JPH11166972A - Synthetic aperture radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a synthetic aperture radar device capable of obtaining high resolution image by detecting a moving target on the ground and the sea surface from a satellite and an aircraft with a simple constitution. SOLUTION: In a synthetic aperture radar device observing the ground by loading on a moving platform such as an aircraft or satellite, transmission/ reception stations 24a and 24b loaded on a plurality of moving platforms, an image reproducing means 25a reproducing a high resolution image from those reception signals, an interference means 26 obtaining the difference of obtained images, an indication means 18 indicating the results to an operator and a control means 27 controlling satellite intervals are provided, a moving target is selectively detected and indicated. Without using a complex and expensive multi-beam antenna, a low velocity moving target is accurately detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic aperture radar apparatus for observing an observation area such as the surface of the earth or the sea surface from a mobile platform such as an aircraft or a satellite, and more particularly to observing an observation area over a wide area and obtaining a high-resolution image thereof. Related to the device.

[0002]

2. Description of the Related Art Conventionally, as this type of synthetic aperture radar apparatus, there has been one shown in FIGS. FIG. 6 is a diagram showing the configuration of the synthetic aperture radar device disclosed in Japanese Patent Laid-Open No. 6-118166, and FIG. 7 is a diagram showing the observation geometry of the synthetic aperture radar device shown in FIG. First, the configuration of such a conventional synthetic aperture radar device will be described with reference to FIGS. In FIG. 6, 1 is a transmitter, 2 is a transmitting antenna, 3 is a receiver, 4 is a multi-beam antenna capable of simultaneously forming a plurality of receiving beams, and 5 is a pulse compression means provided for each receiving antenna beam. , 6
Is connected to the pulse compression means 5 and the Doppler frequency of the radar echo from the main beam direction of each antenna beam is 0.
Doppler compensating means for shifting the Doppler frequency so that

A low-pass filter 7 is connected to the Doppler compensating means 6 for extracting only a radar echo from a stationary object, a resampling means 8 is connected to the low-pass filter 7, a Fourier transform means 9 and a Doppler 10 A high-pass filter connected to the compensating means 6 for extracting only a radar echo from the moving target; 11 a speed compensating means for correcting a Doppler shift caused by a radial velocity of the moving target with respect to the radar echo from the moving target;
Reference numeral 12 denotes spectrum combining means for converting radar echoes from a stationary object or a moving target, which are separated and extracted by each of the plurality of antenna beams, into a spectrum and then combining the radar echoes between the beams.

Reference numeral 13 denotes a reference signal generating means for generating a reference signal used for azimuth compression processing, 14 and 15 denote complex multiplication means and inverse Fourier transform means for realizing azimuth compression, and 16 denotes an amplitude component from a complex image. Is a detecting means for extracting the moving object, 17 is an image synthesizing means for synthesizing the radar echo imaged separately for the stationary object and the moving target, and 18 is a display means for displaying an image. FIG. 7 shows the geometry of observation by this apparatus, 19 is a mobile platform equipped with a radar apparatus, 20a, 20b, 20c, and 20d are the footprints of the reception beam, and 21 is the footprint of the transmission beam. .

Next, the operation of the conventional synthetic aperture radar device will be described with reference to FIGS. FIG. 8 is a diagram illustrating the Doppler frequency of the received signal of the radar. Such a radar device is used by being mounted on a mobile platform such as an aircraft or an artificial satellite. The transmitting antenna 2 irradiates a high-frequency pulse signal generated by the transmitter 1 toward an observation region. At this time, the transmission beam footprint 21
Is set to include all of the plurality of beams 20a to 20d formed by the multibeam antenna 4 for reception, as shown in FIG.

The receiver 3 amplifies the received signals received by each of the antenna beams 20a to 20d of the multi-beam antenna 4 for each beam, performs phase detection, and performs pulse detection.
To perform pulse compression. At this time, antenna beam 2
Assuming that the direction from 0a to 20d is θn (n is the number of the beam), the center value of the instantaneous Doppler frequency of the received signal received by this beam is given by the following [Equation 1]. However,
V is the speed of the mobile platform and λ is the transmission wavelength.

[0007]

(Equation 1)

Accordingly, the center value of the Doppler frequency of the echo from the stationary object can be set to 0 by compensating this frequency by the Doppler compensating means 6 for each beam. Now, considering the radar echo from the target to be observed, the center value of the Doppler frequency of the radar echo after Doppler compensation is given by the following equation using the radial velocity U of the target to be observed.

[0009]

(Equation 2)

In order to separate a stationary object and a moving target by the difference in Doppler frequency, as shown in FIG. 8, the Doppler frequency of the radar echo of the moving object is separated from the Doppler frequency of the radar echo of the stationary object on the frequency axis. Therefore, if the antenna beam width θB is selected so as to satisfy the following equation, the moving target can be separated and detected.

[0011]

(Equation 3)

If θB satisfies the above expression, the received signal after Doppler compensation is divided into two frequency components by the low-pass filter 7 and the high-pass filter 10, so that the output of the low-pass filter 7 is output from a stationary object. A radar echo and a radar echo from a moving target are obtained separately from the output of the high-pass filter 10, respectively. Since the bandwidth of the output of the low-pass filter 7 is reduced, the data is thinned out by the resampling means 8,
After the amount of data is reduced, it is converted into a spectrum by the Fourier transform means 9. Each antenna beam 20a-20
By combining the spectra obtained for each d by the number of beams by the spectrum combining means 12, the bandwidth can be expanded to the number of beams. By performing the same azimuth compression processing as that of the conventional synthetic aperture radar by the complex multiplying means 14 and the inverse Fourier transform means 15 on this band-expanded spectrum, it is as if θB
Can achieve the same high azimuth resolution as when observed with a beam as large as the number of beams.

On the other hand, the output of the high-pass filter 10, that is, the radar echo from the moving target is converted to the Fourier transform means 9.
Is converted to a spectrum. Since the center frequency of this spectrum is shifted by the radial speed U of the moving target, this is compensated by the speed compensating means 11,
The center frequency is set to 0. By performing this compensation, a radar image can be reproduced without causing a positional shift even with respect to a moving target. As in the case of the spectrum of the radar echo from the stationary object, the spectrum after the velocity compensation is combined with the spectrum for the number of beams, as if θ
The same high azimuth resolution can be achieved as when B is observed with a beam as large as the number of beams.

Further, by synthesizing separately reproduced images of the stationary object and the moving target by the image synthesizing means 17, the position of the stationary object and the moving target do not shift with respect to the moving target.
A radar image of a target moving on the ground or on the sea surface can be obtained.

[0015]

However, the above-mentioned conventional synthetic aperture radar apparatus is constructed as described above, and in particular, must be equipped with a multi-beam antenna, which is considerably complicated and increases the weight. There was a problem of doing.

Also, since the spectrum of a stationary object is broadened, if the Doppler frequency of the moving target overlaps with this, the stationary object cannot be detected, and the detectable target speed is limited by [Equation 3]. Therefore, it is difficult to detect a low-speed moving target having a low speed.

The present invention has been made in order to solve the above-mentioned conventional problems, and provides a synthetic aperture radar apparatus capable of detecting a moving target without mounting an expensive multi-beam antenna having a complicated structure. The purpose is to do.
Another object of the present invention is to provide a synthetic aperture radar apparatus having excellent detection performance for a low-speed moving target.

[0018]

According to the present invention, there is provided a synthetic aperture radar apparatus for observing an observation area from a mobile platform, comprising: a transmitting / receiving station mounted on each of a plurality of mobile platforms; An image reproducing unit that reproduces a high-resolution image from each signal; an interference unit that calculates a difference between the images obtained by the image reproducing unit; and a display unit that displays an output of the interference unit. Is selectively detected and displayed.

Further, the synthetic aperture radar apparatus according to the present invention is characterized in that the synthetic aperture radar apparatus further comprises control means for controlling an interval between the moving platforms by an output of the interference means.

Further, the synthetic aperture radar apparatus according to the present invention is characterized in that it comprises a moving target detecting means for automatically detecting the moving target based on an output of the interference means.

Further, in the synthetic aperture radar apparatus according to the present invention, the control means may be arranged so that an output of the interference means is optimal for detecting a moving target having a predetermined radial velocity. Is controlled.

Further, the synthetic aperture radar apparatus of the present invention is a synthetic aperture radar apparatus for observing an observation area from a mobile platform, wherein the transmitting and receiving stations are respectively mounted on three or more mobile platforms arranged on the same orbit; Image reproducing means for reproducing a high-resolution image from the received signal from the transmitting and receiving station, and a plurality of interference means for calculating the difference between the images obtained by the image reproducing means,
Fusion means for combining the outputs of the plurality of interference means;
Display means for displaying an output of the fusion means, wherein a moving target of the observation area is selectively detected and displayed.

Further, the synthetic aperture radar apparatus according to the present invention is characterized in that the synthetic aperture radar apparatus further comprises control means for controlling the intervals between the three or more moving platforms based on the outputs of the plurality of interference means.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Below, attached drawings,
An embodiment of the present invention will be described in detail with reference to FIGS. FIG. 1 is a block diagram showing a configuration of a synthetic aperture radar device according to the first embodiment of the present invention, FIG. 2 is a diagram showing an observation geometry of the synthetic aperture radar device shown in FIG. 1, and FIG. 3 is a second embodiment of the present invention. FIG. 4 is a block diagram showing a configuration of a synthetic aperture radar device in Embodiment 4, FIG. 4 is a block diagram showing a configuration of a synthetic aperture radar device in Embodiment 4 of the present invention, and FIG. 5 shows an observation geometry of the synthetic aperture radar device shown in FIG. FIG.

First, the configuration of the synthetic aperture radar device according to the first embodiment of the present invention will be described with reference to FIG. 1 and FIG. In FIG. 1, 1 is a transmitter, 3 is a receiver, 5 is a pulse compression means (P / C), 9 is a Fourier transform means, 13 is a reference signal generation means for generating a reference signal used for azimuth compression processing, 14 Is a complex multiplication means for realizing azimuth compression, 15 is an inverse Fourier transform means for realizing azimuth compression, 16 is a detection means for extracting an amplitude component from a complex image, 18 is a display means for displaying an image, and 22 is a transmission / reception means. Antenna, 23 is a transmission / reception switch, 24
Reference numerals a and 24b denote transmission / reception stations, reference numerals 25a and 25b denote azimuth compression means, reference numeral 26 denotes interference means, and reference numeral 27 denotes a baseline control means (also simply referred to as control means). Incidentally, the reference signal generating means 13 and the azimuth compressing means 25a, 25
b constitutes an image reproducing means.

In the figure showing the observation geometry of the synthetic aperture radar apparatus shown in FIG. 2, reference numerals 19a and 19b denote mobile platforms on which transmitting / receiving stations 24a and 24b are mounted, and reference numerals 20a and 20b denote beam footprints (# 1 and # 1). 2). In this embodiment, the two transmitting / receiving stations 24a and 24b
a and 19b respectively. Usually, the mobile platforms 19a and 19b are mounted on an aircraft or a satellite, and irradiate a beam onto an observation area on the ground surface or the sea surface to perform observation. The transmitting / receiving stations 24, 24b mounted on the mobile platforms 19a, 19b include a transmitting / receiving antenna 22, a transmitting / receiving switch 2 in the example of FIG.
3, the transmitter 1 and the receiver 3 are included. However, in the present invention, the transmitting and receiving stations 24 and 24b are not limited to such a configuration, and it is only necessary to have a function capable of transmitting and receiving a beam.

Next, the operation of the synthetic aperture radar according to the first embodiment of the present invention will be described with reference to FIGS. In the apparatus shown in FIG. 1, the high-frequency pulse generated by the transmitter 1 is transmitted to the transmission / reception antenna 22
Irradiates the observation areas such as the footprints (# 1, # 2) 20a, 20b. The signal reflected from the observation area is received again by the transmission / reception antenna 22, and is amplified and phase-detected by the receiver 3. This signal is processed by the pulse compression means 5 and the azimuth compression means 25a, 25b to increase the resolution of the range and the azimuth, and a two-dimensional high-resolution image is obtained. These processes are the same as the operation of a conventional well-known synthetic aperture radar device.

As shown in FIG. 2, the moving platforms 19a and 19b circulate on the same orbit at an interval B and both at a speed V.
Radar transmitting / receiving stations 24a, 24 mounted on 9a, 19b
b performs the same operation as described above. Therefore, two images obtained by observing the same area with a time difference of B / V are obtained from the azimuth compressing means 25a and 25b. The interference means 26 calculates the difference between these complex images.
The satellite interval B is called a baseline length.

For a stationary object in the observation area, the image output from the azimuth compression means 25a is exactly equal to the image output from the azimuth compression means 25b, so that the output of the interference means 26 becomes zero. On the other hand, with respect to the moving target, the target moves during the difference B / V between the observation times of the two images, and a phase difference Δφ shown in the following [Equation 4] occurs. Here, λ is the transmission wavelength.

[0030]

(Equation 4)

Therefore, the output of the interference means 26 does not become zero, and an output corresponding to the target speed appears. The output of the interference means 26 is displayed on the display means 18 to notify the operator. By monitoring the display means 18, the operator can know the existence of the moving target and its position on the screen.

However, as can be seen from [Equation 4], when the target speed satisfies the following [Equation 5], the output becomes zero and cannot be detected. Such a target speed is called a blind speed. Here, n is an arbitrary integer.

[0033]

(Equation 5)

Therefore, the baseline control means 27 controls the interval B between the satellites to change the blind speed.
In this case, the target speed to be detected may be determined in advance, and the interval B may be determined so as not to satisfy [Equation 5].

As described above, in the synthetic aperture radar device according to the first embodiment, the transmitting and receiving stations respectively mounted on a plurality of mobile platforms observe the same area on the ground while passing through the same orbit with a time difference. And
The image reproducing means reproduces a high-resolution image from the received signals, the interference means finds the difference between the obtained images, displays the image difference on the display means to the operator, and controls the satellite by the baseline control means. Control the interval.

As described above, according to the configuration of the present embodiment, it is possible to obtain a synthetic aperture radar device capable of detecting a moving target without mounting a multi-beam antenna.
Further, according to the configuration of the present embodiment, since the frequency spectrum of the stationary object is only a DC component, even if the moving speed of the target is low, it can be detected.
It is possible to obtain a synthetic aperture radar device having excellent detection performance for a low-speed moving target.

Embodiment 2 Next, the configuration of the synthetic aperture radar device according to the second embodiment of the present invention will be described with reference to FIG. In FIG. 3, reference numeral 28 denotes a moving target detecting means. The other components are the same as or equivalent to those in FIG. 1, and thus a more detailed description is omitted.

Next, the operation of the synthetic aperture radar according to the second embodiment of the present invention will be described with reference to FIG. FIG.
In FIG. 1, the operation from the transmitter 1 to the detection means 16 is shown in FIG.
Since the operation is the same as that of the first embodiment shown in FIG. The moving target detecting means 28 automatically detects the moving target from the detection output signal. The operation is performed, for example, as in the following [Equation 6]. However, A1
ij and A2ij are the values of the coordinates (i, j) of the two complex images, and A0 is the threshold value.

[0039]

(Equation 6)

Alternatively, the interference means 26 obtains the phase difference Δφij between the two complex images, and
8 may detect the moving target from the phase difference according to the following [Equation 7]. As described above, the moving target detection unit 28
From the output of the interference unit 26 or the detection unit 16, the two complex images are compared, the pixel in which the moving target exists is automatically obtained, and the moving target is automatically detected.

[0041]

(Equation 7)

As described above, in the synthetic aperture radar device according to the second embodiment, the transmitting and receiving stations respectively mounted on a plurality of mobile platforms observe the same area on the ground while passing through the same orbit with a time difference. And
The image reproducing means reproduces a high-resolution image from the received signals, the interference means calculates a difference between the obtained images, and the moving target detecting means automatically determines a pixel where the moving target exists,
The moving target can be automatically detected. Further, the obtained position of the moving target is displayed on the display means, and is displayed to the operator. Further, the interval between satellites is controlled by the baseline control means.

As described above, according to the configuration of the present embodiment,
In addition to the features of the first embodiment, a synthetic aperture radar device that can automatically detect a moving target can be obtained.

Embodiment 3 FIG. Next, a description will be given of a synthetic aperture radar apparatus provided with a method and means for optimally controlling a satellite interval according to a third embodiment of the present invention. this is,
This is a method and means for calculating the satellite interval B suitable for the speed of the moving target to be detected with priority given by the operation of the baseline control means 27 when the speed is given.
Hereinafter, the satellite interval B in the baseline control means 27 will be described.
, That is, the operation of the synthetic aperture radar device will be described. The operation in the third embodiment includes the following steps ST01 and ST02.

Step [ST01]: First, n and α in the following [Equation 8] are obtained. Here, α is a real number having a value of 0 <α <1, n is an arbitrary integer, B is the current satellite interval, and U is the speed of the moving target to be detected with priority.

[0046]

(Equation 8)

Step [ST02]: Assuming that α = 0.5, it substitutes for [Equation 8] to determine the satellite interval B, and outputs this as a new satellite interval.

As can be seen from [Equation 4], using the satellite interval B obtained in this way, the signal of the moving target at the radial velocity U becomes a phase difference π between the two complex images, and the interference means 26 Output is maximized. Also, the satellite interval B obtained in this manner is the solution closest to the original satellite interval among the solutions maximizing the output of the interference means 26, so that the fuel or the fuel required to change the satellite interval can be obtained. It has the advantage of requiring the least amount of time.

As described above, the synthetic aperture radar apparatus according to the third embodiment calculates the distance between satellites suitable for detecting a moving target having a predetermined radial velocity, and sets the distance between the satellites by the baseline control means. Can be controlled.

As described above, according to the configuration of the present embodiment,
In addition to the features of the first embodiment, when a speed of a moving target to be detected with priority is given, it is possible to calculate an interval B between satellites that maximizes detection performance. Further, it is possible to calculate the satellite interval B which requires the least amount of fuel or time to change the satellite interval.

Embodiment 4 FIG. Hereinafter, the configuration of the synthetic aperture radar device according to the fourth embodiment of the present invention will be described with reference to FIGS. In FIG. 4, 16a and 16b are detection means, 24c is a transmitting / receiving station, 25c is azimuth compression means, 26a and 26b are interference means, and 29 is fusion means. The other components are the same or equivalent means as those shown in FIGS. 1 and 3, and therefore, a more detailed description is omitted.

FIG. 5 shows the observation geometry of the synthetic aperture radar device shown in FIG. In FIG. 5, each component is the same or equivalent means as that shown in FIG. 2, but in this embodiment, three transmitting / receiving stations 24a,
Assume that 24b and 24c are mounted on three mobile platforms 19a, 19b and 19c, respectively, and the three mobile platforms 19a, 19b and 19c are separated by a distance B1 and B2, respectively.

Next, the operation of the synthetic aperture radar device according to the fourth embodiment of the present invention will be described with reference to FIGS. In FIG. 4, the transmitter 1 detects detection means 16a, 16a.
The operation up to b is the same as the operation in FIG. The synthetic aperture radar device according to the fourth embodiment includes three moving platforms 19a, 19b, and 19c, and the intervals B1 and B2 are different from each other. Therefore, the blind speed in the interference unit 26a and the blind speed in the interference unit 26b are different. , Respectively, as shown in the following [Equation 9]. However, U1 and U2 are the detection means 1 respectively.
It is the blind speed at the output of 6a, 16b.

[0054]

(Equation 9)

Therefore, by combining these two outputs, the occurrence of blind speed can be reduced. That is, for example, the following [Equation 1]
0]. Here, S1 and S2 are the outputs of the detection means 16a and 16b, respectively, and S0 is the output of the fusion means 29.

[0056]

(Equation 10)

As a result, a new blind speed U0 is given by the following [Equation 11]. Here, GCM is a function for obtaining the greatest common divisor of the argument.

[0058]

[Equation 11]

The baseline control means 27 controls the distances B1 and B2 between the satellites, and controls the baseline lengths B1 and B2 so that the blind speed U0 becomes as large as possible. In this case, the baseline length may be selected so that the greatest common divisor of the two baseline lengths B1 and B2 is as small as possible. For example, the two baseline lengths may be selected so as to be prime numbers.

As described above, in the synthetic aperture radar apparatus according to the fourth embodiment, the transmitting and receiving stations respectively mounted on a plurality of mobile platforms observe the same area on the ground while circling the same orbit at unequal intervals. Then, the image reproducing means reproduces a high-resolution image from the received signals, the interference means finds a difference between the obtained images, the fusion means combines the interference results, and the display means shows the position of the moving target obtained as a result. Is displayed to the operator, and the interval between the satellites is controlled by the baseline control means.

As described above, according to the configuration of the present embodiment,
It is possible to obtain a synthetic aperture radar device that is more excellent in detection performance of a moving target than in the first embodiment.

[0062]

As described above, the present invention has the following advantages. According to the present invention, a moving target can be detected without mounting a multi-beam antenna, and since the frequency spectrum of a stationary object is only a DC component, even if the moving speed of the moving target is low, Therefore, it is possible to obtain a synthetic aperture radar device having excellent detection performance of a low-speed moving target.

Further, according to the present invention, since the moving target detecting means is further provided, a synthetic aperture radar device capable of automatically detecting the moving target can be obtained.

Further, according to the present invention, by giving the speed of the moving target to be detected with priority, it is possible to calculate the interval between the satellites that maximizes the detection performance, and to optimally control the interval between the satellites. it can. In addition, it is possible to calculate the satellite interval that requires the least amount of fuel or time to change the satellite interval.

According to the present invention, the output of a plurality of interfering means obtained by combining at least three moving platforms and combining the obtained outputs by the fusing means is reduced to reduce the occurrence of blind speed. Can be. Further, the interval between satellites can be controlled so as to reduce the occurrence of blind speed and improve the performance of detecting a moving target. It also calculates the satellite spacing that requires the least fuel or time to change the satellite spacing,
Can be controlled, the occurrence of blind speed is small,
A synthetic aperture radar device having excellent moving target detection performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a synthetic aperture radar device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an observation geometry of the synthetic aperture radar device shown in FIG.

FIG. 3 is a block diagram showing a configuration of a synthetic aperture radar device according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a synthetic aperture radar device according to a fourth embodiment of the present invention.

5 is a diagram showing an observation geometry of the synthetic aperture radar device shown in FIG.

FIG. 6 is a block diagram showing a configuration of a conventional synthetic aperture radar device.

7 is a diagram showing an observation geometry of the synthetic aperture radar device shown in FIG.

FIG. 8 is a diagram illustrating a Doppler frequency of a radar reception signal.

[Explanation of symbols]

1 transmitter, 2 transmitting antenna, 3 receiver, 4
Multi-beam antenna, 5 pulse compression means, 6
Doppler compensation means, 7 Low-pass filter, 8
Resampling means, 9 Fourier transform means, 1
0 High-pass filter, 11 Speed compensation means, 12
13 spectrum synthesis means, 13 reference signal generation means, 14 complex multiplication means, 15 inverse Fourier transform means, 16, 16a, 16b detection means, 17 image synthesis means, 18 display means, 19a, 19b, 19c
Mobile platform, 20 receive beam footprint, 2 1 transmit beam footprint, 2
2 transmission / reception antenna, 23 transmission / reception switch, 24a, 2
4b, 24c transmitting / receiving station, 25a, 25b, 25c
Azimuth compression means, 26, 26a, 26b interference means, 27 control means (baseline control means), 2
8 Moving target detection means, 29 fusion means.

Claims (6)

[Claims] 1. A synthetic aperture radar apparatus for observing an observation area from a mobile platform, comprising: a transmitting / receiving station mounted on each of a plurality of mobile platforms; and image reproducing means for reproducing a high-resolution image from a signal received from the transmitting / receiving station. And interfering means for calculating a difference between the images obtained by the image reproducing means, and display means for displaying an output of the interfering means, wherein a moving target of the observation area is selectively detected and displayed. A synthetic aperture radar device characterized by the following. 2. The synthetic aperture radar device according to claim 1, further comprising control means for controlling an interval between the moving platforms based on an output of the interference means. 3. The synthetic aperture radar device according to claim 1, further comprising a moving target detecting unit that automatically detects the moving target based on an output of the interference unit. 4. The apparatus according to claim 1, wherein said control means controls an interval between said plurality of moving platforms so that an output of said interference means is optimal for detection of a moving target having a predetermined radial velocity. The synthetic aperture radar device according to claim 2 or 3, wherein 5. A synthetic aperture radar apparatus for observing an observation area from a mobile platform, comprising: transmitting and receiving stations mounted on three or more mobile platforms arranged on the same orbit; and receiving signals from the transmitting and receiving stations. Image reproducing means for reproducing a high-resolution image, a plurality of interference means for obtaining a difference between respective images obtained by the image reproducing means, a fusion means for combining outputs of the plurality of interference means, and an output of the fusion means And a display unit for displaying a moving target, and selectively detecting and displaying a moving target in the observation area. 6. An output of the plurality of interference means,
6. The synthetic aperture radar device according to claim 5, further comprising control means for controlling a distance between the mobile platforms.