shows the other example of the extraction method of a false image candidate. It is a figure which shows the concept which detects a beam sub false image based on the width | variety of an azimuth | direction direction, and the width | variety of a distance direction. It is a figure explaining linear interpolation. It is a figure which shows the example which sets a reduction process addition area | region. FIG. 8A is a diagram showing the image data before performing the false image reduction processing in polar coordinates, and FIG. 8B is a diagram showing the image data after performing the false image reduction processing in polar coordinates. It is. FIG. 9A is a schematic diagram when the image data before performing the false image reduction process is displayed on the display 18, and FIG. 9B shows the image data after performing the false image reduction process. It is a schematic diagram at the time of displaying on the indicator.

  FIG. 1A is a block diagram showing a configuration of a radar apparatus incorporating the false image reduction apparatus of the present invention. The radar device is a device that is installed on a ship, for example, and transmits and receives electromagnetic waves around the ship to detect targets such as other ships.

  In the figure, the radar apparatus includes an antenna 11, a receiving unit 12, an A / D converter 13, a sweep memory 14, a false image reduction processing unit 15, an image converting unit 16, an orthogonal coordinate image memory 17, and a display 18. ing.

  The antenna 11 transmits an electromagnetic wave in each direction around the ship and receives an echo signal. The receiving unit 12 outputs a value corresponding to the level (echo level) of the echo signal received by the antenna 11 to the A / D converter 13. The A / D converter 13 digitally converts the input analog echo signal and outputs it to the sweep memory 14 as measurement data.

  The sweep memory 14 stores measurement data for one measurement period (360 degrees around the ship). Each measurement data is associated with the coordinates (azimuth and distance) of the polar coordinate system and stored as sweep data. Since the antenna 11 transmits an electromagnetic wave in a pulse shape for each predetermined direction, the sweep data is stored as a discrete value for each predetermined sample for each direction of the antenna 11.

  The image conversion unit 16 receives the sweep data of the polar coordinate system from the sweep memory 14, converts it into an orthogonal coordinate system with the position of the ship as the origin, and outputs it as a pixel luminance value with a gradation corresponding to the echo level. The pixel luminance values of this orthogonal coordinate system are stored in the orthogonal coordinate image memory 17 as orthogonal coordinate image data.

  The display 18 reads the rectangular coordinate image data stored in the rectangular coordinate image memory 17 and displays a radar image (echo image) as shown in FIG. In this embodiment, an example is shown in which a pixel with a white background color and a higher pixel luminance value is displayed in black. Conversely, a pixel with a black background color and a higher pixel luminance value is displayed in white. It may be. Moreover, the aspect displayed as a color image may be sufficient.

  The antenna 11 generates side lobes at a certain level in addition to the direction in which the electromagnetic waves are emitted (the direction of the main lobe). When the side lobe is directed to the direction in which the target is present, an echo signal of a certain level is received, so that sweep data is generated as if an echo signal of a certain level is received from the direction of the main lobe. . Therefore, as shown in FIG. 2A, the beam sub-false image is displayed in the direction where the target does not exist. Since the side lobe is generated in almost the entire azimuth direction, the beam sub-false image is displayed so as to extend long in the azimuth direction on an equal circle having the same distance from the ship.

  Here, in the radar apparatus of the present embodiment, the false image reduction processing unit 15 reads the sweep data stored in the sweep memory 14, extracts the beam sub-false image, performs the level reduction process, and performs the measurement 1 of the sweep memory 14. Update the contents of the sweep data for the period. As a result, the sweep data after the level reduction process is input to the image conversion unit 16, and an echo image from which only the beam sub-false image has been accurately removed is displayed on the display 18 (see FIG. 9).

  Hereinafter, the processing content of the false image reduction processing unit 15 will be specifically described. FIG. 1B is a block diagram illustrating a configuration of the false image reduction processing unit 15. The false image reduction processing unit 15 includes an averaging processing unit 151, a binarization processing unit 152, a binarized data memory 153, a beam sub false image detection unit 154, and a level control unit 155. By these components, the false image reduction processing unit 15 detects beam sub-false images by image processing using the sweep data as polar coordinate image data, and performs false image reduction processing.

  The averaging processing unit 151 reads sweep data (hereinafter referred to as polar coordinate image data) from the sweep memory 14 and performs an averaging process. The averaging process is realized, for example, by performing a low-pass filter process on the polar coordinate image data in the azimuth direction. The low-pass filter process is performed using, for example, an FIR filter.

  FIG. 2B shows a diagram representing polar coordinate image data including a beam sub-false image. In the example of FIG. 5B, the horizontal axis is the distance direction (in the vicinity of the ship in the left direction, the ship is in the far direction in the right direction), and the vertical axis is the azimuth direction. The semi-elliptical echo image shown in the vicinity of the center of the figure is the target, and the echo image extending in the azimuth direction is the beam sub-false image.

  Since a plurality of side lobes emitted from the antenna 11 are generated for each predetermined direction, the beam sub-false image appears intermittently in the azimuth direction. Therefore, the averaging processing unit 151 performs a process of eliminating a short discontinuous portion of the echo image and providing a connection in the azimuth direction as shown in FIG. 3A by performing a low-pass filter process. .

  Next, the binarization processing unit 152 binarizes the pixels of the polar coordinate image data after the low-pass filter processing, with a pixel that is equal to or higher than a predetermined level (threshold) as a maximum value and a pixel that is lower than the predetermined level as a minimum value. To do. That is, a pixel that is equal to or greater than the threshold value is converted to a value 1, and a pixel that is less than the threshold value is converted to a value 0. However, in the radar device, the gain characteristic is corrected according to the distance so that the gain increases as the distance increases in order to suppress the influence of sea surface reflection in the vicinity of the ship. It depends on the distance from the ship. For example, the vicinity of the ship is a threshold A, and the distance of the ship is a threshold B larger than the threshold A (the maximum value is 255, the threshold A = 50, and the threshold B = 60). The binarized polar coordinate image data is temporarily stored in the binarized data memory 153. The binarization processing unit 152 may store the polar coordinate image data input from the averaging processing unit 151 in the binarized data memory 153 after reducing the resolution.

  Next, the beam sub false image detection unit 154 reads the binarized polar coordinate image data from the binarized data memory 153 and detects the beam sub false image.

  The beam sub-false image detection unit 154 first extracts a false image candidate from the binarized polar coordinate image data. The beam sub-false image detection unit 154 determines whether the width in the azimuth direction of the pixel indicating the value 1 is greater than or equal to a predetermined width for the polar coordinate image data at each distance. That is, as shown in FIG. 3B, for polar coordinate image data at each distance, the number of pixels having a value of 1 in the sweep direction is calculated, and the number of continuous sweeps is a threshold Th (for example, 1000 sweeps in all directions). (About 600 sweeps) or more, all the pixels indicating the value 1 at this distance and all pixels adjacent to the value 1 are extracted as false image candidates.

  The extraction of false image candidates can also be performed as follows. FIG. 4 is a diagram illustrating another example of a false image candidate extraction method. As shown in FIG. 4A, the false image reduction processing unit 15 in this example includes a histogram analysis unit 159 instead of the averaging processing unit 151, the binarization processing unit 152, and the binarized data memory 153. ing. The histogram analysis unit 159 calculates the number of pixels of a predetermined level or more from the polar coordinate image data in each distance direction, and obtains a frequency distribution in the distance direction as shown in FIG. The histogram analysis unit 159 extracts a distance indicating a peak of the frequency distribution (a distance indicating a highest frequency that is equal to or higher than a predetermined frequency). In this example as well, the binarization processing unit 152 and the binarized data memory 153 may be further provided, and the frequency distribution may be obtained after binarizing the polar coordinate image data.

  Furthermore, the histogram analysis unit 159 further calculates the number of pixels that change from 0 to 1 in the azimuth direction (pixels that change from less than a predetermined level to more than a predetermined level) as shown in FIG. Find the frequency distribution of. The histogram analysis unit 159 extracts a distance indicating a peak of the frequency distribution (a distance indicating a highest frequency that is equal to or higher than a predetermined frequency). The histogram analysis unit 159 sets a pixel having a predetermined level or higher and a neighboring pixel having a predetermined level or higher among the distances at which the peaks of the two frequency distributions coincide as false image candidates. As described above, since the beam sub-false image appears intermittently in the azimuth direction, the number of pixels that change from 0 to 1 in the azimuth direction tends to be large.

  As described above, it is possible to determine whether the width in the azimuth direction is equal to or larger than the predetermined width based on the number of pixels in the azimuth direction of pixels having a predetermined level or more without performing the averaging process by the FIR filter having a high processing load. Is also possible.

  Next, the beam sub-false image detection unit 154 determines whether the extracted false image candidate is a beam sub-false image based on the width in the azimuth direction of the false image candidate and the width in the distance direction. That is, as shown in FIG. 5A and FIG. 5B, a false image area is extracted from the width of the false image candidate in the distance direction, and the entire length of the false image candidate in the azimuth direction (from the upper end pixel to the lower end pixel). If the ratio of the length (Length Upper, Length Lower) in the azimuth direction of the false image area to the length (Length Whole) is equal to or greater than a predetermined value (for example, 70% or more), the false image area of the false image candidates The inside is determined to be a beam sub-false image.

  The beam sub-false image has a tendency that the width in the distance direction is much narrower than the width in the distance direction of the target portion and becomes very long in the azimuth direction. On the other hand, when the echo image is not a beam sub-false image but a target (land or the like) having a length in the azimuth direction, the width in the distance direction tends to be widened to some extent. Therefore, the beam sub false image detection unit 154 calculates the distance direction width R of each direction in order from the end (upper end pixel and lower end pixel) of the false image candidate. When the distance direction width R is equal to or greater than a threshold value Rth (for example, about 5 pixels), the calculation is finished, and the portion from the upper end pixel to the pixel where R ≧ Rth and the portion from the lower end pixel to the pixel where R ≧ Rth are satisfied Is a false image area. The beam sub-false image detection unit 154 then determines the length in the azimuth direction from the top pixel to the pixel where R ≧ Rth (Length Upper), and the azimuth of the portion from the bottom pixel to the pixel where R ≧ Rth. The length of the direction (Length Lower) is calculated. If (Length Upper + Length Lower) / (Length Whole)> (Length Thres Ratio), it is determined that the false image region of the false image candidate is a beam sub-false image. As described above, the length threshold ratio is set to 70% (0.7), for example. If the beam sub-false image detection unit 154 determines that the false image candidate is a beam sub-false image, the beam sub-false image detection unit 154 outputs information indicating the coordinates of the beam sub-false image to the level control unit 155.

  The level control unit 155 reads the sweep data (polarized image data that has not been binarized) from the sweep memory 14 and performs level control (false image reduction processing) of pixels corresponding to the coordinates of the beam sub-false image. The false image reduction process may be a process in which all values in the false image area are set to 0, but the following process may be performed.

  First, as shown in FIG. 6A, the level control unit 155 detects both end coordinates in each azimuth direction of the beam sub-false image. If the coordinates input from the beam sub-false image detection unit 154 are coordinates based on binarized data, the coordinates corresponding to the non-binarized polar coordinate image data are detected from the input coordinates. When the binarized data has a reduced resolution, one or a plurality of pixels corresponding to the high-resolution polar coordinate image data that has not been binarized are detected as the coordinates of both end pixels.

  The level control unit 155 detects two pixels adjacent to both ends of the beam sub-false image as shown in FIG. When a plurality of pixels are detected as the coordinates of both end pixels, a plurality of adjacent pixels are detected.

  Finally, the level control unit 155 linearly interpolates between the detected adjacent pixels as shown in FIG. This linear interpolation is performed for all data in each azimuth direction in the false image area.

  However, as shown in FIG. 3A, when low-pass filter processing is performed in the azimuth direction, the echo image corresponding to the target is also stretched in the azimuth direction. If only the inside is reduced, a beam sub-false image will remain. Therefore, as shown in FIG. 7, the level control unit 155 additionally performs a reduction process by the amount extended by the low-pass filter process. That is, the level control unit 155 further sets a reduction process addition region by a half of the number of average pixels (the number of taps of the FIR filter) in the downward and upward directions from the pixel where R ≧ Rth, and performs linear interpolation. Add the direction to be performed.

  In consideration of the data that is rounded to 0 when binarized and converted to a value of 1, 0, the reduction process additional region is set to be less than half of the average number of pixels (for example, 10 sweeps). Less).

  As described above, the false image reduction processing unit 15 performs the process of reducing the level in the false image area, and updates the sweep data in the sweep memory 14. As a result, the polar coordinate image data before performing the false image reduction processing as shown in FIG. 8A is converted into polar coordinate image data in which only the beam sub-false image portion is level-reduced as shown in FIG. Is done.

  The image conversion unit 16 reads the updated sweep data, converts it into rectangular coordinate image data, and stores it in the rectangular coordinate image memory 17. As a result, as shown in FIG. 9 (A), the echo image displayed so as to extend long in the azimuth direction on the same circle with the same distance from the ship is shown in FIG. 9 (B). Thus, the echo image disappears while leaving only the unnecessary image.

  As described above, in the false image reduction process in the radar apparatus according to the present embodiment, it is possible to accurately reduce only the beam sub false image by performing image processing that reflects the shape characteristics of the beam sub false image.

  In the radar apparatus according to the present embodiment, an example is shown in which image data is displayed on the display unit 18; however, in addition to the display of the image data, each target is captured and tracked (used as a collision prevention support apparatus). Is also possible. The false image reduction processing of the present embodiment can prevent the false image from being captured and tracked, and is very suitable as a collision prevention support apparatus.

DESCRIPTION OF SYMBOLS 11 ... Antenna 12 ... Reception part 13 ... A / D converter 14 ... Sweep memory 15 ... False image reduction process part 16 ... Image conversion part 17 ... Orthogonal coordinate image memory 18 ... Display

Claims (12)

An image data generation unit that receives an echo signal of an electromagnetic wave transmitted from an antenna and generates image data based on the echo signal;
Among the echo images having a level of the echo signal equal to or higher than a predetermined level, a false image candidate extraction unit that extracts a false image candidate based on the width in the azimuth direction of the echo image;
A false image extraction means for calculating a distance in the distance direction of the false image candidate and extracting an echo image of the false image based on the width in the distance direction and the width in the azimuth direction;
A false image reduction device. The false image reducing device according to claim 1,
A false image reduction device comprising echo signal level control means for controlling the level of the image data of the false image echo image. In the false image reduction device according to claim 2,
The echo signal level control means performs a level control process by interpolating between pixels adjacent to the echo image of the false image among pixels in each direction of the image data. In the false image reduction device according to claim 3,
The false image reduction device, wherein the interpolation between the pixels by the echo signal level control means is linear interpolation. In the false image reduction device according to any one of claims 1 to 4,
Averaging processing means for averaging the image data in the azimuth direction,
The false image reduction device, wherein the false image candidate extraction means extracts false image candidates from the image data averaged in the azimuth direction by the averaging processing means. In the false image reduction device according to any one of claims 1 to 5,
The false image reduction device, wherein the false image candidate extraction unit extracts the false image candidates based on continuity in the azimuth direction of the echo image having the predetermined level or more. In the false image reduction device according to any one of claims 1 to 5,
The false image reduction device, wherein the false image candidate extraction unit extracts the false image candidates based on the number of pixels in the azimuth direction of the echo image having the predetermined level or more. The false image reduction device according to any one of claims 1 to 7,
The false image extracting means extracts an orientation in which the width in the distance direction is equal to or larger than a predetermined width from the false image candidates, and a false image region width from the extracted orientation to an end portion in the orientation direction of the false image candidate The false image reduction device is characterized in that if the false image area width with respect to the width in the azimuth direction of the false image candidate is equal to or greater than a predetermined ratio, the false image candidate is an echo image of the false image.   The false image reduction device according to claim 1, wherein the predetermined level is different depending on a distance. The false image reduction device according to any one of claims 2 to 9,
Display means for displaying an image based on the image data;
With
An image based on the image data, the level of which is controlled by the echo signal level control means, is displayed for the false image echo image among the image data. An image data generation step of receiving an echo signal of an electromagnetic wave transmitted from an antenna and generating image data based on the echo signal;
Among the echo images having a level of the echo signal equal to or higher than a predetermined level, a false image candidate extraction step for extracting a false image candidate based on the width in the azimuth direction of the echo image;
The false image extraction step of calculating the width in the distance direction in each azimuth among the false image candidates, and extracting the echo image of the false image based on the width in the distance direction and the width in the azimuth direction;
A fake image reduction method. An image data generation step of receiving an echo signal of an electromagnetic wave transmitted from an antenna and generating image data based on the echo signal;
Among the echo images having a level of the echo signal equal to or higher than a predetermined level, a false image candidate extraction step for extracting a false image candidate based on the width in the azimuth direction of the echo image;
The false image extraction step of calculating the width in the distance direction in each azimuth among the false image candidates, and extracting the echo image of the false image based on the width in the distance direction and the width in the azimuth direction;
Is a false image reduction program that causes a radar device to execute.