JPS5999385A - Detection of matter embedded in ground - Google Patents

Abstract

PURPOSE:To perform the detection of a plurality of embedded matters and the positional confirmation thereof, by a method wherein a radio wave to which frequency modulation is applied is projected into the ground and complex reflectivity is measured while high speed Fourier transformation is applied to determine the amplitude of the reflected wave from each matter embedded in the ground. CONSTITUTION:An oscillator 1 emits saw-tooth shaped FM wave showing frequency change in the band width of frequency fo-fo+B and an oscillation signal is projected toward the ground surface 7 from a transmission antenna 2 while branched to be applied to an amplitude phase measuring instrument 4. The receiving signal of a receiving antenna 3 for catching the reflected waves from the matters 8a, 8b embedded in the ground is also imparted to the amplitude phase measuring instrument 4. An operator 5 measures complex reflectivity GAMMA(f) while reading the amplitude and the phase measured by the measuring instrument 4 in a plurality of frequencies present in fo-fo+B and applies Fourier transformation to operate of the amplitude GAMMA(x) of reflected wave dependent on the distance (x) to each matter embedded in the ground. From the distance between peaks of amplitudes, the distances x1, x2 between the ground surface and the embedded matters 8a, 8b can be calculated.

Description

[Detailed Description of the Invention] The present invention is based on underground j! ! This paper proposes an FM radar method that can separate and classify buried objects even when there are several buried objects.

It is often necessary to detect underground objects such as gas pipes, explosives, etc. for construction work.

Conventional detection methods include JP-A-56-140276;
As shown in Japanese Unexamined Patent Publication No. 57-56769, there is a known method for locating the buried position by passing an electric current through an underground object and detecting the electric field generated by the electric field using a coil on the ground. However, there are limits to what can be applied due to conditions such as the existence of the object to be detected being obvious and the ability to conduct electric current, and when there are multiple buried objects, it is difficult to separate and identify them. It's impossible.

! A method of detecting objects buried underground using the principle of electromagnetic induction from above the ground surface is also known, but the detection target must be a conductive object and it is impossible to separate and identify multiple buried objects. It has the disadvantage of being.

In contrast, as shown in Tokuko Sho 57-17273
When using a method that uses the principle of FM radar, there are no restrictions on the objects to be detected, but multiple objects of the same type (with the same radio wave propagation constant)
Special engineering is required to separate and identify buried objects when they exist.

It is an object of the present invention to provide an entire method for detecting underground objects in such an FM radar method, which is capable of separately detecting the presence or absence of a plurality of buried objects and locating their positions with high precision.

The method for detecting underground objects according to the present invention is to project a radio wave with a frequency change ρM in a predetermined band V and width into the ground, and to use the projected wave and the reflected wave from the underground to The method is characterized by measuring the complex reflectance for a large number of frequencies within a width, and applying fast Fourier transform to the measured values to determine the amplitude of the reflected wave from the underground object.

First, the principle of the present invention will be explained.

If a frequency modulated (hereinafter referred to as FM modulated) wave is projected toward an object at a depth The reflectance r (f) can be expressed by the following formula [l].

1- (f) oc f I' (x) e-j 2π
fx dx' - (Ij Since this shows the form of Fourier transform, the following equation (2) can be obtained using inverse Fourier transform.

I-(x) cc J f' (f) e+j2mf
af ... (2) If we pay attention to this equation (2), in order to detect the magnitude of reflection with respect to the depth from the ground surface, in other words, the presence or absence of buried objects, and the depth position),
It can be seen that it is sufficient to measure the complex reflectivity r(f) for a large number of frequencies and perform inverse Fourier transform on them.

The complex reflectance l''(f) can be obtained by measuring the amplitude and phase of the reflected wave. However, since it is desirable that underground objects be detected within a short period of time,
In the calculation, fast Fourier transform will be performed.

Next, the method of the present invention will be specifically explained with reference to the drawings.

FIG. 1 schematically shows the implementation of the method of the invention.

The oscillator 1 generates frequencies #, with a period T, as shown in Fig. 2 (a).
It oscillates a sawtooth-shaped FM modulated wave that shows a linear frequency adjustment of the bandwidth of f, ~fo+B, and this oscillation wave is projected from the transmitting antenna (antenna) 2 toward the ground surface 7. At the same time, the signal is branched at the transmission line to the antenna 2 and given to the amplitude/phase measuring device 4 .

A receiving antenna 3 is provided near the transmitting antenna 2 to capture reflected waves from underground objects 8a and 8b, and this received signal is also given to the amplitude/phase measuring device 4. Furi 1 yen! ! ``The phase measuring device 4 receives the input signal.

Measure the amplitude and phase of the reflected wave from the received signal.

The amplitude and phase measured by the 5-digit calculator 4 are both f. A large number of frequencies f+, f2... et al-3. fn [see Figure 2 (a)] and performs Fourier transform using the values at each frequency to calculate the amplitude 'r (X) of the reflected wave, which depends on the distance X from antenna 2 to the underground object. It is.

Figure 2 (b) Kel! 11 Relative amplitude r at each frequency fl+f2...fll-1nfn measured by the regulator 4
(f) shows the change in relative phase θ(f), and -) in FIG.

Now the transmitted wave'(rAte"j2πft 9 signal wave is Ar
Let it be expressed as e+j2m(t-τ(X)). However, the formula effect indicates the time delay due to underground objects at depth X, and is expressed as τ(x) = 2x/C (C: radio wave propagation speed underground).

Then, the complex reflectance r (f) at the frequency &f is expressed by the following equation (3). −L” (0(:CA t/A, , e-j 2πfx
-F(x) e-j2πfx -f'(x)e-jθ ...(
3) Therefore, 8 in the earth! If there are multiple facilities, as shown in the formula m, it becomes r(f) ccfr (x) e−j 2πfxdx, and then Fourier transform is applied to this, and in the case of H+3+, r(X) QCJ I (f) e+ j2mf d
(= 1” (f) e+2]θ(f) df-= +
It becomes 4+.

The switcher 5 has a large number of frequencies f(f, , f2・
Relative vibration IQF (f
), relative phase θ(f)F is used to perform Fourier transformation based on the l factor of equation (4), and the amplitude F of the reflected wave from the internal part (1,
(x) is obtained.

FIG. 3 shows an example of the calculation output of the calculation unit 5,
For example, it is recorded by a recorder 6 such as a pen recorder.

In Figure 3 V (3 peak values can be recognized, but the part with the smallest X value is the reflection on the ground surface, B).

C (7) After 6 minutes, B is closer to A, and buried object 8 is closer to the ground surface.
Reflection at point a, and point C are due to reflection at buried object 8b, which is farther from the ground surface. Therefore, the beak IIυ of A, B, and C
Distance j) a table ~ We thing 8 a, 8 b Ill
k t'& XI I X2 can be determined individually. As mentioned above, if you use the 1st method, it's a cotton den, and if it's something other than sex, it's also tirf.
! 'irga], and even if there were more than one, it would be possible to divide them into dogs, and the gods''i'i
Even in the part where the ' body is a complex embedded ζ force, their existence is 1 t 1 ' min -1 (i] J ability to be distinguished into Hl.

[Brief explanation of drawings]

Figure 1 shows the implementation of the present invention! Schematic diagram showing the island, No. 2 and 1 (
b) ~C'1 are signal waveform diagrams for explaining the method of the present invention,
No. 3: This is a chart showing the 3rd section IC measurement h'□East. l...G CIL* device 2, 3...Antenna 4...
・Amplitude/phase measuring instrument 5...Calculator 6...Recorder special f1 Applicant: Sumitomo Planning Industries Co., Ltd. P1!
Person Patent Attorney Noboru Kono Daikabu 1. Figure 2. 2. Zuen 3.

Claims (1)

[Claims] 1. Project a frequency-modulated radio wave into the ground with a predetermined bandwidth, and measure all complex reflectances for a large number of frequencies within the bandwidth using the projected wave and the reflected wave from the ground. An underground object detection method characterized in that the measured value is subjected to fast Fourier transform to determine the amplitude of a reflected wave from the underground object.