JPH09113615A - Interferometry sar system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the measurement accuracy from lowering at the time of using a plurality of platforms by a constitution wherein a DGPS reference station installed on the ground measures its own position utilizing GPS satellites and imparts the position thus measures as reference positional information for determining the precise position of each SAR. SOLUTION: SAR1-SAR3 mounted on a plurality of platforms telemetering of a target 4. A DGPS reference station 6 installed on the ground measures its own positron utilizing a plurality of GPS satellites 5 radiating reference radio wave and imparts reference positional information for determining the precise position to each SAR. Each SAR determines precise position utilizing the satellites 5 and reference station 6 and then processes the data measured by each SAR based on the positional information. Since each SAR determines precise position utilizing the satellites 5 and reference station 6, the measurement accuracy can be prevented from lowering when the SARs are mounted on a plurality of platforms.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a remote sensing system, and more particularly to interferometry SAR.
About the method.

[0002]

2. Description of the Related Art Conventionally, in a remote sensing system for remotely measuring the earth or planets from a platform such as an aircraft or an artificial satellite, an observation device is mounted on the platform and the data measured by the observation device is separately installed. In addition, a method of processing and analyzing is adopted in the reception processing system.

There are various types of observation devices mounted on the platform, and among them, SAR (Synthetic Aperture Radar) is widely used.

In the SAR, radio waves are radiated to the ground on the side of the traveling direction of the mounted platform,
By receiving the reflected wave from the ground, two-dimensional data for reproducing the ground image can be obtained.

The SAR is described in JP-A-62-3.
No. 676 and Japanese Patent Laid-Open No. 62-8081.

What is observed using SAR is elevation data of the terrain. A method of observing topographical elevation data (three-dimensional data) using SAR is called cross-track interferometry SAR.

FIG. 9 is a diagram showing the concept of cross-track interferometry SAR.

Cross-track interferometry S
The AR is, as shown in FIG. 9, two SARs 101 and 102.
The same target 104 was observed at SAR1
Two SAs observed in 01 and 102 respectively
The altitude Ht of the target 104 is measured by the interference of the R images.

The cross-track interferometry SAR is disclosed in Japanese Patent Laid-Open No. 63-262578.

In the cross-track interferometry SAR using the SAR mounted on an aircraft, two SAR antennas are mounted on the same body, and radio waves are radiated to the ground from only one antenna and received waves are received by both antennas. Cross-track interferometry SAR is realized by processing the two SAR images received and received by both antennas.

In the cross-track interferometry SAR using the satellite-mounted SAR, a return orbit is used and the same target is observed twice to obtain two image SARs. As an example of cross-track interferometry SAR using a regression trajectory,
There are SAR onboard Japanese satellite "Fuyo" and SAR onboard European satellite EERS-1.

However, in the cross-track interferometry SAR using the SAR mounted on the satellite, the number of recurring days is from several days to several tens of days, so that the first observation and
The target may change between the second observation and in that case, the observation accuracy will decrease, and the observation efficiency will decrease due to long return days and high dependency on orbital conditions. There is a problem.

As means for solving the above-mentioned problems, the following means are considered.

(1) Interferometry SAR is realized by arranging a plurality of satellites equipped with SAR in close parallel orbits and simultaneously observing the same target.
Here, in irradiating the target with radio waves, 1
Only one SAR is used, and the reflected waves from the target are received by a plurality of SARs.

(2) Interferometry SAR is realized by arranging a plurality of satellites equipped with SAR in close proximity on the same orbit and observing the same target almost at the same time. Here, in irradiating the target with the radio wave and receiving the reflected wave from the target, each S
S for the observation area for the observation area that is caused by the rotation of the earth during the time difference between observations at each SAR.
Cross-track interferometry SAR is realized by utilizing the difference in AR position.

Another thing that can be observed using SAR is the moving speed of a moving object. A method of observing the moving speed of a moving object using SAR is called along track interferometry SAR.

FIG. 10 is a diagram showing along track interferometry SAR, in which (a) is a conceptual diagram,
(B) is a figure which shows a measurement principle.

In the along track interferometry SAR, as shown in FIG. 10, first, the target 114 is observed in the SAR 111, and after a short time Δt, the target 114 is observed in the SAR 112 and observed in each of the SAR 111 and 112. By measuring the phase difference of the target 114,
The moving speed of the target 114 parallel to the SARs 111 and 112 in the line-of-sight direction is measured. In addition,
In irradiating the target 114 with radio waves and receiving the SAR image from the target, the SARs 111, 11
It is done in each of the two.

The above-mentioned cross-track interferometry SAR and along-track interferometry SAR are collectively referred to as interferometry S.
Call it AR.

[0020]

However, the conventional SAR as described above has the following problems.

(1) In a SAR using a low frequency or a SAR mounted on a satellite, it is necessary to increase the distance between the antennas of a plurality of SARs. Therefore, when a plurality of SARs are arranged on the same platform, There is a limit to the size, and it becomes impossible to use a small platform.

(2) When a plurality of platforms are used, it is difficult to accurately measure the relative position between the antennas of the SAR mounted on the platform, so the measurement accuracy of the interferometry SAR decreases.

(3) As a characteristic of SAR, it is necessary to widen the beam width of the radio wave to be emitted, but cross-track interferometry SA by a plurality of satellites on the same orbit
R, along track interferometry SAR
In that case, due to its characteristics, a plurality of SARs have to be operated in close proximity to each other, so that the beam irradiation ranges of the SARs overlap with each other, and signal waves from other SARs are mixed, resulting in SAR after data processing. The image quality is degraded.

(4) In the Nadia echo (reflected radio wave from directly below), the reception level is very high. Therefore, in the SAR mounted on the satellite, the Nadia echo reception timing does not overlap the reception timing from the observation area. In addition, in the SAR mounted on the aircraft, the reception timing of Nadia echo and the reception timing of the observation area do not overlap with each other.

However, SARs on multiple platforms
In the interferometry SAR according to the above, there is a possibility that the received wave from the observation area of one SAR is mixed with Nadia echo due to the transmitted wave of another SAR, and the image quality of the SAR image is significantly deteriorated.

By the way, since the SAR mounted on the satellite is for space use, there are severe restrictions on weight and power consumption. Therefore, it is not appropriate to increase the weight and the power consumption so much especially in the SAR mounted on the satellite.

The present invention has been made in view of the problems of the above-described conventional technique, and can prevent the deterioration of the image quality of the SAR image without significantly increasing the weight and the power consumption. It is an object of the present invention to provide an interferometry SAR system by SAR mounted on a plurality of possible platforms.

[0028]

In order to achieve the above object, the present invention is an interferometry SAR system for performing remote measurement of a target by SAR mounted on each of a plurality of platforms in close proximity to each other. Installed on the ground with multiple GPS satellites that emit reference radio waves,
It is characterized by comprising a DGPS reference station which measures its own position using the GPS satellites and gives the measured position to the SAR position as position information serving as a reference for precise measurement.

Further, one of the SARs is another SA.
A SAR other than the SAR provided with a transmitter and an antenna for transmitting a common original signal for establishing a coherency of a transmission wave to R and for a synchronous operation of transmission and reception. Includes a receiver and an antenna for receiving the original vibration signal.

Each of the SARs operates based on the reference radio wave.

The chirp modulation in each of the SARs is characterized in that one of the adjacent SARs has an up-chirp and the other one has a down-chirp.

(Operation) In the present invention configured as described above, since the respective positions of the SAR are accurately calculated by using the GPS satellites, the interferometry SAR excellent in measurement accuracy is implemented. .

Further, since each of the transmission waves of the plurality of SARs is formed based on the original vibration signal, the SAR
Coherency between them is established.

Further, since each of the plurality of SARs performs the synchronous operation based on the original vibration signal or the reference signal, the reception timing of the Nadia echo of the SAR itself and the reception timing of the reflected wave from the observation area are different in advance. If set, Nadia echoes from other SARs will not be mixed into the reflected wave from the observation area of the SAR itself.

Since one chirp modulation of the adjacent SARs is up-chirp and the other chirp modulation is down-chirp, the level of the unwanted wave mixed in the reflected wave from the observation area of the SAR itself is suppressed. To be done.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a diagram showing a first embodiment of the interferometry SAR system of the present invention.

As shown in FIG. 1, this embodiment is mounted on each of a plurality of platforms (not shown) and performs remote measurement on the target 4 SAR1, SAR2, SAR.
3, a plurality of GPS satellites 5 that emit reference radio waves, and a reference that is installed on the ground and uses the GPS satellites 5 to measure its own position and calculate the precise position of each of SAR1, SAR2, and SAR3. Given as position information
It is composed of a GPS reference station 6.

In the interferometry SAR system configured as described above, the accurate position of each of SAR1, SAR2, and SAR3 is calculated by using the GPS satellite 5 and the DGPS reference station 6, and the calculated position information is calculated. The data measured in SAR1, SAR2, and SAR3 are processed based on the above.

In this embodiment, the number of SARs is 3
However, it is not limited to this.

(Second Embodiment) FIG. 2 is a diagram showing a second embodiment of the interferometry SAR system of the present invention, (a) showing the overall principle, and (b). Is S
It is a figure which shows the operating principle of AR.

As shown in FIG. 2, this embodiment comprises SAR11 and SAR12 mounted on each of a plurality of platforms (not shown) for performing remote measurement on the target 14, and the original vibration signal is transmitted from SAR11 to SAR12. Sent.

Here, the SAR 11 is provided with a transmitter 11b and an antenna 11c for transmitting an original vibration signal,
The SAR 12 has a receiver 12b for receiving the original vibration signal.
And an antenna 12c are provided.

In the interferometry SAR system configured as described above, a common source signal is transmitted from SAR1 to SAR2 for establishing coherency of a transmission wave and for synchronizing operation, and SAR1 and SAR are transmitted.
The coherency with 2 is established and the synchronized operation is performed.

Also, this allows the SARs of different frequencies to be
Interferometry SAR can be realized even in the interim.

(Third Embodiment) FIG. 3 shows an interferometry SA by a plurality of SARs arranged close to each other.
It is a figure showing R.

As shown in FIG. 3, when a plurality of SARs are arranged close to each other, the beam irradiation range 21b of the SAR 21 and the beam irradiation range 2 of the SAR 22 are arranged close to each other.
2b, an overlapping portion is generated, and in the SAR 21, the reflected wave 21c of the radio wave emitted from the SAR 21 itself is emitted from the SAR 22, and the beam irradiation range 21
The reflected wave 22c reflected at b is received.

Here, in the SAR 21, the reflected wave 2
2c is an unnecessary wave, and the quality of the reproduced image is deteriorated by receiving the unnecessary wave.

FIG. 4 shows the interferometry S of the present invention.
It is a figure which shows 3rd Embodiment of AR system, (a) is a schematic block diagram of the whole, (b) is a figure which shows the structure of SAR shown in (a).

As shown in FIG. 4, this embodiment is mounted on each of a plurality of platforms (not shown) and performs remote measurement on a target (not shown) SAR21, SAR.
22 and a plurality of GPS satellites 25 that emit reference radio waves. Each of the SAR 21 and the SAR 22 is shown in FIG.
As shown in (b), a GPS receiver 33 that receives the clock signal 31 transmitted from the GPS satellite 25, and a calculator 34 that calculates a synchronization signal 35 from the clock signal 31.
And a GPS device 37 that calculates the position information 38 of the SAR itself from the clock signal 31 and a SAR device 36 that remotely measures the target based on the synchronization signal 35. The GPS receiver 33 receives radio waves. An antenna 32 for receiving is provided.

In the interferometry SAR system configured as described above, the SAR 21 and the SAR 2 are utilized by using the clock signal 31 transmitted from the GPS satellite 25.
2 is synchronized in the operation with SAR21 and SA
Remote measurement of the target in each of R22 is performed at the same timing.

FIG. 5 is a diagram showing SAR operation timing in the interferometry SAR system shown in FIG.

As shown in FIG. 5, in the present embodiment, S
The AR21 and the SAR22 have the same timing of receiving the Nadia echo. Thereby,
If you set beforehand the reception timing of your own Nadia echo and the reception timing of the reflected wave from the observation area, the Nadia echo due to the SAR installed in close proximity will reflect from your own observation area. It doesn't mix in the waves.

In the present embodiment, when the DGPS is used to determine the position of the platform, the GPS receiver can be diverted, so the only additional hardware that needs to be added is a computing unit that generates a synchronization signal. And the increase in power consumption is small.

In the second embodiment, the SAR
When the original vibration signal is transmitted in order to establish coherency between them, the synchronization signal can be generated based on the original vibration signal, and the synchronous operation becomes possible.

(Fourth Embodiment) FIG. 6 is a diagram showing a chirp modulation characteristic of a transmission wave of SAR, wherein (a) is a diagram showing up-chirp modulation and (b) is a diagram showing down-chirp modulation. Is.

In the present embodiment, the chirp modulation characteristics of the transmission waves of adjacent SARs are made opposite to each other. That is, to explain with reference to FIG. 3, the transmission wave of the SAR 21 is up-chirp-modulated (frequency becomes higher with time).
Then, the transmission wave of the adjacent SAR 22 is down-chirp-modulated (frequency becomes lower with time change). Also,
Conversely, the transmission wave of the SAR 22 may be down-chirp-modulated and the transmission wave of the adjacent SAR 21 may be up-chirp-modulated.

FIG. 7 is a diagram showing a received wave when the chirp modulation characteristics of the transmitted waves of adjacent SARs are made opposite to each other. FIG. 7A is a diagram showing a state before signal compression, and FIG. 7B is a diagram.
FIG. 6 is a diagram showing a state after signal compression.

Here, the pulse compression of SAR is the reception wave and the reference wave (its chirp modulation characteristic is the reverse of the chirp modulation characteristic of the transmission wave (the same as the chirp modulation characteristic of the reception wave)).
When the correlation processing with is performed, the principle that the energy of the received wave that has been diffused in time is concentrated at one point is used.

Therefore, as shown in FIG.
If the chirp modulation characteristics of the transmission waves of the Rs (SAR21, SAR22 (see FIG. 3)) are reversed, when the pulse compression of the reception wave is performed, a signal that is a reflected wave of the irradiation radio wave of the SAR21 (see FIG. 3) The wave 41a becomes the emphasized signal wave 41b because the chirp modulation characteristic is opposite to the chirp characteristic of the reference wave in the pulse compression, and the S wave adjacent to the wave 41a
The unnecessary wave 42a, which is a reflected wave of the irradiation radio wave of the AR 22 (see FIG. 3), has no correlation because it is the same as the chirp characteristic of the reference wave in pulse compression, and becomes an unnecessary wave 42b that is noise without being emphasized.

On the other hand, when the chirp modulation characteristics of the transmission waves of the adjacent SARs are the same, the unnecessary wave is also emphasized.

As described above, when the chirp modulation characteristics of the transmission waves of the adjacent SARs are reversed, compared to the case where the chirp modulation characteristics of the transmission waves of the adjacent SARs are the same, the signal wave after compression is The ratio between the level of 41b and the level of the unwanted wave 42b increases by the compression ratio of pulse compression.

Further, in the polarimetric SAR by applying the above-described technique, the chirp characteristics of the vertically polarized waves and the horizontally polarized waves which are alternately transmitted are reversed so that the transmitted waves having different polarized waves are generated. It is possible to suppress mixing of unnecessary waves.

FIG. 8 is a diagram showing an example in which the interferometry SAR system in the first, third and fourth embodiments is applied.

This embodiment, as shown in FIG. 8, is mounted on each of a plurality of platforms (not shown), and SAR51, SAR52, and
SAR53 and a plurality of GPS satellites 55 that emit reference radio waves
And a DGPS reference station 56 that is installed on the ground and uses the GPS satellite 55 to measure its own position and provides it as position information that serves as a reference for calculating the precise position of each of SAR51, SAR52, and SAR53. ing.

[0066]

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

According to the first aspect, the SAR
Since each of the positions is accurately calculated using the GPS satellite and the DGPS reference station, the measurement accuracy in the interferometry SAR system can be improved even when the SAR is mounted on each of the plurality of platforms.

It also allows the use of small platforms.

According to the second aspect of the invention, since the operation in each of the plurality of SARs is performed based on the original vibration signal emitted from one SAR, the plurality of SARs are
The coherency between the transmission waves of 1 is established, the measurement accuracy of the interferometry SAR can be improved, and the synchronization operation of the transmission / reception timing is established, and mixing of Nadia echo due to the transmission waves of other SARs can be avoided. In addition, interferometry SAR can be realized especially between SARs having different frequencies.

According to the third aspect, the operation in each of the plurality of SARs is performed based on the reference radio wave emitted from the GPS satellite, and therefore, the same effect as the synchronous operation in the second aspect is obtained.

According to the fourth aspect of the present invention, one of the adjacent SARs has the chirp modulation as the up-chirp and the other chirp modulation as the down-chirp, so that it is mixed in the reflected wave from the observation area of the SAR itself. It is possible to suppress the level of unwanted waves that occur.

With the above effects, it is possible to prevent the deterioration of the image quality of the SAR image without significantly increasing the weight and the power consumption.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of an interferometry SAR system of the present invention.

FIG. 2 is a diagram showing a second embodiment of the interferometry SAR system of the present invention, (a) showing the overall principle, and (b) showing the operating principle between SARs. .

FIG. 3 is a diagram showing an interferometry SAR with a plurality of SARs arranged in close proximity.

FIG. 4 is a diagram showing a third embodiment of an interferometry SAR system of the present invention, (a) is a schematic configuration diagram of the whole, and (b) is a diagram showing a configuration of the SAR shown in (a). Is.

5 is a diagram showing SAR operation timing in the interferometry SAR system shown in FIG.

6A and 6B are diagrams showing chirp modulation characteristics of a transmission wave of SAR, FIG. 6A is a diagram showing up-chirp modulation, and FIG. 6B is a diagram showing down-chirp modulation.

FIG. 7 is a diagram showing a received wave when the chirp modulation characteristics of the transmitted waves of adjacent SARs are made opposite to each other,
(A) is a figure which shows the state before signal compression, (b) is a figure which shows the state after signal compression.

FIG. 8 is a diagram showing an example to which the interferometry SAR system in the first, third and fourth embodiments is applied.

FIG. 9 Cross-track interferometry SAR
It is a figure which shows the concept of.

[Figure 10] Along track interferometry S
It is a figure which shows AR, (a) is a conceptual diagram, (b) is a figure which shows a measurement principle.

[Explanation of symbols]

1-3, 11, 12, 21, 21, 22, 51-53 SA
R 4,14,54 Target 5,25,55 GPS satellite 6,56 DGPS reference station 11a, 12a SAR signal 21b, 22b Beam irradiation range 21c, 22c Reflected wave 31 Clock signal 32 Antenna 33 GPS receiver 34 Arithmetic unit 35 Sync signal 36 SAR device 37 GPS device 38 Position information 41a, 41b Signal wave 42a, 42b Unwanted wave

Claims (4)

[Claims] 1. An interferometry SAR system for performing remote measurement of a target by SAR mounted on each of a plurality of platforms that are close to each other, and a plurality of GPS satellites that emit reference radio waves and are installed on the ground. An SA mounted on a plurality of platforms, comprising: a DGPS reference station that measures its own position using the GPS satellites and provides it as position information that serves as a reference for precise measurement of the SAR position.
R interferometry SAR method. 2. The interferometry SAR system by SAR mounted on the plurality of platforms according to claim 1, wherein one of the SARs is for establishing coherency of a transmission wave with respect to another SAR and for transmitting and receiving. SAR other than the SAR including the transmitter and the antenna for transmitting a common source signal for the synchronous operation of
Is an interferometry SAR system by SAR mounted on a plurality of platforms, which is equipped with a receiver and an antenna for receiving the original vibration signal. 3. The interferometry SAR system based on SAR mounted on a plurality of platforms according to claim 1, wherein each of the SARs operates based on the reference radio wave. Interferometry SAR method by SAR. 4. The interferometry SAR system by SAR mounted on the plurality of platforms according to claim 1, wherein the chirp modulation in each of the SARs is performed by one of the adjacent SARs. SA mounted on multiple platforms, characterized in that the modulation is up-chirp and the other one is down-chirp
R interferometry SAR method.