JP2015052549A - Synthetic aperture radar apparatus and image processing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a synthetic aperture radar system capable of reliably detecting a moving target even when an image shift occurs on the moving target.SOLUTION: The synthetic aperture radar system acquires images while electronically controlling scanning beam direction according to a movement of a moving body to which the radar system is mounted. The synthetic aperture radar system acquires the images at a constant period of each cycle according to a moving axis of the moving body mounted with the radar system. N points of maximum values of the strength are extracted from the respective images acquired in each cycle. A correlation tracking is made between the images for each of the maximum values to calculate a velocity vector based on the positional changes of the maximum values between the images. An absolute value of the velocity vector is compared with a predetermined velocity threshold. When the absolute value of the velocity vector is equal to or smaller than the velocity threshold, the absolute value of the velocity vector is suppressed as a fixed target, and the points being equal to or greater than the velocity threshold are extracted as a moving target.

Description

  The present embodiment relates to a synthetic aperture radar device that is mounted on a moving body and images a moving target, and an image processing method thereof.

  In a conventional synthetic aperture radar apparatus, in the case of a fixed target, in a SAR (Synthetic Aperture Radar) process, the position is fixed within the synthetic aperture time. Can be combined so that the maximum vector is obtained, and imaging can be performed at the correct position (see Non-Patent Documents 1, 2, and 3). On the other hand, in the case of a moving target, since the position 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, and there is a problem that a large error occurs in the relative positional relationship from the fixed coordinate point and the moving target is lost (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) DBS (Doppler Beam Sharpning) method: “Introduction to Airborne Radar”, Hughes Aircraft Company, p.561 (1983) SAR processing method (polar format conversion reconstruction processing): MEHRDAD SOUMEKH, “Synthetic Aperture Radar Signal Processing”, JOHN WILEY & SONS, INC., Pp.319-325 (1999) SAR processing method (range stack method reconfiguration processing): MEHRDAD SOUMEKH, “Synthetic Aperture Radar Signal Processing”, JOHN WILEY & SONS, INC., Pp.349-354 (1999) SAR processing method (range stack method reconfiguration processing): MEHRDAD SOUMEKH, “Synthetic Aperture Radar Signal Processing”, JOHN WILEY & SONS, INC., Pp.354-359 (1999) Tracking filter (α-β, etc.): Yoshida, 'Revised radar technology', IEICE, pp.264-267 (1996) Pulse compression: Yoshida, 'Revised radar technology', IEICE, pp.275-280 (1996) Edge detection: Tamura, “Computer Image Processing”, Ohmsya (2002) pp.182-199

  As described above, the conventional synthetic aperture radar apparatus has a problem that a large error occurs in the relative positional relationship from the fixed coordinate point due to the image shift of the moving target.

  The present embodiment has been made in view of the above-described problems. Even when an image shift occurs in the moving target, the moving target can be reliably detected, and the relative opening from the fixed coordinate point can be corrected. An object of the present invention is to provide a radar apparatus and an image processing method thereof.

  In order to solve the above problems, the synthetic aperture radar apparatus and the image processing method thereof according to the present embodiment are used when acquiring an image while electronically scanning the beam direction as the mounted mobile body moves. The image is acquired at a constant cycle for each cycle according to the moving axis of the mounted mobile body, the local maximum value obtained for each cycle is extracted at N points, and the images are correlated for each local maximum value. Tracking, calculating a velocity vector due to a change in the position of the maximum value between images, comparing the absolute value of the velocity vector with a predetermined velocity threshold, and if it is less than the velocity threshold, suppressing it as a fixed target, It is set as the aspect which extracts the point more than a threshold as a movement target.

The block diagram which shows the structure of the synthetic aperture radar apparatus which concerns on 1st Embodiment. The flowchart which shows the flow of a process of the signal processing part of the synthetic aperture radar apparatus shown in FIG. The conceptual diagram which shows the positional relationship of the body flight axis (flight path | route) and imaging range of the synthetic aperture radar apparatus shown in FIG. FIG. 4 is a conceptual diagram for obtaining a SAR image by correlation tracking processing of a plurality of cycles of the apparatus shown in FIG. 3. The conceptual diagram for acquiring the velocity vector of a moving point from the acquired image in the multiple time of the apparatus shown in FIG. The conceptual diagram for demonstrating the definition of the coordinate in the SAR image of the synthetic aperture radar apparatus shown in FIG. The conceptual diagram for demonstrating the correlation tracking of the synthetic aperture radar apparatus shown in FIG. The block diagram which shows the structure of the synthetic aperture radar apparatus which concerns on 2nd Embodiment. The flowchart which shows the flow of a process of the synthetic aperture radar apparatus shown in FIG. The conceptual diagram for demonstrating the correction process of the image shift of the synthetic aperture radar apparatus shown in FIG. The conceptual diagram for demonstrating the effect of the correction process of the image shift of the synthetic aperture radar apparatus shown in FIG. The block diagram which shows the structure of the synthetic aperture radar apparatus which concerns on 3rd Embodiment. The flowchart which shows the flow of a process of the synthetic aperture radar apparatus shown in FIG. The conceptual diagram for demonstrating the flow of a process of the synthetic aperture radar apparatus shown in FIG.

  Hereinafter, embodiments will be described with reference to the drawings.

(First embodiment)
With reference to FIG. 1 thru | or FIG. 7, the synthetic aperture radar apparatus mounted in the aircraft which concerns on 1st Embodiment is demonstrated.

  FIG. 1 is a block diagram showing the configuration. In FIG. 1, an antenna 1 is a phased array antenna in which a plurality of antenna elements are arranged to form a large aperture array, and a transmission pulse signal (hereinafter referred to as “transmission pulse signal”) having a specific frequency repeatedly supplied from a transmission / reception unit 21 of the transceiver 2. A PRF (Pulse Repetition Frequency) signal) is transmitted in a designated direction and the reflected wave is received. The transmission / reception unit 21 performs phase control on the signals received by the plurality of antenna elements of the antenna 1 according to instructions from the beam control unit 22 and combines them to form a reception beam in a range to be imaged. A reception signal obtained by the reception beam is sent to the signal processor 3.

  The signal processor 3 includes an AD (Analog-Digital) conversion unit 31, a range compression unit 32, an Az compression unit 33, a maximum value extraction unit 34, a correlation tracking unit 35, a velocity vector extraction unit 36, a moving target extraction unit 37, and A movement target display unit 38 is provided.

  The AD conversion unit 31 converts the PRF reception signal supplied from the transceiver 2 into a digital signal, and the conversion result is sent to the SAR processing unit by the range compression unit 32 and the Az compression unit 33. In this SAR processing unit, the PRF reception signal of the digitized aperture array is pulse-compressed in the range (distance) direction by the range compression unit 32 and the Az compression unit 33 in the azimuth angle direction for each synthetic aperture reception cycle. Use pulse compression. Thereby, the resolution in the range direction and the resolution in the cross range direction are improved. There are various methods for simplifying and speeding up the basic processing, and representative processing includes Doppler beam sharpening (DBS, Doppler Beam Sharpening, see Non-Patent Document 5), polar format conversion reconstruction processing ( Non-Patent Document 6), range stack reconstruction processing (see Non-Patent Document 7), and back-projection reconstruction processing (see Non-Patent Document 8). Since details of the processing method are described in each document, they are omitted in the description of this embodiment.

  The maximum value extraction unit 34 extracts the maximum value of the reception intensity as a target candidate for each reception cycle from the SAR processing output. The correlation tracking unit 35 determines the identity for each target cycle obtained by the local maximum value extraction for each reception cycle, and tracks the local maximum value determined to be the same as the target candidate. The speed vector extraction unit 36 extracts the speed vector of each target candidate from the correlation processing result. The moving target extraction unit 37 compares the speed vector extraction result of the target candidate with the speed threshold, and determines that it is a fixed target if it is less than the threshold, and determines that it is a moving target if it exceeds the threshold. Then, the presence of the movement target is displayed on the movement target display unit 38 and output as movement target information.

  FIG. 2 is a flowchart showing a specific processing flow of the signal processor 3 in the radar apparatus having the above-described configuration. First, a PRF reception signal of the aperture array is received by PRF transmission / reception of the transmitter / receiver 2 (step S1), converted into a digital signal by the AD conversion unit 31 (step S2), and range compressed by the range compression unit 32 and the Az compression unit 33. And SAR processing is performed by performing Az compression (steps S3 and S4). Subsequently, the local maximum value extraction unit 34 extracts a cell having a local maximum value for each SAR reception cycle and fills its periphery with 0 (step S5), and compares each local maximum value with a cell having the maximum value. Extract (step S6). Here, it is determined whether or not the maximum value exceeds the threshold (step S7), and if not (NO), the processing of steps S5 to S7 is repeated. If the maximum value exceeds the threshold in step S7 (YES), a track number is added to each cell of the maximum value, and correlation processing and tracking processing are sequentially performed by the correlation tracking unit 35 for each track number cell. After that (steps S8 and S9), a velocity vector is extracted from the maximum value cell correlated and tracked by the velocity vector extraction unit 36 (step S10), and a cell having a velocity vector exceeding the velocity threshold is extracted as a moving target. (Step S11). When the processing of all track numbers is completed by the track number change loop of steps S8 to S13, the cell of the track number from which the speed vector exceeding the speed threshold is obtained is output and displayed as the movement target (step S14). Move to the processing of the cycle.

  Here, the SAR processing in the above-described synthetic aperture radar apparatus mounted on an aircraft will be described. In the case of the spotlight SAR (see Non-Patent Document 3), as shown in FIG. 3, in the aircraft on the flight path, the on-board radar device always irradiates the real aperture beam toward the imaging range, and the synthetic aperture time ( In one cycle), data is acquired in units of range cells in the PRI for each pulse transmitted at the PRI interval. SAR processing is performed using the acquired data to obtain a SAR image. When the SAR image of the imaging range is acquired in cycles 1 to N of the synthetic aperture length in this way, the correlation tracking process is performed on the SAR image of cycles 1 to N as shown in FIG. As shown in 4 (b), a moving target and a fixed target existing in the imaging range can be detected. Further, when a SAR image of the imaging region is obtained within the synthetic aperture time (one cycle), for example, at times T1, T2, and T3 in FIGS. 5A, 5B, and 5C, the fixed point is suppressed. By doing so, the movement of the moving point can be represented by a velocity vector. The examples in FIGS. 3 to 5 are for the spotlight SAR, but it goes without saying that other methods such as a strip map SAR for observing the side may be used as long as a SAR image can be obtained.

  The SAR image is an array of the intensity of each cell, and each coordinate is expressed as I (x, y). The definition of the coordinates is shown in FIG. Here, the X axis represents the range, and the Y axis represents the cross range in the flight direction. Here, the flight speed of the aircraft is V, the coordinates of the movement target are (X, Y), the distance from the aircraft position (origin) is Rc, and the angle (azimuth angle) formed by the movement target with respect to the flight direction is θaz.

Under the above conditions, the maximum value of intensity is extracted from I (x, y). For example, the following procedure is used as this method.
(1) I (x, y) The maximum value of Iamp is calculated by setting the intensity at each coordinate of the image as Iamp (x, y), and the coordinate (x, y) that becomes the maximum value is extracted.
(2) The intensity in a predetermined range is set to zero around the coordinate (x, y) at which the maximum value is obtained.
Thereafter, by repeating the processes (1) and (2) until the maximum value becomes equal to or less than the predetermined amplitude, all the coordinates (x, y) that become the maximum value are extracted.

  Subsequently, after extracting coordinates (xi, yi) (i = 1 to M) that are maximum values for a SAR image of a certain cycle n, the correlation between cycles is obtained for each point of (xi, yi). Perform tracking processing. As the correlation tracking method, various combinations are conceivable as correlation processing and tracking processing (αβ filter, Kalman filter, etc.). Here, in order to simplify the explanation, correlation processing is NN (Nearest Neighbour) processing, tracking processing. Is a case of an αβ filter (see Non-Patent Document 9).

First, the correlation tracking coordinates are expressed in one dimension (X-axis or Y-axis only) for simplicity. It is easy to expand to two dimensions. Observation (position) vector as y, smooth vector as

And the prediction vector is

Then, the coordinates of correlation tracking can be expressed by the following equation.

  Next, the correlation tracking process will be described with reference to FIG.

First, the initial value (smooth value of the previous prediction cycle)

And In the next cycle predicted by this initial value, when there are a large number of detection targets (observed values: determined by the center of gravity by velocity grouping) (j is a plurality), P targets in order from the highest S / N target , Subject to correlation tracking. Among these, when the NN process is adopted for the correlation, the NN observation value is selected using the prediction value of the previous cycle, the smooth value is obtained from the prediction value and the NN observation value, and further using the smooth value, the next value is obtained. Calculate the cycle prediction value. Thereafter, the correlation tracking of the detection target is realized by repeatedly executing this process.

  With the above correlation tracking process, a velocity vector (x, y) can be calculated as a tracking track for each target. If the absolute value of the velocity vector is greater than or equal to a predetermined velocity threshold, it is extracted as a moving target, and if it is less than or equal to the velocity threshold, it can be suppressed as a fixed target. This makes it possible to reliably detect and notify the movement target.

(Second Embodiment)
Next, an airborne synthetic aperture radar apparatus according to the second embodiment will be described with reference to FIGS.

  FIG. 8 is a block diagram showing a configuration of an aircraft-mounted synthetic aperture radar apparatus according to the second embodiment, and FIG. 9 is a flowchart showing a specific processing flow of the signal processor 3 in the radar apparatus having the above configuration. However, in FIGS. 8 and 9, the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals, and redundant description is omitted here.

  As shown in FIG. 8, the radar apparatus according to the second embodiment uses a moving target speed vector extracted by the speed vector extracting unit 36 according to the first embodiment, and a moving target detecting unit 37 moves the moving target. Is detected, the moving target correction unit 39 for correcting the image shift amount of the moving target is added, and the fixed target / moving target display unit 40 displays the moving target together with the fixed target obtained by the SAR processing in a more accurate relative position. Can be displayed. To this end, during N cycles, the phase due to the distance difference of the moving target from the fixed reference point is calculated for each PRI, the SAR composite beam pointing direction shift is calculated from the phase shift for each PRI, and the direction of the pointing direction is calculated. The shift is corrected as the shift amount of the SAR image of the moving target so that the positional relationship with the fixed target can be accurately displayed.

For the target i in cycle n, the phase shift φ is formulated as follows.

here,
x (i, m, n); x value at cycle of target i = n, pri = m
y (i, m, n); y value at cycle of target i = n, pri = m
xf (m, n); x value at aircraft cycle = n, pri = m
yf (m, n); y value at aircraft cycle = n, pri = m
λ: Wavelength
R (i, m, n): relative distance of target i in cycle = n, pri = m
φ (i, m, n); phase of target i in cycle = n, pri = m x and y can be expressed by the following equations.
x (i, m, n) = x0 + vx (m, i) × t
y (i, m, n) = y0 + vy (m, i) × t (3)
here,
vx: x component of the target moving speed vector smooth value
vy: y component of the target moving speed vector smooth value
t: Time from the reference position
x0: x component at the reference position (the center of the synthetic aperture length)
y0: y component of the reference position (the center of the synthetic aperture length)
It is expressed.

If the phase shift is calculated from the velocity vector smooth value of the moving target, the shift in the directivity direction of the SAR output can be calculated by the following equation.

here,
d (m): Data acquisition position for each PRI (corresponding to the element position of the SAR large aperture array)
λ: Wavelength
θ (i, n): Directional direction deviation θ (i, n) can be calculated by substituting equation (2) for φ (i, m, n) in equation (4) above.

Using this θ (i, n), the position of the reflection point of the moving target is corrected by the following equation.

here,
x (i, n); x value of the reflection point of the generated image in the cycle of the target i = n
y (i, n); cycle value of target i = y value of reflection point of generated image in n
xcal (i, n); corrected x value in cycle of target i = n
ycal (i, n); corrected y value in cycle of target i = n
(Note) x, y (0, 0) is a reference point such as the center of the synthetic aperture length.

  If the movement target is displayed at the positions xcal and ycal, an image of the corrected movement target can be obtained.

  Specifically, as shown in FIG. 9, when the moving target extraction process (step S11) is performed, the wavefront deviation of the large aperture array is calculated (step S21), and the directivity direction deviation is calculated (step S22). Then, a correction for shifting the image of the SAR image is performed based on these deviation amounts (step S23). After completion of the image shift correction, the wake number is updated (steps S12 and S13). Finally, the fixed target and the moving target are simultaneously output and displayed (step S24), and the process proceeds to the next cycle process.

  The processing contents of the image shift correction will be described with reference to FIGS.

  FIG. 10 shows a moving target having a predetermined velocity vector in the beam directing direction (squint angle) of the observation beam in the range X-cross range Y coordinate system in the synthetic aperture radar apparatus mounted on the aircraft flying at the speed V. The correction process in the case of being performed is shown. Now, assuming that a moving target having a predetermined velocity vector is extracted as shown in FIG. 10A, the observed image is affected by the phase plane shift due to the velocity vector, as shown in FIG. 10B. An image shift occurs. Therefore, image shift correction of the observed image is performed in consideration of the fact that the observation phase is determined based on the relationship between the phase plane when the target is fixed and the phase plane shift caused by the target velocity vector.

  FIG. 11 shows a comparison between the cases (a1) and (a2) when no image shift correction is performed and the cases (b1) and (b2) when correction is performed in the XY coordinate system shown in FIG. First, when correction is not performed, as shown in FIG. 11 (a1), when the phase plane (1) when the target is fixed and the phase plane deviation (2) due to the target velocity vector are considered, the observation phase is (1) + (2), and the synthetic aperture radar beam shifts as shown in FIG. 11 (a2). Therefore, as shown in FIG. 11 (b1), the phase shift caused by the target velocity vector is phase-corrected. Thereby, according to this embodiment, the synthetic aperture beam can be shift-corrected in the original direction as shown in FIG.

  In FIG. 11, the target observation phase is described by a curve. However, when performing the SAR image processing, a reference signal having a characteristic opposite to that of the curve (target position and phase curve due to flying of the aircraft) is used. And Az compression processing is performed.

  Before correction, the wavefront of the large aperture array is shifted due to the velocity vector of the moving target and a shift occurs in the SAR beam pointing direction. Therefore, if the shift amount is calculated, an image of the moving target can be generated at the normal position.

(Third embodiment)
Next, an airborne synthetic aperture radar apparatus according to a third embodiment will be described with reference to FIGS.

  FIG. 12 is a block diagram showing a configuration of an aircraft-mounted synthetic aperture radar apparatus according to the third embodiment, and FIG. 13 is a flowchart showing a specific processing flow of the signal processor 3 in the radar apparatus having the above configuration. However, in FIGS. 12 and 13, the same parts as those in FIGS. 1, 2, 8, and 9 are denoted by the same reference numerals, and redundant description is omitted here.

  In the radar apparatus according to the third embodiment, as shown in FIG. 12, a moving target position correcting unit 41 that corrects the relative positional relationship of the moving target with respect to the fixed target is arranged in the preceding stage of the fixed target / moving target display unit 40. ing.

  As shown in FIG. 13, the processing flow of the signal processing unit 3 in this case is such that the position of the moving target corrected in step S23 is superimposed on the position of the fixed target (step S26). It is determined whether or not to perform (step S27). That is, the moving target in which the image shift component due to the speed is corrected can be displayed superimposed on the originally obtained fixed target image. At this time, if the fixed target and the moving target intersect, it can be determined that an error has occurred in the image shift correction of the moving target. Therefore, when the periphery of the fixed target (building) is extracted by image edge detection processing (Non-Patent Document 11) and the intersection of the moving target is confirmed, the position of the moving target is set outside the fixed target. It is corrected (step S28) and displayed together with the fixed target (step S29).

  A specific example is shown in FIG. First, as shown in FIG. 14 (a1), as shown in FIG. 14 (a2), as a result of performing edge detection processing when a moving target that has undergone image shift correction overlaps a fixed target (a collection of fixed points). If the moving target is within the edge of a building or the like, the position of the moving target is corrected to the outside of the nearest edge (the minimum distance to the moving target point and the edge) as shown in FIG.

  Further, as shown in FIG. 14 (b1), when the aspect ratio of the edge shape is equal to or higher than a predetermined threshold and it is determined that the road or runway is, the moving target is within the edge as shown in FIG. 14 (b2). Is determined as a moving vehicle on the road, and no correction is performed as shown in FIG. 14 (b3).

  Therefore, according to the configuration of the present embodiment, when the image shift correction result of the moving target is displayed on the fixed target, the positional relationship with the fixed target is grasped, and if it overlaps, the edge of the fixed target does not overlap. If the fixed target is a road, a runway, etc., the display position is recognized from the aspect ratio of the fixed target. It is possible to display the movement target at an appropriate position by a simple method of keeping the value as it is.

  As for the synthetic aperture processing method, polar format conversion image reconstruction processing (Non-Patent Document 6), range stack image reconstruction processing (Non-Patent Document 7), back-projection image reconstruction processing ((Non-Patent Document 8), Needless to say, any method may be used as long as imaging by radar (image reconstruction) is possible, such as Doppler beam sharpening image reconstruction processing (Non-patent Document 9).

  Although the case of the spotlight SAR has been described, the present invention can be applied to the case of a strip map SAR (same as side-looking mapping, non-patent document 3) for side monitoring.

  Note that the present embodiment is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements 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, 3 ... Signal processor, 31 ... AD (Analog-Digital) converter, 32 ... Range compression part, 33 ... Az compression part, 34 ... maximum value extraction unit, 35 ... correlation tracking unit, 36 ... velocity vector extraction unit, 37 ... movement target extraction unit, 38 ... movement target display unit, 39 ... movement target correction unit, 40 ... fixed target / movement target display unit, 41 ... Movement target position correction unit.

Claims (6)

In a Synthetic Aperture Radar (SAR) device that acquires an image while electronically scanning the beam direction as the mounted mobile body moves,
Image acquisition means for acquiring an image at a constant cycle for each cycle according to the movement axis of the mounted mobile body;
A maximum value of intensity in each image acquired for each cycle by the image acquisition means is extracted at N points, and correlation tracking is performed between images for each maximum value, and a velocity vector based on a change in position of the maximum value between images. Image processing means for comparing the absolute value of the velocity vector with a predetermined velocity threshold and suppressing it as a fixed target if it is less than the velocity threshold, and extracting a point above the velocity threshold as a moving target. Synthetic aperture radar device.   The image processing means uses the velocity vector of the moving target to calculate a phase due to the distance difference of the moving target from a fixed reference point for each data acquisition interval PRI (Pulse Repetition Interval) during N cycles, The SAR (Synthetic Aperture Radar) composite beam directivity direction shift is calculated from the phase shift for each PRI, and the directivity direction shift is corrected as a shift amount of the SAR image of the moving target and displayed together with the fixed target. A synthetic aperture radar device according to claim 1.   The image processing means superimposes the SAR image of the moving target corrected for the deviation in the pointing direction on the fixed target, the moving target intersects the fixed target, and the moving target exists within the fixed target. The synthetic aperture radar apparatus according to claim 2, wherein when the state is reached, the moving target is corrected and displayed so as to be positioned outside the edge of the fixed target. In an image processing method of a synthetic aperture radar (SAR) device that acquires an image while electronically scanning and controlling the beam direction as the mounted mobile body moves,
According to the movement axis of the mounted mobile body, an image is acquired at a constant cycle for each cycle,
N points are extracted for the maximum value of intensity in each image acquired for each cycle, and correlation tracking is performed between images for each maximum value, and a velocity vector is calculated according to a change in the position of the maximum value between images, An image processing method for a synthetic aperture radar device, which compares the absolute value of the velocity vector with a predetermined velocity threshold, suppresses it as a fixed target if it is less than the velocity threshold, and extracts points above the velocity threshold as moving targets.   Using the velocity vector of the moving target, the phase due to the distance difference of the moving target from a fixed reference point is calculated for each PRI (Pulse Repetition Interval) of the data acquisition interval during N cycles, and the phase shift for each PRI is calculated. 5. The synthetic aperture radar according to claim 4, wherein a deviation in a directivity direction of a SAR (Synthetic Aperture Radar) synthetic beam is calculated, the deviation in the directivity direction is corrected as a shift amount of a SAR image of a moving target and displayed together with the fixed target. Image processing method of the apparatus.   When the SAR image of the moving target corrected for the deviation in the directivity direction is superimposed on the fixed target, the moving target intersects the fixed target and the moving target exists in the fixed target. The image processing method of the synthetic aperture radar apparatus according to claim 5, wherein the moving target is corrected and displayed so as to be positioned outside an edge of the fixed target.

Images