JPH0227286A - Sampling method and apparatus of underground radar - Google Patents

Abstract

PURPOSE:To know searching depth and to enhance resolving power by making a change of a sampling cycle proportional to a change of transmission frequency so that a sampling receiving cycle is raised at the time of the searching of a shallow position but lowered at the time of the searching of a deep position. CONSTITUTION:A high frequency generator 2 generates a high frequency signal in synchronous relation to the reference pulse Pr generated by a reference pulse generator 1 and said signal is subjected to non-equilibrium/equilibrium conversion by a balancing transformer 13 to emit a radio wave into the ground from a transmission antenna 5. The high frequency signal generated by the generator 2 is cyclically changed on the basis of the voltage from a delay voltage generator 10 and the reflected wave from the ground is received by a receiving antenna 5 to obtain a receiving signal Sr. This signal Sr is subjected to non-equilibrium/equilibrium conversion by a balancing transformer 6 to be sampled by a sampling circuit 7. The receiving signal SS becoming a pulse like state is held by a holding circuit 8 to obtain an output signal SH. By this constitution, the difference in depth becomes that in the delay quantity of a pulse and delay quantity is measured by a time difference measuring circuit 12 to make it possible to know the depth up to a reflecting body.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a sampling method and device for an underground radar that uses radio waves to search for underground objects, etc. This article relates to a ground penetrating radar sampling method and device that can improve resolution.

[Conventional technology]

In conventional underground radar, the distance from the antenna to the target is very short, so the transmission signal uses a pulse or monocycle wave with a width of about several +1 seconds. In addition, since the existence time of one reflected wave is very short, the received wave is regenerated by sampling a part of the received wave each time it is transmitted, moving the sampling position each time it is transmitted, and repeating the transmission and reception many times. Was. Related devices of this type include, for example, Japanese Unexamined Patent Publication No. 11682/1982.

) [Problem to be solved by the invention] In order to deepen the exploration depth using the monocycle transmission wave used in the above-mentioned prior art, the frequency of the transmission wave must be lowered. However, when the frequency is lowered, The width of the transmitted wave becomes longer and the resolution decreases, and
In order to increase the frequency of the transmitted wave and deepen the exploration depth, it is possible to increase the transmitted power, but since the dynamic range of reception is limited, the reflected waves with high reflected power from shallow depths are saturated. As a result, it becomes impossible to identify the target.

An object of the present invention is to provide an underground laser sampling method and apparatus that can improve the resolution as well as the exploration depth.

[Means to solve the problem]

The above purpose is to change the frequency of a transmission wave with a constant transmission period using a stepwise or continuous chirp wave at one exploration position, and radiate it underground. Sampling of reflected waves from underground is performed once every transmission cycle. When the transmission frequency is high, samples corresponding to shallow depths are sampled at short sampling intervals, and when the transmission frequency is low, This is achieved by sampling portions corresponding to deep and shallow depths at long sampling intervals, making changes in the sampling intervals proportional to changes in the transmission frequency, and converting the output signal frequency after sampling to a constant frequency.

[Effect]

In the underground radar sampling method of the present invention, transmitting and receiving waves from a high frequency to a low frequency are emitted for each exploration position, and as the frequency changes from high to low, the reflected waves move from shallow to deep depths. By moving the sample position, the resolution at shallower depths is improved, and even if the transmitted waves at high frequencies are attenuated and no reflected waves can be obtained, reflected waves at low frequencies can be obtained, and the exploration depth can also be improved.

The frequency of the received reflected waves changes with time, but
By changing the sampling interval of the received wave in proportion to the change in the transmitting frequency at the time of sampling, one frequency change is 1
The signal is compressed to one frequency and becomes a low-frequency signal. As a result, there is no need to add a special circuit after sampling, and it is possible to easily provide an underground radar with improved exploration depth.

〔Example〕

An embodiment of the present invention will be explained below with reference to the accompanying drawings.

FIG. 1 is a block diagram of the underground radar of this embodiment. As shown in FIG. 1, this underground radar includes a reference pulse generator 1. High frequency generator 2. Balun transformer 3, transmitting antenna 4, receiving antenna 5, balun transformer 6, sample circuit 7. It consists of a hold circuit 8, a high speed sawtooth wave generator 9, a delay voltage generator 10, and a sample pulse generator 11.

Next, the individual operations of each configuration will be explained.

The reference pulse generator 1 outputs a reference pulse Pr with a period Tr, and in synchronization with it, the high frequency generator 2 generates a high frequency signal with a period Tr, which is unbalanced-balanced converted by the balun transformer 3 and sent from the transmitting antenna 4. Emit radio waves underground.

The frequency of the high frequency signal generated by the high frequency generator 2 changes periodically depending on the voltage from the delayed voltage generator 10. The reflected wave from underground is received by the receiving antenna 5, and a received signal Sr is obtained. The received signal Sr is subjected to balanced-unbalanced conversion by a balun transformer 6 and sampled by a sampling circuit 7. Received signal Ss sampled and pulsed
1 is held by the hold circuit 8, and the output signal S
, get.

The high frequency signal used for transmission may be a monocycle wave or a chirp wave, but this embodiment shows a case where a monocycle wave is used.

The transmitted wave is generated at a constant period in synchronization with the reference pulse, and the frequency changes stepwise or continuously depending on the voltage from the delay voltage generator. As an example, assume that the frequency changes as shown in FIG. 2. When a transmission wave with such a frequency change is radiated underground and the transmission frequency is fl, the reception wave S shown in Fig. 3 is generated.
As shown in step R, the portion appearing at time t1 after transmission is sampled at a short sampling interval Δt1, and the received signal that reaches the receiving antenna 5 at time t is not sampled.The received wave Sr with a transmission frequency f, The received signal that reaches the receiving antenna 5 at time tL is not sampled, but the received wave that arrives at time t is sampled at long sampling intervals. This sample is sampled once for each transmission, and when the transmission frequency is fl, the sample position is delayed by Δt1, and when the transmission frequency reaches f, it is delayed by Δt,
One received wave sample is completed with 300 transmissions.

Figure 4 shows the timing of the reference pulse Pr and the hold circuit 8.
An example of the output signal sH of is shown.

The relationship between frequency and sample interval is as shown in the sample example in Figure 3. By setting the number of samples per cycle at the transmission frequency at the time of sampling to be the same, changes in the transmission frequency will be As shown in Figure 4, the signals are compressed to the same frequency and frequency converted.

The generation of the sample pulse Ps is performed by a sample pulse generator 11 consisting of a comparator that generates a pulse at the intersection of the voltage from the delayed voltage generator 10 and the voltage from the fast sawtooth generator 9. Delay voltage generator 10
The sample delayed voltage from is an example waveform shown in FIG. This period T0 is the time during which received wave sampling at one exploration position is performed. The sample delay voltage change is synchronized with the reference pulse Pr, and becomes 1 after n times of the reference pulse Pr.
The period is T, :nTr. The fast sawtooth wave is also synchronized with the reference pulse Pr, and at the intersection with the sample delay voltage, the sample pulse generator 1111 generates the sample pulse Ps. The slope of the amount of change in the delayed pulse voltage increases as the transmission frequency decreases from f1 to f, and the amount of change in the delay time tdn of the reference pulse of the sample pulse Ps, Δt=tdn+1−tdn, also increases.

In order to frequency convert the received wave Sr at each transmission frequency f□~f by sampling, each sample interval Δt is proportional to the time per cycle of the transmission frequency at the time of sampling, depending on the slope of the sample delay voltage at each frequency. let

In FIG. 6, reflected waves P□ from underground 0.25++ and underground 0.25++ when the transmission frequency changes from f to f3.
Reflected wave from 5m Pat Reflected wave from underground L5m P3,
Taking the reflected wave P4 from 4.5m underground as an example, the output signal S from the hold circuit 8 is converted to the same frequency as shown in the figure, and the output is P 1'P 2' P 3' P 4' obtain.

As mentioned above, the difference in depth becomes the difference in the amount of delay of each pulse P□'~P,' t□T tut tel t4,
By measuring the delay amount t using the time difference measuring circuit 12,
You can know the depth to the reflecting object.

〔Effect of the invention〕

According to the present invention as described in claims 1 and 2, even if the transmission frequency is changed during the search for one position, the frequency can be converted to the same frequency after receiving the sample.

Therefore, when transmitting a high frequency, it is possible to search with good resolution up to the depth of exploration obtained with that frequency, and depths that cannot be probed with a high frequency can be probed by sampling when transmitting a low frequency, and the depth of exploration can be can be deepened. The total number of samples in one received wave is not more than necessary, and data can be acquired efficiently. Furthermore, since the signal frequency after sampling is constant, the signal processing circuit can be constructed easily and inexpensively.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention. Fig. 2 is a graph showing changes in the transmission frequency used in the example, Fig. 3 is a waveform diagram showing the operation of frequency conversion by sampling, Fig. 4 is a diagram showing an example of the waveform of the output signal after holding, and Fig. 5 The figure is a waveform diagram showing the operation of generating a sample pulse and the operation up to obtaining an output signal after holding, and FIG. 6 is a waveform diagram showing an example of a received wave and an output signal. 1... Reference pulse generator, 2... High frequency generator, 3
... Balun transformer, 4... Transmitting antenna, - Receiving antenna, 6... Balun transformer, 7... Sample circuit, 8... Hold circuit, 9... High speed sawtooth wave generator, 10... Delay voltage generator, 11... Sample pulse generator, 12... Time difference measuring circuit. Patent applicant: Hitachi Shonan Electronics Co., Ltd. Representative Patent Attorney: Masami Akimoto (1 other person) Compilation of the summary! Jugo

Claims (1)

[Claims] 1. In an underground radar that transmits microwaves underground, samples and receives reflected waves from underground, and visualizes buried objects and underground conditions, When searching for a deep location, the transmitting frequency is raised to increase the sampling period for sampling reception, and when searching for a deep location, the transmitting frequency is lowered to lower the sampling period for sampling reception, and this change in sampling period is reflected in the transmission frequency. A ground-penetrating radar sampling method in which the sampling reception output remains at a constant frequency even if the transmission frequency changes by making it proportional to the change in frequency. 2. a reference pulse generator that outputs a reference pulse, a high frequency generator that generates a high frequency signal in synchronization with the reference pulse, and a transmitting antenna that radiates the high frequency signal underground;
a delay voltage generator that periodically changes the frequency of the high-frequency signal; a receiving antenna that receives reflected waves from underground; a sampling circuit that samples the received signal received by the antenna; and an output of the sampling circuit. The difference in the amount of delay between the reference pulse of the reference pulse generator and the output signal from the hold circuit is determined by the high-frequency sawtooth wave generation circuit and sample pulse generation circuit that supply sampling signals to the hold circuit and the sampling circuit. An underground radar sampling device comprising a time difference measuring circuit for displaying.