JP3301292B2 - Interferometric high-resolution radar device and terrain height measuring method using high-resolution radar device - Google Patents

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 device (SAR: Synthetic Aperture R) mounted on a platform such as an aircraft or an artificial satellite.
adar) or DBS device (Doppler Be)
am Sharpening), which is used to measure the terrain and other objects with high accuracy over a wide area and monitor the fluctuations of the terrain and other objects caused by disasters and development. The present invention relates to a resolution radar apparatus and a terrain height measurement method using a high resolution radar apparatus.

[0002]

2. Description of the Related Art From the viewpoint of disaster prevention or regional development, it is required to quickly and accurately create an altitude map of terrain. For this purpose, a high-resolution radar is mounted on an aircraft or a satellite platform, and an altitude map of the terrain is created based on this data. The terrain data is obtained by the platform flying over an area where an altitude map is to be formed while operating the radar sensor.

A conventional interference type high resolution radar apparatus of this type is disclosed in US Pat. No. 4,551,724.
There is one in which two synthetic aperture radar devices are mounted on an aircraft.

In this device, in order to avoid position ambiguity, receiving antennas are respectively provided on both wings of the aircraft (separated in a direction perpendicular to the direction of travel of the aircraft), and each of them performs a synthetic aperture process. These two antennas are oriented so as to cover the same area in the direction orthogonal to the traveling direction. The angle between the traveling direction and the beam of the antenna is called a squint angle. In this case, the squint angle is 90 degrees (perpendicular to the traveling direction). The data for each antenna is processed for both tilt distance and Doppler frequency.

[0005] As a result of these two processes, two images of the same part of the terrain are obtained. These images are given the phase of the reflected wave with respect to the transmission wave for each pixel.
Therefore, by obtaining the phase difference while correlating between these two images, these two images for a specific point can be obtained.
You can see the shape of the triangle formed by the two antennas and the terrain. Because the position of the platform is known, the altitude of the area can be known by simple triangulation.

[0006]

There are several problems with the conventional interferometric high-resolution radar apparatus for obtaining the above-mentioned elevation map of the terrain.

First, at least two observations are required.
It is necessary to mount one antenna. This is because only one type of image can be obtained with one antenna. This is because the comparison cannot be performed without the two types of images, and thus the phase difference cannot be obtained. Therefore, not only is the configuration of the device complicated, but also the weight increases, making it difficult to mount the device on an aircraft or the like. In addition, a space for installing two antennas becomes a problem.

[0008] Second, to make accurate measurements, it is necessary to know the exact attitude of the platform in addition to the exact position. This is because, when the attitude changes, the phase difference between the signals received by the two antennas changes, and an error occurs when specifying the shape of the triangle. One of the data indicating this attitude is the roll angle. However, the measurement accuracy of the roll angle measuring device provided in the aircraft is not so high, and it is unavoidable that an error occurs in the measurement altitude. As an interferometric high-resolution radar device that solves this second problem, Japanese Patent Application Laid-Open No.
Although there is one described in US Pat. No. 5,108,859,
This device requires a radio altimeter to measure the altitude of the actual terrain, in addition to the two synthetic aperture radar devices. Therefore, the device becomes more complicated and the weight increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a simple configuration and an interference-type high-resolution radar device capable of reducing a measurement error caused by a change in the attitude of a platform. It is an object of the present invention to provide a terrain height measuring method using a radar device.

[0010]

According to a first aspect of the present invention, there is provided a terrain height measuring method using a high-resolution radar apparatus, wherein the terrain height is obtained by observing terrain from different observation points using a high-resolution radar apparatus mounted on a moving body. In a terrain height measuring method using a high-resolution radar device for measuring a terrain height by comparing a plurality of images obtained, an antenna position of a first moving object on which the first high-resolution radar device is mounted is set to a first position. of the observation point, a second high-resolution radar device mounted, en of the second moving body
Assuming that the tena position is the second observation point , the first observation point
And the second observation point are located at different positions on the same path.
When the distances between the terrain point to be measured and the first observation point and the second observation point are defined as a first distance and a second distance, respectively, Irradiating the terrain with the beams of the first and second high-resolution radars oblique to the path of the moving object so that the second distance is different from the terrain;
The terrain height is measured by comparing a first image of the first observation point with a second image of the second observation point.

The moving object is called a platform, and an aircraft, an artificial satellite, or the like is used. A high-resolution radar device is a radar device that obtains a resolution higher than the resolution determined by an antenna by signal processing, and is also called an image radar device. For example, a synthetic aperture radar device (SAR: Sy
nettical Aperture Radar) or DBS device (Doppler Beam Shar)
pening).

The comparison of a plurality of images is to compare the amplitude or phase of the received signal for each pixel constituting the image while associating with the points on the actual terrain. The received signal for each pixel is generally a complex signal having an amplitude and a phase. If the phase difference is determined by comparison, the difference in distance is immediately determined because the wavelength is known. Therefore, the height of the terrain can be obtained based on the geometric principle.
In the conventional photogrammetry, the height of the terrain is obtained by measuring not the distance to the terrain but the angle of the terrain viewed from the observation point. However, according to the present invention, the difference is that the distance to the terrain is measured. Generally, the angle measurement has a larger error.

[0013] The first observation point and the second observation point are on the same course. A line connecting these two points is called a baseline. In the conventional example, the baseline was orthogonal to the course. The angle that the beam makes with the path is the squint angle. The squint angle is 0 to 180 degrees.
To direct the beam obliquely to the path of the moving body means to set the squint angle to any angle other than 0, 90, and 180 degrees. For example, 45 degrees,
Set to 135 degrees.

According to a second aspect of the present invention, in the method for measuring terrain height using a high-resolution radar apparatus, the first moving body and the second moving body are the same, and the first observation point is set to the first observation point. The position of the moving object at a time is set, and the second observation point is set as the position of the moving object at a second time.

According to a third aspect of the present invention, there is provided a terrain height measuring method using a high resolution radar apparatus, wherein the beam of the high resolution radar apparatus is divided into a first portion and a second portion, and a point on the same terrain is determined. , At the first observation point with the first beam, and at the second observation point with the second beam. Beam division is performed to obtain two types of images from two viewpoints with one beam, and is performed on the frequency axis or the time axis.

According to a fourth aspect of the present invention, there is provided a terrain height measuring method using a high-resolution radar apparatus, wherein the first observation point and the second
At the observation point (1), the beam of the high-resolution radar device is observed while being controlled so as to irradiate a point on the same terrain. The control of the beam direction is performed to obtain two types of images from two viewpoints with one beam without dividing the beam.

According to a fifth aspect of the present invention, there is provided a method for measuring terrain height using a high-resolution radar apparatus, wherein a path of a moving body is set as a path to ascend or descend.

According to a sixth aspect of the present invention, there is provided a terrain height measuring method using a high-resolution radar apparatus, wherein the first high-resolution radar apparatus and the second high-resolution radar apparatus are arranged at different positions on a line intersecting the path of the moving body. Using a high-resolution radar device, observation is performed at the first observation point by the first high-resolution radar device, and observation is performed at the second observation point by the second high-resolution radar device.

According to a seventh aspect of the present invention, there is provided an interferometric high-resolution radar apparatus mounted on a moving body, wherein a transmitter for outputting a high-frequency signal and a transmission / reception beam are oblique to the moving body. A transmitter / receiver antenna that is directed and irradiates a high frequency signal to the ground from the transmitter and receives a reflected signal from the ground, a receiver that receives a reflected signal from the transmitter / receiver and performs reception processing, and a direction of the transmitted / received beam. A pulse compression section for improving the range resolution of the signal, a signal division section for dividing an output of the pulse compression section in accordance with a position in a transmission / reception beam, and outputting the divided signals as a first signal and a second signal; A first signal and a second signal that respectively receive a signal and a second signal, improve cross-range resolution in a direction intersecting the direction of the transmission / reception beam, and obtain high-resolution radar images, respectively. An image reproducing unit, a high-resolution radar image from a first observation point obtained by the first image reproducing unit, and a high-resolution radar from a second observation point obtained by the second image reproducing unit An interference processing unit that obtains terrain height information by interfering with an image, and a reflection point when the beam of the transmission / reception antenna is irradiated on a plane serving as a reference for measuring the terrain height as a virtual reflection point, A virtual reflection point interference processing unit that obtains height information of the virtual reflection point by calculating based on the position of the moving body, and comparing an output of the interference processing unit with an output of the virtual reflection point interference processing unit. And an altitude difference calculator for calculating the height of the terrain.

The virtual reflection point is, for example, a point on a horizontal plane. If the position and altitude of the moving body are known, the relative positional relationship between the observation point and the virtual reflection point can be obtained by calculation. By introducing the virtual reflection point, the accuracy in calculating the altitude difference is improved.

According to an eighth aspect of the present invention, in the interference type high resolution radar apparatus, the signal division unit passes a frequency lower than a frequency corresponding to a division position in a transmission / reception beam, and
, And a high-pass filter that passes a high frequency and outputs the second signal.

According to a ninth aspect of the present invention, when the transmission / reception beam is divided into a first part and a second part by the signal division unit, the signal from the pulse compression unit is transmitted to the signal division unit. A delay unit that delays by a time corresponding to a time required for the first portion to pass through one point of the terrain with the movement of the moving body and outputs the delayed signal as the second signal; The signal from the pulse compression section is output as it is as the first signal.

An antenna control apparatus for controlling the directivity of the transmitting / receiving antenna such that the transmitting / receiving beam illuminates a point on the same terrain as the moving body moves. It is provided with.

An interferometric high-resolution radar device according to an eleventh aspect of the present invention includes an ascent / descent velocimeter for detecting the ascent or descent speed of the moving body, and the altitude difference calculating section is configured to calculate an altitude based on an output from the ascent / descent velocity meter. The height of the terrain is obtained by comparing the output of the interference processing unit with the output of the virtual reflection point interference processing unit.

According to a twelfth aspect of the present invention, there is provided an interferometric high-resolution radar apparatus according to the present invention, wherein a transmitter for outputting a high-frequency signal and a transmitting / receiving beam are inclined with respect to the moving body. A first antenna that is directed to irradiate a high frequency signal from the transmitter to the ground surface and receives a reflected signal from the ground surface, and a receiving beam is directed obliquely to the moving body to generate a reflected signal from the ground surface. A second antenna for receiving, and first and second antennas for receiving reflected signals from the first and second antennas and performing reception processing, respectively.
, A first and second pulse compression section for receiving the outputs of the first and second receivers and improving the range resolution in the beam direction, respectively, and first and second pulse compression sections The first and second image reproducing units, which receive the outputs of the respective units and improve the cross range resolution in the direction intersecting with the beam direction and obtain high-resolution radar images, respectively, and the first and second image reproducing units Interference processing for obtaining topographical height information by interfering with the obtained high-resolution radar image from the first observation point and the high-resolution radar image from the second observation point obtained by the second image reproducing unit. And the reflection point when the beam of the antenna is irradiated on a plane serving as a reference for measuring the height of the terrain is defined as a virtual reflection point, and the virtual point is calculated based on the position of the moving body. Reflection point height information A virtual reflection point interference processing unit, and an altitude difference calculation unit that obtains the height of the terrain by comparing the output of the interference processing unit with the output of the virtual reflection point interference processing unit. The two antennas are arranged at different positions on a line intersecting the path of the moving body.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 of the Invention Hereinafter, Embodiment 1 of the present invention will be described with reference to the drawings. Embodiment 1 of the present invention
Uses an aircraft as a platform and a synthetic aperture radar device as a high-resolution radar device.

The following description is based on Embodiment 1 of the present invention.
(1) Principle of operation, (2) Numerical expression for obtaining altitude, (3) Specific configuration and operation in the order of description.

[Principle of Operation] The principle of the interference type high resolution radar apparatus is to obtain the altitude of a target point by comparing two images having different fields of view obtained by irradiating radio waves from different positions. This is based on the same principle as so-called stereo vision. However, the stereo vision obtains the altitude based on the difference in the inclination (distortion) of the object represented in the image, but in the first embodiment of the present invention, the altitude is obtained based on the phase difference of the reflected wave from the object. They differ in gaining altitude. Even if the position of the radio wave emission point required to obtain these two images is shifted in parallel to the traveling direction,
Alternatively, they may be shifted vertically.

For example, as shown in FIG. 2, it is assumed that two aircraft 101-1 and 101-2 are flying at the same altitude and in the same direction and are separated from each other by a baseline B. According to FIG. 2, it can be considered that there are two aircraft or that one aircraft is represented on the same diagram at different time positions. The following discussion takes the latter view, which is more practical.

FIG. 3 is a view of the ground surface viewed from a vertical direction.
FIG. 3 is a diagram of the aircraft 101 viewed from the traveling direction (the aircrafts 101-1 and 101-2 overlap).
In these figures, the xy plane is taken on the horizontal plane, and the z-axis is taken perpendicular to this plane (the coordinate system is not limited to the orthogonal coordinate system but may be the (r, θ) polar coordinate system). The aircraft 101 is flying in a positive direction at an altitude H on the x-axis. 2 and 3, the point P _1, the point P ₂ is the aircraft 101 -
Position. Point Q is a reflection point on the terrain, and point R is a virtual reflection point on the reference surface of the terrain of point Q (for example, the level surface of Tokyo Bay). Points Q and R are on the y-axis. The difference between the height of the point Q and the height of the point R corresponds to the height (altitude) h of the point Q. The device according to the first embodiment of the present invention is for obtaining the height h. r _1Q is the distance between point P ₁ and point Q, r
_2Q is the distance between the distance between the point P ₂ and the point Q, a distance between the r _1R is the point P ₁ and the point R, r _2R is a point P ₂ and the point R.
Further, the coordinates of the point P ₁ are (x ₁ , 0, H), the coordinates of the point P ₂ are (x ₂ , 0, H), and the coordinates of the point Q are (0, y ₀ ,
h) and the coordinates of the point R are (0, y ₀ , 0).

As can be seen from FIG. 2, the beam of the antenna is directed obliquely rearward of the aircraft 101. The angle between the beam and the x-axis is called a squint angle (the angles formed by the line segments P ₁ Q and P ₂ Q with the x-axis do not always match the squint angle. The beam has a certain width. Because it is). The antenna beam may be directed to either the right or left side of the aircraft, or may be diagonally forward.
Conventionally, the squint angle is 90 degrees, but in the first embodiment of the present invention, the squint angle is selected to be, for example, about 45 degrees. The reason will be described later.

With the aircraft 101-1 and 101-2,
Two types of images, an image A and an image B, shown in FIG. 6 are obtained. In this case, different viewpoints (positions of antennas) P
_Since two images from ₁ and P ₂ are obtained, the altitude h of the target point Q can be obtained by comparing these to obtain the position information.

In FIG. 6, φ _A1 , φ _B1,.
.., Φ _A9 and φ _B9 each indicate the phase of one pixel. These are some of the pixels constituting the images A and B. φ _A1 and φ _B1, φ _A2 and φ _B2, ··· are each shown the same point on the terrain. Images A and B as shown in FIG.
Is, as is well known, obtained by performing two-dimensional Fourier transform on time-series data obtained by a high-resolution radar. The same point on the terrain does not always appear at the same position in the images A and B, but the correspondence can be obtained by comparing the two images for each pixel. Also, φ _A1 , φ _B1 ,... Can be easily measured by measuring the time until the reflected signal is received in the radar device.

Here, for example, φ _A1 and φ _B1 correspond to Q in FIG.
Assume that they correspond to points. The phase difference Δφ ₁
= Φ _B1 −φ _A1 is obtained. Δφ ₁ corresponds to the difference (r _2Q −r _1Q ) between the distance P ₂ Q and the distance P ₁ Q. Aircraft 101
Their positions P ₁ (x ₁ , 0, H) and P ₂ (x ₂ ,
0, H) is to be known, the baseline B is the speed v at that time is obtained easily from the time t _1, P ₂ at time t ₂ Metropolitan of _{P 1 (B = v (t} 2 -t 1) ). As described above, the difference in the distance to the point Q (r _2Q −r _1Q ) and the viewpoint position P ₁ (x
Given a base line B between the viewpoints and ( ₁ , 0, H) and P ₂ (x ₂ , 0, H), a curved surface (hyperboloid) on which the point Q should exist is determined. FIG. 7 is, for example, a view of the yz plane viewed from the positive direction of the x-axis. If the dotted line in FIG. 7 is this curved surface, the portion A of the curve is cut out by φ _A1 and φ _B1 . The position of the point Q (0, y ₀ , h) by this A part
Is given. When an average is obtained in the processing described later, the middle of the part A in the figure is output as the position of the point Q.

A virtual reflection point R (a point obtained by projecting the point Q on a reference plane; not a real reflection point but used as a reference for obtaining the height h) is determined based on the point Q. Since the positions of point Q and point R are obtained by the above processing,
The height of the point Q is known.

Here, a brief description will be given of how the device of the first embodiment of the present invention solves the problems of the conventional device. (1) Points that do not require two antennas To map the terrain, it is necessary to compare the same points in two images and obtain the phase difference. Since only one image can be obtained with one antenna, the conventional device is not shown in FIG.
And two antennas as shown in FIG. On the other hand, two images can be obtained by focusing on the fact that the platform is moving. In this case, as shown in FIGS. 10 and 11, no phase difference occurs between the distances r and r 'in both cases. (R = r '), it is not possible to get the height of the terrain. Therefore, when two antennas are provided, they are arranged on a line perpendicular to the traveling direction of the platform as shown in FIGS.

However, in the apparatus according to Embodiment 1 of the present invention, the squint angle is not 90 ° (for example, 45 °).
°), a phase difference occurs at the same point in the two images obtained by focusing on the fact that the platform is moving, and the height of the terrain can be obtained as described above.

(2) The point where it is not necessary to know the roll angle and the altitude to the terrain surface In the conventional device, two antennas are arranged on a line perpendicular to the traveling direction of the platform as shown in FIGS. Therefore, when the platform was tilted as shown by the dotted line in FIG. 9, a phase difference was generated between the two antennas due to the tilt (roll angle), causing an error in the measurement altitude. However, in the device according to the first embodiment of the present invention,
Since there is only one antenna, such a problem does not occur in principle. Therefore, no roll angle meter or radio altimeter for error correction is required. However, the change in the roll angle needs to be within a range where the beam of the antenna irradiates the same portion.

[Equation for Determining Altitude] The height of the point Q can be determined according to the above operation principle. Next, a description will be given of mathematical expressions that provide a preferable specific processing method for that purpose.

As shown in FIGS. 2 and 3, the round-trip radio wave propagation distance when observing the observation point Q from the platform P ₁ is r _1Q , and the round-trip radio wave propagation when observing the observation point Q from the platform P _{2. Assuming} that the distance is r _2Q , it can be written as follows. r _1Q = 2 ｛(H−h) ² + x ₀ ² + y ₀ ² ｝ ^1/2 (1) r _2Q = _2Ｈ (H−h) ² + (x ₀ + B) ² + y ₀ ² ｝ ^1/2 ( 2) Here, x ₁ = x ₀ and x ₂ = x ₀ + B.

When these expressions are Taylor-expanded and the second-order terms are obtained, and the difference Δr _Q between these two distances r _1Q and r _2Q is obtained, the following expression (3) can be obtained. _{Δr Q = r 2Q -r 1Q ≒} 2 [(x 0 B + (B 2/2)) · {(1 / R 1) + (h · H / R 1 3) + (h 2/2) ((3H ^{_{2 / R 1 5) - (}} 1 / R 1 3))} - (x 0 2 B 2/2) {(1 / R 1 3) + (h · 3H / R 1 5) + (h 2/2 ^{_{) (15H 2 / R 1 7}} - (3 / R 1 5))}] (3) provided ^{_{that, R 1 = (H 2 +}} x 0 2 + y 0 2) 1/2 (4)

The difference Δr _Q is the phase difference Δφ of the pixel at the observation point Q.
_Q (corresponding to Δφ ₁ = φ _B1 −φ _A1 described above) and equation
(5). Δφ _Q = (2π / λ) · Δr _Q (5) where λ is the wavelength of the radio wave radiated from the antenna.

H, B, and λ are known, and the above equations (3),
As can be seen from (4) and (5), Δφ _Q is a function of x ₀ , y ₀ , and h. Assuming that the function determined from these equations is Q, Δφ _Q = Q (x ₀ , y ₀ , h) (6) As described above, Δφ _Q compares the phase of each pixel of the two images as described above. It is obtained by doing. FIG. 12 shows an example of a drawing that expresses Δφ _Q in a plan view. FIG. 12 shows contour lines of the phase difference. If the terrain is completely flat, a vertical stripe pattern with many parallel lines appears. The contour lines are disturbed on the left and right sides of the figure, but these parts are undulating terrain such as mountains. Given a certain coordinate (x ₀ , y ₀ ), the height can be known by solving the above equation (6) for h. That is, h = h (x ₀ , y ₀ , Δφ _Q ) (7)

The height h can be determined in principle by the above equation. However, there are some problems in the actual calculation. Looking at equation (3), there are terms that include h and terms that do not.
Since h≪R ₁ in general, (term including h) ≪ (term not including). When adding or subtracting values whose absolute values are significantly different from each other on a computer as described above, the number of digits of the computer is limited, so that the calculation error cannot be ignored.

The inconvenience is solved by introducing the concept of a virtual reflection point. The virtual reflection point is a reflection point when the terrain has a planar shape. Since the virtual reflection point is a point on a perfect plane, it becomes a vertical stripe pattern in which many parallel lines appear in an image as shown in FIG. When the difference between the phase difference Δφ _Q according to the above equations (3) and (5) and the phase difference due to the virtual reflection point is taken, terms not including h are eliminated, and the above-described problem does not occur.

Assuming that the virtual observation point R is observed from the platforms P ₁ and P ₂ , if the radio wave propagation distances to and from these points are r _1R and r _2R respectively, then the following can be written. r _1R = 2 ｛H ² + x ₀ ² + y ₀ ² ｝ ^1/2 = 2R ₁ (8) r _2R = 2 ｛H ² + (x ₀ + B) ² + y ₀ ² ｝ ^1/2 (9) where x ₁ = a _{x 0, x 2 = x 0} + B.

The difference Δr _R between these two distances can be written as in equation (10), similar to equation (3). Further, the phase difference Δφ _R of the virtual observation point R is obtained by Expression (11).

The _{Δr R = r 2R -r 1R ≒} 2 [(x 0 B + (B 2/2)) · (1 / R 1) - (x 0 2 B 2/2) (1 / R 1 3)] (10) Δφ _R = (2π / λ) · Δr _R (11)

From the above, the difference Δφ between Δφ _Q and Δφ _R is obtained by the following equation (10). _{Δφ = Δφ R -Δφ Q ≒ -} (4π / λ) · [{x 0 + (B / 2) - (3Bx 0 2 / 2R 1 2)} · (h · BH / R 1 3) + {(3H ^{_{2 / R 1 2) -1)}} (x 0 + (B / 2)) - (3Bx 0 2/2) ((5H 2 / R 1 4) - (1 / R 1 2)} · (B / R ^{_{1 3) (h 2/2}} )] (12)

By the way, as described above, the aircraft 10
Since the altitude H of 1 is known, R ₁ is a function of x ₀ and y ₀ (R ₁ = g (x ₀ , y ₀ )). Also, the baseline B and the wavelength λ of the transmission signal are known. Therefore, equation (1
The right side of 2) is a function of x ₀ , y ₀ and h. Rewriting equation (12) gives Δφ = f (x ₀ , y ₀ , h) (13).

On the other hand, Δφ _Q is, as described above,
(Δφ _Q =
φ _B1 −φ _A1 ). Δφ _R can be obtained by calculation because the coordinates of the points P ₁ and P ₂ are known (Δφ _R = m (x ₀ , y ₀ )). Therefore, equation (13)
Is obtained by the calculation of Δφ _R −Δφ _Q.
FIG. 13 shows an example of a drawing in which Δφ is represented in a plane. FIG.
3 is an enlarged view of the left part of FIG.
The terrain represented by the peninsula-shaped contour line on the right of the center corresponds to the terrain on the left side of FIG. In the figure, the contour lines correspond to the contour lines, and this figure can be used as a topographic map. Therefore, the height can be obtained by solving equation (13) for h. h = h ′ (x ₀ , y ₀ , Δφ) (14)

[Specific configuration and description of its operation] Next, a specific configuration of the apparatus according to the first embodiment of the present invention will be described. In FIG. 1, 1 is a transmitter that generates a transmission signal, 2 is an antenna that radiates the transmission signal and receives a reflected wave from the terrain, 3 is a signal that supplies a signal from the transmitter 1 to the antenna 2 and A transmission / reception switch 4 for supplying a reception signal to the receiver 4, a receiver 4 for performing reception processing such as frequency conversion, detection, and the like, 5 a demodulation processing corresponding to a modulation processing performed by the transmitter 1, and a range direction (antenna) The pulse compression unit 6 improves the resolution in the beam direction (6), a signal division unit 6 for dividing the output of the pulse compression unit 5 (a specific division method will be described later), and 7a and 7b are divided by the signal division unit 6. Synthetic aperture processing (SAR processing) provided for each signal
And a synthetic aperture processing unit 8 for performing synthetic aperture processing.
An interference processing section for comparing the outputs of
Is an interference processing unit that performs interference processing on the above-described virtual reflection point based on the squint angle θ _S (the angle between the traveling direction of the aircraft 101 and the beam), 10 is a squint angle meter that outputs the squint angle θ _S , and 11 is the interference An altitude difference calculator for obtaining an altitude h based on the output of the processor 8 and the output of the virtual reflection point interference processor 9, and a three-dimensional terrain database 12 for storing the altitude h of the terrain calculated by the altitude difference calculator 11. It is.

For the pulse compression processing performed by the transmitter 1 and the pulse compression unit 5, a known processing method such as chirp modulation or modulation using a Barker code is used. By this pulse compression processing, high resolution in the range direction is achieved. The signal dividing unit 6 includes a low-pass filter 6a and a high-pass filter 6b having a frequency fd described later as a boundary. A known processing method using a matched filter is used for the synthetic aperture processing performed by the synthetic aperture processing units 7a and 7b. By this synthetic aperture processing, high resolution in a cross range direction (a direction orthogonal to the range direction) is achieved. The resolution of the entire radar image is increased in conjunction with the synthetic aperture processing and the above-described pulse compression processing, and a high-resolution radar image similar to an aerial photograph is obtained. Synthetic aperture processing section 7a,
7b outputs, for example, images A and B in FIG. 6, respectively.

The interference processing section 8 calculates the phase difference between the two images as described above. That is, arbitrary coordinates (x ₀ , y
_{For 0} ), obtain Δφ _Q = φ _B1 −φ _A1 . Note that (x
₀ , y ₀ ) is not directly given, and when the position information (baseline B, altitude H, speed v, time t) of the aircraft 101 is obtained, the squint angle θ _S may be used. The output of the interference processing unit 8 is Δφ _Q in Expression (12).

The virtual reflection point interference processing section 9 calculates Δφ _R in equation (12) by calculating equation (10). Since the phase of the image is not given by observation in this process, the coordinates (x) based on the position information (baseline B, altitude H, speed v, time t) of the aircraft 101 and the squint angle θ _S output by the squint angle meter 10. _0, y ₀₎ seek calculated and.

The squint angle θ _S output by the squint goniometer 10 is the angle that the beam of the antenna 2 makes with the course of the aircraft 101 as its platform. Therefore, the squint goniometer 10 is an angle indicating device such as a rotary encoder or a synchro transmitter mechanically coupled to the axis of the antenna 2.

The altitude difference calculator 11 calculates the expression Δφ _Q output from the interference processor 8 and the Δφ _Q output from the virtual reflection point interference processor 9.
The difference from _R is obtained, and Δφ in Expression (12) is obtained. At the same time, the expression (1
Calculate the right side of 2). Then, a polynomial for h is obtained, so solving for h yields an altitude h (x ₀ , y ₀ ).

Next, a specific operation of the signal dividing section 6 for obtaining two types of images A and B will be described. Aircraft 10
1 is moving, the aircraft 101-1, 10 shown in FIG.
1-2 can be the same. However, the same point Q must be irradiated on the aircraft 101-1 and the aircraft 101-2. This is possible because the beam of the antenna 2 has a certain spread.

Referring to FIG. 4, a beam 102-1 of an aircraft 101-1 irradiates a ground surface area (foot area) 103-1. Here, the area 103-1 is changed to the area A (103
-1A) and the area B (103-1B). According to FIG. 4, the area A does not illuminate the point Q,
Region B illuminates point Q. Therefore, beam 10
If the received signal in the area B is extracted from the received signal according to 2-1 and subjected to the synthetic aperture processing, a high-resolution radar image viewed from the aircraft 101-1 can be obtained.

Next, it is assumed that the aircraft has moved to the position 101-2. At this time, the area A irradiates the point Q, and the area B does not irradiate the point Q. Therefore, a high-resolution radar image viewed from the aircraft 101-2 can be obtained by extracting the reception signal of the area A from the reception signal of the beam 102-2 and performing the synthetic aperture processing.

As can be understood from the above description, if one beam 102 is divided so as to sequentially irradiate the same point as the aircraft 101 advances (for example, it is divided into the right and left sides of the beam irradiation center), Two beams can obtain two kinds of radar images from different viewpoints.

Such beam division can be performed, for example, by dividing a received signal into a low-frequency part and a high-frequency part with a certain frequency fd as a boundary. FIG. 5 is an example of the frequency distribution of the power of the received signal. As can be seen from the figure, the spectrum of the received signal is distributed with a constant width Δf (= Δf _L + Δf _U ) around the frequency fd. This is because since the squint angle θ _S is not 90 °, the Doppler frequency has a spread according to the spread of the beam (when θ _S = 90 °, the Doppler frequency fd is zero and the spread of the spectrum is narrow). Doppler frequency f
d and the spectral distributions Δf _L and Δf _U
The position is determined by the position of the boundary line for the division within 2 and the velocity component v · cos θ _{S of the} aircraft 101 and the wavelength λ. Note that before the squint angle θ _S is 90
Although it has been described that the height h can be obtained by not setting the angle to °, this is also necessary for dividing one beam into two in Embodiment 1 of the present invention.

The low-frequency component Δ centered on the frequency fd in FIG.
f _L and the high-frequency component Δf _U are respectively calculated in the region 103− in FIG.
1B, 103-1A. This is the area 103-1
This is because the absolute value of the Doppler frequency becomes higher because the squint θ _S corresponding to A is larger than that of the region 103-1B.

The low-pass filter 6a and the high-pass filter 6b of the signal dividing section 6 output the low-frequency component Δf _L and the high-frequency component Δf _U of FIG. 5, respectively. Synthetic aperture processing units 7a, 7
b respectively perform the synthetic aperture processing, the aircraft 1
A radar image viewed from 01-1 and a radar image viewed from aircraft 101-2 are obtained.

Although the beam 102 is directed obliquely behind the aircraft 101 in FIG. 4, the beam 102 may be directed obliquely forward. The division of the beam is not limited to two, but may be three or more. In this case, the signal dividing unit 6 has three filters, one of which is a band-pass filter.

Next, a method of setting the squint angle θ _S will be described. In the conventional strip mapping SAR, the squint angle is 90 degrees. However, as described above, one beam is divided into two signals by dividing the frequency of the signal.
It is not possible to obtain one image and determine the height with one antenna. For these two purposes, it is more advantageous for the squint angle θ _S to be closer to 0 ° (or 180 °). However, the cross range resolution of the SAR deteriorates as the squint angle θ _S approaches 0 ° (or 180 °). Therefore, the squint angle θ _S is desirably about 45 °. However, the present invention is not limited to this, and the squint angle θ _S may be set as close to 0 ° (or 180 °) as possible within a range in which the required cross range resolution can be secured.

As described above, according to the first embodiment of the present invention, the following excellent effects can be obtained. (1) The squint angle is not 90 °, for example, 45 ° (1
35 °) and by obliquely directing the beam,
The difference in the first distance between the platform at a certain location and a point on the ground and the second distance between the platform at a different location on the same track and a point on the same ground causes the same path Distance (phase) information for measuring the height of the terrain can be obtained based on a plurality of images obtained by the plurality of platforms above or the same platform at a plurality of different positions. The conventional device requires two antennas to obtain distance (phase) information for measuring the height of the terrain, but according to the first embodiment of the present invention, only one antenna is required.

(2) Since only one antenna is required, the antenna is not affected by the inclination (roll angle) of the platform in principle. Conventionally, since there are two antennas, the phase difference between the signals received by both antennas changes due to the inclination. Preferably, the antenna is located at the center of the platform. (3) The squint angle is not 90 °, for example, 45 ° (1
35 °) and by obliquely directing the beam,
Since a width is generated in the frequency distribution of the received signal by one beam, one beam can be divided using a filter. Therefore, even when there is only one beam, a plurality of images viewed from different viewpoints can be obtained. Therefore, there is no need to prepare a plurality of platforms. (4) Since the height h is obtained based on the equation (12) that gives the phase difference between the reflection point of the actual terrain and the virtual reflection point, the calculation becomes easy and the calculation error can be reduced.

Embodiment 2 of the Invention In the first embodiment of the present invention, focusing on the fact that the frequency distribution of the received signal is widened, the signal dividing unit 6 is divided into two filters 6a and 6b.
It was constituted by. The signal dividing unit 6 is not limited to this, and focuses on the fact that the beam moves.
May be used.

FIG. 14 is a functional block diagram of the device according to the second embodiment of the present invention. In the figure, reference numeral 14 denotes a delay line that delays the output of the pulse compression unit 5 for a predetermined time and outputs the delayed output to the synthetic aperture 7b. Synthetic aperture 7 a directly receives the output of pulse compressor 5. Other components are the same as those shown in FIG.

Next, the operation will be described. Signal division unit 6
Outputs the output signal of the pulse compression section 5 as it is, and at the same time, delays the output signal for a predetermined time before outputting. This allows the beam to be split.

This is based on the following principle. In FIG. 4, the aircraft 101 moves in the positive x-axis direction. Assuming that the beam 102 is divided into two beams 103A and 103B, the point Q first enters the region B of the beam 103B, and then enters the region A of the beam 103A. Therefore, there is a certain delay time between signals for obtaining two types of radar images of the aircraft 101-1 and 101-2 for the same point Q. Conversely, if a certain time difference is given to the signal, two types of radar images can be obtained. The output of pulse compression means 5 is beam 1
03B, the output of delay line 13 is beam 1
03A.

The delay time of the delay line 13 is the beam 1
03B corresponds to the time when the point 03B passes through the point Q. Beam 103
Width L _B, and the delay time and the speed v of the aircraft 101 T _d when the cut in a straight line parallel to the x axis B is L _B / v. The delay function may be provided in the synthetic aperture processing unit 7b. Further, the divided reception pulse train may be partially overlapped and divided. In general, since the synthetic aperture processing unit is realized by digital operation, the delay line can be substituted by a storage device such as a memory.

As described above, according to the second embodiment of the present invention, a signal can be divided using a delay line. This method is advantageous when it is difficult to divide by a filter because the bandwidth of the signal is narrow due to the low speed of the platform.

Third Embodiment of the Invention The first and second embodiments of the present invention are intended to continuously obtain topographical information by dividing a beam to obtain two types of images. It is not necessary to split the beam when obtaining some terrain information, and another configuration can be adopted.

FIG. 15 is a functional block diagram of the device according to the third embodiment of the present invention. In the figure, 14 is an antenna control device for controlling the direction of the antenna 2 so that the beam irradiates a certain area, 15 is a switch for switching the output destination of the synthetic aperture processing unit 7, and 16 is a switch for receiving the output of the switch 15. An image storage unit that stores a radar image. The other components are the same as those shown in FIG. FIG.
1 is different from the configuration of FIG.
The difference is that the image storage unit 16 is provided, the signal division unit 6 is not provided, and only one synthetic aperture processing unit 7 is provided.

Next, the operation will be described with reference to FIG. In FIG. 16, beam 102 of aircraft 101-1
-1 irradiates the area 103. Also, aircraft 101
-2 beam 102-2 irradiates the same region 103. Accordingly, since two types of images can be obtained without splitting the beam, the height of the terrain in the area 103 can be known by the same processing as in the first embodiment of the invention. In this case, the squint angle θ _S1 of the aircraft 101-1 and the aircraft 10
Since the squint angle θ _S2 is not equal to 1-2, the beam 10
2 so that a constant area 103 is always illuminated.
Is required.

The antenna control device 14 controls the antenna 2 as described above. Location of area 103 and aircraft 101-
Since the positions of 1, 101-2 are known, the respective squint angles θ _S1 and θ _S2 can be obtained by simple calculations. When the same aircraft 101 moves, the antenna control device 1
4 continuously controls the direction of the antenna 2 between the squint angles θ _{S1 and} θ _S2 .

The synthetic aperture processing unit 7 includes the aircrafts 101-1 and 101-1,
The two images 01-2 are generated. While the signal of the area 103 is continuously obtained while the aircraft 101 is moving, for example, when the observation time is 10 seconds, an image is generated based on the signal of the first 5 seconds, and the image is generated based on the signal of the second 5 seconds. Generate The former is an image A of the aircraft 101-1 and the latter is an image B of the aircraft 101-2. The switch 15
The switching operation is performed for each image output by the synthetic aperture processing unit 7. The image A is stored in the image storage unit 16. Image B
Is input from the switch 15 directly to the interference processing unit 8. Subsequent processing is the same as in the first embodiment of the invention.

As shown by the solid line in FIG.
01 may move on a straight line, or may move while turning as shown by a dotted line.

As described above, according to the third embodiment of the present invention, the direction of the antenna is controlled so that the beam continuously irradiates one place, and a plurality of images are obtained by one beam. This eliminates the need for a signal division unit and requires only one synthetic aperture processing unit. Therefore, the configuration is simplified.

Embodiment 4 of the Invention Embodiment 4 of the Invention
Will be described with reference to the drawings. FIG. 17 is a functional block diagram of the device according to the fourth embodiment of the present invention. In the figure, reference numeral 17 denotes a descent speedometer for measuring the descent speed of the platform.
The altitude difference calculator 11 calculates an altitude difference based on the descent speed. Transmitter 1 to 3D terrain database 12 is shown in FIG.
Is the same as or equivalent to that shown in FIG. Also,
FIG. 17 shows an observation geometry according to the fourth embodiment of the present invention.

Next, the operation will be described. In FIG. 17, the operation from the transmitter 1 to the interference processing unit 8 is the same as that in FIG. The descent speed meter 17 measures the descent rate α of the orbit and outputs it to the altitude difference calculator 11. The rate of descent α is shown in FIG.
As shown in FIG. 8, when the aircraft 101 lowers the altitude at a constant rate as it progresses, this is the rate of decrease. The altitude difference calculator 11 calculates the altitude in consideration of the descent rate α, as described later, and obtains three-dimensional terrain data. Aircraft 1
Assuming that the moving distance of 01 is B, the decrease in altitude is αB.

The descent speedometer 17 indicates the descent rate α to the aircraft 10
The output may be obtained by differentiating the output of a radio altimeter (not shown) normally mounted on the device 1 with time, or may be obtained based on the output of a navigation device such as a GPS (Global Positioning System) used for obtaining the position.

A feature of the fourth embodiment of the present invention is that when observing an interfering SAR image from a descending trajectory, three-dimensional topographic data is obtained while calculating the altitude in consideration of the descending rate. Observing from such a descending orbit improves the altitude resolution.

These operations will be described using mathematical expressions. The following equation is obtained in the same manner as in the first embodiment of the invention. r _1Q = 2 ((H−h) ² + x ₀ ² + y ₀ ² ) ^1/2 (15) r _2Q = 2 ((H−h−αB) ² + (x ₀ + B) ² + y ₀ ² ) ^{1 / 2} (16) r _1R = 2 (H ² + x ₀ ² + y ₀ ² ) ^1/2 (17) r _2R = 2 ((H−αB) ² + (x ₀ + B) ² + y ₀ ² ) ^1/2 ( 18)

Here, variables R ₁ and R ₂ are defined as follows. R ₁ = (H ² + x ₀ ² + y ₀ ² ) ^1/2 (19) R ₂ = ((H−αB) ² + (x ₀ + B) ² + y ₀ ² ) ^1/2 (20)

By substituting R ₁ and R ₂ into equations (15) and (16),
When these expressions are Taylor-expanded and the second-order terms are obtained, the following expression can be obtained. _{r 1Q ≒ 2 [R 1 -h} (H / R 1) + (h 2/2) ((1 / R 1) - (H 2 / R 1 3))] (21) r 2Q ≒ 2 [R 2 -h ((H-αB) / R 2) + (h 2/2) ((1 / R 2) - ((H-αB) 2 / R 2 3))] (22) r 1R = 2R 1 ( 23) r _2R = 2R ₂ (24)

Therefore, the difference Δr ₂ between r _1Q and r _1R and r _2Q
And the difference Δr ₃ between r _2R can be written as: _{Δr 2 = r 1Q -r 1R =} 2 [-h (H / R 1) + (h 2/2) ((1 / R 1) - (H 2 / R 1 3))] (25) Δr 3 = _{r 2Q -r 2R = 2 [-h} ((H-αB) / R 2) + (h 2/2) ((1 / R 2) - ((H-αB) 2 / R 2 3))] ( 2
6)

Further, when R ₁ and R ₂ are subjected to Taylor expansion, Δr ₃ can be rewritten as follows. _{Δr 3 ≒ 2 [{(BH} / R 1 3) (x 0 + (B / 2) - (3Bx 0 2 / 2R 1 2)) - (H / R 1) + (αB / R 1) + (αBH ^{_{/ R 1 3) (- H}} + (3Bα / 2)) + (αB 2 H / R 1 5) (3x 0 H + (3BH / 2) - (9αBx 0/2) - (3αH 2/2) + (3α ^{2 HB / 2)) + B} 3 αH 2 / R 1 7 (- (15x 0 2/2) + (15 αHx 0/2)) + B 2 α / R 1 3 (-x 0 - (B / 2 ^{) - (α 2 B / 2} )) + (3B 3 α / 2R 1 5)} h {(B / R 1 3) (- x 0 - (B / 2) + (3H 2 x 0 / R 1 2 ^{) + (3H 2 B / 2R} 1 2) - (3Bx 0 2/2) ((5H 2 / R 1 4) - (1 / R 1 2))) + (1 / R 1) - (H 2 / ^{_{R 1 3) + (1 /}} R 1 3) (3αHB- (3α 2 B 2/2)) + (1 / R 1 5) (- 9 αHB 2 x 0 -3 α 2 B 2 H 2 +3 αBH _{^{3) - (1 / R 1}} 3) ((15α 2 H 4 B 2/2) +15 αH 3 B 2 x 0)} (h 2/2)] (27)

[0091] The difference .DELTA..PHI the phase difference .DELTA..PHI _R of the retardation .DELTA..PHI _Q and the virtual observation point R of the pixel observation point Q obtained by the altitude difference calculating unit 11 is obtained as follows based on the above equation. ΔΦ = ΔΦ _Q −ΔΦ _R = (2π / λ) ((r _2Q −r _1Q ) − (r _2R −r _1R )) = (2π / λ) (Δr ₃ −Δr ₂ ) = (4π / λ) [ ｛(BH / R ₁ ³ ) (x ₀ + (B / 2)-(3Bx ₀ ² / 2R ₁ ² )) + (αB / R ₁ ) + (αBH / R ₁ ³ ) (-H + (3 αB / ^{2)) + (αB 2 H} / R 1 5) (3x 0 H + (3BH / 2) - (9αBx 0/2) - (3 αH 2/2) + (3α 2 HB / 2)) + (αB 3 ^{_{H 2 / R 1 7) (}} - (15x 0 2/2) + (15αHx 0/2)) + (αB 2 / R 1 3) (- x 0 - (B / 2) - (α 2 B / 2 ^{)) + (3 αB 3 /} 2R 1 5)} h {(B / R 1 3) (- x 0 - (B / 2) + (3H 2 x 0 / R 1 2) + (3H 2 B / 2R ^{_{1 2) - (3Bx 0 2}} /2) ((5H 2 / R 1 4) - (1 / R 1 2))) + (1 / R 1 3) (3αHB- (3 α 2 B 2/2) ^{_{) + (1 / R 1 5}} ) (- 9 αHB 2 x 0 -3 α 2 B 2 H 2 +3 αBH 3) - (1 / R 1 3) ((15α 2 H 4 B 2/2) +15 _{^{αH 3 B 2 x 0)}}} (h 2/2)] (28)

The altitude difference calculating section 11 can calculate the altitude h of the observation point Q using the equation (28). By the way, the expression (2
8) is different from equation (12) in the first embodiment of the present invention in that the trajectory is lowered at a constant descent rate α.
This difference ΔΦ _d is given by the following equation. _{ΔΦ d = (4π / λ)} α [{(B / R 1) + (BH / R 1 3) (- H + (3Bα / 2)) + (B 2 H / R 1 5) (3x 0 H + (3BH _{/ 2) - (9αBx 0/} 2) - (3 αH 2/2) + (3α 2 HB / 2)) + (B 3 H 2 / R 1 7) (- (15x 0 2/2) + (15αHx _0/2 )) + (B ² / R ₁ ³ ) (-x _0- (B / 2)-(α ² B / 2)) + (3B ³ / 2R ₁ ⁵ )｝ h + ｛(1 / R ^{_{1 3) (3 HB- (3}} αB 2/2)) + (1 / R 1 5) (- 9HB 2 x 0 -3αB 2 H 2 + 3BH 3) - (1 / R 1 3) ((15αH 4 ^{B 2/2) + 15H 3} B 2 x 0)} (h 2/2)] (29)

Further, the following equation is obtained by differentiating ΔΦd with the orbit descent rate α. _{d (ΔΦ d) / dα =} (4π / λ) [h (B / R 1) {1- (1 / R 1 2) (H 2 + Bx 0 + (B 2/2) (1 + 3 α 2 ^{))} + h (3αHB 2} / R 1 3) (1- (H 2 / R 1 2)) + h (3x 0 B 2 H 2 / R 1 5) (1- (3αB / H) - (3h ^{/ 2H)) + (h 2} /2) (3BH / R 1 3) (1- (αB / H)) + (h 2/2) (3BH 3 / R 1 5) (1-2αB / H) + ^{(h / 2) (9α 2} B 3 H 2 / R 1 5) (1- (5Hx 0 / 3R 1 2) (h / B)) + (h / 2) (3B 3 H 2 / R 1 5) _{^{(1- (5H 2 / R 1}} 2) (h α / B)) + h (3B 3 x 0 2/2)] (30)

Here, the necessary conditions for each term on the right side of the equation (30) to take a positive value are that the following four relationships hold. _{^{x 0 2 + y 0 2>}} Bx 0 + (B 2/2) (1 + 3α 2) (31) 3 (Bα + (h / 2)) <H (32) (5/3) (H / R ₁ ) (x ₀ / R ₁ ) (h / B) <1 (33) 5α (H ² / R ₁ ² ) (h / B) <1 (34)

The interference type synthetic aperture radar according to the fourth embodiment of the present invention is used under the condition that the relations of equations (31) to (34) are satisfied. Therefore, under the condition of α> 0, d (Δ
Φ _d ) / dα> 0. When α = 0, ΔΦ _d
As can be seen from = 0, ΔΦ _d takes a positive value under the condition of α> 0.

This means that the phase ΔΦ of the equation (28) of the fourth embodiment of the present invention becomes larger as the value of the phase ΔΦ becomes larger as compared with the phase ΔΦ of the equation (12) of the first embodiment of the present invention. means. That is, the phase change of the echo can be increased by lowering the orbit (α> 0). When the measurement accuracy of the phase is the same, the measurement error decreases as the phase change increases. Therefore, according to the method of the fourth embodiment of the present invention, the height h of the observation point Q is higher than that of the first embodiment of the present invention. Can be measured with higher accuracy.

Note that the area irradiated by the antenna may be set obliquely forward of the platform to raise the trajectory of the platform.

Embodiment 5 of the Invention In the first to third embodiments of the present invention, the radar image is obtained based on the synthetic aperture processing. However, the method for obtaining the radar image is not limited to the synthetic aperture processing. For example, DBS (Doppler Beam Sharp
ening).

Embodiment 5 of the Invention Using DBS
Will be described. In FIG. 19, reference numerals 18a and 18b denote DBS image reproducing units, and the synthetic aperture processing units 7a and
7b. The transmitter 1 to the three-dimensional terrain database 12 in FIG. 19 are the same as or correspond to those shown in FIG.

Each of the DBS image reproducing sections 18a and 18b includes a range migration correcting section 181, a phase compensating section 182, a phase compensating reference signal section 183, and an FFT 184. These operations will be described later. Further, the basic geometry of the observation in the fifth embodiment of the present invention is the same as that in the first embodiment of the present invention.

Next, the operation will be described. In FIG. 19, the operation from transmitter 1 to band division section 6 is the same as that in the first embodiment of the invention.

The feature of the fifth embodiment of the present invention is that the SAR
The well-known DBS (Doppler Beam Sharpening) is used for the image reproduction processing instead of the synthetic aperture processing. DBS is a high-resolution radar system in line with SAR. SAR achieves high resolution in the azimuth direction using a matched filter, whereas DBS uses a Doppler filter.

In FIG. 19, a DBS image reproducing unit 18a
Converts one of the divided signals into a complex radar image,
The S image reproducing unit 18b converts the other divided signal into a complex radar image, and outputs the images φ _A (x ₀ , y ₀ ) and φ
_B (x ₀ , y ₀ ) is output. The operation of the interference processing unit 8 receiving these two images is the same as that of the first embodiment, and outputs the phase difference Δφ _Q (x ₀ , y ₀ ) for each pixel of the two radar images. Is obtained. Finally, the altitude calculation unit 11 calculates the altitude based on the phase difference Δφ _Q (x ₀ , y ₀ ) and the phase difference Δφ _R (x ₀ , y ₀ ) related to the virtual reflection point,
It is stored in the three-dimensional terrain database 12.

The operation of the DBS image reproducing unit 18 will be described with reference to FIGS. FIG. 20 shows the observation geometry. The points Q, Q ′, and Q ″ are three observation points that are within the same distance (range) as viewed from the antenna 2 but have different positions in the beam cross-range direction (azimuth direction).

As the radar platform 101 moves, the distance to the observation points Q, Q ', and Q "increases (decreases when the beam is obliquely forward). FIG. 21 shows the state before the range migration correction.
It is a graph which shows the state where the range of the observation target point moves with time. Range migration correction unit 181
Calculates the time rate of change of the range based on the altitude and speed of the platform 101, the squint angle of the antenna beam 102, and radar specifications, and corrects the range so that the range becomes constant with time.

As the radar platform 101 moves, the rate of increase in the distance to the observation points Q, Q ', Q "changes, so that the Doppler frequencies of these echoes change with time. FIG. 22 shows a range migration correction unit. It is a graph which shows the time change of the Doppler frequency of the output of 181. In the same figure, Q, Q ', Q "
Each shows the Doppler frequency change of the echo at the observation point. The slopes of the graphs Q, Q ′, and Q ″ can be obtained in advance based on the altitude and speed of the platform 101, the squint angle of the antenna beam 102, and radar specifications.

The phase compensation reference signal section 183 prepares these inclinations as phase compensation reference signals. FIG.
FIG. 3 is a diagram illustrating an example of a phase compensation reference signal. When the inclination is the same for a plurality of observation target points, only one reference signal is required.

The phase compensator 182 multiplies the input signal subjected to the range migration correction by the complex conjugate number of the phase compensation reference signal, thereby changing the slopes of the graphs Q, Q ′, and Q ″ in FIG. The phase compensator 1 compensates to correct the Doppler frequency of the received signal with respect to time.
Due to 82, the Doppler frequency becomes constant over time as shown in FIG.

As can be seen from FIG. 24, the signals from the observation points Q, Q ', and Q "separated in the azimuth direction are separated in the Doppler frequency direction. The FFT 184 is a Doppler filter that forms a number of bandpass filters therefor.

As described above, since the DBS image reproducing unit 18 improves the resolution in the azimuth direction by using the Doppler filter, the amount of calculation can be greatly reduced as compared with the synthetic aperture processing unit 7 using the matched filter. The feature is that radar images can be reproduced at high speed with a simple configuration.

Further, in relation to the first embodiment of the present invention, in the case of the synthetic aperture processing, the squint angle is desirably 90 °, and the performance is deteriorated when approaching 0 ° (180 °). , 90 ° degrades the performance, so it is desirable to make the beam oblique. This is because, in the DBS, when the direction orthogonal to the orbit is observed, the Doppler band is narrowed and the resolution is deteriorated. Therefore,
This is very suitable for operation with a sufficiently large squint angle.

Embodiment 6 of the Invention Embodiment 6 of the Invention
Will be described. FIG. 25 is a functional block diagram of the device according to the sixth embodiment of the present invention. This apparatus is provided with two sets of synthetic aperture radar apparatuses like the conventional apparatus, but the beam is directed obliquely to improve the measurement accuracy.

In the figure, the antenna 2a to the synthetic aperture processing section 7a constitute one synthetic aperture radar device. Also, the antenna 2b to the synthetic aperture processing unit 7b constitute another synthetic aperture radar device. The components of these radar devices are the same as those shown in FIG. The reason why only one transmitter 1 and one transmission / reception switch 3 are provided is that a transmission signal can be commonly used by two radar devices. FIG. 26 shows an observation geometry according to the sixth embodiment of the present invention.

Next, the operation will be described. In FIG. 25, the operation from the transmitter 1 to the synthetic aperture processing units 7a and 7b is the same as that in the embodiment of the present invention. Each of the transmitting and receiving antennas 2a and 2b is adjusted in direction of the main beam so as to irradiate the same ground surface in a direction inclined from a plane orthogonal to the orbit. For example, the squint angle of the beam is 45 °
It is about. The directions of the main beams of these two antennas are adjusted to be slightly different in the orbital direction.

For example, as shown in FIG. 26, it is assumed that the main beam of the transmitting / receiving antenna 2a is directed to the rear left, and the main beam of the receiving antenna 2b is directed further behind the main beam of the transmitting / receiving antenna 2a. At this time, the area observed by the antenna 2a at the position of the platform 101-1 can be observed again by the receiving antenna 2b at the position of the platform 101-2.

That is, the phase difference between the complex SAR image observed by the antenna 2a of the platform 101-1 and the complex SAR image observed by the antenna 2b of the platform 101-2 is obtained from the output of the interference processing unit 8.

The squint goniometer 10 outputs the squint angle of the antenna to the altitude difference calculator 11. Then, the altitude difference calculator 11 calculates the altitude from the phase, and obtains three-dimensional terrain data.

The feature of the sixth embodiment of the present invention is that two sets of antennas and receivers are used. Antennas 2a, 2b
Is provided at both ends of the wing of the aircraft 101, it can be observed at a two baselines B _y in the direction perpendicular to the track. Since the altitude difference is calculated based on the observation result and the observation result with the base line _Bx separated in the orbit direction, the resolution of the altitude is improved.

The above operation will be described using mathematical expressions. The round-trip radio wave propagation distance when observing the observation point Q from the antenna 2a of the platform 101-1 is r _1AQA , the round-trip radio wave propagation distance when observing the virtual observation point R is r _1ARA , and the antenna 2a of the platform 101-2 When the radio wave propagation distance for observing the observation point Q when transmitting from the antenna 2b and receiving at the antenna 2b is r _2AQB , and the radio wave propagation distance for the _{reciprocation} when observing the virtual observation point R is r _2ARB , then (3
5) to (38).

R _1AQA = 2 (x ₀ ² + y ₀ ² + H ² ) ^1/2 = 2R ₁ (35) r _1ARA = ((x ₀ + B _x ) ² + y ₀ ² + H ² ) ^1/2 + ((x ^{_{0 + B x) 2 + (}} y 0 + B y) 2 + H 2) 1/2 (36) = R 3 + R 4 r 2AQB = 2 (x 0 2 + y 0 2 + (H-h) 2) 1/2 ( _{37) r 2ARB = ((x} 0 + B x) 2 + y 0 2 + (H-h) 2) 1/2 + ((x 0 + B x) 2 + (y 0 + B y) 2 + (H-h) ² ) ^1/2 (38)

However, R ₁ , R ₃ and R ₃ are as follows. ^{_{R 1 = (x 0 2 +}} y 0 2 + H 2) 1/2 (39) R 3 = ((x 0 + B x) 2 + y 0 2 + H 2) 1/2 (40) R 4 = ((x 0 + B _x ) ² + (y ₀ + B _y ) ² + H ² ) ^1/2 (41)

[0122] Here, H is the altitude of the radar platform 1, Bx orbital direction of the base line length of, By the direction of the baseline length of the perpendicular to the track, x ₀ is the observation point Q and the radar platform 1 The distance y ₀ on the x-axis of the antenna 2 is the distance between the observation point Q and the antennas 2a and 2b on the y-axis.

[0123] and the difference Δr _2AQRB of r _2AQB and r _2ARB, r _1AQA
And the difference Δr _1AQRA between r _1ARA can be written as the following equations (42) and (43) by approximation by Taylor expansion. _{Δr 2AQRB = r 2AQB -r 2ARB ≒} R 3 -h (H / R 3) - (h 2/2) (- (H 2 / R 3 3) + (1 / R 3)) + R 4 -h ( _{H / R 4) + (h} 2/2) (- (H 2 / R 4 3) + (1 / R 4)) - (R 3 + R 4) ≒ (2 / R 3) ((h 2 / 2) -Hh) + (1 / R 3 3) {((h 2/2) -Hh) (- y 0 B y - (B y 2/2)) - H 2 h 2} + (3 / 2R ^{_{3 5) {((h 2}} /2) -Hh) y 0 2 B y 2 + (y 0 B y + (B y 2/2)) H 2 h 2} - (15H 2 h 2 y 0 2 B ^{_{y 2 / 4R 3 7) (}} 42) Δr 1AQRA = r 1AQA -r 1ARA ≒ 2 [R 1 -h (H / R 1) + (h 2/2) (- (H 2 / R 1 3) + ( _{1 / R 1))] -} 2R 1 ≒ (2 / R 3) ((h 2/2) -Hh) + (2 / R 3 3) {((h 2/2) -Hh) (x 0 B ^{_{x - (B x 2/2}} )) - H 2 h 2} + (3 / R 3 5) {((h 2/2) -Hh) x 0 2 B x 2 + (- x 0 B x + ( ^{_{B x 2/2)) H}} 2 h 2} - (15H 2 h 2 x 0 2 B x 2 / 2R 3 7) (43)

Accordingly, the phase difference ΔΦ _Q between the pixel at the observation point Q and the phase difference ΔΦ between the virtual observation point R obtained at the output of the interference processing unit 8
The phase difference ΔΦ from Φ _R is obtained as follows by subtracting Expression (43) from Expression (42).

ΔΦ = (2π / λ) [(r _2AQB −r _1AQA ) − (r _2ARB −r _1ARA )] = (2π / λ) [Δr _2AQRB −Δr _1AQRA ] = (2π / λ) [( _1/1 / ^{_{R 3 3) ((h 2}} /2) -Hh) {(- y 0 B y - (B y 2/2)) - 2 (x 0 B x - (B x 2/2))} + (3 ^{_{/ 2R 3 5) {((}} h 2/2) -Hh) (y 0 2 B y 2 -2x 0 2 B x 2) + (y 0 B y + (B y 2/2) + 2x 0 B x ^{_{-B x 2) H 2 h 2}} } + (15H 2 h 2 / 4R 3 7) (2x 0 2 B x 2 -y 0 2 B y 2)] (44)

The altitude calculation unit 11 calculates the observation point Q using equation (44).
Can be calculated. By the way, the improvement ΔΦs of the phase difference due to the squinting of the antenna is
Since this corresponds to the term including Bx in equation (44), it is given by the following equation.

[0127] ^{_{ΔΦs = (2π / λ) [}} (2 / R 3 3) (Hh- (h 2/2)) (x 0 B x -
_{^{(B x 2/2))}} + (3 / R 3 5) {(Hh- (h 2/2)) x 0 2 B x 2 + (x 0 B x - (B x
^{2/2)) H 2 h} 2} + (15H 2 h 2 x 0 2 B x 2 / 2R 3 7)] (45)

In the interference type synthetic aperture radar device according to the sixth embodiment of the present invention, ΔΦs takes a positive value because each term on the right side of the equation (45) is generally used under the condition that it is positive. That is, the phase change of the echo can be increased by squinting the antenna, and the altitude h of the observation point Q can be measured with higher accuracy than the conventional device.

As described above, it is an important feature of the present invention that the antenna is squinted in order to improve the sensitivity of the phase difference ΔΦ to the altitude h.

In the present invention, the area irradiated by the transmitting / receiving antenna may be obliquely forward of the platform.

[0131]

As described above, according to the first aspect of the present invention, a plurality of images obtained by observing the terrain from different observation points by a high-resolution radar device mounted on a moving body are compared. In a terrain height measuring method using a high-resolution radar device for measuring terrain height, a first observation point and a second observation point are arranged along a path of a moving body, and a point on a terrain to be measured is measured. When the distances between the first observation point and the second observation point are a first distance and a second distance, respectively, such that the first distance and the second distance are different. Since the first and second high-resolution radar beams irradiate the terrain with the beam inclined with respect to the path of the moving body, a long baseline can be secured in the traveling direction of the moving body, so that the measurement accuracy is improved.

According to the second aspect of the present invention, the first
And the second moving body are the same, and the first moving body
Is the position of the moving object at the first time,
Since the second observation point is the position of the moving body at the second time, the topography height can be measured by one moving body.

According to the third or seventh to ninth aspects of the present invention, the beam of the high-resolution radar device is divided into a first part and a second part, and a beam on the same terrain is obtained. Since the observation is performed with the first beam at the first observation point and the second beam is observed at the second observation point, two images can be obtained with one antenna and the terrain height can be obtained. Can be measured.

According to the fourth or tenth aspect of the present invention, at the first observation point and the second observation point, the beam of the high-resolution radar device irradiates a point on the same terrain. , Two images can be obtained with one antenna and the height of the terrain can be measured without splitting the beam.

According to the fifth or eleventh aspect of the present invention, since the moving path of the moving body is set to the rising or falling path, the measurement accuracy is further improved.

According to the sixth or twelfth aspect of the present invention, the first high-resolution radar device and the second high-resolution radar device are arranged at different positions on a line intersecting the path of the moving body. Since the observation is performed at the first observation point by the first high-resolution radar device and the observation is performed at the second observation point by the second high-resolution radar device, the measurement accuracy is further improved.

[Brief description of the drawings]

FIG. 1 is a functional block diagram illustrating a configuration of an interference type high resolution radar device according to Embodiment 1 of the present invention.

FIG. 2 is a diagram for explaining an operation of the interference type high resolution radar device according to the first embodiment of the present invention. It is the figure which looked at the xy plane from the positive direction of the z-axis.

FIG. 3 is a diagram for explaining an operation of the interference type high resolution radar device according to the first embodiment of the present invention; It is the figure which looked at the yz plane from the positive direction of the x-axis.

FIG. 4 is a diagram showing an observation geometry according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a frequency distribution of a received signal according to Embodiment 1 of the present invention.

FIG. 6 is a diagram for explaining an operation of the interference type high resolution radar device according to the first embodiment of the present invention; Images A and B
One of the squares means one pixel.

FIG. 7 is a diagram for explaining an operation of the interference type high resolution radar device according to the first embodiment of the present invention; It is the figure which looked at the yz plane from the positive direction of the x-axis. An area divided by a straight line parallel to the z-axis means one pixel.

FIG. 8 is a diagram showing a conventional antenna arrangement for explaining the operation of the interference type high resolution radar device according to the first embodiment of the present invention.

FIG. 9 is a diagram showing a geometry in a conventional antenna arrangement for explaining an operation of the interference type high resolution radar device according to the first embodiment of the present invention.

FIG. 10 is a diagram illustrating an operation of the interferometric high-resolution radar apparatus according to the first embodiment of the present invention, in which the squint angle is 9;
It is a figure which shows the geometry at the time of setting it as 0 degree.

FIG. 11 shows a squint angle of 9 for explaining the operation of the interference type high resolution radar apparatus according to the first embodiment of the present invention.
It is a figure which shows the geometry at the time of setting it as 0 degree.

FIG. 12 is a diagram illustrating an example of phase difference contours obtained by the interference type high resolution radar device according to the first embodiment of the present invention.

FIG. 13 is a diagram illustrating an example of phase difference contours obtained by the interference type high resolution radar device according to the first embodiment of the present invention.

FIG. 14 is a functional block diagram showing a configuration of an interference type high resolution radar device according to Embodiment 2 of the present invention.

FIG. 15 is a functional block diagram showing a configuration of an interference type high resolution radar device according to Embodiment 3 of the present invention.

FIG. 16 is a diagram illustrating an observation geometry of the interferometric high-resolution radar device according to the third embodiment of the present invention;

FIG. 17 is a functional block diagram showing a configuration of an interference type high resolution radar device according to Embodiment 4 of the present invention.

FIG. 18 is a diagram illustrating a geometry of an observation-type interference high-resolution radar device according to a fourth embodiment of the present invention.

FIG. 19 is a functional block diagram showing a configuration of an interference type high resolution radar device according to Embodiment 5 of the present invention.

FIG. 20 is a diagram showing a geometry of an observation interferometric high-resolution radar device according to the fifth embodiment of the present invention.

FIG. 21 is a graph showing a time change of a range in the interference type high resolution radar apparatus according to the fifth embodiment of the present invention.

FIG. 22 is a graph showing a time change of a Doppler frequency in the interference type high resolution radar device according to the fifth embodiment of the present invention.

FIG. 23 is a graph showing a reference signal for phase compensation in the interference type high resolution radar apparatus according to Embodiment 5 of the present invention.

FIG. 24 is a graph showing an output of a phase compensator in the interference type high resolution radar device according to the fifth embodiment of the present invention.

FIG. 25 is a functional block diagram showing a configuration of an interference type high resolution radar device according to Embodiment 6 of the present invention.

FIG. 26 is a diagram showing a geometry of an observation-type interference high-resolution radar apparatus according to Embodiment 6 of the present invention;

[Explanation of symbols]

1 transmitter, 2 antennas, 3 duplexer, 4 receiver, 5 pulse compressor, 6 signal divider, 7 synthetic aperture processor, 8 interference processor, 9 virtual reflection point interference processor,
10 squint goniometer, 11 altitude difference calculator, 12
3D terrain database, 13 delay line, 14
Antenna control device, 15 switch, 16 image storage unit, 17 descent speedometer, 18 DBS image reproduction unit.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-288843 (JP, A) JP-A-7-110377 (JP, A) JP-A-7-72244 (JP, A) JP-A-7-72 159529 (JP, A) JP-A-8-16647 (JP, A) JP-A-9-5433 (JP, A) JP-A-9-113615 (JP, A) Edited by Joji Iizaka, edited by The Japan Society of Photogrammetry, Synthesis Aperture Radar Image Handbook, Asakura Shoten, Japan, May 20, 1998, 68-77 (58) Field surveyed (Int. Cl. ⁷ , DB name) G01S ⁷ /00-7/42 G01S 13/00- 13/95 G01C 5/00

Claims (12)

(57) [Claims] 1. A terrain using a high-resolution radar device that measures a terrain height by comparing a plurality of images obtained by observing the terrain from different observation points by a high-resolution radar device mounted on a moving body. in the height measuring method, a of the first moving body equipped with the first high-resolution radar system
The antenna position as a first observation point, equipped with a second high-resolution radar system A of the second moving body
When the antenna position is set as the second observation point , the first observation
The point and the second observation point are located at different positions on the same path.
When the distances between the terrain point to be measured and the first observation point and the second observation point are defined as a first distance and a second distance, respectively, The first and second high-resolution radar beams are irradiated on the terrain at an angle to the path of the moving object so that the second distance is different from the first distance. A terrain height measurement method using a high-resolution radar device for measuring a terrain height by comparing with a second image from the second observation point. 2. The method according to claim 1, wherein the first moving body and the second moving body are the same, the first observation point is a position of the moving body at a first time, and the second observation point is a second observation point. 2. The method for measuring a terrain height using a high-resolution radar device according to claim 1, wherein the position of the moving body is set at a time of 2. 3. The beam of the high resolution radar device is first
And a second portion are observed, and a point on the same terrain is observed at the first observation point with the first beam, and observed at the second observation point with the second beam. A method for measuring terrain height using the high-resolution radar device according to claim 2. 4. The method according to claim 1, wherein the beam of the high-resolution radar device is observed at the first observation point and the second observation point while controlling the beam so as to irradiate a point on the same terrain. A terrain height measurement method using the high-resolution radar device according to 2. 5. A method for measuring terrain height using a high-resolution radar device according to claim 1, wherein the path of the moving body is a path that rises or descends. 6. A first high-resolution radar device and a second high-resolution radar device arranged at different positions on a line intersecting a path of a moving body.
Using the first high-resolution radar device at the first observation point, and observing the second high-resolution radar device at the second observation point. Claim 1 to Claim 5
A terrain height measurement method using the high-resolution radar device according to any one of the above. 7. An interferometric high-resolution radar device mounted on a moving object, comprising: a transmitter for outputting a high-frequency signal; and a transmitting / receiving beam being directed obliquely to the moving object, and transmitting the high-frequency signal from the transmitter to the ground. A transmitting and receiving antenna that receives a reflected signal from the ground surface, a receiver that performs a receiving process by receiving a reflected signal from the transmitting and receiving antenna, and a pulse compressor that improves the range resolution in the direction of the transmitted and received beam, A signal dividing unit that divides an output of the pulse compression unit according to a position in a transmission / reception beam and outputs the divided signal as a first signal and a second signal; and receives the first signal and the second signal, respectively. A first and a second to improve a cross range resolution in a direction intersecting a direction of a transmission / reception beam and obtain a high-resolution radar image, respectively.
And a high-resolution radar image obtained from the first observation point obtained by the first image reproduction unit, and a high-resolution radar image obtained from the second observation point obtained by the second image reproduction unit An interference processing unit that obtains height information of the terrain by interfering with the radar image, and a reflection point when the beam of the transmitting / receiving antenna is irradiated on a plane serving as a reference for measuring the height of the terrain is set as a virtual reflection point. A virtual reflection point interference processing unit that obtains height information of the virtual reflection point by calculating based on the position of the moving object; and compares an output of the interference processing unit with an output of the virtual reflection point interference processing unit. An interferometric high-resolution radar device comprising an altitude difference calculator for determining the height of the terrain. 8. A low-pass filter that passes a low frequency with respect to a frequency corresponding to a division position in a transmission / reception beam and outputs the first signal, and a high frequency that passes through the signal division unit. The high-resolution interferometric radar device according to claim 7, further comprising a high-pass filter that outputs the second signal. 9. The transmission / reception beam is transmitted to the signal division unit by a first
When dividing the signal into a second part and a second part, the signal from the pulse compression unit is divided into a time corresponding to a time required for the first part to pass through one point of the terrain as the moving body moves. 8. The interference according to claim 7, further comprising delay means for delaying the signal and outputting the second signal as the second signal, wherein the signal division unit outputs the signal from the pulse compression unit as the first signal as it is. Type high resolution radar device. 10. An antenna control device for controlling a directivity of said transmitting / receiving antenna so that said transmitting / receiving beam illuminates a point on the same terrain as the moving body moves. An interference-type high-resolution radar device as described in the above. 11. An ascent / descent velocimeter for detecting an ascent / descent speed of the moving body, wherein the altitude difference calculating section includes
The height of the terrain according to claim 7, wherein the height of the terrain is obtained by comparing the output of the interference processing unit and the output of the virtual reflection point interference processing unit based on the output of the ascent / descent speedometer. Resolution radar device. 12. An interferometric high-resolution radar device mounted on a moving object, comprising: a transmitter for outputting a high-frequency signal; and a transmitting / receiving beam being directed obliquely to the moving object, and transmitting the high-frequency signal from the transmitter to the ground. A first antenna for receiving a reflected signal from the ground, a second antenna for receiving a reflected signal from the ground, and a receiving beam being directed obliquely to the moving body; , A first and a second receiver for receiving the reflected signal from the second antenna and performing a receiving process, respectively, and receiving the outputs of the first and the second receiver and setting the range resolution for the direction of the beam, respectively. First and second pulse compression units to be improved, and the outputs of the first and second pulse compression units are respectively received to improve the cross range resolution in a direction intersecting with the direction of the beam, thereby providing a high-resolution radar image. First and second image reproducing units for obtaining images respectively; a high-resolution radar image from a first observation point obtained by the first image reproducing unit; and a high-resolution radar image obtained by the second image reproducing unit. When an interference processing unit that obtains terrain height information by interfering with a high-resolution radar image from a second observation point, and when the beam of the antenna is irradiated on a plane serving as a reference for measuring the terrain height A virtual reflection point interference processing unit that obtains height information of the virtual reflection point by calculating based on the position of the moving body, where the reflection point is a virtual reflection point, and an output of the interference processing unit and the virtual reflection. An altitude difference calculator for determining the height of the terrain by comparing the output of the point interference processor with a different position on a line intersecting the path of the mobile object with the first and second antennas Interferometric High Resolution Radar System .