JP2017106799A - Synthetic-aperture radar device and radar signal processing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an error occurring to the relative position relation of a fixed target and a mobile target, and superimpose images of them.SOLUTION: An SAR radar device of the present invention transmits/receives a Σ beam and a Δ beam formed on an Az plane by dividing the actual aperture of an antenna into two parts on movement direction axis of a mobile entity toward an imaging range, and acquires a Σ signal and a Δ signal by transmission/reception of the Σ beam and Δ beam. A signal processing system performs the operations of: compression-processing the Σ signal in frequency domain, and creating the whole image of the imaging range including the fixed target; acquiring a Σ signal and a Δ signal at a point N along the movement direction axis from the Σ signal and Δ signal; compressing-processing them in frequency domain and generating an RD signal; extracting the mobile target from the RD signal and creating a symbol or image of the mobile target; measuring a monopulse angle using the Σ signal and Δ signal of range-Doppler cell of the extracted mobile target; calculating the position of the mobile target by the measured angle and the detected range; and superimposing the symbol or image of the mobile target on the whole image of the imaging range that includes the fixed target.SELECTED DRAWING: Figure 1

Description

  The present embodiment relates to a synthetic aperture radar apparatus that outputs a fixed target and a moving target using synthetic aperture processing in an environment where a fixed target and a moving target coexist, and a radar signal processing method thereof.

  In a conventional synthetic aperture radar (SAR), the SAR process uses an array antenna with a large synthetic aperture length (hereinafter referred to as a large aperture array) to align the phase with a fixed target, and the maximum vector. Synthesize so that According to this processing, in the case of a fixed target, since it is at a fixed position within the synthetic aperture time, it can be imaged at the correct position (see Non-Patent Documents 1, 2, and 3). On the other hand, since the position of the moving target changes within the synthetic aperture time, the phase changes and the wavefront shift of the large aperture array occurs, and an image is generated at a position shifted from the correct position. This is a phenomenon called image shift. When a moving target image is superimposed on a fixed target image, there is a problem that a large error occurs in the relative positional relationship between the fixed target and the moving target (see Non-Patent Document 4).

SAR method (range compression), Ouchi, “Basics of Synthetic Aperture Radar for Remote Sensing”, Tokyo Denki University Press, pp.131-149 (2003) SAR method (Az compression), Ouchi, “Basics of Synthetic Aperture Radar for Remote Sensing”, Tokyo Denki University Press, pp.171-178 (2003) SAR method (Large aperture array synthesis, spotlight SAR), Yoshida, "Revised radar technology", IEICE, pp.280-283 (1996) SAR method (moving object image shift), Ouchi, “Basics of Synthetic Aperture Radar for Remote Sensing”, Tokyo Denki University Press, pp.218-223 (2003) Phase monopulse (phase comparison monopulse) system, Yoshida, “Revised radar technology”, IEICE, pp.280-283 (1996) Amplitude monopulse (amplitude comparison monopulse) system, Yoshida, “Revised radar technology”, IEICE, pp.280-283 (1996) Sampling processing, Charles V. Jakowats. JR., “Spotlight-Mode Synthetic Aperture Radar: A Signal Processing Approach”, Springer, pp. 136-139 (1996)

  As described above, in the conventional synthetic aperture radar apparatus, there is a problem that a large error occurs in the relative positional relationship between the fixed target and the moving target when the moving target image is superimposed on the fixed target image due to the influence of the image shift. It was.

  The present embodiment has been made in view of the above problems, and when a moving target image is superimposed on a fixed target image, a synthetic aperture radar apparatus capable of reducing errors generated in the relative positional relationship between the fixed target and the moving target. And a radar signal processing method thereof.

  In order to solve the above-described problems, the present embodiment includes a transmission / reception unit and a signal processing unit in a synthetic aperture radar (SAR) radar device mounted on a moving body. The transmission / reception means transmits / receives a Σ beam and a Δ beam formed by dividing the actual aperture of the antenna into the Az plane and divided into two apertures on the moving direction axis of the moving body toward the imaging range. The signal processing means extracts a fixed target and a moving target from the Σ signal and Δ signal acquired by transmitting and receiving the Σ beam and the Δ beam, and superimposes the respective images. Unit and an image superimposing unit. The fixed target processing unit compresses the Σ signal in the frequency domain and creates an entire image in the imaging range including the fixed target. The movement target processing unit obtains N (N is a natural number) signals along the movement direction axis from the Σ signal and Δ signal, respectively, and compresses the N points of the Σ signal and Δ signal in the frequency domain, respectively. Then, a range-frequency axis RD (Range Doppler) signal is generated, a moving target is extracted from the RD signal to generate a moving target symbol or image, and the extracted moving target range-Doppler cell Σ signal and Δ Monopulse angle measurement is performed using the signal, and the position of the moving target is calculated from the angle measurement value and the detected range. The image superimposing unit superimposes the symbol or image of the moving target on the entire image of the imaging range including the fixed target.

The block diagram which shows the structure of the synthetic aperture radar apparatus which concerns on 1st Embodiment. The figure which shows the positional relationship of a body flight axis (flight path | route) and the imaging range in the apparatus shown in FIG. The figure which shows the coordinate system which defines the image display in the case of spotlight SAR in the apparatus shown in FIG. The figure for demonstrating the method of calculating | requiring a target angle by monopulse angle measurement in the apparatus shown in FIG. The block diagram which shows the structure of the synthetic aperture radar apparatus which concerns on 2nd Embodiment. The figure which shows the Doppler component of the movement target in the range axis | shaft and cross range axis | shaft in the apparatus shown in FIG. 5 when moving to a flight direction. The figure which shows the observation phase at the time of carrying out the division | segmentation of the synthetic aperture length in the apparatus shown in FIG. The block diagram which shows the structure of the synthetic aperture radar apparatus which concerns on 3rd Embodiment. The figure which shows a mode that it divides | segments into M sub-apertures about the total synthetic | combination aperture length in the apparatus shown in FIG. 8, and produces | generates a RD image for every this division | segmentation unit. FIG. 9 is a diagram showing a state in which M sub-apertures are formed on the flight axis while being sequentially shifted while allowing overlap in the apparatus shown in FIG. 8. The figure which shows the phase difference observation result and the movement target extraction result in each of the whole image by all the aperture surfaces, and the division image by M sub-apertures in the apparatus shown in FIG. In the apparatus shown in FIG. 8, the imaging range is angle-divided, and a diagram representing a human histogram with respect to a phase difference at an amplitude extreme point extracted for each division. The block diagram which shows the structure of the synthetic aperture radar apparatus which concerns on 4th Embodiment. The block diagram which shows the structure of the synthetic aperture radar apparatus which concerns on 5th Embodiment. The figure for demonstrating the sample condition and integration range in the case of the thinning sample with respect to a simultaneous sample in the apparatus shown in FIG. The figure for demonstrating the image shift by a phase change of a moving target in a synthetic aperture radar apparatus.

  In the conventional synthetic aperture radar apparatus, in the SAR processing, the phase of a fixed target is adjusted using a large aperture array, and the moving target image is synthesized with the fixed target image so as to be the maximum vector. , (B), the position of the moving target changes within the synthetic aperture time, so that the phase changes and the wavefront shift of the large aperture array occurs as shown in FIG. An image is generated at a position shifted from the position. This is a phenomenon called image shift. When a moving target image is superimposed on a fixed target image, a large error occurs in the relative positional relationship between the fixed target and the moving target. An embodiment for solving this problem will be described with reference to the drawings. In the description of each embodiment, the same portions are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
FIG. 1 is a block diagram showing the configuration of the synthetic aperture radar apparatus according to the first embodiment. In the radar apparatus shown in FIG. 1, an antenna 1 is a phased array antenna formed by arranging a plurality of antenna elements to form a large aperture array.

  The transmitter / receiver 2 sends a transmission pulse signal of a specific frequency (hereinafter referred to as a PRF (Pulse Repetition Frequency) signal) transmitted from the transmitter / receiver 21 at a PRI (Pulse Repetition Interval) interval within the synthetic aperture time (one cycle) to the antenna 1. Then, the beam is transmitted in the designated direction from the beam control unit 22 and the reflected wave is received. Here, the beam control unit 22 directs the beam to a range to be imaged. Further, the transmitter / receiver 2 performs phase control on the signals received by the plurality of antenna elements of the antenna 1 in the transmitter / receiver 21 in accordance with an instruction from the beam controller 22 and combines them in a desired direction (Σ ) And difference (Δ) reception beams are formed to acquire respective PRF reception signals (hereinafter referred to as Σ signal and Δ signal) and send them to the signal processor 3. Here, the Σ signal and the Δ signal are outputs of a sum signal and a difference signal when the aperture is divided into two on the azimuth plane (Az plane) of the actual antenna aperture. When obtaining the Σ and Δ signals, weighting for reducing the side lobes may be used.

  The Σ signal and Δ signal input to the signal processor 3 are converted into digital signals by an AD (Analog-Digital) converter 31. Among these, the Σ signal is distributed to the fixed target processing system and the moving target processing system, and the Δ signal is sent to the moving target processing system.

  In the fixed target processing system, the range compression unit 32 and the Az compression unit 33 respectively convert the digitized aperture array PRF received signal into the range (distance) direction and the cross range (azimuth angle) direction for each synthetic aperture reception cycle. Compressed into The compression process is a correlation process between the input signal and the reference signal for compression, and performs multiplication of the FFT result of the input signal and the FFT result of the reference signal on the frequency axis. To obtain an entire image of the imaging range including the fixed target. This whole image is sent to the image superimposing unit 34.

  On the other hand, in the movement target processing system, the input processing unit 35 acquires data for each range cell in the PRI from the Σ signal. The data of each range cell is imaged by the range compression unit 36 and the Az compression unit 37 by compression processing in the range direction and the cross range direction by FFT (Fast Fourier Transform) processing including polar format conversion as necessary (hereinafter, referred to as the “range cell”). , SAR image), and then sent to the local maximum value extraction unit 38. The maximum value extraction unit 38 extracts maximum values from the maximum amplitude to the Pth from the SAR image. The maximum value extraction result is sent to the movement target extraction unit 39. The movement target extraction unit 39 detects a phase difference with respect to the maximum value of the SAR image, and extracts a pixel whose phase difference exceeds a threshold as a movement target. The extracted pixels are sent to the movement target cell extraction unit 310. The moving target cell extracting unit 310 extracts a cell in which a moving target extraction pixel exists, and the Σ data of the extracted cell is sent to the monopulse angle measuring unit 311.

  In the movement target processing system, the input processing unit 312 acquires data in units of range cells in the PRI from the Δ signal, but the movement target extraction unit 39 extracts the movement target and uses the movement target. Based on the result, the data of the range cell in which the moving target exists is acquired. The extracted range cell data is symbolized by the range compression unit 313 and the Az compression unit 314 by compression processing in the range direction and the cross range direction by FFT (Fast Fourier Transform) processing including polar format conversion as necessary. Alternatively, after being imaged (hereinafter referred to as SAR image), it is sent to the movement target cell extraction unit 315. The movement target cell extraction unit 315 extracts a cell corresponding to the Δ signal based on the extraction result of the movement target cell extraction unit 310 on the Σ signal side. The Δ data of the extraction cell is sent to the monopulse angle measuring unit 311.

  The monopulse angle measurement unit 311 performs monopulse angle measurement on the Σ data and Δ data of the extraction cell, thereby obtaining an angle at which the moving target exists. The monopulse angle measurement result is sent to the movement target position calculation unit 316. The movement target position calculation unit 316 calculates a position where the movement target exists based on the monopulse angle measurement result. The movement target position calculated here is sent to the image superimposing unit 34, and the image superimposing unit 34 calculates the entire image of the imaging range including the fixed target obtained from the Σ signal from the Σ signal and the Δ signal. The symbol of the movement target or the image of the movement target is superimposed and output at the position of the movement target.

  In the radar apparatus having the above configuration, the SAR method will be described. FIG. 2 shows a case of a spotlight SAR (see Non-Patent Document 3). The beam is directed so as to always irradiate an imaging range with an actual aperture beam by the on-board radar, and the PRI within a synthetic aperture time (one cycle). Data is acquired in units of range cells in the PRI for each pulse transmitted at (Pulse Repetition Interval) intervals. FIG. 3 shows the definition of the coordinate system. SAR processing is performed using the acquired data to obtain a SAR image. FIG. 3 is a diagram in the case of a spotlight SAR, but other methods such as a strip map SAR for observing the side may be used as long as a SAR image can be obtained.

  In the radar apparatus shown in FIG. 1, a beam is directed to a range to be imaged by beam control (22), the beam is transmitted / received by the antenna 1, and a signal obtained thereby is converted into a digital signal by AD conversion (31). Convert.

Here, a method for generating an FFT image and a method for extracting a moving target value in the FFT image will be described. First, range compression (32) by pulse compression is performed. Pulse compression is a correlation process between an input signal and a reference signal for pulse compression, and this is performed on the frequency axis (see Non-Patent Document 1). On the frequency axis, the FFT result of the input signal and the FFT result of the reference signal are multiplied.

In order to make it on the time axis, the signal s after pulse compression may be subjected to inverse Fourier transform. However, in order to perform Az compression (33) (cross-range compression, see Non-Patent Document 2) after this, The (ω, u) axis remains unchanged. Next, a cross-range reference signal fs0 is generated.

The signal cs is obtained by multiplying the aforementioned s by the cross-range compression fs0.

Using this, the signal fcs (ω, ku) is obtained by performing FFT on the u-axis.

The output of a range-Doppler image (hereinafter abbreviated as RD (Range Doppler) image) can be calculated by inverse FFT with respect to the ω axis of fcs.

In the RD image, the X axis corresponds to a range by pulse compression (proportional to the round trip time t to the target, t axis), and the Y axis corresponds to a cross range by FFT (proportional to the Doppler component, ku axis).

With the above processing, an RD image can be generated. Therefore, a method of detecting a moving target by searching for a reference signal using speed / acceleration (second embodiment), a phase shift of the RD image for each sub-aperture (third embodiment), and an amplitude shift (first) 4), a moving target is detected by a method of extracting a moving target, a range-Doppler cell is selected, and angle measurement is performed using Σ and Δ cells. Here, Δ is the output of the difference signal when the aperture is divided into two on the azimuth plane (Az plane) of the actual antenna aperture. When obtaining the Σ and Δ signals, weighting for reducing side lobes may be used.

FIG. 4A shows the angle-amplitude characteristics and the angle-error voltage characteristics of FIG. As shown in FIGS. 4A and 4B, phase monopulse angle measurement is performed by comparing the error voltage ε with an error voltage table created in advance (see Non-Patent Document 5).

As for SAR angle measurement, the case of phase monopulse angle measurement based on Σ and Δ signals has been described. Good. In this case, the error voltage is as follows.

The angle can be measured by using the error voltage ε and the error voltage table created in advance, but the angle can be measured even in the case of an amplitude monopulse using only the amplitude (see Non-Patent Document 6).

Using this angle measurement value and distance, a two-dimensional position is imaged (34) by the following equation.

  As described above, in the synthetic aperture radar apparatus according to the first embodiment, the input signals (1 to N points) acquired according to the flight axis in the output of the Σ and Δ beams obtained by dividing the real aperture antenna into the Az plane divided into two apertures. On the other hand, from the FFT (Fast Fourier Transform) range (X) -frequency (Y) axis output, the angle-measured value obtained by monopulse angle measurement using the Σ and Δ signals of the range-Doppler cell from which the moving target is extracted Based on the detected distance (range), the position of the moving target is calculated and superimposed on the entire image of the imaging range including the fixed target. That is, by extracting the moving target and calculating the position of the moving target using the angle-measured value and distance (range) of the range-Doppler cell, it is possible to reduce the position error due to the speed of the moving target.

(Second Embodiment) Moving Target Detection by Searching for Reference Signal In the first embodiment, a method for detecting a moving target, measuring the moving target with high resolution, and calculating an accurate position has been described. In the present embodiment, a method using a reference signal search method for detecting a moving target will be described.

  FIG. 5 is a block diagram showing a configuration of the synthetic aperture radar apparatus according to the second embodiment. 5 is different from the synthetic aperture radar apparatus of the first embodiment shown in FIG. 1 in that speed / acceleration correction units 317 and 318 are arranged in place of the input processing units 38 and 312 of the moving target processing system. These correction units 317 and 318 correct the velocity and acceleration due to the Doppler component affecting the moving target for the Σ signal and Δ signal, respectively. Further, instead of the movement target extraction unit 39 shown in FIG. 1, a movement target extraction unit 319 with the maximum extreme value is arranged. The moving target extraction unit 319 detects a phase difference with respect to the maximum value of the SAR image, and does not extract a pixel whose phase difference exceeds the threshold as a moving target, but moves the pixel having the maximum extreme value of the SAR image. Extract as a target.

  In the present embodiment, first, differences in images between a moving target and a fixed target will be described with reference to FIGS. 6 and 7. As shown in FIG. 6, on the range axis and cross range axis of the on-board radar that moves at a speed V in the flight direction, in the case of a moving target, the Doppler component is represented by the velocity vector component in the radial direction (line-of-sight direction) as viewed from the radar. Will occur. Therefore, as shown in FIG. 7, in the division of the synthetic aperture length 1, 2,..., N, taking into account (1) the phase plane when the target is fixed and (2) the phase plane deviation due to the target velocity vector. , (3) A phase difference (phase 1, 2,..., N) occurs for the observed phase (1) + (2). As a result, an image is generated at a position shifted from the actual position (see Non-Patent Document 4).

In order to focus on a moving target and form an image, it is necessary to perform Az compression using a reference signal in which relative velocity (Vx, Vy) and relative acceleration (Ax, Ay) are corrected. For this reason, when equation (4) is modified using M speeds and accelerations within a predetermined range, the following equation is obtained.

Subsequently, M RD images are obtained using Expression (12) and Expressions (5) to (7), and a cell having the largest amplitude extreme value is extracted. At this time, in order to distinguish from the fixed image, the movement target uses the fact that the cell spread is smaller than the fixed target. For this purpose, the spread of the cell is detected around the extreme value, and if it is below a predetermined threshold, it is determined as a movement target. With respect to the extracted cells, the two-dimensional coordinates of the moving target can be obtained using the equations (8) to (11).

  As described above, in the second embodiment, in order to extract a movement target, a predetermined range (imaging range) is divided by a predetermined unit, and at least a correction speed and a correction acceleration for each division unit area. RD signal is corrected using either one of the correction signals, a range-Doppler image is obtained from the corrected RD signal, and a range-Doppler cell having the maximum amplitude is extracted from each corrected speed-corrected acceleration image. Then, the position of the moving target is calculated from the angle measurement value obtained by monopulse angle measurement and the detected range, and is superimposed on the entire image including the fixed target. That is, since the movement target is detected by obtaining the maximum amplitude value of the image generated by the correction signal of at least one of the correction speed and the correction acceleration, the position error can be reduced.

(Third Embodiment) Moving Target Detection Based on Sub-Aperture Phase In the first embodiment, a method for detecting a moving target, measuring the moving target with high resolution, and calculating an accurate position has been described. In this embodiment, a method of dividing into sub-apertures in order to detect a moving target will be described.

  FIG. 8 is a block diagram showing the configuration of the synthetic aperture radar apparatus according to the third embodiment. 8 is different from the synthetic aperture radar apparatus of the first embodiment shown in FIG. 1 in that a data dividing unit 320 is arranged in place of the Σ signal input processing unit 35 of the moving target processing system, and the input processing unit The Δ signal is directly input to the range compression unit 313 without arranging the 312, and the movement target extraction unit 321 based on the phase difference between a plurality of images is arranged instead of the movement target extraction unit 39.

  In this embodiment, first, as shown in FIGS. 9 and 10, the total synthetic aperture length is divided into M sub-apertures while allowing the overlap and sequentially shifting. An RD image is generated for each of the M division units. Next, an amplitude extreme value is extracted from each of these images.

  The RD images by M SARs are arrays of amplitude intensities and are expressed as I (m) (x, y) (m = 1 to M). Here, x is a range and y is a cross range. The state of the image is shown in FIG. In FIG. 11, (a) shows the entire image, and (b) shows the images of the divisions 1 to M, respectively.

  Next, a maximum value is extracted from I (m) (x, y) (38). As this method, for example, the following procedure is used.

(1) With the intensity of the I (m) (x, y) image as Iamp (m) (x, y), the maximum value of Iamp (m) is calculated and x and y that are the maximum values are extracted.
(2) The intensity in a predetermined range around x and y is set to zero.
(3) After that, (1) and (2) are repeated until the maximum value is less than or equal to the predetermined amplitude, and the amplitude value Iamp (m) and phase Iphs (m) of the reflection point that becomes the maximum value and its coordinates , y) (m) (m = 1 to M) is obtained.

Here, in order to generate a divided image, data of different sample points is required. Therefore, assuming that the total number of samples of the synthetic aperture length is Nall, when dividing into M, Nall = N × M sample points are required. When the number of observation points is smaller than that, it may be processed as xz with the number of sample points increased by a technique using zero padding and FFT shown in the following equation.

  As another method for increasing the number of sample points, there is also a method of interpolating sampling data by weighting observation data with a sinc function using a sampling theorem (see Non-Patent Document 7).

  Next, a method for correcting the image position by dividing the fixed target and the moving target will be described. Here, as a method for distinguishing between the fixed target and the moving target, a method based on the difference by the frequency distribution of the phase difference will be described.

  In the case of a fixed target, the phase difference is almost the same between a plurality of images, and in the moving target, the phase difference is different from that of the fixed target according to the speed. Using this principle, for example, the imaging range is angularly divided as shown in FIG. 12A, and the position at the amplitude extreme point extracted using a predetermined amplitude threshold (FIG. 12B) for each division is obtained. When the phase difference is expressed in a human stogram which is a frequency distribution with respect to the phase difference, it is as shown in FIG. In general, there are more fixed target points than moving targets, so if you extract a reflection point that exceeds a predetermined phase threshold in the histogram with reference to the phase of the reflection point with the highest frequency, the moving target is extracted from the fixed target. can do.

Specifically, since there are M images as the phase difference used in the histogram, the phase difference is calculated by the following equation.

A histogram may be generated using the average value Iphs_ave of the phase difference. Needless to say, the phase difference may be calculated using any two of the M images.

  If the moving target is extracted, the two-dimensional coordinates of the moving target can be obtained for the range-Doppler cell using equations (8) to (11).

  As described above, in the third embodiment, in order to extract a fixed target or a moving target, it is divided into M sub-apertures including overlap, and extreme values from the maximum amplitude to the Pth are calculated. The phase difference of the M outputs at the extreme value is made a histogram with the phase difference as the horizontal axis. Then, a phase difference target whose frequency is larger than a predetermined threshold is determined as a fixed target, the other target is extracted as a moving target point, and monopulse angle measurement is performed by using the Σ signal and Δ signal of the extracted range-Doppler cell. The position of the moving target is calculated from the angle measurement value and the detected range, and is superimposed on the entire image including the fixed target.

  In other words, since the moving target is extracted from the fixed target using the change in the phase amount divided into M sub-apertures including the overlap, the movement obtained using the range and the angle measurement value. The target position error can be reduced.

(Fourth Embodiment) Moving Target Detection Based on Sub-Aperture Amplitude In the third embodiment, a method of detecting a phase difference by dividing into sub-apertures to detect a moving target has been described. In this embodiment, a method for detecting a movement target using an amplitude movement amount will be described.

  FIG. 13 is a block diagram showing the configuration of the synthetic aperture radar apparatus according to the second embodiment. In FIG. 13, the difference from the synthetic aperture radar apparatus of the third embodiment shown in FIG. 8 is that a moving target extraction unit 322 by amplitude movement between multiple images is used instead of the movement target extraction unit 321 by phase difference between multiple images. It is in the arrangement.

  In the present embodiment, the amplitude weighted centroid of a cell exceeding a predetermined threshold is calculated using the amplitude extreme value obtained by the maximum value extraction (38) of the third embodiment. When the amount of movement of the position of the center of gravity for each sub-aperture is calculated, the velocity components of Vx (range) and Vy (cross range) can also be calculated from the positional deviation of the range-cross range and the time interval of the sub-aperture. When this Vx or Vy exceeds a predetermined value, it is determined as a movement target.

  If the moving target is extracted, the two-dimensional coordinates of the moving target can be obtained for the range-Doppler cell using equations (8) to (11).

  As described above, in the fourth embodiment, in order to extract a fixed target or a moving target, it is divided into M sub-apertures including overlap, and extreme values from the maximum amplitude to the Pth are calculated. Then, a point where the movement amount of the amplitude extreme value exceeds a predetermined threshold is extracted as a movement target. Then, using the extracted Σ signal and Δ signal of the range-Doppler cell, the position of the moving target is calculated from the measured value obtained by monopulse measurement and the detected range, and is superimposed on the entire image including the fixed target. Yes.

  That is, even when the reception channel is 1ch, when the Σ beam and the Δ beam are switched and received in the PRI unit to obtain a 2ch signal, the phase centers of the Σ signal and the Δ signal on the Doppler axis are matched to each other. Since the angle is measured with high accuracy using the Σ signal and Δ signal obtained by synthesizing the received signals, the position error of the moving target obtained using the range and the angle measurement value can be reduced. .

(Fifth Embodiment) Thinning Sampling In the first to fourth embodiments, a 2ch reception system of Σ and Δ is required. In this embodiment, in order to reduce the hardware scale due to cost reduction or the like, when only a 1ch reception system can be equipped, a method of switching between 2ch of Σ and Δ for each sampling on the flight axis (u axis) Is described.

  FIG. 14 is a block diagram showing a configuration of a synthetic aperture radar apparatus according to the fifth embodiment. 14 differs from the synthetic aperture radar apparatus of the first embodiment shown in FIG. 1 in that the transmitter / receiver 2 outputs the output of the transmitter / receiver 21 for each sampling on the flight axis (u-axis). The Σ / Δ switching unit 23 for switching between 2 channels is provided.

  That is, in consideration of the time lag of the moving target, when simultaneous samples of Σ and Δ (here, ΔAz) are obtained as shown in FIG. 15A, in each sampling, as shown in FIG. The phase center of the Doppler bank signal after the FFT needs to be adjusted so that the angle can be measured. For this purpose, the average values of the sampling points of Σ and ΔAz on the u axis are matched.

  The two-dimensional position of the moving target can be calculated by applying the same method as in the first to fourth embodiments using Σ and Δ.

  Note that at least the signal on the Az plane is used as the Δ signal, but the position of the moving target is calculated from the distance and the angle of Az and EL by using the Δ signal on the elevation angle plane (EL plane) by the same method. be able to.

  As described above, in the fifth embodiment, when the reception channel is 1ch, Σ and Δ are switched and received in PRI units, the phase centers of the integration times are matched, and the integration number of Σ is compared with Δ. The angle is measured by suppressing the grating lobe of the Σ Doppler axis.

  That is, even when the reception channel is 1ch, when the Σ and Δ are switched and received in PRI units to obtain a 2ch signal, the phase centers of the Σ and Δ signals on the Doppler axis are made to coincide with each other. It is possible to measure the angle with high accuracy using the Σ and Δ signals obtained by synthesizing the received signals, and to reduce the position error of the moving target using the range and the angle measurement value.

  The synthetic aperture processing method has been described for the RD image, but polar format converted image reconstruction processing (see Non-Patent Document 7) may be used.

  Further, although the case of the spotlight SAR has been described, the method of the above embodiment can be applied even to the case of a strip map SAR for side monitoring (same as side-looking mapping, see Non-Patent Document 3).

  In addition, the present embodiment is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  DESCRIPTION OF SYMBOLS 1 ... Antenna, 2 ... Transmitter / receiver, 21 ... Transmitter / receiver, 22 ... Beam control part, 23 ... Σ / (DELTA) switching part, 3 ... Signal processor, 31 ... AD (Analog-Digital) conversion part, 32 ... Range compression part 33 ... Az compression unit, 34 ... Image superposition unit, 35 ... Input processing unit, 36 ... Range compression unit, 37 ... Az compression unit, 38 ... Maximum value extraction unit, 39 ... Moving target extraction unit, 310 ... Moving target cell Extraction unit, 311 ... monopulse angle measurement unit, 312 ... input processing unit, 313 ... range compression unit, 314 ... Az compression unit, 315 ... movement target cell extraction unit, 316 ... movement target position calculation unit, 317, 318 ... speed / Acceleration correcting unit, 319... Moving target extracting unit based on maximum extreme value, 320... Data dividing unit, 321... Moving target extracting unit based on phase difference between multiple images, 322.

Claims (6)

In a synthetic aperture radar (SAR) radar device mounted on a moving object,
Transmission / reception means for transmitting and receiving a Σ beam and a Δ beam formed by dividing an actual aperture of the antenna into an Az plane and being divided into two apertures on the moving direction axis of the moving body
Signal processing means for extracting a fixed target and a moving target from the Σ signal and Δ signal acquired by transmitting and receiving the Σ beam and the Δ beam, and superimposing the respective images;
The signal processing means includes
A fixed target processing unit that compresses the Σ signal in a frequency domain to create an entire image of an imaging range including a fixed target;
N-point signals (N is a natural number) along the moving direction axis are obtained from the Σ signal and Δ signal, respectively, and the N-point Σ signal and Δ signal are compressed in the frequency domain, respectively, to obtain a range-frequency axis. RD (Range Doppler) signal is generated, a moving target is extracted from the RD signal to create a symbol or image of the moving target, and monopulse measurement is performed using the extracted Σ signal and Δ signal of the range-Doppler cell of the moving target. A moving target processing unit that calculates the position of the moving target from the measured angle value and the detected range;
A synthetic aperture radar apparatus comprising: an image superimposing unit that superimposes a symbol or an image of the moving target on an entire image of an imaging range including the fixed target.   The movement target processing unit divides the imaging range by a predetermined unit, corrects the RD signal using a correction signal of at least one of a correction speed and a correction acceleration for each division unit region, and performs correction. The synthetic aperture radar apparatus according to claim 1, wherein a range-Doppler cell having a maximum amplitude is extracted from moving targets extracted from a later RD signal, and the monopulse angle is measured with respect to the extracted moving target.   The movement target processing unit divides the Σ signal into M (M is a natural number of 2 or more) sub-apertures including overlap, generates an RD image for each of the M sub-apertures, Amplitude extreme values are extracted from each of the M RD images, and the M amplitude extreme values are calculated from the maximum to the Pth (P is a natural number of 2 or more), and the M phase differences of the outputs at the respective extreme values. A horizontal axis is used to create a histogram, a target having a phase difference whose frequency shown in the histogram is larger than a predetermined threshold is determined as a fixed target, and other targets are extracted as moving target points. The synthetic aperture radar apparatus according to claim 1, wherein monopulse angle measurement is performed using a Σ signal and a Δ signal of a range-Doppler cell.   The movement target processing unit divides the Σ signal into M (M is a natural number of 2 or more) sub-apertures including overlap, generates an RD image for each of the M sub-apertures, Amplitude extreme values are extracted from each of the M RD images, and the M amplitude extreme values are calculated from the maximum to P (P is a natural number of 2 or more), and the movement amount of each amplitude extreme value is a predetermined threshold. The synthetic aperture radar apparatus according to claim 1, wherein a point exceeding the threshold is extracted as a moving target, and monopulse angle measurement is performed using the Σ signal and Δ signal of the range-Doppler cell of the extracted moving target point. When the receiving channel is 1ch, the transmission / reception means switches between the Σ signal and the Δ signal and receives them in PRI units,
The movement target processing unit integrates the Σ signal and the Δ signal that are switched and input in units of PRI with the phase centers thereof matched, and increases the number of integrations of the Σ signal as compared with the Δ signal. The synthetic aperture radar apparatus according to claim 1, wherein the angle is measured while suppressing a grating lobe of the Doppler axis. In a radar signal processing method for a synthetic aperture radar (SAR) radar device mounted on a moving object,
On the moving direction axis of the moving body, a Σ beam and a Δ beam formed by dividing the actual aperture of the antenna into the Az plane and divided into two apertures are transmitted and received toward the imaging range,
A method of superimposing respective images by extracting a fixed target and a moving target from the Σ signal and Δ signal acquired by transmission and reception of the Σ beam and Δ beam,
The Σ signal is compressed in the frequency domain to create an entire image of the imaging range including a fixed target,
N (N is a natural number) signals along the movement direction axis are obtained from the Σ signal and Δ signal,
The N-point Σ signal and Δ signal are each compressed in the frequency domain to generate a range-frequency axis RD (Range Doppler) signal,
A moving target is extracted from the RD signal to create a moving target symbol or image,
Range of the extracted moving target-monopulse angle measurement using the Σ signal and Δ signal of the Doppler cell, and the position of the moving target is calculated from the measured angle value and the detected range,
A radar signal processing method for a synthetic aperture radar device, wherein a symbol or image of the moving target is superimposed on an entire image of an imaging range including the fixed target.

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