JPH10232282A - Synthetic aperture radar and moving target detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a synthetic aperture radar having higher probability of detecting a moving target. SOLUTION: The synthetic aperture radar placed on a moving platform such as an aircraft or satellite comprises a transmitting and receiving antenna 1, a transmitter for supplying a high frequency signal to the antenna 1, a receiver for amplifying and demodulating a signal received by the antenna 1, a pulse compressing unit 4 for improving range resolution of the output signal of the receiver, an aperture divider 15 for dividing the received series of pulse train, an azimuth compressing unit 5 for improving an azimuth resolution of the divided train to obtain a complex image, an interference circuit 17 for obtaining a phase difference of two complex images obtained by the unit 5, and a controller 18 for deciding a base line length of the aperture and controlling the divider. In this case, the length can be variably controlled by the controller 8.

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 system mounted on a moving body such as an aircraft or a satellite, and more particularly to an interference type synthetic aperture radar system which detects a moving target such as a vehicle or a ship and measures its position. Things.

[0002]

2. Description of the Related Art As a conventional interference type synthetic aperture radar apparatus, for example, there is one shown in FIG. 23 described in Japanese Patent Application Laid-Open No. 58-223078. FIG. 23 shows the configuration of this interference type synthetic aperture radar device. Reference numerals 1a and 1b denote transmission / reception antennas for transmitting radio waves to a moving target and receiving the reflected waves, respectively. A receiver amplifies and demodulates a received signal, 2b amplifies and demodulates a signal received by a transmitting / receiving antenna 1b, and 3 a transmitter for supplying a high-frequency signal to the transmitting / receiving antennas 1a and 1b. is there.

[0003] Reference numerals 4a and 4b denote pulse compressors for compressing the received signals amplified and demodulated by the receivers 2a and 2b, and 5a and 5b denote pulse compressors 4a and 5b.
This is an azimuth compression apparatus that generates a SAR image by azimuth-compressing the received signal that has been pulse-compressed by the signals a and b. Reference numeral 6 denotes a registration unit that performs registration of two SAR images obtained by the azimuth compression devices 5a and 5b, 7 denotes an adder that takes a phase difference between the two SAR images, and 8 denotes an imaginary component of the SAR image. This is a detection circuit that obtains the amplitude from the data and the real component. Reference numeral 17 denotes an interference circuit including the registration unit 6, the adder 7, and the detection circuit 8.

FIG. 24 shows the geometry of observation by the interference type synthetic aperture radar device, 9 is a radar platform on which the interference type synthetic aperture radar device is mounted, 10a is a transmission / reception beam from the transmission / reception antenna 1a, 10b is a transmission / reception beam from the transmission / reception antenna 1b,
Reference numeral 11 denotes an area observed by the beam 10a, and reference numeral 12 denotes a transmission / reception antenna 1a or 1
The baseline of the two openings according to b, 9 ', is the platform after moving by baseline 12.

Next, the operation will be described. The transmitting / receiving antenna 1 irradiates a high-frequency pulse signal generated by the transmitter 3 from two apertures to an observation area, and receives reflected waves at the respective apertures. Here, it is assumed that the two apertures 1a and 1b of the transmitting / receiving antenna 1 are separated from each other by a baseline length 12 in the orbital direction, and the direction of the beam is adjusted in a direction perpendicular to the orbital.

[0006] The received echoes are amplified and demodulated by two receivers 2 respectively, and pulse-compressed by a pulse compressor 4 to improve the range resolution. Usually, in this type of radar, the transmission pulse is linearly FM-modulated to improve the distance resolution and the bandwidth is extended, and a distributed delay line whose frequency vs. delay time characteristics are paired with the transmission side is used. To restore a high-resolution pulse waveform. Further, the azimuth compression device 5 uses the time change of the Doppler frequency generated with the movement of the platform, and improves the azimuth resolution by a matched filter with a conjugate reference function.
As described above, a complex SAR image can be obtained by the process of improving the resolution, which is well known as the image reproduction process of the synthetic aperture radar.

The registration unit 6 adjusts the images so that the two complex SAR images obtained by the azimuth compression devices 5a and 5b show the same area. At this time, the SAR image observed by the antenna 1a is the SAR image observed from the position of the platform 9 and the SAR image observed by the antenna 1b.
The images correspond to those observed from the position of the platform 9 '. Since both beams 10 are adjusted in the direction orthogonal to the trajectory, the positional relationship with the observation region 11 is equal, and therefore, the phases of the two SAR images are equal in any pixel. However, if a moving target exists, the target also moves while the platform moves from 9 to 9 ′, so that the phase changes by the distance change. Therefore, when the complex image adder 7 performs a complex subtraction on the two registered SAR images, and the detection circuit 8 converts the SAR image into an amplitude, the signal on the ground surface is erased, and the signal on only the pixel where the moving target exists is removed. Appears.

[0008] These operations will be described using mathematical expressions. FIG. 25 shows the geometry. In the figure, reference numeral 13 denotes a moving target. Assuming that the distance from the antenna to the target is r0, the target phase of an image obtained by observation with the antenna 1a is given by the following equation.

[0009]

(Equation 1)

The target phase of an image obtained by observation with the antenna 1b at the position of the platform 9 'is given by the following equation. Where u is the platform speed, v is the target speed, θ is the target speed v is LOS (Line
f Sight), B is the baseline length.

[0011]

(Equation 2)

Therefore, the output signal s of the detection circuit 8 is represented by the following equation. However, it is assumed that the target echo intensities A1 and A2 in the two images are substantially equal.

[0013]

(Equation 3)

From equation (3), no signal appears at the output of the detection circuit 8 when the target is stationary, and an output signal is obtained only when the target is moving. It turns out that it operates as a target detection device.

Alternatively, the interference type synthetic aperture radar device can be realized also with the configuration shown in FIG. In the figure, 14 is a transceiver, and 15 is an aperture dividing device. FIG. 27 shows the observation geometry. In the figure, 1 and 9 to 12 are the same as those shown in FIG. In this device, the antenna has only one aperture, and a series of received signals obtained by the antenna is divided into two, and each is subjected to the synthetic aperture processing to obtain two SAR images. The required aperture length is determined from the azimuth resolution, and the relationship is given by: Here, Δx is the azimuth resolution, λ is the transmission wavelength, A is the aperture length, and ρ is the slant range.

[0016]

(Equation 4)

FIG. 28 is a schematic diagram of the aperture division by this device.
Shown in The same effect can be obtained by the same principle as the method using the two openings described above. This is described in another way as follows. FIG. 29 shows the observation geometry, and FIG. 30 shows changes in the instantaneous Doppler frequency and phase of the received signal. Focusing on the point P, the instantaneous Doppler frequency of the moving target and the stationary target undergoes frequency shift due to the Doppler effect. This is shown in FIG. The phase φs1 and φs2 of the stationary target at the center of the aperture 1 and the aperture 2 are equal, but the phase φ of the moving target is
m1 and φm2 do not match, and a phase difference Δφ of the following equation appears.

[0018]

(Equation 5)

Therefore, when the target is stationary, no voltage appears at the output of the detection circuit 8, but only when the target is moving, a voltage is obtained, and this device operates as a moving target detecting device. You can see that.

[0020]

From the equation (3), it can be seen that in the conventional interference type synthetic aperture radar apparatus, there is a speed at which the target cannot be detected even if the target is moving. This speed is called the blind speed and is given by the following equation. However,
n is an arbitrary integer.

[0021]

(Equation 6)

As can be seen from equation (6), the blind speed exists periodically. Since the period is inversely proportional to the baseline length B, the blind speed can be changed by, for example, changing the baseline length. However, FIG.
In the device with the configuration shown in Fig. 1, the distance between the two apertures of the antenna is fixed, so that if the target speed coincides with one of the blind speeds, it cannot be detected. There is. Further, the apparatus having the configuration shown in FIG. 26 does not have a function of controlling the interval between the two openings (base line length), so that when the target speed coincides with one of the blind speeds, Has a problem that this cannot be detected.

Alternatively, in the apparatus having any one of the structures shown in FIGS. 23 and 26, the interval between the openings can be narrowed to increase the period in which the blind speed is generated.
There is a problem that the detection sensitivity of the low-speed moving target is reduced. This is shown in FIG. This figure shows the relationship between target speed and detection sensitivity. In the figure, the solid line is the baseline length b
And the broken line shows the detection sensitivity when the baseline length is b / 3. In the case of the base line length b, the blind speed is generated at intervals of Vbl. However, by reducing the baseline length to one third, the interval of the blind speed can be extended to 3Vbl. However, at the same time, the detection sensitivity decreases in the low-speed range. Since such a radar apparatus is often used particularly for detecting a low-speed moving target, it is not desirable that the detection sensitivity is reduced in such a low-speed range.

SUMMARY OF THE INVENTION It is a first object of the present invention to solve the above problems and to prevent the blind speed of a synthetic aperture radar from being fixed and to increase the probability of detecting a moving target. I do. A second object is to increase the probability of detecting a moving target by obtaining a plurality of detection results having different blind speeds. further,
A third object is to increase the probability that a moving target can be detected by controlling the period of the blind speed to be efficiently extended. Still another object is to increase the probability of detecting a moving target by combining a plurality of detection results having different blind speeds. A fourth object is to increase the probability of detecting a moving target even in observation in the squint mode. Further, a fifth object is to obtain a three-dimensional image having a small error in the height direction even when a moving target exists.

[0025]

SUMMARY OF THE INVENTION A synthetic aperture radar apparatus according to the present invention is provided on a moving body and transmits a radio wave to a moving target. The transmitting antenna is provided on the moving body and reflected by the target. A receiving antenna for receiving the received radio wave, a range compression unit for range-compressing a reception signal sequence obtained from the radio wave received by the reception antenna, and a reception signal sequence compressed by the range compression unit corresponding to a plurality of apertures. Opening dividing means for dividing by
Baseline length determining means for determining a baseline length between the plurality of apertures for division by the aperture dividing means, and azimuth compression of a received signal sequence corresponding to the plurality of apertures divided by the aperture dividing means Thus, there is provided an azimuth compression means for generating a plurality of images, and a calculation means for calculating a phase difference between the plurality of images generated by the azimuth compression means.

A synthetic aperture radar device according to the present invention is provided on a moving body and transmits a radio wave to a moving target. The transmitting antenna is provided on the moving body and receives the radio wave reflected by the target. Receiving antenna, and an aperture dividing means for dividing a received signal sequence obtained from radio waves received by the receiving antenna in accordance with a plurality of apertures, and between the plurality of apertures for division by the aperture dividing means A baseline length determining means for determining a baseline length; a compression means for generating a plurality of images by performing range compression and azimuth compression on a received signal sequence corresponding to the plurality of apertures divided by the aperture dividing means; Calculation means for calculating a phase difference between the plurality of images generated by the compression means.

Further, the above-mentioned baseline determining means changes the above-mentioned baseline length.

A synthetic aperture radar device according to the present invention is provided on a moving body and transmits a radio wave to a moving target. The transmitting antenna is provided on the moving body and receives the radio wave reflected by the target. Receiving range, a range compressing unit for range-compressing a received signal sequence obtained from radio waves received by the receiving antenna, and at least three received signal sequences compressed by the range compressing unit.
Opening dividing means for dividing by three openings, a baseline length determining means for determining a baseline length between the three openings for the division by the opening dividing means, and at least three divided by the opening dividing means. Azimuth compression means for generating first, second, and third images by azimuth-compressing a received signal sequence corresponding to one of the apertures;
Among the first, second, and third images generated by the azimuth compressing means, the phase difference between the first image and the second image and the phase difference between the first image and the third image And a calculating means for calculating.

The base line determining means may include a base line length between the first opening and the second opening of the three openings, and a first opening and a third opening of the three openings. It is determined so that the baseline length between them is different.

Further, the base line determining means may be arranged so that the base line length between the first opening and the second opening of the three openings is equal to the first opening and the third opening of the three openings. The length is determined so as to be a length other than an integral multiple of the baseline length between each other.

Further, the phase difference between the first image and the second image and the phase difference between the first image and the third image are calculated by the calculating means. And combining means for combining the two images.

The receiving antenna has a radiating direction of a radio wave with respect to a moving direction of the moving body, and a phase offset removing means for removing a phase offset caused by having the squint angle. Have

Further, a three-dimensional image transmitting antenna provided on the moving body for transmitting radio waves to the object, and a third antenna for receiving radio waves reflected by the object at two different points on the moving body. 1, a second three-dimensional image receiving antenna, and a three-dimensional image range compressing unit for range-compressing two received signal sequences obtained from radio waves received by the first and second three-dimensional image receiving antennas. A three-dimensional image azimuth compression means for azimuth-compressing two received signal sequences range-compressed by the three-dimensional image range compression means, and the moving target obtained by calculating a phase difference by the calculation means. Detection results,
And a three-dimensional image creating means for creating a three-dimensional image based on the phase difference obtained from the two images generated by the three-dimensional image azimuth compressing means.

A moving target detecting method according to the present invention is a moving target detecting method for detecting a moving target by a synthetic aperture radar provided on a moving body, wherein the moving target is detected while the moving body is moving. A transmitting step of transmitting a radio wave, a receiving step of receiving the radio wave reflected by the target, a range compression step of range-compressing a received signal sequence obtained from the radio wave received in the receiving step, An aperture division step of dividing the compressed received signal sequence corresponding to the plurality of apertures, and a baseline length determination step of determining a baseline length between the plurality of apertures for the division in the aperture division step. Azimuth-compressing the received signal sequence corresponding to the plurality of apertures divided in the aperture division step. The one having the azimuth compression step of generating a plurality of images, and calculating a phase difference between a plurality of images mutually generated by the azimuth compression step.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. Hereinafter, an apparatus according to Embodiment 1 of the present invention will be described with reference to FIG. In FIG. 1, 4, 5,
26, 7, 8, 14, and 17 are the same or equivalent means as those in FIG. Reference numeral 16 denotes a recording device that stores a signal that has been pulse-compressed by the pulse compression device 4. The storage device 16 is connected to the aperture dividing device 15. Reference numeral 18 designates a base line length to determine the aperture dividing device 1
The control device 18 is connected to the aperture dividing device 15. The observation geometry of this device is the same as in FIG.

Next, the operation will be described. Transceiver 14
The high-frequency pulse generated in is transmitted through the transmitting / receiving antenna 1 to the observation area 11 where the moving target exists, and the reflected wave echo is received by the transmitting / receiving antenna 1.
Here, it is assumed that the transmission / reception beam 10 is directed in a direction orthogonal to the trajectory of the platform 9. The transceiver 14 amplifies and demodulates the received echo, and the pulse compression device 4 performs pulse compression to improve the range resolution. Here, the pulse compression refers to a process of converting a wide pulse width signal subjected to a certain modulation into a narrow pulse width signal by a correlation process, and this process increases the resolution in the range direction.
Since these operations are the same as those of the conventional device, the description is omitted. This pulse compression is generally called range compression.

The aperture dividing device 15 extracts signals corresponding to a plurality of apertures from the pulse-compressed received signal sequence. FIG. 2 illustrates how signals corresponding to a plurality of apertures are extracted from a pulse-compressed received signal sequence.
(A) shows a case where two openings overlap each other,
(B) shows the case where the two openings are separated. In FIG. 2, what is described as a received signal sequence is a pulse-compressed received signal sequence, and the received signal sequence has predetermined data with respect to a hit (or time) indicated on the horizontal axis. .

From the received signal sequence, a signal corresponding to the aperture 1 and a signal corresponding to the aperture 2 are extracted. At this time, as shown in FIG. It doesn't matter. As described above, when the two openings are overlapped, the same information is partially used in both the opening 1 and the opening 2. Therefore, it is effective to record the received signal sequence in the storage device 16 once. is there. Whether the signal is extracted so that the two openings overlap or the signal is extracted so as to be separated is determined by the control device 18 described later.

The azimuth compression device 5 includes an aperture dividing device 15
The azimuth resolution of the signals corresponding to the two apertures extracted by using the matched filter is improved to obtain two complex SAR images. That is, one complex SAR image is obtained from the signal corresponding to each aperture. This complex SAR image is an image including both a stationary target and a moving target.
Here, the azimuth compression is by separating the Doppler frequency difference caused by the difference in the arrival direction of the echo,
This is a process for improving the resolution in the azimuth direction.

Then, the registration device 6 of the interference circuit 17 aligns the two complex images obtained by the azimuth compression device 5. Then, the interference device 17
In, the phase difference between two complex images obtained by the azimuth compression device 5 is obtained. By such a process, a signal appears only in the pixel where the moving target exists. This is because the phase of the two complex images is the same in the case of a stationary target, whereas the phase of the two complex images is different due to the Doppler effect for the moving target. Therefore, by taking the phase difference between the two complex images, the stationary target is canceled and only the moving target having a different phase remains as an image.

The controller 18 controls the aperture dividing device 15 to change the interval between the two apertures, that is, the baseline length. Therefore, as shown in the equation (6), the blind speed also changes, and the target is set. The probability of no detection can be reduced.
Here, the base line length is a value indicating the distance between the center of the opening 1 and the center of the opening 2, and is one index indicating the distance between the opening 1 and the opening 2. Note that when recalculating by changing the base line length, the aperture dividing device 15 reads and uses the data recorded in the recording device 16, so that it is not necessary to repeat the observation twice. The control device 18 changes the baseline length several times, and the aperture dividing device 15, the azimuth compression device 5, and the interference device 17 repeatedly perform the above-described processing according to the change, thereby detecting the moving target.

As described above, according to the configuration of the present embodiment,
Since the control device 18 controls the aperture dividing device 15 to generate a set of SAR images having different baseline lengths, a plurality of detection results having different blind speeds can be obtained, and the target speed matches the blind speed. Thus, the probability that this cannot be detected can be reduced.

In this specification, azimuth compression is used in a broad sense to improve azimuth resolution.
Also includes those that perform processing.

In this specification, the signal corresponding to the aperture is extracted from the received signal train after the pulse compression. However, it is not always necessary to perform the processing in such an order, and the signal corresponding to the aperture is extracted. After that, pulse compression and azimuth compression may be performed. However, if the processing is performed in the latter procedure, when the two openings have an overlap, the pulse compression is performed on each of the overlapped portions, so that the processing amount is increased. Therefore, extracting the signal corresponding to the aperture from the received signal sequence after the pulse compression is effective in that the processing amount can be reduced.

Further, the transmission antenna and the reception antenna may be configured separately without using the transmission / reception antenna 1. Further, in this specification, as shown in FIG. 2, it is described that a signal sequence corresponding to an aperture is obtained by extracting a continuous signal sequence from a received signal sequence. It is also possible to obtain an aperture by synthesizing the signal trains. However, in the case of employing the latter, it is necessary to make the interval between the reception pulses of the transmitting / receiving antenna 1 shorter than in the case of employing the former. Conversely,
The interval between the chopped signal trains is determined in relation to the interval between the reception pulses of the transmitting / receiving antenna 1, and if the interval between the chopped signal trains is too large with respect to the pulse interval, image degradation will occur. .

Embodiment 2 Hereinafter, an apparatus according to a second embodiment of the present invention will be described with reference to FIG. In FIG. 3, 1 to 18 are the same or equivalent means as those in FIG. 19 is a combination detection circuit.
The observation geometry of this device is the same as in FIG.

Next, the operation will be described. In FIG. 3, the operation of the transmitting / receiving antenna 1 to the aperture dividing device 15 is the same as that of the device of FIG. However, the aperture dividing device 15 is the
As shown in (1), the pulse-compressed received signal sequence is divided corresponding to at least three apertures. FIG. 4 is a diagram showing how signals corresponding to three or more apertures are extracted from the received signal sequence. In the figure, B1 and B2 are the baseline lengths of the combined aperture, and u is the speed of the radar platform. At that time, the openings may be separated or overlap. The control device 18 controls the aperture dividing device 15 so that the baseline lengths B1 and B2 are different from each other. The azimuth compression device 5 obtains a complex SAR image by improving the azimuth resolution of each of the divided signals, and the interference circuit 17 obtains a difference between the two complex images.

At the outputs of the two interference circuits 17a and 17b, a signal appears only at the pixel where the moving target exists, but the period at which the blind speed occurs at each output corresponds to the base line lengths B1 and B2. is there. Since the control device 18 controls B1 and B2 so as not to have the same value, the periods at which these blind speeds occur do not become the same value.

The combination detection circuit 19 includes two interference circuits 1
By combining the outputs 7a and 7b, a distribution map of the moving target is created. This function can be realized, for example, by simply adding the outputs of the interference circuits 17a and 17b. As a result, a blind is generated at the output of the combination detecting circuit 19 at a period corresponding to the least common multiple of the blind speed obtained by substituting B1 and B2 into the equation (6). Therefore, the probability that the moving target cannot be detected due to the blind speed can be reduced.

As described above, according to the configuration of the present embodiment,
The control device 18 controls the aperture dividing device 15 to generate two pairs of SAR images having different baseline lengths, and the blind is generated to a value corresponding to the least common multiple of the blind speed determined by the two baseline lengths. The cycle can be extended. Therefore, the probability that the target can be detected can be increased. The control device 18 in this embodiment
The aperture dividing device 15 operates so as to extract signals corresponding to three apertures. However, the number is not necessarily three, and signals corresponding to more apertures may be extracted. By extracting signals corresponding to as many apertures as possible, the probability that the target can be detected increases.

Embodiment 3 FIG. Hereinafter, an apparatus according to a third embodiment of the present invention will be described with reference to FIG. This embodiment achieves the same effect with a configuration different from that of the second embodiment. In FIG. 5, 1 to 19 are the same or equivalent means as those of FIG. The observation geometry of this device is the same as in FIG.

Next, the operation will be described. In FIG. 5, the operation of the transmitting / receiving antenna 1 to the aperture dividing device 15 is the same as that of the device of FIG. However, the aperture dividing device 15 cuts out a signal sequence corresponding to one aperture from the pulse-compressed received signal sequence in one process. Also, the aperture dividing device 15
Records the output of the pulse compression device 4 in the storage device 16a. The azimuth compression device 5 obtains a complex SAR image by improving the azimuth resolution of the cut-out signal, and
7 is recorded in the storage device 16b.

Next, the control device 18 controls each device to repeat a series of processes again. First, the aperture dividing device 15 reads a signal from the storage device 16a and cuts out a signal sequence corresponding to one aperture. At this time, the control device 18 controls so as to cut out a signal sequence different from the previously cut out signal. The azimuth compression device 5 improves the azimuth resolution of the cut-out signal to obtain a complex SAR image, and the interference circuit 17 records it in the storage device 16b. The control device 18 controls this operation to be repeated twice, and as a result, three complex SAR images obtained from three apertures are recorded in the storage device 16b. At this time, the control device 1
8 indicates that the relationship between the baseline lengths of these three openings is B1.
And the aperture dividing device 15 is controlled so as to satisfy B2.

The interference circuit 17 reads out two complex images from the storage device 16b and obtains the difference between them. The combination detection circuit 19 records the result in the storage device 16c. The control device 18 controls this operation to be repeated one more time,
As a result, two interference results obtained from the three complex SAR images are recorded in the storage device 16c.

The combination detection circuit 19 reads out the two interference results from the storage device 16c and combines them to create a distribution map of the moving target. This function can be realized, for example, by simply adding the two outputs of the interference circuit 17. As a result, a blind is generated in the output of the combination detecting circuit 19 at a cycle corresponding to the least common multiple of the blind speed obtained by substituting B1 and B2 into Equation (6).

In the case of the second embodiment, the processing is performed in parallel, so that there is an advantage that the processing time can be reduced. However, in the case of the present embodiment, the processing time is the same as that of the second embodiment. There is an advantage that the same effect can be obtained with a simpler configuration without providing two devices.

Embodiment 4 FIG. Hereinafter, a control device according to this embodiment will be described with reference to FIG. The control device in this embodiment is a control device 1 of the device shown in FIG. 3 or FIG.
8 operates. In FIG. 6, 16, 1
8 is the same or equivalent means as that of FIG. 23 is an aperture length calculator, and 24 is a baseline calculator.

Next, the operation will be described. In FIG. 6, the aperture length calculator 23 determines the length of a signal sequence cut out from the received signal sequence by the aperture dividing means. Its value is determined by the following equation.

[0059]

(Equation 7)

On the other hand, the base line calculator 24 determines the interval (base line length) between a plurality of signal sequences that the aperture dividing means 15 cuts out from the received signal sequence. The selection of the base line lengths so as not to be equal to each other has already been described in the second embodiment. However, in order to more efficiently extend the period in which the blind occurs, the following two conditions must be satisfied. You only have to decide. Here, Bi is the ith baseline length (the interval between the first opening and the (i + 1) th opening), and n is an arbitrary integer (i = 0, ± 1, ± 2,...).
・ ・).

[0061]

(Equation 8)

These conditions prevent the baseline length from becoming a common multiple of each other. Since the blind occurs at a period corresponding to the least common multiple of the blind speed obtained by substituting Bi into Equation (5), the period of the blind speed is selected by selecting the base line length so as not to be a common multiple of each other. Effectively extended. In addition, since the recording device 16 stores the calculated baseline length, when calculating the next opening, the baseline calculator 24 reads and uses the value.

As described above, according to the configuration of the present embodiment,
Since the controller 18 can calculate the opening length and the baseline length instructed to the aperture dividing device 15, and furthermore, the base line length can be selected so as not to be a common multiple of each other.
The period in which the blind occurs can be efficiently extended, and the probability that the target can be detected can be increased.

Embodiment 5 Hereinafter, the apparatus according to this embodiment will be described with reference to FIG. In FIG. 7, 1 to 18 are the same or equivalent means as those in FIG. 20 is a phase offset removing circuit.

FIG. 8 shows the observation geometry obtained by this apparatus. In the figure, 9 to 12 are the same or equivalent means as those in FIG. This device assumes a so-called squint mode in which the transmitting and receiving antennas are shifted from a direction orthogonal to the orbit of the platform and observed.
The angle at which the beam swings (Ψ in the figure) is generally called the squint angle. FIG. 9 shows the instantaneous frequency and phase of a signal received by this device. FIG. 9A is a diagram showing a time change of the Doppler frequency, and FIG. 9B is a diagram showing a time change of the phase. In FIG. 9A, reference numerals 46a to 46d denote instantaneous Doppler frequencies of echoes from observation points separated in the azimuth direction, respectively.

Next, the operation will be described. The operation from the transmission / reception antenna 1 to the azimuth compression device 5 is the same as that of the device in FIG. The operation of the interference circuit 17 is the same as that of the device shown in FIG.

When the transmitting / receiving antenna 1 is squinting (Ψ ≠ π / 2), a phase offset depending on the squint angle occurs. As shown in FIG.
The phase difference Δφs between the echoes of the stationary target at the two apertures does not become zero. This phase offset is expressed by equation (10), and therefore the output of the interference circuit 17 is expressed by equation (11).

[0068]

(Equation 9)

In the equation (11), a term relating to the squint angle is added as compared with the equation (3). Therefore, even if the target speed is zero, a constant component appears in the output of the interference circuit 17. Therefore, the interference circuit 17 compensates for the phase error determined by the wavelength λ, the base line length B, and the squint angle Ψ, and removes this constant component. These values are all known or measurable, and the amount of phase compensation can be calculated by the following equation.

[0070]

(Equation 10)

As described above, according to the configuration of the present embodiment,
Since the interference circuit 17 removes the phase offset caused by the squint of the antenna, even when observing the antenna beam in front of or behind the platform, it is possible to efficiently extend the period in which the blind occurs, The probability that the target can be detected can be increased.

In this embodiment, the phase offset removing circuit 20 is provided on the output side of the azimuth compression devices 5a and 5b, and performs the phase offset after the azimuth compression. However, the present invention is not limited to this. For example, it is also possible to provide the phase offset removing circuit 20 between the aperture dividing device 15 and the azimuth compressing device 5 and perform azimuth compression after performing the phase offset removing process on the signal corresponding to each aperture.

Embodiment 6 FIG. In this embodiment, as one example of the azimuth compression apparatus 5 in the above embodiment, a phase compensation process and an FFT (Fast Fouri) are described.
er Transform) processing will be described. Hereinafter, an apparatus according to Embodiment 6 of the present invention will be described with reference to FIG. In FIG. 10, the means are the same as or equivalent to those in FIG.

Reference numeral 21 denotes a phase compensation circuit, and reference numeral 22 denotes an FFT processing circuit (Fast Fourier Transform).
It is. The phase compensation circuit 21 and the FFT processing circuit 22
Is a configuration example of the azimuth compression device 5. Also,
The observation geometry by this device is the same as that shown in FIG. This device assumes a squint mode in which the transmitting and receiving antennas are observed while being shifted from a direction orthogonal to the orbit of the platform.

Further, in this apparatus, DBS using FFT is used instead of ordinary azimuth compression for improving azimuth resolution by a matched filter with a reference function.
(Doppler Beam Sharpening)
Is assumed.

Next, the operation will be described. The operation from the transmitting / receiving antenna 1 to the aperture dividing device 15 is the same as that of the device in FIG. The operation of the interference circuit 17 is the same as that of the device shown in FIG. First, a description will be given of the image reproduction processing of the DBS constituted by the phase compensation circuit 21 and the FFT processing circuit 22. DBS is an image reproduction method that uses only a part of the antenna aperture observed in the squint mode. Although the resolution is lower than that of the normal synthetic aperture processing in which the signal of the full aperture is compressed using a matched filter, FF
Since the processing can be performed by T, there is an advantage that the operation can be speeded up.

FIG. 11 shows the instantaneous Doppler frequency of the DBS received signal. FIG. 11A is a diagram showing a time change of the Doppler frequency when the aperture is sufficiently short.
(B) is a diagram showing a time change of the Doppler frequency when the aperture is long. If the opening is short enough, FIG.
As shown in (a), since a difference occurs in the Doppler frequency of each echo, it can be separated by FFT. However, when a higher resolution is required or when the aperture is long as shown in FIG. 11B, the slope of the Doppler frequency is removed in advance to obtain a signal as shown in FIG. , And FFT this.

The phase compensation circuit 21 compensates the phase so as to eliminate the slope of the Doppler frequency when the aperture is long as shown in FIG. 11B, and the compensation amount is given by the following equation. Where ρ is the slant range, u is the speed of the platform, t is time, and all variables are known.

[0079]

[Equation 11]

Further, the FFT processing circuit 22 converts the signal compensated by the phase compensating circuit 21
Process to improve azimuth resolution. As a result, the output of the FFT processing circuit 22 includes the complex SA of the observation area.
An R image is obtained.

Next, the operation of the phase offset removing circuit 20 will be described. First, since the antenna is squinted and observed, a phase error depending on the squint angle occurs in the SAR image as described in the fifth embodiment. Further, in the DBS, a phase error depending on the azimuth coordinate of the image is newly added. This is because in the normal synthetic aperture processing in which azimuth compression is performed by a matched filter, image reproduction processing is performed using the same reference signal for all observation points arranged in the azimuth direction. However, in DBS in which image reproduction processing is performed by the FFT processing circuit 22, This is because the initial phase of the reference signal differs for each point of the azimuth coordinates. The magnitude of this initial phase is expressed by the following equation.

[0082]

(Equation 12)

Here, ΔΨ is an angle at which two observation points separated in the azimuth direction are viewed. FIG. 12 shows this relationship.
Points P and Q are two observation points separated in the azimuth direction, and ΔΨ is an angle when the two points are viewed from the center of the antenna aperture.

As described above, when an image is reproduced by the DBS, a phase dependent on the azimuth coordinate is added in addition to the phase offset dependent on the squint angle, and it is necessary to remove the phase. The quantity is represented by the sum of equations (12) and (14).

As described above, according to the configuration of the present embodiment,
The phase compensation circuit 21 and the FFT processing circuit 22 realize azimuth compression by DBS,
Removes the phase offset depending on the squint angle and the phase fluctuation depending on the azimuth coordinates. Therefore, D
Even if azimuth compression is realized with a simpler configuration than the normal azimuth compression using a matched filter by the BS method, the probability that blinds can be efficiently extended and the target cannot be detected Can be reduced.

Embodiment 7 In this embodiment, a moving target detecting method for detecting a moving target by controlling the aperture division interval (base line length) and changing the blind speed in the interference type synthetic aperture radar of the first embodiment is shown in FIG. It will be described based on.

As described in the first embodiment, in this type of radar, a blind speed occurs at which a moving target cannot be observed depending on the baseline length. Therefore, by repeating the search while changing the baseline length, the possibility of detecting the moving target is improved. The procedure is described as follows.

[ST01] The observation area 11 is irradiated with high frequency pulses as radio waves. [ST02] An echo which is a reflected wave of the transmitted radio wave is received. [ST03] The received echo is amplified and demodulated, the obtained received signal is pulse-compressed, and the received signal sequence obtained by this pulse compression is stored.

[ST04] The base line length between the two openings is determined. [ST05] The signals corresponding to the two apertures are extracted from the stored received signal sequence according to the determined baseline length.
The length of the opening is determined according to equation (7). Note that the two openings may be overlapped or separated.

[ST06] The signals corresponding to the two apertures are each subjected to azimuth compression to obtain two complex SAR images.

[ST07] The two complex SAR images are superimposed to obtain a phase difference, the amplitude of the difference is obtained for each pixel, and recorded as a moving target distribution map. A moving target exists for a pixel whose amplitude is not zero.

As described above, according to the method of the seventh embodiment, the detection result of a moving target having a different blind speed can be obtained by variably determining the base line length. Can be detected by changing the baseline length.

Embodiment 8 FIG. In this embodiment, in the interferometric synthetic aperture radar according to the second embodiment, a moving target is detected by controlling the aperture division interval (baseline length) to change the blind speed and obtaining the synthesis result. The moving target detection method will be described with reference to FIG.

As described in the second embodiment, in this type of radar, a blind speed at which a target cannot be observed occurs depending on the baseline length. Therefore, by repeating the search while changing the baseline length, the possibility of detecting the moving target can be improved. The procedure is described as follows.

[ST11] The observation region 11 is irradiated with high-frequency pulses as radio waves. [ST12] An echo which is a reflected wave of the transmitted radio wave is received. [ST13] The received echo is amplified and demodulated, the obtained received signal is pulse-compressed, and the received signal sequence obtained by this pulse compression is stored.

[ST14] The base line length is determined to a preset initial value. [ST15] According to the determined baseline length, signals corresponding to the two apertures are extracted from the stored received signal sequence. The length of the opening is determined according to equation (7). In addition,
The two openings may be overlapping or separated.

[ST16] The signals corresponding to the two apertures are each subjected to azimuth compression to obtain two complex SAR images.

[ST17] The two complex SAR images are superimposed to obtain a phase difference, the amplitude of the difference is obtained for each pixel, and recorded as a moving target distribution map. A moving target exists for a pixel whose amplitude is not zero.

[ST18] It is determined whether the base line length is changed and the process is performed again. [ST19] If it is determined that the processing is to be performed again after changing the base line length, the base line length is changed. For example, the baseline length is shorter or longer by one pulse hit than the previous baseline length. Then, the processing from step 15 to step 17 is performed again on the changed baseline length. [ST110] A plurality of moving target distribution maps obtained by repeating steps 14 to 17 are displayed in combination. As a result, a result with a different blind speed is added, so that a moving target distribution map with a higher detection probability can be obtained.

According to the present embodiment, moving target detection results having different blind speeds are obtained by changing the base line length, and the synthesized result is obtained. Can be reduced. In this embodiment, after the pulse compression (ST13), the aperture division processing (ST13) is performed.
15), but it is not always necessary to carry out in this order, and a signal corresponding to the aperture is extracted (ST1).
5) After that, pulse compression (ST13) and azimuth compression (ST16) may be performed. However, if the processing is performed in the latter procedure, when two openings have an overlap, pulse compression is applied to each of the overlapped portions, so that the processing amount is increased. Therefore, after the pulse compression (ST13), the aperture division processing (ST13)
Performing 15) is effective in that the processing amount can be reduced. This point is the same in other embodiments.

Embodiment 9 FIG. This embodiment is a method of obtaining a division interval (baseline length) of an aperture for more efficiently detecting a moving target in the interference type synthetic aperture radar of the fourth embodiment.

As described in the second embodiment, in this type of radar, a blind speed at which a target cannot be observed occurs depending on the baseline length. Therefore, by combining the results obtained by changing the baseline length, the possibility of detecting the moving target can be improved. Further, as described in the fourth embodiment, if the base line lengths are selected so as not to have a common multiple relationship with each other, it is possible to reduce the probability that the target speed coincides with the blind speed and cannot be detected.
The procedure for that is shown in FIG. In the following procedure, the procedure for determining the baseline length is specifically described, and the procedure for the other processing is the same as in the previous embodiment, and thus the description is omitted.

[ST21] The base line length B1 of the first opening and the second opening is determined according to a predetermined initial value.

[ST22] The base line length B2 of the first opening and the third opening is determined so as to satisfy the conditions of the equations (8) and (9). Here, Bi is the ith base line length (the interval between the first opening and the (i + 1) th opening), where i is (opening number -1). Also, n
Is an arbitrary integer (i = 0, ± 1, ± 2,...).
For example, B2 is shorter than B1 by one pulse hit,
Alternatively, assume a long baseline length, and use equations (8) and (9)
This is repeated until the condition is satisfied.

[ST23] Step 22 is repeated by the required number of openings, and the operation ends.

As described above, according to the method of the ninth embodiment, the base line length can be selected so as not to be a common multiple of each other, so that the period in which the blind occurs can be efficiently extended. It is possible to reduce the probability that the target speed matches the blind speed and cannot be detected.

Embodiment 10 FIG. Hereinafter, the device according to this embodiment will be described with reference to FIG. In FIG.
1 to 20 are the same or equivalent means as those in FIG. 25 is a terrain phase fluctuation removal circuit, 2
Reference numeral 6 denotes a three-dimensional terrain database. FIG. 17 shows the observation geometry obtained by this device. The beam swing angle (Ψ in the figure) is the squint angle, and this device assumes a squint mode in which the transmitting and receiving antennas are shifted from a direction orthogonal to the platform orbit and observed.

Next, the operation will be described. The operation from the transmitting / receiving antenna 1 to the phase offset removing circuit 20 is shown in FIG.
It is the same as the device of the above. As shown in FIG. 17, when the transmitting / receiving antenna 1 is squinting, the phase of the SAR image changes according to the height of the terrain, even when the target is stationary. As a result, the expression (1) is obtained for the two SAR images.
The phase difference Δφ given in 5) occurs. Here, λ is the transmission wavelength, h is the terrain altitude, η is the off-nadir angle, Ψ1 is the squint angle that looks at the observation point P from the center of the first opening, and Ψ2 is the squint angle that looks at the observation point P from the second opening. .

[0109]

(Equation 13)

The phase fluctuation Δφ increases when the squint angle is large and the terrain is large, and may be erroneously detected as a moving target. Therefore, the terrain phase fluctuation removal circuit 25 reads the height h of the terrain from the three-dimensional terrain database 26, calculates two phase differences Δφ based on the equation (15), and adds this to the second image. Perform phase compensation.

As described above, according to the configuration of the present embodiment,
Since the terrain phase fluctuation removal circuit 25 removes the phase error caused by the terrain undulation, the blinds can be used even when observing the antenna beam in front of or behind the platform while tilting it, and even when the terrain is large. The cycle that occurs can be extended efficiently,
The probability that the target cannot be detected can be reduced.

Embodiment 11 FIG. Hereinafter, the device according to this embodiment will be described with reference to FIG. In FIG.
1 to 18 are the same or equivalent means as those in FIG. 27 is a moving target detection unit, 28 is an adder, 29 is a phase difference calculation unit, and 30 is a three-dimensional map generation unit. The observation geometry by this device is the same as that shown in FIG. FIG. 21 shows a supplement to this. In the figure, 1a and 1b are two antennas mounted on the platform 9, 35 is an observation point, 3
6 is a virtual observation point.

FIG. 19 shows an example of the configuration inside the three-dimensional map generation means 30. In the figure, reference numeral 31 denotes a virtual interference image generating unit, 32 denotes a contour image generating unit, 33 denotes a phase unwrapping unit, and 34 denotes a contour image generating unit.

First, the transmitting / receiving antenna 1 to the adder 2
The operation up to 8 will be described. The operation from the transmitting / receiving antenna 1 to the interference circuit 17 is the same as that of the device in FIG. The registration unit 6a aligns the two SAR images. Further, the adder 28 adds the moving target distribution output from the interference circuit 17. Alternatively, the logical sum of the moving target detection result is obtained. Therefore, as the output, a result of at least one of the detection of the moving target is obtained from the SAR image observed by the receiving antenna 1a or from the SAR image observed by the receiving antenna 1b.

Next, the operation from the azimuth compressors 5c and 5d to the three-dimensional map generator 30 will be described. The geometry of the observation by this device is similar to that shown in FIG. 29, with the antenna beam directed in a direction perpendicular to the orbit. However, as shown in FIG. 21, even if two antennas are mounted at a distance in the direction orthogonal to the antenna beam, or a platform equipped with one antenna is repeatedly observed twice in parallel orbits. good.

The outputs of the pulse compressors 4a and 4b are converted into complex SAR images by the azimuth compressors 5c and 5d. The registration unit 6b aligns the two images, the phase difference calculation unit 29 calculates the phase difference between the two images to generate an interference image, and the three-dimensional map generation unit 30 generates the interference image. Three-dimensional terrain data is obtained from the phase of the image.

These operations will be described using mathematical expressions. First, when the observation point 35 is observed from the transmitting / receiving antenna 1a, the round-trip radio wave propagation distance is ra5a, and the receiving antenna 1b is
Is the round trip radio wave propagation distance when observing the observation point 35 from r
a5b can be written as follows. Here, H is the altitude of the radar platform 9, B is the distance between the two transmitting and receiving antennas (base line length), and d is the distance between the transmitting and receiving antenna 1a and the observation point 35 in the horizontal plane.

[0118]

[Equation 14]

When these equations are Taylor-expanded to obtain a second-order term, the difference Δr5 between these two distances is expressed by equation (18).
Which is in the relationship of the equation (20) with the phase difference ΔΦ5 of the pixel at the observation point 35 obtained by the phase difference calculation unit 29.

[0120]

(Equation 15)

On the other hand, if the round-trip radio wave propagation distance when observing the virtual observation point 36 from the transmitting / receiving antenna 1a is ra6a, and the round-trip radio wave propagation distance when observing the virtual observation point 36 from the receiving antenna 1b is ra6b, The difference Δr6 between these two distances can be similarly written as in Expression (23), and has a relationship of Expression (24) with the phase difference ΔΦ6 of the virtual observation point 36.

[0122]

(Equation 16)

When the difference ΔΦ between ΔΦ5 and ΔΦ6 is further obtained, the following equation is obtained.

[0124]

[Equation 17]

The virtual interference image generation unit 31 obtains ΔΦ6 using these equations, and obtains the phase difference ΔΦ from the output ΔΦ5 of the phase difference calculation unit 29. Since the unknown in the equation (25) is only the altitude h of the observation point 35, h can be calculated from ΔΦ.

FIG. 2 shows the operation of the three-dimensional map generator 30.
0 and FIG. FIG. 20 is a diagram showing a process up to obtaining an isophase image from an interference image, wherein 37 is a contour diagram, 38 is a virtual interference image, 39 is an interference image, 40 is an isophase diagram, 41 is a contour line, and 42 is an isomorphogram. It is a phase line. FIG.
2 is a diagram showing a process from obtaining the three-dimensional topographic data from the isometric map, 43 is a phase curve showing a cross section of the isometric map, 44 is a phase curve after unwrapping, 45 is a cross section of the three-dimensional topographic data. FIG.

The phase of the interference image 39, which is input data of the three-dimensional map generation unit, is given by the equation (20), and the equiphase lines arranged in the range direction are distorted by the terrain. Therefore, the virtual interference image generation unit 31 calculates a virtual interference image observed when the terrain is a plane (h = 0) based on Expression (24). This virtual interference image 38
The equiphase lines are arranged in parallel in the range direction. The equal phase line image generation unit 32 subtracts the phase of the virtual interference image 38 from the phase of the interference image 39, and extracts only the phase change due to the terrain. The phase of this image corresponds to equation (25),
A pattern similar to the contour diagram 37 is obtained.

However, since the isophase line image has only phase information, when observing its cross section, the phase curve 43 is folded back at a value of 0 to 2π as shown in FIG. 22, and cannot be used as it is as terrain data. Therefore, it is necessary to perform a process of folding (unwrapping) the folded phase. The phase unwrap unit 33 looks at the slope of the phase curve 43 and
By connecting the phases folded back to 2π, a phase curve 44 is obtained.

Further, the contour image generating section 34 calculates the equation (25)
The phase is highly converted using the relationship between ΔΦ and h obtained from the above. As a result, the phase curve 44 is converted into a terrain cross section 45 to obtain three-dimensional terrain data. 3 obtained by this method
The dimensional topographic data is a relative altitude, but if at least one point having a known altitude exists in the image, the absolute altitude can be obtained based on that point. Such a method of measuring the height of the terrain by viewing the SAR image in stereo is called interferometric SAR.

Incidentally, in the case of a satellite-mounted radar, there is only one antenna, so that the antennas 1a and 1b are realized by flying twice in parallel orbits and observing. However, in that case, if a moving target such as a car exists in the observation area, an error occurs in the phase of the pixel. As a result, an error occurs in the obtained three-dimensional topographic map.

Further, the phase unwrapping section 33 calculates the phase curve 4
To see the gradient of 3 and connect the folded phases. If the moving target is present and the phase becomes discontinuous, a malfunction occurs and not only the pixel where the moving target exists but also
The error also propagates to surrounding pixels.

Therefore, in the configuration of FIG. 18 and FIG. 19 of the present invention, the moving target is detected in advance and the result is given to the phase unwrap unit 33. Therefore, the phase unwrap unit 33 can perform processing by jumping over the pixel where the movement target exists, and can avoid malfunction. Further, from the obtained three-dimensional topographic map, it is possible to exclude data of pixels for which a moving target exists and whose altitude is not required.

Note that the phase unwrap unit 33 may perform unwrapping ignoring the pixel where the moving target exists, and obtain the phase of the pixel where the moving target exists by interpolating from the absolute phase obtained in the surroundings. Alternatively, unwrapping may be performed after the phase of the pixel where the moving target exists is obtained by interpolation.

As described above, according to the configuration of the present embodiment,
The interference circuit 17 detects the moving target and the phase unwrap unit 3
3 uses the result and unwraps avoiding the pixel where the moving target exists, so that a three-dimensional topographic map with little error in the height direction can be obtained even if the moving target exists. That is, when a three-dimensional image is created without considering the position of the moving target, a phase change due to the presence of the moving target may be erroneously recognized as a phase change due to a change in height. Does not occur as described above because the existence of the moving target is considered. Therefore, it is possible to obtain a three-dimensional topographic map with a small error in the height direction.

In this embodiment, the transmitting / receiving antenna 1a
And the receiving antenna 1b are used for detecting a moving target and creating a three-dimensional image. That is, it can be said that the transmitting / receiving antenna 1a and the receiving antenna 1b in this embodiment function as a transmitting / receiving antenna for creating a three-dimensional image and a transmitting / receiving antenna for detecting a moving target. As another embodiment, a transmitting / receiving antenna for detecting a moving target and a transmitting / receiving antenna for creating a three-dimensional image may be separately provided. Further, although the purpose of this embodiment is to create a three-dimensional topographic map, the present invention is not limited to the topographic map, and can be used to create other three-dimensional images.

[0136]

Since the present invention is configured as described above, it has the following effects.

A synthetic aperture radar device according to the present invention is provided on a moving body and transmits a radio wave to a moving target. The transmitting antenna is provided on the moving body and receives the radio wave reflected by the target. Receiving antenna to perform, range compression means for range-compressing a received signal sequence obtained from radio waves received by the receiving antenna, and aperture division for dividing the received signal sequence compressed by the range compressing means into a plurality of apertures. Means, a baseline length determining means for determining a baseline length between the plurality of openings for division by the aperture dividing means, and a received signal sequence corresponding to the plurality of openings divided by the aperture dividing means. Azimuth compression means for generating a plurality of images by azimuth compression; and a plurality of images generated by the azimuth compression means. Because having a calculating means for calculating a phase difference between each other, change the blind speed according to the baseline length of the decision result by the baseline length determining means,
The blind speed can be prevented from being fixed.

A synthetic aperture radar device according to the present invention is provided on a moving body and transmits a radio wave to a moving target. The transmitting antenna is provided on the moving body and receives the radio wave reflected by the target. Receiving antenna, and an aperture dividing means for dividing a received signal sequence obtained from radio waves received by the receiving antenna in accordance with a plurality of apertures, and between the plurality of apertures for division by the aperture dividing means A baseline length determining means for determining a baseline length; a compression means for generating a plurality of images by performing range compression and azimuth compression on a received signal sequence corresponding to the plurality of apertures divided by the aperture dividing means; Calculating means for calculating a phase difference between the plurality of images generated by the compressing means. Change the blind speed according to the determination result of the line length, can prevent immobilization of the blind speed.

Further, since the base line determining means changes the base line length, it is possible to obtain images having different blind speeds according to the change in the base line length, and the probability of detecting a moving target is increased.

A synthetic aperture radar device according to the present invention is provided on a moving body and transmits a radio wave to a moving target. The transmitting antenna is provided on the moving body and receives the radio wave reflected by the target. Receiving range, a range compressing unit for range-compressing a received signal sequence obtained from radio waves received by the receiving antenna, and at least three received signal sequences compressed by the range compressing unit.
Opening dividing means for dividing by three openings, a baseline length determining means for determining a baseline length between the three openings for the division by the opening dividing means, and at least three divided by the opening dividing means. Azimuth compression means for generating first, second, and third images by azimuth-compressing a received signal sequence corresponding to one of the apertures;
Among the first, second, and third images generated by the azimuth compressing means, the phase difference between the first image and the second image and the phase difference between the first image and the third image , The probability that the target can be detected is increased by obtaining a plurality of detection results having different blind speeds.

Further, the base line determining means includes a base line length between the first opening and the second opening of the three openings, a first opening and a third opening of the three openings. Since the base line lengths are determined to be different from each other, images having different blind speeds can be obtained, and the probability of detecting the target can be further increased.

Further, the base line determining means may be arranged so that the base line length between the first opening and the second opening of the three openings is equal to the first opening and the third opening of the three openings. Since the length is determined so as to be a length other than an integral multiple of the baseline length between each other, the baseline length can be controlled so that the period in which the blind occurs is efficiently extended, and the probability that the target can be detected increases. .

Furthermore, it is obtained by calculating the phase difference between the first image and the second image and the phase difference between the first image and the third image by the calculating means. Since there are combination means for combining the two images, the probability that the target can be detected is increased by combining a plurality of detection results having different blind speeds.

Further, the receiving antenna has a phase offset removing means for removing a phase offset caused by the radio wave irradiation direction having a squint angle with respect to the moving direction of the moving body. Therefore, the target can be detected even in observation in the squint mode.

Further, a three-dimensional image transmitting antenna provided on the moving body for transmitting a radio wave to the object, and a third antenna for receiving the radio wave reflected by the object at two different points on the moving body. 1, a second three-dimensional image receiving antenna, and a three-dimensional image range compressing unit for range-compressing two received signal sequences obtained from radio waves received by the first and second three-dimensional image receiving antennas. A three-dimensional image azimuth compression means for azimuth-compressing two received signal sequences range-compressed by the three-dimensional image range compression means, and the moving target obtained by calculating a phase difference by the calculation means. Detection results,
A three-dimensional image creating means for creating a three-dimensional image based on the phase difference obtained from the two images generated by the azimuth compressing means for three-dimensional images. , A three-dimensional image with few images can be obtained.

A moving target detecting method according to the present invention is a moving target detecting method for detecting a moving target by a synthetic aperture radar provided on a moving body, wherein the moving target is detected while the moving body is moving. A transmitting step of transmitting a radio wave, a receiving step of receiving the radio wave reflected by the target, a range compression step of range-compressing a received signal sequence obtained from the radio wave received in the receiving step, An aperture division step of dividing the compressed received signal sequence corresponding to the plurality of apertures, and a baseline length determination step of determining a baseline length between the plurality of apertures for the division in the aperture division step. Azimuth-compressing the received signal sequence corresponding to the plurality of apertures divided in the aperture division step. And a calculation step of calculating a phase difference between the plurality of images generated by the azimuth compression step, thereby determining a baseline length by the baseline length determination means. The blind speed changes according to the speed, and the blind speed can be prevented from being fixed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an interference type synthetic aperture radar device according to a first embodiment.

FIG. 2 is a diagram showing aperture division in the first embodiment.

FIG. 3 is a configuration diagram of an interference type synthetic aperture radar device according to a second embodiment.

FIG. 4 is a diagram showing aperture division in the second embodiment.

FIG. 5 is a configuration diagram of an interference type synthetic aperture radar device according to a third embodiment.

FIG. 6 is a configuration diagram of an interference type synthetic aperture radar device according to a fourth embodiment.

FIG. 7 is a configuration diagram of an interference type synthetic aperture radar device according to a fifth embodiment.

FIG. 8 is a diagram illustrating an observation geometry according to the fifth embodiment.

FIG. 9 is a diagram illustrating an instantaneous Doppler frequency and a phase of a received signal according to the fifth embodiment.

FIG. 10 is a configuration diagram of an interference type synthetic aperture radar device according to a sixth embodiment.

FIG. 11 is a diagram illustrating an instantaneous Doppler frequency of a received signal according to the sixth embodiment.

FIG. 12 is a diagram illustrating an observation geometry according to the sixth embodiment.

FIG. 13 is a flowchart showing a processing procedure of the interference type synthetic aperture radar according to the seventh embodiment.

FIG. 14 is a flowchart showing a processing procedure of the interference type synthetic aperture radar according to the eighth embodiment.

FIG. 15 is a flowchart showing a processing procedure of the interference type synthetic aperture radar according to the ninth embodiment.

FIG. 16 is a configuration diagram of an interference type synthetic aperture radar device according to a tenth embodiment.

FIG. 17 is a diagram illustrating an observation geometry according to the tenth embodiment.

FIG. 18 is a configuration diagram of an interference type synthetic aperture radar device according to an eleventh embodiment.

FIG. 19 is a diagram illustrating a configuration of a three-dimensional map generation unit 30 according to an eleventh embodiment.

FIG. 20 is a diagram illustrating a process up to obtaining an equiphase line image from an interference image in the eleventh embodiment.

FIG. 21 is a diagram supplementing the observation geometry in the eleventh embodiment.

FIG. 22 is a diagram showing a state obtained from the isophase diagram
It is a figure showing a process until obtaining three-dimensional terrain data.

FIG. 23 is a configuration diagram of a conventional interference type synthetic aperture radar device.

FIG. 24 is a diagram showing an observation geometry of a conventional interference type synthetic aperture radar device.

FIG. 25 is a diagram illustrating the position and the movement of a moving target.

FIG. 26 is a diagram showing another configuration of a conventional interference type synthetic aperture radar device.

FIG. 27 is a diagram showing an observation geometry by the interference type synthetic aperture radar device of FIG. 26;

28 is a schematic diagram of aperture division by the interference type synthetic aperture radar device of FIG. 26;

FIG. 29 is another diagram showing the geometry of observation by the interferometric synthetic aperture radar apparatus of FIG. 26;

30 is a diagram illustrating an instantaneous Doppler frequency and a phase of a received signal in the interference type synthetic aperture radar device of FIG. 26;

FIG. 31 is a diagram illustrating a relationship between the speed of a moving target and detection sensitivity according to the first embodiment.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 transmission / reception antenna, 2 receiver, 3 transmitter, 4 pulse compression device, 5 azimuth compression device, 6 registration unit, 7 complex image adder, 8 detection circuit, 9
Radar platform, 10 transmit / receive beam, 11
Observation area, 12 baseline, 13 moving target, 14
Transceiver, 15 aperture splitting device, 16 recording device, 17
Interference circuit, 18 control device, 19 combination detection circuit, 2
0 phase offset removal circuit, 21 phase compensation circuit, 22
FFT, 23 aperture length calculator, 24 baseline calculator, 25 terrain phase fluctuation elimination circuit, 26 three-dimensional terrain database, 27 moving target detector, 28 adder,
29 phase difference calculator, 30 three-dimensional map generator, 31
Virtual interference image generation unit, 32 Equiphase line image generation unit, 33
Phase unwrapping unit, 34 contour image generation unit, 35
Observation points, 36 virtual observation points, 37 contour diagrams, 38 virtual interference images, 39 interference images, 40 isophase diagrams, 41 contour lines, 42 isophase lines, 43 phase curves showing cross sections of the isophase diagram, 44 after unwrapping Phase curve, 45 terrain cross section showing 3D terrain data cross section, 46 instantaneous Doppler frequency of echo

Claims (10)

[Claims] 1. A transmitting antenna provided on a moving body for transmitting radio waves to a moving target, a receiving antenna provided on the moving body for receiving the radio waves reflected by the target, and the receiving antenna Range compression means for range-compressing a received signal sequence obtained from radio waves received by the above-described method; aperture dividing means for dividing the received signal sequence compressed by the range compressing means into a plurality of apertures; Baseline length determining means for determining a baseline length between the plurality of apertures for division, and a plurality of images obtained by azimuth-compressing a received signal sequence corresponding to the plurality of apertures divided by the aperture dividing means Azimuth compression means for generating a phase difference; and a calculating means for calculating a phase difference between the plurality of images generated by the azimuth compression means. A synthetic aperture radar device comprising: a step; 2. A transmitting antenna provided on a moving body and transmitting a radio wave to a moving target, a receiving antenna provided on the moving body and receiving the radio wave reflected by the target, and the receiving antenna Aperture dividing means for dividing a received signal sequence obtained from radio waves received according to a plurality of apertures, and a baseline for determining a baseline length between the plurality of apertures for division by the aperture dividing means Length determination means, compression means for generating a plurality of images by range compression and azimuth compression of the received signal sequence corresponding to the plurality of apertures divided by the aperture division means, and a plurality of images generated by the compression means Calculating means for calculating a phase difference between images. 3. The synthetic aperture radar device according to claim 1, wherein said baseline determining means changes said baseline length. 4. A transmitting antenna provided on a moving body and transmitting a radio wave to a moving target, a receiving antenna provided on the moving body and receiving the radio wave reflected by the target, and the receiving antenna Range compression means for range-compressing a received signal sequence obtained from radio waves received by the above-described method; aperture dividing means for dividing the received signal sequence compressed by the range compressing means into at least three apertures; For this purpose, a first base line length determining means for determining a base line length between the three apertures and an azimuth compression of a received signal sequence corresponding to at least three apertures divided by the first aperture splitting means are provided. , Azimuth compression means for generating the second, third images, and the first, second, and second images generated by the azimuth compression means. Calculating means for calculating a phase difference between the first image and the second image and a phase difference between the first image and the third image among the three images. Radar equipment. 5. The base line determining means includes: a base line length between a first opening and a second opening of the three openings; a first opening and a third opening of the three openings. 5. The synthetic aperture radar device according to claim 4, wherein the base line lengths are determined so as to be different from each other. 6. The base line determining means, wherein the base line length between the first opening and the second opening of the three openings is equal to the first opening and the third opening of the three openings. The synthetic aperture radar device according to claim 4 or 5, wherein the length is determined so as to be a length other than an integral multiple of a base line length between them. 7. It is obtained by calculating the phase difference between the first image and the second image and the phase difference between the first image and the third image by the calculating means. 7. The synthetic aperture radar device according to claim 4, further comprising a combination unit that combines two images. 8. The receiving antenna according to claim 1, wherein a radiation direction of the radio wave has a squint angle with respect to a moving direction of the moving body, and a phase offset removing means for removing a phase offset caused by having the squint angle. The synthetic aperture radar device according to any one of claims 1 to 7, comprising: 9. A three-dimensional image transmitting antenna provided on the moving body and transmitting a radio wave to the object, and a three-dimensional image transmitting antenna for receiving the radio wave reflected by the object at two different points on the moving body. 1. a second three-dimensional image receiving antenna; and a three-dimensional image range compressing unit for range-compressing two received signal sequences obtained from radio waves received by the first and second three-dimensional image receiving antennas. A three-dimensional image azimuth compression means for azimuth-compressing two received signal sequences range-compressed by the three-dimensional image range compression means; and the moving target obtained by calculating a phase difference by the calculation means. Three-dimensional image creating method for creating a three-dimensional image based on the detection result of the three-dimensional image and the phase difference obtained from the two images generated by the three-dimensional image azimuth compressing means. Synthetic aperture radar device according to any one of claims 1 to 8, characterized in that it has and. 10. A moving target detecting method for detecting a moving target by a synthetic aperture radar provided on a moving body, comprising: a transmitting step of transmitting a radio wave to the target while the moving body is moving; A receiving step of receiving the radio wave reflected by the target, a range compression step of range-compressing a received signal sequence obtained from the radio wave received in the receiving step, and a plurality of received signal sequences compressed in the range compression step An opening division step of dividing the openings in accordance with the openings; a baseline length determination step of determining a baseline length between the plurality of openings for the division in the opening division step; Generate multiple images by azimuth-compressing received signal sequences corresponding to multiple apertures A moving target detection method, comprising: an azimuth compression step; and a calculation step of calculating a phase difference between a plurality of images generated by the azimuth compression step.