JPS60173490A - Survey system for underground buried body by frequency division and multiplexing - Google Patents

Abstract

PURPOSE:To reduce the overload on an antenna and to survey effectively an underground buried body by dividing a wide-band signal into plural narrow bands and processing them by respective band antenna groups, and multiplexing receive pulses. CONSTITUTION:A transmitter 1 generates signals of plural narrow bands of the wide band signal successively under the drive of a transmission control part 10 and they are radiated from corresponding antenna elements of an antenna 13. Then, a reflected wave from the underground buried body 15 is received by a receiver 18 through the element group 14 and stored in memory 19 together with a position coordinate detection signal generated by a position coordinate signal generator 16 according to the movement of an antenna 13. A pulse multiplexing processing part 20 multiplexes pulse waveforms with short duration at every observation point to survery the underground buried body with the resulting composite band pulse waveform. This wide band signal which is not a single signal is used to reduce the overload on the antenna and also survery the underground buried body effectively with a high-resolution which has small distortion, etc.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for exploring underground buried objects using wave motion. Underground buried object exploration method that allows effective use of broadband signals in collection % formula % In the conventional underground buried object exploration method, a configuration as shown in FIG. 1 is used.

This is based on the principle of pulse radar, which is used in the air for various purposes, but because the distance to the buried object is short, the distance measurement resolution needs to be higher than that of airborne radar. Therefore, a baseband impulse signal with a pulse If11 narrower than that of an airborne radar and a baseband of at most 1 rev n5ec is used. As is well known, impulse signals have an extremely wide frequency band. It is well known that having this wide frequency band contributes to increasing the resolution of distance measurement. this! At present, attempts have been made to use chirped pulses with swept frequencies in addition to impulse signals, but there is no essential difference and they are included in the conventional example shown in Figure 1, so here we will discuss the case of impulse signals. In theory, an electrical signal with a wide frequency Wi and band passes through a T/R switch 2 that has the function of switching between the transmission (Lt state) and the reception state, and is transmitted to a single wideband antenna 3.
The broadband antenna 3 emits an impulse-like radio wave signal 4 toward the ground. '1 wave (i1 4) is reflected by an underground object 5, detected by a broadband antenna 3, converted to an electrical signal again, and sent to a receiver through a T/R switch 2 switched to the receiving state. 7, undergoes amplification, detection, etc., and is recorded as waveform data on a data recorder 8.Furthermore, it is displayed on a graphic recorder 9 as necessary.Moving the antenna 6-L, the antenna position Detection, U, and b are performed by repeating measurements with a position generator 6 built into the moving mechanism.Without using the T/R switch 2, a wideband antenna for transmission only and a wideband antenna for reception only can be used. Although there is a method of separating the antenna and the antenna, they are essentially the same type.

As described above, in the conventional method, in order to ensure the resolution of distance measurement, an extremely wide band electric signal is used, and this is applied to an immediate antenna for transmission, and the reflected wave is received by a single antenna. Because I was using a method,
The antenna used is required to have extremely wide frequency characteristics, and the disadvantage is that it is difficult to realize an antenna that is the key to collecting information from underground. In addition, in the implemented one, the radiated pulsed tsunami signal 4 has an insufficient bandwidth compared to the applied impulse-like electric signal.
However, if emphasis was placed on ensuring broadband performance, the efficiency of the antenna would drop significantly, making it difficult to obtain sufficient wave energy for lossy underground exploration. The problem was that I couldn't get it.

Furthermore, in conventional systems, a single antenna receives a wideband signal, so it is difficult to reduce negative effects such as variations in antenna characteristics due to the presence of the ground and strong reflections from the ground surface. There is a problem. That is, in order to suppress these effects, it is necessary to match the antenna with the ground over a wide band, but this has been difficult to achieve. Additionally, in order to reduce reflections from the ground surface, a method using a cross dipole antenna has been proposed, which takes advantage of the fact that reflections from near-flat reflectors such as the ground surface do not change the plane of polarization. However, it has the disadvantage that it may become unresponsive to reflections from underground exploration objects and that energy use efficiency is low. In addition, in order to reduce the effects of antenna mismatch, a method has been proposed in which a dummy antenna is connected in parallel to the transmitting and receiving antenna to generate reflections in the opposite phase to cancel unnecessary reflections. Since the energy loss that does not contribute to the loss is always as high as 3 dB, it has not been an advantageous solution as a lossy underground exploration method.

On the other hand, a method has been proposed that uses one frequency and does not require the use of a wideband antenna, but this method has the disadvantage that the ranging resolution is extremely low because it uses only a single frequency component. Another problem was that alignment with the ground for efficient underground transmission was not taken into consideration.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide an underground object exploration method that can effectively use a wideband signal while reducing excessive burden on the antenna. Furthermore, it is another object of the present invention to provide an underground buried object exploration method that can reduce harmful effects such as ground surface reflection over a wide band by dividing the frequency.

[Structure of the invention]

The present invention divides the wideband signal required for exploration into a plurality of narrow frequency bands, divides each band into a group of relatively narrowband antennas to share the signal collection process, and moves the antennas during exploration. The method is characterized in that after receiving the information, the divided frequency components are used to synthesize a pulse signal with an equivalent short duration to perform underground exploration while effectively utilizing the information.

〔Example〕

Hereinafter, the present invention will be explained in detail based on FIGS. 2 to 9.

In the following explanation, we will take into consideration the case of collecting reflected 1# information from underground using electric omega waves and searching for buried objects, but the present invention can also be applied using other wave media such as sound waves. Of course, the method can be applied.

FIG. 2 shows one embodiment of the present invention, and first of all, the figure shows the characteristic points of the exploration method of the present invention, that is, the wideband signal necessary for exploration is divided into bands a, This paper explains how to distribute the city area to separate antennas to reduce the requirement for custom-built broadband antennas, and to use position signals generated by antenna movement to synthesize equivalent broadband pulses after reception. It's number 1.

In this method, the broadband 1po signal required for exploration is divided into N bands in advance and handled. That is, the transmission tr
! All is generated under the control of the transmission control unit 10 while switching signals tl-1m that belong to frequency bands divided into N pieces. The specific shape of the signal is, for example, a sine wave with a frequency f in each of N bands.
, f , f , . At this time, since the frequency is switched within a certain amount of time, the generated signal has a band broadening to some extent depending on the duration, but becomes a narrow band signal having frequencies from f1 to f1. If one frequency is generated for a duration that includes a sufficiently large number of cycles relative to the frequency, each signal can be considered to be substantially a continuous wave and can be considered to have a line spectrum.

First, at a certain point in time, the frequency f1 belonging to the first band
The entire method will be explained assuming that a signal is generated.

The generated signal has a function of establishing a path for applying the 'd''A signal to a T/R switch that switches between a transmitting state and a receiving state, and a predetermined antenna in an antenna element group 14 that constitutes an antenna 13, which will be described later. passing through a functional block 12 having
The signal is applied to the antenna element in charge of the first band in the antenna element group 14. The functional block 12 is a transmitter i
t+ll fal1 section 100 establishes the transmission/reception state and the application path to the antenna element using the suppression signal in synchronization with the applied signal. The antenna 13 is composed of a plurality of antenna element groups 14, and each antenna element of the antenna element group 14 shares a different relatively narrow frequency band, converts an electrical signal into a radio signal, and radiates the signal. It has the function of

Now, a signal f is radiated from the antenna element sharing the first band in the antenna element group 14, and when this is reflected by an underground object 15, the signal becomes 1 again. The signal is detected by the antenna element responsible for the frequency band to which it belongs, is switched to a receiving state, and is guided through the 7'C function block 12 to the receiver 18. A reference signal 17 that is coherent with the electrical signal applied to the antenna 13 is sent from the transmitter 17 to the receiver 18, and the information in the reflected signal necessary for later pulse synthesis processing is extracted from the reflected signal. is taken out. For example, by comparing the reflected signal and the reference signal, phase and amplitude information of the reflected signal at frequency f1 can be obtained. The process of extracting such information in the frequency domain is well known as the detection of amplitude and phase information in a network analyzer or the technique of electronic reference waves in long wavelength holography, so details are omitted.

The complex number width information of the signal f1 is A/D converted and stored in the memory 19 in an appropriate format. At this time, as the antenna is moved by the antenna moving means, a position t generated from the position signal generator 16 indicating the position t of the antenna 13 is generated.
It is essential to store the i signal in the memory 19 in association with the reflected signal.

Upon completion of the data collection using the signal f1, the transmission control unit 10 controls the functional block 12 to transmit a signal for transmission to a predetermined antenna element in the antenna element group I4 that handles the second frequency band. The route is established, and in synchronization with this, the transmitter 11 is brought into a state of transmitting the signal f2. The necessary information for the signal f1 is extracted by the receiver 18 through the same process as for the signal f1, and is stored in the memory 19 together with the signal indicating the measurement position of the signal f1.

Similarly, the signals f3. f4. ...A similar operation is performed for fNVr.

In this way, the signals f1~ belonging to each divided frequency band are
The information extracted in the frequency domain by fN is then synthesized into Valsui J in the pulse synthesis processing section 20. The synthesized pulse waveforms are arranged, for example, at the position coordinates j@ and displayed in a cross-sectional diagram on the graphic recorder 21 as υ, or stored in the data recorder 22 for more advanced signal processing, analysis, and display. or

Knowing the frequency components of a signal in the frequency domain and synthesizing them into a pulse waveform in the time domain is possible using the Fouri-transform relationship, and can be performed numerically using the FFT algorithm. . However, if each phase component of information extracted from signals belonging to different frequency bands is simply extracted using a reference signal, arbitrary phase shifts may occur between the signals. Therefore, the reference signal 17 supplied from the transmitter 11 to the receiver 18 needs to be phase-locked and give a common phase reference to the 4G signal belonging to each frequency band. There is.

Furthermore, in the above description of the pulse synthesis processing section 20, it is implicitly assumed that ig'+4if1~fN are collected at the same observation point, but as is clear from FIG. , each antenna element forming the antenna element group 14 is located at a spatially different location and does not satisfy this assumption. The following will explain how signals f1 to fN at the same observation point can be stored in the memory 29 and read out for pulse synthesis processing despite this arrangement of antenna element groups.

FIG. 3 shows an enlarged view of the antenna 13 in the embodiment shown in FIG. The antenna 13 has a group of antenna elements 14 that share signals belonging to divided frequency bands, and these are designated as A, A, and A, respectively.
, . . Ay m ”' AN23.The antenna 13 is also equipped with a mechanism for movement and a generator 16 for generating antenna position coordinate signals.
It is equipped with Each antenna element of the antenna element group 14 receives a signal f1. f2゜...fk,...
An independent route is provided for transmitting and receiving I fN. Antenna element A,, A2. A3. ....

Ak, . . . AN are arranged spatially separated, and the signals to be sent and received are sequentially switched from time to time, thereby suppressing crosstalk as much as possible. In this respect, it is essentially different from a log-periodic antenna, which has multiple elements but is configured to act as a single wide-area antenna as a whole.

Since the receiving antenna elements are located at different spatial positions, the signals f1+12+...fk,...fN are transmitted and received at different points. Compared to the moving speed of the antenna 13, the time required for transmitting and receiving signals can be made sufficiently small, so the deviation between the transmitting and receiving points of No. 1J can be ignored, but this spatial deviation of each antenna element is Since the underground propagation path of No. a is separate, it is inconvenient to synthesize the pulse waveform using the information collected in one measurement cycle from signal 1 to fN. However, if the antenna 13 moves four times along the side line of the underground exploration, it is possible to synthesize signals f1 to fN collected at the same observation point. Now, suppose that antenna element A1 is at a certain point on the ground at a point where X = XO, and observation i11++ is performed using 4rJ@f1. At this time, each of the other antenna elements is positioned one position behind X-Xo by the sum of the array intervals of the antennas.
Each of them will do their part (observations are being made with fi. Therefore, fd f1 will be associated with lft coordinates that clearly indicate that it is the result of observation with X = Xo,
Let R(fl) be the information obtained from the signal f1, and (
The memory 19 is loaded in the form of R(f, ), Xn). Since the array spacing of the antennas is known, for example, the information from the antenna strands A,2 is (K (f2) *
Xo-d 1 ) (where dl is the arrangement interval between A1 and A2). antenna 13
As the measurement from signal f1 to i'H is repeated while moving the antenna element A2, X=X, O
The time will come when it will take [7 to reach the point, so at this time (R(f
2), XO) are accumulated. Similarly, for any antenna element A1c, (R(fK), XO
> is obtained.

In this way, by reading the label using the position coordinate signal and collecting data, you can check the same observation point X-X0 later.
fN can be extracted from 1 using the number II.

FIG. 4 shows the antenna 19)'A shown in the embodiment of FIG.
- This is an example of using a dipole antenna with ft-characteristics that is suitable for sharing signals as a comparatively narrow band antenna group. Of course, antennas other than dipole antennas can also be used. The essence of this is to use a group of antenna elements that divide and share the frequency band.

Furthermore, in the embodiment shown in FIG. 2, a case has been described in which the antenna 13 is switched between the transmitting state and the receiving state, but as shown in FIG.
are separated into antenna element groups 24 and 24', respectively.
It is also possible to provide the following. In this case, function block 1
2 does not need to have a T/R switch function. Furthermore, in the functional block 12, the transmission signal and the reception signal may be separated by a directional coupler instead of the 'r/R switch.

Next, a description will be given of the configuration of an antenna to be applied to the wooden sword type in which the frequency band is divided and assigned to each antenna element to improve matching with the ground.

In the case of FIG. 6, each antenna element of the antenna element group 26 constituting the antenna 25 corresponds to the maximum frequency of the frequency numbers f1 to fH used, and the narrow bit length
((λK) It is placed sufficiently close to the ground at a distance that is sufficiently small compared to (1≦to≦N), and this arrangement allows the antenna element to be strongly influenced by the refractive index of the ground, and If the antenna is matched to an impedance of This prevents the structure from becoming complicated, and also reduces the effects of critical angles when reflected waves travel from the ground to the ground.When using an impedance between each antenna element and the ground, it is important to design a shikomo balun. In the figure, 27 indicates a mechanism for moving the antenna 25, which is configured to generate a positioning signal.

FIG. 7 shows another embodiment in which the antenna element group 29 constituting the antenna 28 is rearranged into a dielectric medium 30.

The refractive index n of the dielectric medium 30 is the refractive index nB of the earth.
is equal to or almost equal to . Therefore, since the boundary between the antenna 28 and the earth where the refractive index differs can be ignored, reflection from the earth's surface can also be ignored, and in the dielectric medium, from antenna element A1 to If the ANs are impedance matched to the signals f1 to f~, respectively, efficient transmission and reception of radio waves becomes possible. In the figure, 31 is a moving mechanism for the antenna 28, which is configured to generate a position coordinate signal. The refractive index of the earth n. Since is always greater than 1, the antenna element placed in the dielectric 30 is made smaller due to the wavelength shortening effect compared to when the surrounding medium is air. Therefore, in this configuration,
An advantage is that a smaller antenna 28 can be used.

In addition, since the earth can be considered to be non-magnetic in most cases, the refractive index mentioned above is actually equivalent to the dielectric constant.

FIG. 8 shows still another embodiment, in which an antenna element group 33 constituting an antenna 32 is made of a dielectric medium 3 with a relative refractive index n.
4, the antenna element is placed at a position h... hK... etc. whose height from the ground satisfies the phase condition for preventing reflection of the wavelength in the dielectric medium 34 of the signal carried by the antenna element. Ru. In general, since the force ζ antenna element group 33 that causes reflection from the ground surface is located at a position that satisfies the phase condition for preventing reflection from the ground surface, the reflection from the ground surface occurs in the antenna in an opposite phase.

FIG. 9 shows an antenna element group 37 constituting the antenna 36.
Satisfies the anti-reflection amplitude condition of 1 for the refractive index ns of Yakenji.
The antenna element is arranged in a dielectric medium 38 with a low refractive index, and its height is set at a distance of 1'k from the ground surface so as to satisfy the anti-reflection phase condition.
An embodiment is shown in which the device is placed at a height from the ground at a distance h/1... h'K... different from that shown in the figure. this is,
It satisfies the requirements for what is called an antireflection layer in optics, and can be expected to more effectively suppress ground surface reflection. Reference numeral 39 denotes an antenna moving mechanism, which is configured to generate a position coordinate signal. In the embodiments shown in FIGS. 8 and 9, the height from the ground surface at which the antenna element group is arranged is It is different for each element. Therefore, in order to synthesize data from the same observation point, it is necessary to correct the phase of the collected data by a known location in advance, but this correction amount is stored in advance in the memory 19.
It can be kept inside.

The configurations shown in FIGS. 6 to 9 are possible with the system of the present invention, which divides No. 1H into a plurality of comparatively narrow-band antennas and handles them. This cannot be achieved by using a single wideband antenna.

In the embodiments described above, a wideband signal component is divided into a plurality of relatively narrowband signals, and a single signal with the same wave number component representing each band is assigned to each antenna element. As explained above, an antenna with a configuration in which the number of antenna elements is reduced by dividing the band into bands that can be reasonably achieved with a single antenna and reassigning one or more frequency components to one antenna element. The present invention can be applied even if it is used.

〔Effect of the invention〕

As explained above, in the present invention, the wideband signal components required for exploration are divided into multiple relatively narrow frequency bands, and each frequency band is assigned to a different antenna element to collect data. Since this method performs exploration by synthesizing short-duration wide-band pulse waveforms through signal processing after data collection, the requirements for frequency characteristics are strict, and the wide-band frequency characteristics have drawbacks such as reduced efficiency due to the wide band. This method has the advantage that a broadband signal can be used without using an antenna, and underground buried object exploration with good resolution can be performed effectively.

Furthermore, since each antenna element only needs to share a relatively narrow signal band, it is possible to use an antenna configuration suitable for suppressing strong unnecessary reflections from the ground surface. It has the advantage of being able to conduct underground buried object exploration.

Therefore, if the present invention is used for underground buried object exploration or underground structure exploration, broadband underground information can be obtained and exploration with high resolution can be performed.

Furthermore, the method of the present invention is useful not only underground but also when it is desired to non-destructively inspect the inside of a medium other than soil using a broadband signal.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional underground object exploration method using a broadband antenna, FIG. 2 is a schematic diagram of an embodiment of the underground object exploration method of the present invention, and FIG. 3 is an explanatory diagram of an underground object exploration method of the present invention. FIG. 4 is an enlarged side view of the configuration of the antenna in the method of detecting underground objects of the present invention, FIG. Figure 6 is a schematic diagram of the antenna configuration in the underground buried object exploration method of the present invention, Figures 7, 8, and 9.
The figures are schematic diagrams of other embodiments of antenna configurations that reduce the influence of ground surface reflection by 1 f for use in underground buried object exploration according to the present invention. 10...Transmission control unit, 11...446
machine, 12...', [+1@block, 13...
...Antenna, 14...Antenna element group,
15...Buried object, 16...Position coordinate signal generator, 17...Reference signal, 18...
・Receiver, 19...Memory, 20...
Pulse synthesis processing unit, 21... Graphic recorder, 22... Data recorder, 23... Group.
Antenna, 23'・Old...Antenna, 24...
Antenna element group, 24'...Antenna element L
25... Antenna, 26... Antenna element group, 27... Antenna moving mechanism, 28...
...Antenna, 29...Antenna element group,
3o...Dielectric medium, 31...Antenna moving mechanism, 32...Antenna, 33...
...Antenna element group, 34...Dielectric medium, 3
5... Antenna moving mechanism, 36... Antenna, 37... Antenna element group, 38...
...Dielectric medium, 39...Antenna movement mechanism. Fig. 3 fNfKf3f2fI 24' Fig. 9 k-h-f3h f+

Claims (1)

[Scope of Claims] (1) In a method of collecting underground information using waves and exploring underground objects, a group of antenna elements of a certain number is required to obtain a wideband signal required for exploration. Using an antenna consisting of, dividing the frequency band and supplying electrical signals with different frequency components to each of the transmitting antenna elements
The transmitting and receiving antennas are moved, and each of the antenna elements that make up the receiving antenna collects the reflected waves of each frequency component in association with the position coordinate signal indicating the antenna position, and these received waveforms are used to collect the reflected waves of each frequency component. This is an underground exploration method using frequency division and synthesis, which is characterized by synthesizing short-duration pulse waveforms for each observation point and conducting underground exploration using the broadband pulse waveform obtained by synthesis. 12+ The antenna elements constituting the transmitting and receiving antennas move close to the ground surface at a distance sufficiently shorter than the minimum wavelength among the center wavelengths of waves emitted by the antenna elements. An underground buried object exploration method using frequency division and synthesis according to claim 1. (31) The antenna elements constituting the transmitting antenna 11 and the receiving antenna are located in and move in a dielectric material having a refractive index equal to or almost equal to the refractive index of the earth. Exploration method for underground objects using frequency division and synthesis described in Section 4. (4) A group of anti-Funa elements constituting the transmitting and receiving antennas calculates the height of each antenna element from the ground surface using each antenna element. A method for exploring underground objects by frequency division and synthesis according to claim 1, characterized in that the method moves at a height that satisfies a phase condition for anti-reflection with respect to waves radiated into a surrounding medium. (5) The antenna elements constituting the transmitting and receiving antennas are located in a dielectric material having a refractive index that satisfies anti-reflection conditions for the waves radiated by each antenna element, and 2. A method for searching for underground objects by frequency division and synthesis according to claim 1, characterized in that the method moves to a position at a height from the ground surface that satisfies the above requirements.