JP3987451B2 - Ground surface fluctuation measurement method using synthetic aperture radar - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is based on the ground surface of a measurement target point by performing synthetic aperture interference processing on the ground surface reflected wave of a pulsed radio wave emitted from a synthetic aperture radar (SAR) mounted on a flying object such as an artificial satellite. The present invention relates to a method for measuring a fluctuation amount. Although this technique is not specifically limited, For example, it is useful for the remote measurement of the minute ground surface fluctuation amount, such as investigation of a landslide sign.
[0002]
[Prior art]
[Patent Document 1]
Japanese Patent Laid-Open No. 7-72244
One technique for observing the ground surface is to use a synthetic aperture radar mounted on a flying object such as an aircraft or an artificial satellite. This is an advanced signal processing called synthetic aperture interference processing that emits a short pulse radio wave obliquely downward and perpendicular to the direction of travel from a navigating projectile and receives a reflected wave from the ground surface. This is a technique for observing the properties of the earth's surface. Note that this synthetic aperture interference processing is similar to triangulation using a phase difference between two reflected wave signals received from two spatially separated antennas. This is a method for obtaining the direction and distance of an object based on the principle.
[0004]
In the measurement by the synthetic aperture radar, there are a method in which a plurality of synthetic aperture radars are mounted on a single flying object, or a method in which a synthetic aperture radar is mounted on each of a plurality of flying objects. As another simpler system, there is a method using only one flying object equipped with one synthetic aperture radar. Since this method uses only the same synthetic aperture radar, there is essentially no variation in characteristics and is effective in improving measurement accuracy.
[0005]
This type of Synthetic Aperture Radar enables observation with very high resolution, even when using a small antenna, virtually the same as when a large antenna is used. Unlike optical cameras, it can be observed day and night and in all weather. It has excellent characteristics such as being. Therefore, for example, Patent Document 1 discloses that, for example, earthquake prediction, volcanic eruption prediction, debris flow prediction, etc., using two antennas mounted on a flying object, simultaneously outputting a transmission wave and simultaneously inputting a reception wave. In addition, an interferometric synthetic aperture radar apparatus and a terrain change observation method that are applicable to a field that requires extraction of subtle terrain fluctuations with an accuracy of several centimeters are disclosed.
[0006]
By the way, even if only one artificial satellite equipped with a single synthetic aperture radar is used, it is possible to identify on the ground surface by performing synthetic aperture interference processing on the ground surface reflected wave of the pulsed radio wave emitted from the synthetic aperture radar. It is possible to measure the fluctuation amount of the point (measurement target point). For example, a method is used in which one radio wave reflector is installed at the measurement target point, a reflected wave is acquired twice in either an ascending or descending orbit, and synthetic aperture interference processing is performed using the reflected wave data. is there. With the progress of technological development in recent years, measurement accuracy has been further improved, and measurement accuracy of cm order or less has been obtained.
[0007]
[Problems to be solved by the invention]
As described above, the surface observation by the synthetic aperture radar has an excellent feature that it can be measured in all weather regardless of day and night, and can be performed with high accuracy. However, the fluctuation amount of the ground surface obtained by the conventional method is only the fluctuation amount in the oblique direction connecting the satellite on the orbit and the radio wave reflector, and the presence or degree of the ground surface fluctuation can be detected. The actual amount of variation along the line cannot be determined. Therefore, it was not possible to accurately measure minute displacements along the ground surface, such as observing signs of landslides.
[0008]
As a method for directly measuring a change at a specific point on the ground surface, a GPS satellite may be used. Since the position of a specific point on the ground surface can be obtained directly by using a GPS satellite, if the position is measured by a GPS satellite at an arbitrary time point and compared with the past position, in principle, the position to be measured The amount of surface fluctuation can be obtained directly. However, at present, the position measurement by the GPS satellite is low in accuracy, and cannot meet the required accuracy of the order of cm or less necessary for predicting landslides. In addition, since measurement is performed using a plurality of GPS satellites, there is an influence such as variation in characteristics due to the combination of the satellites, and thus the accuracy is not essentially improved, and it is not suitable for measuring minute ground surface fluctuations.
[0009]
An object of the present invention is to use a single synthetic aperture radar mounted on a flying object, and to obtain an actual fluctuation amount along a ground surface of a measurement target point such as a sign of landslide with high accuracy. It is to provide a variation measurement method. Another object of the present invention is suitable for implementation of a method for measuring the amount of ground surface fluctuation using a synthetic aperture radar, and is not buried even during snowfall, so that ground surface fluctuation can be continuously measured regardless of the season. It is an object to provide a radio wave reflecting structure in which the reflection characteristics are hardly deteriorated due to the influence of rainwater or the like.
[0010]
[Means for Solving the Problems]
The present invention relates to a method for determining a ground surface fluctuation amount by performing synthetic aperture interference processing on a ground-surface reflected wave of a pulsed radio wave emitted from a single synthetic aperture radar mounted on a flying object. A ground structure is provided on the ground surface, a pair of radio wave reflectors are provided on the base, one is in the direction to reflect the radio wave emitted by the synthetic aperture radar on the ascending orbit, and the other is the synthetic aperture on the descending orbit Installed in the direction to reflect the radio waves emitted by the radar, and obtained the distance from the ascending orbit to the measurement target point by performing synthetic aperture interference processing of the reflected waves acquired twice in the ascending orbit, and descending orbit The distance from the descending trajectory to the measurement target point is obtained by performing synthetic aperture interference processing between the reflected waves acquired twice in step 1, and both the distance data are satisfied at the same time and the ground surface fluctuation direction specified on the ground structure is determined. The conditions It is ground surface variation measurement method using a synthetic aperture radar, characterized in that determining the amount of variation from the past position along the ground surface of the measurement object point by obtaining.
[0011]
Here, the “flying object” refers to a platform that navigates outer space in polar orbit, such as an artificial satellite or a space shuttle. In the present invention, measurement can be performed using only one flying object, which is preferable. However, the ascending and descending orbits can be measured using different flying objects.
[0012]
The condition of the fluctuation direction of the ground surface specified by the ground structure typically includes a condition that the landslide fluctuation occurs along the maximum slope line of the slope, and the amount of landslide fluctuation can be obtained thereby. In addition, when the fluctuation direction of the ground surface is limited due to the presence of active faults, this direction is added as a condition for the fluctuation direction of the ground surface.
[0013]
Moreover, this invention is a radio wave reflection structure used with the ground surface fluctuation amount measuring method using such a synthetic aperture radar. The radio wave reflecting structure includes a tower-type base body having a rigid structure standing on the ground surface and a pair of radio wave reflectors installed in opposite directions on the base body, and the base body is covered with a radio wave absorber. However, the radio wave reflector has a structure that is installed in the middle and upper stages, adjusted to a height not buried in the snow.
[0014]
Here, the radio wave reflector is composed of, for example, a corner reflector formed by combining three right-angled isosceles triangular metal plates and joining the right-angle portions to each other, and the opening of the corner reflector has a water repellency. The structure is closed by the body. Alternatively, the radio wave reflector may be composed of a corner reflector formed by combining three right-angled isosceles triangular metal plates and joining the right-angle portions to each other to form a triangular pyramid, and a drain hole is formed at the bottom of the corner reflector. In addition, it is possible to use a flat radio wave reflector.
[0015]
【Example】
FIG. 1 is an explanatory diagram showing an embodiment of a ground surface variation measuring method using a synthetic aperture radar according to the present invention. A radio wave reflecting structure 14 having a pair of radio wave reflectors 12a and 12b is installed on the ground surface 10 to be measured so as not to move. Then, a pulsed radio wave is emitted from the synthetic aperture radar 18 mounted on the artificial satellite 16, and the reflected waves from the radio wave reflectors 12a and 12b installed on the ground surface to be measured are received and the synthetic aperture is received. Interference processing. By using this result, the fluctuation amount of the ground surface is obtained. There is only one artificial satellite 16 used in this embodiment, and only one synthetic aperture radar 18 needs to be mounted thereon.
[0016]
In the method of the present invention, both the reflected wave data from the radio wave reflector 12a received by the artificial satellite 16 during the ascending orbit travel and the reflected wave data from the radio wave reflector 12b received by the same artificial satellite 16 during the descending orbit navigation. Is used. Therefore, as shown in the figure, a pair of radio wave reflectors 12a and 12b are attached to the radio wave reflecting structure 14 in opposite directions. In FIG. 1, A shows the state during the ascending orbit, and B shows the state during the descending orbit. Accordingly, one radio wave reflector 12a reflects the radio wave emitted by the synthetic aperture radar 18 on the ascending trajectory, and the other radio wave reflector 12b reflects the radio wave emitted by the synthetic aperture radar on the descending orbit. , Each orientation is adjusted.
[0017]
In the present embodiment, the radio wave reflecting structure 14 includes a tower-type base body 20 having a rigid structure that is firmly erected on the ground surface 10 to be measured, and a pair of the base-type base bodies 20 that are installed in opposite directions on the tower-type base body 20. It consists of radio wave reflectors 12a and 12b. The tower-type base body 20 has a rigid structure that does not bend even when wind or snow acts. For example, three pillars 22 are arranged so as to form a triangular prism, and shelves 24a, 24b is fixed, and one radio wave reflector 12a is attached to the middle shelf 24a, and the other radio wave reflector 12b is attached to the upper shelf 24b. When the tower base 20 is installed particularly in a snowy area, the length of the column 22 and the height of the shelves 24a and 24b are adjusted so that both radio wave reflectors 12a and 12b are not buried in the snow.
[0018]
In the method of the present invention, the artificial satellite 16 carrying the synthetic aperture radar 18 travels in a polar orbit. The synthetic aperture radar 18 emits a short pulse-shaped radio wave (for example, C band: frequency 5.3 GHz) toward the ground surface obliquely downward (for example, the lower left side) perpendicular to the traveling direction at regular intervals. Thus, for example, in an ascending orbit (orbit from the south side to the north side), radio waves are incident from the east side and reflected by one radio wave reflector 12a, and in a descending orbit (orbit from the north side to the south side) A radio wave enters and is reflected by the other radio wave reflector 12b. The emission direction of the radio wave from the synthetic aperture radar 18 mounted on the artificial satellite 16 is determined, and the orbit of the artificial satellite 16 is determined (orbital deviation can be corrected). Therefore, both trajectory data and image data are acquired, and necessary analysis is performed based on them.
[0019]
In the present invention, the reflected wave data is acquired twice in the ascending orbit, and the reflected wave data is also acquired in the descending orbit. Then, by performing synthetic aperture interference processing on the reflected waves obtained in the ascending orbit, the distance from the artificial satellite 16 on the ascending orbit to the measurement target point can be obtained with an accuracy of cm order or less. Similarly, by performing synthetic aperture interference processing on the reflected waves obtained in the descending orbit, the distance from the artificial satellite 16 on the descending orbit to the measurement target point can be obtained with an accuracy of cm order or less. Therefore, if there is a difference between the past measurement results, the difference is caused by the ground surface fluctuation during that time.
[0020]
FIG. 2 is a conceptual diagram showing how to determine the actual ground surface variation by the method of the present invention. A measurement target point (past position) before the change is represented by P1. Assuming that the linear distance between the satellite position Sa on the ascending orbit before the change and the measurement target point P1 is La0, the distance after the change after a certain time can be expressed by La0 + da. At this time, the changed measurement target point is located somewhere on the spherical surface 30 having a radius La0 + da centered on the artificial satellite position Sa on the ascending orbit. Similarly, it is assumed that the linear distance between the satellite position Sd on the descending orbit before the change and the measurement target point P1 is Ld0 and changes to Ld0 + dd after the change. Then, the measurement target point after the change is located somewhere on the spherical surface 32 having the radius Ld0 + dd centered on the satellite position Sd on the descending orbit. Here, the circle 34 represents an intersection line between the one spherical surface 30 and the other spherical surface 32, and is a set of points that simultaneously satisfy the measurement value in the ascending orbit and the measurement value in the descending orbit. Therefore, the measurement target point after the change exists somewhere on the circle 34. However, it is not possible to specify the actual measurement target point by itself.
[0021]
Therefore, in the present invention, the ground structure at the measurement target point is taken into consideration, and the fluctuation direction of the ground surface specified on the ground structure is added as a condition. That is, the direction in which the ground surface moves (or the direction in which it can move) is assumed from the viewpoint of geotechnical engineering. Here, since the purpose is to observe a sign of landslide on the slope, it is assumed that the measurement target point is on the slope. Then, it can be assumed that the fluctuation of the ground surface occurs in the direction along the maximum slope line of the slope (the direction indicated by the arrow 36). When this condition is added, the intersection P2 between the maximum inclination line direction 36 and the circle 34 is obtained from the measurement target point P1 before the change, and this point P2 indicates the actual measurement target point after the change. In this way, it is possible to measure the actual fluctuation amount along the ground surface of the measurement target point.
[0022]
In the above explanation, since the purpose is to observe the landslide sign of the slope, it is assumed that the measurement target point is on the slope, and that the ground surface changes along the maximum slope line of the slope. When the method of the present invention is applied to, for example, ground surface fluctuation amount measurement in an active fault zone, for example, it is possible to specify the measurement target point after the fluctuation by assuming that the ground surface fluctuation occurs along the active fault. The actual amount of fluctuation along the ground surface can be measured.
[0023]
As shown in FIG. 1, the radio wave absorption structure used in the method of the present invention includes a tower-type base body 20 having a rigid structure standing on the ground surface and a pair of tower-type base bodies 20 installed in opposite directions to each other. A structure composed of the radio wave reflectors 12a and 12b is desirable. The tower base 20 is preferably coated with a radio wave absorber or affixed to the pillars 22 and the shelves 24a and 24b, so that the tower type substrate 20 can be separated from parts other than the radio wave reflectors 12a and 12b. Unnecessary reflected waves can be suppressed. In addition, by attaching both radio wave reflectors 12a and 12b to the middle and upper stages, they can be installed at the same point, and by adjusting the height, observation can be continued throughout the four seasons without being buried in snow. It becomes.
[0024]
The radio wave reflector may be a radio wave reflector, but as shown in FIG. 3, three right-angled isosceles triangular metal plates 40 are combined in a triangular pyramid shape, and the right-angle portions of these metal plates 40 are joined by welding or the like. The corner reflector 42 is preferred. At the time of installation, the orientation and the like are adjusted so that the opening faces the position of the artificial satellite. As a result, the synthetic aperture radar radio wave can be returned toward the artificial satellite in a direction corresponding to the incident direction.
[0025]
Such a corner reflector 42 may cover the opening with a radio wave transmitting plate 44 as shown in FIG. 3A in order to prevent rain or snow from entering the opening. In that case, it is preferable that the plate material 44 is made of a water-repellent material or a water-repellent film is provided on the surface of the plate material 44 so that rain or snow does not adhere to the surface of the radio wave permeable plate material 44. . When the opening is not covered, as shown in FIG. 3B, a small-diameter drain hole 46 is formed in the bottom bottom of the corner reflector 42 so that rainwater and the like that have entered from the opening can be quickly discharged. preferable.
[0026]
In the present invention, not only passive radio wave reflectors such as corner reflectors and radio wave reflectors but also active radio wave reflectors such as transponders can be used as radio wave reflectors. In that case, by using an omnidirectional antenna, it is also possible to use a single transponder to reflect synthetic aperture radar radio waves in both ascending and descending orbits. However, since the transponder has a function to amplify and transmit the received radio wave, the electrical characteristics may change depending on the environmental temperature, etc., and sufficient accuracy in the synthetic aperture interference processing that measures by the phase difference It is actually quite difficult to secure. In view of such circumstances, as described in the embodiment, a method using a passive radio wave reflector, particularly a corner reflector is preferable because it is inexpensive, has good and stable reflection performance, and is easy to install. .
[0027]
【The invention's effect】
As described above, the present invention uses a synthetic aperture radar and a pair of radio wave reflectors to perform ascending and descending orbits by performing synthetic aperture interference processing on the ground surface reflected waves in the ascending and descending orbits. In this method, the distance from the measurement target point to the measurement target point is obtained, and the condition of the fluctuation direction of the ground surface is further added and processed. Therefore, the actual fluctuation amount along the ground surface can be accurately obtained. In the present invention, in particular, since the measurement can be performed by one artificial satellite mounted synthetic aperture radar, there is an advantage that measurement values are less varied, the accuracy is improved, and the measurement can be performed at low cost.
[0028]
In addition, the radio wave reflecting structure according to the present invention can be configured so that the radio wave reflector is not buried even during snowfall, and therefore it is possible to continuously measure ground surface variations regardless of the season. In addition, by covering the opening of the corner reflector with a radio wave permeable plate or providing a drain hole at the bottom of the corner reflector, it is less susceptible to the effects of snow, rainwater, etc., and changes or deterioration of the reflection characteristics are less likely to occur. Therefore, it becomes possible to carry out good measurement continuously over a long period of time.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an embodiment of a ground surface variation measuring method according to the present invention.
FIG. 2 is a conceptual diagram showing how to determine the actual ground surface fluctuation amount by the method of the present invention.
FIG. 3 is an explanatory diagram showing a structure example of a radio wave reflector.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Ground surface 12a, 12b used as measurement object Radio wave reflector 14 Radio wave reflection structure 16 Artificial satellite 18 Synthetic aperture radar 20 Tower type base | substrate

Claims (5)

In a method for determining the amount of fluctuation of the ground surface by performing synthetic aperture interference processing on the ground surface reflected wave of the pulsed radio wave emitted from one synthetic aperture radar mounted on the flying object,
A rigid base is provided on the ground surface to be measured, and a pair of radio wave reflectors are provided on the base, one in a direction to reflect radio waves emitted by the synthetic aperture radar on the ascending orbit, and the other on the descending orbit. Installed in a direction to reflect the radio wave emitted by the synthetic aperture radar, and by performing synthetic aperture interference processing of the reflected waves acquired twice in the ascending orbit, the distance from the ascending orbit to the measurement target point is obtained, Obtain the distance from the descending trajectory to the measurement target point by performing synthetic aperture interference processing between the reflected waves acquired twice in the alternating trajectory, and satisfy both distance data at the same time and change the ground surface specified in the ground structure A ground surface variation measuring method using a synthetic aperture radar, characterized in that a variation amount from a past position along a ground surface of a measurement target point is obtained by adding a direction condition. The composition according to claim 1, wherein the condition of the direction of fluctuation of the ground surface specified by the ground structure is a condition that the landslide fluctuation occurs along the maximum slope line of the slope, and the amount of landslide fluctuation is obtained by adding the condition. Ground surface fluctuation measurement method using aperture radar. A radio wave reflecting structure used in a ground surface variation measuring method using the synthetic aperture radar according to claim 1 or 2,
A tower-type base body having a rigid structure standing on the ground surface and a pair of radio wave reflectors installed opposite to each other on the base body, the base body being covered with a radio wave absorber, and the radio wave reflector being snow covered Radio wave reflection structure for measuring ground surface fluctuations installed in the middle and upper tiers, adjusted to a height that is not buried in the ground. The radio wave reflector consists of a corner reflector made by combining three right-angled isosceles triangular metal plates and joining the right-angled parts to each other, and the opening of the corner reflector is closed with a radio wave-transmitting material exhibiting water repellency. The radio wave reflecting structure for measuring the amount of ground surface fluctuation according to claim 3, wherein The radio wave reflector is composed of a corner reflector formed by combining three right-angled isosceles triangular metal plates and joining the right-angle portions to each other, and a drain hole is formed at the bottom of the corner reflector. The radio wave reflecting structure for measuring the ground surface fluctuation amount described.

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