JP2632653B2 - Depth measuring 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 depth measuring apparatus mounted on a flying object such as a lunar orbiting satellite for measuring the depth and thickness distribution of a surface structure having a known permittivity of an object to be observed. .

[0002]

2. Description of the Related Art Conventionally, as a device mounted on a flying object such as a lunar orbiting satellite and measuring the thickness of a surface structure of an object to be observed, it is mounted on a lunar orbiting satellite of Apollo 11 in the United States. There is a lunar subsurface radar system that measures the thickness of topsoil (regolith) covering the moon surface. As shown in the schematic diagram of FIG. 4, this radar device is mounted on a lunar orbiting satellite 1, uses a transmitting pulse of a single frequency from a transmitting / receiving unit 2, and has a relatively small aperture due to restrictions on mounting. From 3,
It is configured to transmit toward the lunar surface 4, receive echo signals from the first surface 4-1 and the second surface 4-2 of the lunar surface 4, and observe the thickness and the like of the regolith.

[0003]

However, when the lunar surface is observed from a height away from the lunar surface using the radar device having such a configuration, the end of the beam pattern 5 of the antenna 3 (mostly from the antenna 3). While the echo signal f _A ′ for the transmission pulse signal f from one intersection A between the long distance portion and the first surface 4-1 of the lunar surface 4 does not reach the transmission / reception unit 2, the antenna 3 Intersection B between the vertical axis 6 lowered to the moon surface 4 and the second surface 4-2 (the antenna 3 and the second
Most distance between the surface 4-2 'arrived, yet the echo signal f _A from point A of the first surface of the moon' echo signal f _B from short section) towards the power of, the second surface B Since the echo signal from the point is much larger than f _B ′, f _B ′ is buried in f _A ′, and it is difficult to separate f _B ′. This aspect is shown in the timing chart of FIG.
In FIG. 5, f _H ′ is a vertical axis 6 lowered to the lunar surface 4.
5 shows an echo signal from an intersection H between the first surface 4-1 of the moon surface and the first surface 4-1.

[0004] As described above, the echo signal from the underground in the direction of the point directly below the satellite serving as the target regolith thickness information is buried in the echo signal from the side of the beam caused by the width of the transmission beam. As a result, there is a problem that the thickness of the regolith cannot be observed.

To avoid this, it is necessary to physically distinguish the echo signal f _A ′ from point _A and the echo signal f _B ′ from point _B in the transmission / reception section, and f _A ′ reaches the transmission / reception section. After that, f _B ′ must arrive.
In order to realize this, it is generally necessary to form a very narrow beam so as not to include an echo signal in the direction of the point A, which requires a large aperture antenna and a satellite altitude h ( In order to identify the thickness δh (about 5 m) of the regolith, which is said to be considerably thinner than, for example, 100 km), a very narrow transmission pulse width is required, and it is extremely difficult to realize the radar apparatus.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem of a conventional radar apparatus for performing underground exploration and the like.
It is an object of the present invention to provide a depth measuring device capable of measuring an observation target in a depth direction with high accuracy without using a large-aperture antenna.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is mounted on a flying object such as a lunar orbiting satellite , and when measuring depth using a radar device, the beam is used.
The echo signal of the measurement target point is included in the echo signal from the side.
From a position away from the more observation object surface is buried in the depth measuring device for measuring the dielectric constant of the depth of the known surface structure of the observed object surface soil for covering the lunar surface, the function of changing a frequency an oscillator to be <br/> oscillation source of continuous or pulsed traveling wave with an antenna for radiating the observation object surface direction as the transmission radio wave traveling wave output from the oscillator is output from the oscillator Directional coupler for separating the traveling wave and the transmitted radio wave radiated from the antenna from the surface of the object to be observed and the lower surface of the surface structure and separating the reflected wave received by the antenna, and the direction. Traveling wave detector for detecting a traveling wave through a sexual coupler and the direction
A reflected wave detector for detecting the reflected wave via a sexual coupler;
And a standing wave measuring device for calculating a voltage standing wave ratio based on a ratio between outputs of the traveling wave detector and the reflected wave detector.

As described above, the resonance state of the reflected wave in the surface structure is detected at the time when the voltage standing wave ratio becomes the minimum, and the free space wavelength and the observation based on the principle of the standing wave measurement method such as the permittivity are measured. A resonance wavelength in the surface structure associated with the dielectric constant of the surface structure of the object is obtained, and the depth of the surface structure can be determined with high accuracy from the resonance wavelength.

[0009]

Next, an embodiment will be described. First, before describing the embodiments, the principle of the “method of measuring a standing wave such as a dielectric constant” applied in the present invention will be described. As shown in FIG. 1, this measuring method uses a rectangular waveguide (TE ₁₀ waves) 11
A rectangular parallelepiped sample 12 is placed inside the waveguide 11 so as to fill the inside of the waveguide 11, and both end faces are arranged so as to be perpendicular to the axis of the waveguide 11. Then, a state is created in which only the sample 12 resonates with a traveling wave of a certain wavelength, and a material property of the sample 12 such as a dielectric constant or a dielectric loss is measured from the length L of the sample 12 at that time. This is a well-known technique as shown in the Space and Aeronautical Research Institute of the University of Tokyo, Vol. 4, No. 3, (B) pp. 476-482. In the apparatus used for this measurement, as shown in FIG.
A frequency variable oscillator 13 is provided at one end and a non-reflection terminator 14 is provided at the other end. A standing wave measuring device 15 comprising a directional coupler and a detector is provided in front of the position where the sample 12 is arranged.
Is arranged. Further, a wavelength meter 16 is provided near the oscillator 13.
Is arranged, and a variable attenuator 17 is arranged in the waveguide 11 between the oscillator 13 and the standing wave measuring device 15.

Next, a description will be given of a measuring operation in the measuring apparatus thus configured. The frequency of the traveling wave transmitted from the oscillator 13 is changed (swept), and the ratio of the traveling wave from the oscillator 13 to the reflected wave from the sample 12, that is, the voltage, is measured by the standing wave measuring device 15 for each frequency. Measure the standing wave ratio (VSWR). At the frequency f _{0 at} which the voltage standing wave ratio is minimum, the sample 12 having the thickness L is １ ／.
It is considered that the traveling wave from the oscillator 13 passes through the sample 12 and is absorbed by the non-reflection terminator 14, which is a load.

At this time, the wavelength L _go of the traveling wave in the resonance tube composed of the waveguide in which the sample 12 is disposed, and the thickness L of the sample 12
Has the relationship shown in the following equation (1). n × (L _go / 2) = L (1) where n is an integer, and n is determined by performing measurement on several samples having different thicknesses L. Can be.

On the other hand, in microwave engineering, it is well known that there is a relationship expressed by the following equation (2) between the wavelength L _go of the traveling wave in the resonance tube and the complex permittivity ε of the sample 12. I have. L _go = L _m ｛ε− (L _m / L _c ) ² ｝ ^1/2 (2) where L _m is a free space wavelength, and L _c is a cutoff wavelength of the waveguide. is there.

Therefore, from the above equations (1) and (2),
Sample 12 thickness L, free space wavelength _Lm , cutoff wavelength L
_{Once c} is known, the complex permittivity ε can be determined.

The present invention is intended to apply this measurement principle to the measurement of an object to be observed not from a waveguide scale but from a flying object such as an artificial satellite. When applying to the measurement of the regolith depth of
The equivalent of the waveguide is the free space between the lunar orbiting satellite and the lunar surface, and the equivalent of the sample is the regolith covering the lunar surface.

Next, a specific embodiment of the present invention will be described. In this embodiment, the present invention is applied to the measurement of the thickness of a regolith covering a lunar surface. FIG. 2 shows a conceptual diagram of the measurement mode, and FIG. 3 shows a configuration of a measurement device. In FIG. 2, reference numeral 21 denotes a lunar orbiting satellite having a satellite altitude h, and the satellite 21 is equipped with a depth measuring device. As shown in FIG. 3, the depth measuring device includes a variable frequency oscillator 22, an antenna 24 that radiates a traveling wave transmitted from the oscillator 22 via a directional coupler 23 as a transmission radio wave, and a directional coupling. It comprises a traveling wave detector 25 and a reflected wave detector 26 connected to the detector 23. The traveling wave output from the variable frequency oscillator 22 may be either a pulsed wave like a conventional radar device or a continuous wave (CW wave), and the frequency is such that it can easily dive into the regolith on the lunar surface. In this case, a VHF band of 300 MHz or less (wavelength of 1 m or more) is used. Also, the directional coupler 23
Has a function of separating and extracting the traveling wave transmitted from the oscillator 22 and the reflected wave reflected by the first surface and the second surface of the moon and received by the antenna 24. With the coupler 23, the traveling wave detector 25, and the reflected wave detector 26,
The standing wave measuring device 27 is configured. As the antenna 24,
A similar radar antenna having a size of about 2 to 10 m is used.

In the depth measuring device having such a configuration,
When a traveling wave is transmitted from the variable frequency oscillator 22, the traveling wave detector 25 detects the strength of the traveling wave via the directional coupler 23, and radiates as a radio wave from the antenna 24 toward the moon 31. You. The reflected wave reflected from the first surface 31-1 or the second surface 31-2 of the moon surface 31 is received by the antenna 24, and is separated from the traveling wave by the directional coupler 23 and separated as a reflected wave component. , The intensity of which is detected by the reflected wave detector 26. By calculating the ratio of the signals detected by the detectors 25 and 26, the voltage standing wave ratio is obtained.

A radio wave radiated from the antenna 24 enters the regolith 32 from the lunar surface 31, and a reflected wave corresponding to the depth of the radio wave reflected by the second surface 31-2 of the lunar surface corresponds to the depth of the regolith 32. L and the wavelength in the regolith 32 (corresponding to the wavelength in the resonance tube) L
_When the relation of _go becomes a frequency satisfying the expression (1),
Resonance occurs in the regolith 32 and does not return to the antenna 24 side. Therefore, in this case, the reflected wave component detected by the reflected wave detector 26 in the standing wave measuring device 27 disappears apparently, and shows the minimum value as the voltage standing wave ratio. At frequencies that do not resonate, the first surface 31-1 and the second surface 31 of the moon surface 31
Since the two reflected wave components from -2 are mixed, the level of the voltage standing wave ratio is always higher than the level at the time of resonance.
Therefore, it is possible to confirm that the resonance state is established when the minimum value of the voltage standing wave ratio level is detected.

In the standing wave measurement method applied to the present invention, the dielectric constant is originally determined from the length of the sample as described above. The depth L of the corresponding regolith is obtained, and the dielectric constant of the regolith in this case is a value obtained from a sample brought back by the Apollo probe returned after landing on the moon (referred to as about 2.0). Used. In addition, the integer n in the equation (1) can be determined as a harmonic relationship of resonance from the wavelengths at which a plurality of voltage standing wave ratios are minimized by varying the frequency of the oscillator.

Since there is no cut-off wavelength in free space corresponding to the cut-off wavelength I _c of the waveguide in the equation (2), the cut-off wavelength is treated as I _c = ∞. Therefore, in the present invention, the above equation (2) is modified to be expressed as the following equation (3). L _go = L _m / ε ^1/2 (3) As described above, at the time of resonance at which the voltage standing wave ratio is minimized, from equations (3) and (1), Regolith 32 depth L
Is required.

At this time, only the component perpendicular to the surface of the reflected wave of the signal entering the moon and ground returns, and the other components are irregularly reflected on the surface. Therefore, unlike the case of the VHF radar mounted on the Apollo spacecraft, the measurement accuracy (resolution in the depth direction) is not restricted by the aperture size, beam width, and the like of the antenna.

In the above embodiment, the present invention is applied to the underground exploration of the moon to measure the depth of a regolith. However, the present invention is not limited to this, and the present invention is not limited to this. Even in the case of a body radar, there is a case where a side echo and a target echo overlap. For example, the radar is applicable to a wide range such as underwater exploration from the aircraft, underground exploration, and the like.

Further, the standing wave measuring device 27 in the above embodiment is used.
In, the attenuator can be placed before the traveling wave detector 25, or the amplifier can be placed before the reflected wave detector 26, and it is possible to detect the change of the standing wave ratio with higher accuracy. Become.

[0023]

As described above with reference to the embodiments,
According to the present invention, using a continuous wave or a pulse wave, applying the principle of measuring a standing wave, the surface structure of the object to be observed which was difficult in principle with a conventional lunar subsurface radar system or the like And a depth measuring device that does not require a long antenna and can be easily mounted on a flying object.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of a standing wave measuring method such as a dielectric constant.

FIG. 2 is a conceptual diagram showing an example of a depth measurement mode by the depth measurement device according to the present invention.

FIG. 3 is a schematic configuration diagram showing an embodiment of a depth measuring device according to the present invention.

FIG. 4 is a schematic diagram showing a configuration example of a conventional lunar subsurface radar device.

FIG. 5 is a timing chart for explaining the operation and problems of the conventional example shown in FIG.

[Explanation of symbols]

 11 Waveguide 12 Sample 13 Variable frequency oscillator 14 Non-reflective terminator 15 Standing wave measuring instrument 16 Wavelength meter 17 Variable attenuator 21 Lunar orbiting satellite 22 Frequency variable oscillator 23 Directional coupler 24 Antenna 25 Traveling wave detector 26 Reflected wave detector 27 Standing wave measuring instrument

Claims (1)

(57) [Claims] Claims: 1. Mounted on a flying object such as a lunar orbiting satellite,
In the case of depth measurement with a radar device, from the side of the beam
Echo signal at the measurement target point is buried in the echo signal of
From a position away from Ruhodo observation object surface, at a depth measuring device for measuring the dielectric constant of the depth of the known surface structure of the observed object surface soil for covering the lunar surface, it has a frequency variable function and oscillation source become oscillator successive or pulsed traveling wave, and an antenna for radiating the traveling wave output from the oscillator to the observation object surface direction as the transmission radio wave, traveling wave output from the oscillator the The transmitted radio wave radiated from the antenna is reflected on the boundary surface of the surface of the object to be observed and the lower surface of the surface structure, and is transmitted through the directional coupler and the directional coupler for separating the reflected wave received by the antenna. Traveling wave detector for detecting a traveling wave and the directional coupler
Detecting the reflected wave via the reflected wave detector and Tona
A standing wave measuring device for calculating a voltage standing wave ratio based on a ratio between the output of the traveling wave detector and the output of the reflected wave detector.