JP2016173239A - Position estimation device, and synthetic aperture radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To display the true position of a detected mobile entity on a road map in mobile entity detection by a synthetic aperture radar device.SOLUTION: Provided is a position estimation device for displaying on a road map the position of a target detected on the basis of the differential image of radar images acquired by two antennas arranged in parallel to the traveling direction of a platform in which a synthetic aperture radar device is mounted, the position estimation device being configured from: a correction unit for calculating the amount of deviation in a target position by Doppler shift and correcting the target position; a road detection unit for detecting, from a road map, a road present within a prescribed range of distance centering around the corrected target position; a distance comparison unit for detecting, from among detected roads, a road that is in the traveling direction of the platform and in the shortest distance from the corrected target position as a point of reference; and a display unit for displaying the detected position on the road as a true target position on the road map.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for detecting a moving body with a synthetic aperture radar apparatus and obtaining position information of the detected moving body with high accuracy.

Conventionally, as a position estimation technique using a synthetic aperture radar device, the antenna aperture is divided in the direction of movement, the antenna is equivalently stationary between two consecutive pulses, and the difference between the obtained radar images is calculated. A technique for suppressing clutter from a stationary target (Synthetic Aperture Radar Moving Target Indicator: hereinafter referred to as SAR-MTI) has been proposed (for example, Non-Patent Document 1).
Similarly, as a position estimation technique using a synthetic aperture radar apparatus, a moving target detection apparatus that eliminates a positional shift of a moving target in the azimuth direction due to a Doppler shift has been proposed (for example, Patent Document 1).

JP 2008-256447 A

Kei Suwa. Range direction target velocity estimation method in multi-aperture SAR-MTI method. Proceedings of the 2013 IEICE General Conference. 2013, B-2-15.

A conventional SAR-MTI will be briefly described. SAR-MTI suppresses clutter from a stationary target by using two radar images taken at the same location from the same position at the time shifted by one pulse interval and calculating the difference between the two radar images. Then, the target moving body is detected from the captured radar image.
FIG. 3 is an observation geometry diagram showing an example when a moving object is observed using a synthetic aperture radar apparatus. In FIG. 3, the traveling direction 110 of a platform (hereinafter referred to as a platform) on which a synthetic aperture radar apparatus is mounted is defined as an azimuth direction, and the traveling direction 110 is defined as a positive direction. The range direction is a direction perpendicular to the azimuth direction, and the direction away from the platform is the positive direction. When the moving body has the velocity component Vtgt in the range direction, it is displayed on the radar image by shifting in the azimuth direction from the position originally existing on the radar image by Doppler shift. The Doppler shift amount at this time is calculated by the following equation (1).

  Here, Vtgt is the speed of the moving body, Vplt is the speed of the platform, R is the slant range distance to the moving body, and θ is the off-nadir angle.

  FIG. 4 is a diagram illustrating an example of Doppler shift of a moving body detected in SAR-MTI. As shown in FIG. 4, the position K′a of the moving body detected in the SAR-MTI is displayed while being shifted in the azimuth direction according to the velocity component Vtgt in the range direction of the moving body. Therefore, conventionally, the shift in the azimuth direction has been corrected by estimating the velocity Vtgt of the moving body with respect to the shift in the azimuth direction and calculating the Doppler shift amount using the equation (1).

However, since an estimation accuracy error or the like also occurs due to noise during signal processing, an error also occurs in the estimated velocity Vtgt of the moving body.
For this reason, an error also occurs in the position of the moving body in which the Doppler shift amount is corrected, and there is a problem that when the position of the moving body is displayed on the map, it is not displayed at the true position.

  The present invention has been made to solve such problems, and provides a position estimation device capable of improving the accuracy of a target position by a synthetic aperture radar device and displaying the target position on a map with higher accuracy. The purpose is to do.

  A position estimation device according to the present invention detects a target based on a radar image acquired by two antennas arranged in parallel with the traveling direction of a platform on which a synthetic aperture radar device is mounted, and acquires the target position. A detection unit; a correction unit that calculates a shift amount of the target position due to Doppler shift; corrects the target position using the shift amount; a storage device that stores a digital road map; and the corrected target A road detection unit that detects a road existing within a predetermined distance from the position of the digital road map from the digital road map, and a road detected by the road detection unit based on the corrected target position A distance comparison unit that detects a position coordinate of a closest road in a direction parallel to the traveling direction of the platform, and the position coordinate detected by the distance comparison unit , Composed of a display unit for displaying on the digital road map as the true coordinates of the target.

  According to the position estimation apparatus according to the present invention, the accuracy of the target position estimated by the synthetic aperture radar apparatus can be improved, and the target position can be accurately displayed on the map.

It is a figure showing the structure of the synthetic aperture radar apparatus 1 which concerns on Embodiment 1 of this invention, and the position estimation apparatus 2. FIG. It is a figure which shows the example of the position error correction after the Doppler shift correction | amendment of the moving body which concerns on Embodiment 1 of this invention. It is a figure which shows the observation geometry which shows an example when a moving body is observed using a synthetic aperture radar apparatus. It is a figure which shows the example of the difference image after a mobile body detection process in SAR-MTI. It is a figure explaining the position error after Doppler shift correction of a moving body in SAR-MTI.

Embodiment 1 FIG.
Hereinafter, the position estimation apparatus according to Embodiment 1 of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a synthetic aperture radar apparatus 1 according to Embodiment 1 of the present invention and a position estimation apparatus 2 that is one component of the synthetic aperture radar apparatus 1. FIG. 3 is a diagram showing an observation geometry showing an example when a moving object is observed using a synthetic aperture radar device as described above, and FIG. 5 is a positional error after the Doppler shift correction of the moving object in SAR-MTI. FIG.

The synthetic aperture radar device 1 is mounted on, for example, an unillustrated aircraft or artificial satellite, and includes antennas 3a and 3b, a transmission / reception unit 4, an airplane information detection unit 5, an image reproduction processing unit 6, a position estimation device 2 according to the present invention, a display. The unit 17 is provided.
Here, the position estimation device 2 includes a moving body detection unit 8, a speed estimation unit 9, a Doppler shift correction unit 10, a storage device 11 having a digital road map 12, a coordinate detection unit 13, a road detection unit 14, and a distance comparison unit. 15, a position correction unit 16 and a display unit 17.
The operation of each configuration will be described below.

The antennas 3a and 3b are both antennas that can irradiate a high-frequency pulse signal toward the observation region and receive the high-frequency pulse signal reflected from the observation region.
The antenna according to the present embodiment uses two antennas 3a and 3b in order to obtain two radar images acquired at the time when the same area is shifted by one pulse interval from the same position. Are arranged in parallel with the direction of travel 110 of the platform.

  The transmission / reception unit 4 generates a high-frequency pulse signal and transmits it to the antennas 3a and 3b, and amplifies the high-frequency pulse signal that is a reflected signal from the observation region received by the antennas 3a and 3b. Then, the amplified high-frequency pulse signal is transmitted to the image reproduction processing unit 6.

  The flight information detection unit 5 detects information such as the platform speed, altitude, position, and posture with a motion sensor and transmits the information to the image reproduction processing unit 6.

  The image reproduction processing unit 6 is based on the amplified high-frequency pulse signal input from the transmission / reception unit 4 and the platform speed, altitude, position, posture, and other information input from the flight information detection unit 5 to provide a two-dimensional high resolution. Radar images 7a and 7b, which are images, are reproduced. Note that the principle and method of the reproduction processing of the radar images 7a and 7b performed by the image reproduction processing unit 6 are known from conventional literatures and the like, and the description thereof is omitted here.

  The radar images 7a and 7b are image data generated from the image reproduction processing unit 6 on the basis of the high-frequency pulse signals from the antennas 3a and 3b, respectively. The two images are shifted from the same position by one pulse interval from the same area. Obtained at different times. The radar images 7a and 7b are composed of pixels composed of complex data.

  The moving object detection unit 8 that is a component of the position estimation device 2 can detect the moving object more accurately by taking the complex difference between the radar images 7a and 7b and suppressing clutter from the stationary target.

FIG. 4 is a diagram illustrating an example of the Doppler shift of the moving object detected in the SAR-MTI as described above, and is an example of the difference image 100 after the moving object detection process by the moving object detection unit 8.
Here, the position K′a of the moving object detected by the moving object detection unit 8 has a velocity component Vtgt in the range direction. Therefore, there is a problem that the detected position K′a of the moving body is displayed in a azimuth direction shifted from the position M1 of the true moving body by Doppler shift.

  First, the speed estimation unit 9 calculates the following equation (2) from the phase difference between the moving object displayed in the radar image 7a detected by the moving object detection unit 8 and the moving object displayed in the radar image 7b. The speed Vtgt in the range direction of the moving body is estimated.

  Here, λ is the wavelength of the high frequency pulse signal, φ is the phase difference of the moving body between the radar images 7a and 7b, L is the baseline length between the antennas 3a and 3b, and θ is the off-nadir angle.

  The Doppler shift correction unit 10 calculates the Doppler shift amount according to the equation (1) based on the moving body speed Vtgt estimated by the speed estimation unit 9.

Then, the position K′a of the moving body is corrected in the azimuth direction according to the calculated Doppler shift amount.
Here, the speed Vtgt in the range direction of the moving body estimated by the speed estimation unit 9 causes an estimation accuracy error or the like due to noise during signal processing, as described above. Contains. For this reason, an error also occurs in the Doppler shift amount obtained by Expression (3), and the position of the moving body after the Doppler shift correction also includes an error with respect to the position M1 of the true moving body.
Therefore, the position estimation apparatus according to the present embodiment further performs the following processing.

  The storage device 11 stores a digital road map 12 therein. The digital road map 12 is a map that includes general geographical information, road information, and the like, and includes the position of the road in two-dimensional coordinates as numerical information that can be processed electronically. .

The coordinate detection unit 13 detects the coordinates Ka (Xa, Ya) of the position Ka of the moving body after the Doppler shift correction unit 10 corrects the Doppler shift.
Then, the coordinate detection unit 13 performs a process of plotting the position Ka (Xa, Ya) after the Doppler shift correction on the coordinates of the digital road map 12 stored in the storage device 11.

  Next, the road detection unit 14 exists within a predetermined distance with the coordinate Ka (Xa, Ya) of the position Ka of the moving body after the Doppler shift correction plotted on the digital road map 12 by the coordinate detection unit 13 as the center. A process for detecting a road is performed. Note that the predetermined distance can be input by the operator of the apparatus using the input means.

The distance comparison unit 15 compares the distance between the road detected by the road detection unit 14 and the position Ka of the moving body after Doppler shift correction, so that the distance is closest to the position Ka of the moving body after Doppler shift correction. A process for detecting a road is performed.
Here, in detecting the closest road, since the displacement from the true position of the moving body due to the Doppler shift occurs on the azimuth, the azimuth direction based on the position Ka of the moving body after the Doppler shift correction, In other words, the closest road among the roads in the direction parallel to the traveling direction of the platform is detected. Here, the moving body is a moving body traveling on a road, for example, a vehicle.

  Next, the position correction unit 16 moves to the coordinate M1 (X1, Y1) on the road closest to the position Ka of the moving body after the Doppler shift correction detected by the distance comparison unit 15 in the azimuth direction. A process of correcting the position coordinate Ka (Xa, Ya) of the body Ka is performed.

  The display unit 17 recognizes the position coordinates M1 (X1, Y1) output from the position correction unit 16 as the true position of the moving body and displays it on the digital road map.

  Below, the specific operation | movement of the mobile body estimation apparatus 2 which concerns on this Embodiment is demonstrated.

The Doppler shift correction unit 10 corrects the position of the moving body in the azimuth direction according to the Doppler shift amount calculated by the Doppler shift correction unit 10 with respect to the position K′a of the moving body detected by the moving body detection unit 8. Thus, the position Ka of the moving body after the Doppler shift correction is calculated (FIG. 5).
At this time, when the detected velocity component Vtgt in the range direction of the moving body is in a direction approaching the platform, the display position K′a of the detected moving body is displayed in the same direction as the traveling direction 110 of the platform. The display position K′a is corrected in the direction opposite to the platform traveling direction 110 and the position K′a of the moving body is corrected according to the Doppler shift amount.
On the other hand, in the case of the direction away from the platform, the display position K′a of the detected mobile object is displayed in the direction opposite to the platform traveling direction 110, so the display position K′a is set in the same direction as the platform. The position K′a of the moving body is corrected according to the Doppler shift.

The processing after the coordinate detection unit 13 will be described with reference to the example of FIG.
FIG. 2 is a diagram illustrating an example of position error correction after Doppler shift correction of the moving body according to Embodiment 1 of the present invention. The coordinate detection unit 13 detects the corrected position coordinates Ka (Xa, Ya) of the moving body corrected by the Doppler shift correction unit 10 and plots them on the digital road map 12.

  Based on the position coordinates Ka (Xa, Ya) of the moving object plotted at the same coordinates on the digital road map 12, the road detection unit 14 detects roads existing within a predetermined distance from the position coordinates Ka (Xa, Ya). To detect. The predetermined distance is a numerical value that can be arbitrarily set by the user using an input means such as a keyboard.

Next, the distance comparison unit 15 compares the distance between the position coordinates Ka (Xa, Ya) of the moving body after the Doppler shift correction and the adjacent road for each of the road candidates detected by the road detection unit 14. As a result of the comparison, the distance comparison unit 15 detects the road having the shortest distance from the position coordinates Ka (Xa, Ya) of the moving body.
Here, the displacement of the moving body from the true position due to the Doppler shift occurs in the azimuth direction, that is, the traveling direction of the platform on which the synthetic aperture radar device is mounted. For this reason, the road for which the distance is compared is an adjacent road in the positive and negative directions on the same azimuth axis as the moving body, with the position of the moving body as the center. The distances ra2 and ra1 to the adjacent roads in the positive and negative directions on the azimuth axis are compared by the following equations (3) and (4).

Here, ra1 and ra2 are obtained from the following equations (5) and (6) from Ka (Xa, Ya), the point M1 (X1, Y1) on the road, and the point M2 (X2, Y2). be able to.

When Expression (3) is satisfied, ra1> ra2, and the adjacent road where the point M1 (X1, Y1) on the road exists is the closest road.
On the other hand, when Expression (4) is satisfied, ra1 <ra2 is satisfied, and the adjacent road where the point M2 (X2, Y2) on the road exists is the closest road.
In the example of FIG. 2, since ra1 <ra2, the road on the left side of the detected moving object is detected as the closest road.
The position correction unit 16 is located on the road determined to be the closest by the distance comparison unit 15 and is on the same azimuth axis as the moving body, M1 (X1, Y1), and Ka (Xa, Ya). The position coordinates are plotted and output to the display unit 17.
The display unit 17 displays the position coordinates M1 (X1, Y1) output from the position correction unit 16 on the digital road map 12.

As described above, according to the position estimation apparatus according to the present embodiment, the position accuracy of the target estimated by the synthetic aperture radar apparatus can be improved, and the position of the target can be accurately displayed on the map. The position estimation apparatus according to the present invention can be used for aerial surveys, traffic surveys, and the like, and has high versatility.
Note that the position estimation apparatus according to the present invention can also be applied in the range direction by a similar method.

  DESCRIPTION OF SYMBOLS 1 Synthetic aperture radar apparatus, 2 Position estimation apparatus, 3a antenna, 3b antenna, 4 Transmission / reception part, 5 Flight information detection part, 6 Image reproduction process part, 7a Radar image, 7b Radar image, 8 Moving body detection part, 9 Speed estimation 10 parts, 10 Doppler shift correction part, 11 storage device, 12 digital road map, 13 coordinate detection part, 14 road detection part, 15 distance comparison part, 16 position correction part, 17 display part, 18 road, 100 moving body detection process Difference image after, 110 platform direction, 120 Doppler shift corrected position and true moving body position error

Claims (4)

A target detection unit that detects a target based on a radar image acquired by two antennas arranged in parallel with the traveling direction of the platform on which the synthetic aperture radar apparatus is mounted, and acquires the position of the target;
A correction unit that calculates a shift amount of the target position due to a Doppler shift, and corrects the target position using the shift amount;
A storage device for storing a digital road map;
A road detection unit that detects a road existing within a predetermined distance from the corrected target position from the digital road map;
A distance comparison unit that detects a position coordinate of a closest road in a direction parallel to the traveling direction of the platform from the road detected by the road detection unit based on the corrected target position When,
A display unit that displays the position coordinates detected by the distance comparison unit on the digital road map as the true position coordinates of the target;
A position estimation device comprising:   The position estimation apparatus according to claim 1, wherein the target is a moving body that moves on a road of the digital road map.   The position estimation device according to claim 1, wherein the radar image is two radar images obtained by acquiring the same area from the same position for a predetermined time with the two antennas. Two antennas arranged in parallel with the traveling direction of the platform on which the synthetic aperture radar device is mounted;
A transmitter / receiver that generates a high-frequency pulse signal and transmits it to the antenna, and amplifies a high-frequency pulse signal that is a reflected signal from the observation region received by the antenna;
A flight information detector for detecting information about the speed and altitude of the platform with a sensor;
An image reproduction processing unit for reproducing a radar image based on a high-frequency pulse signal input from the transmission / reception unit, a platform speed input from the flight information detection unit, and altitude information;
A target detection unit that detects a target based on the radar image and obtains a position of the target;
A correction unit that calculates a shift amount of the target position due to a Doppler shift, and corrects the target position using the shift amount;
A storage device for storing a digital road map;
A road detection unit that detects a road existing within a predetermined distance from the corrected target position from the digital road map;
A distance comparison unit that detects a position coordinate of a closest road in a direction parallel to the traveling direction of the platform from the road detected by the road detection unit based on the corrected target position When,
A display unit that displays the position coordinates detected by the distance comparison unit on the digital road map as the true position coordinates of the target;
A synthetic aperture radar device comprising:

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