JPH10197631A - Radar type underground prospecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an amplifying section to accurately amplify reflected waves in an area separated from the ground surface even when reflected waves exist near the ground surface by preventing signals higher than a prescribed level from entering an amplifying section by means of a blocking means. SOLUTION: The pulse generating section 52 of a blocking means 50 generates a control pulse in response to a transmitting trigger pulse of a 1-μs cycle generated from a transmitting trigger generator 11 and sends the control pulse to a delay circuit 53. When the section 52 sends the control pulse, an analog switch 55 permits the passage of the control pulse to a high-frequency switch 51 from the delay circuit 53 when a sensitivity time control(STC) exceeds a threshold. During this period, the switch 51 is turned off and blocks the passage of reflected waves to an amplifier 22 from a receiving section 14. Since the temporal area of the strong signal level of a reflecting body near the ground surface 2 cuts in such a way, it becomes unnecessary to worry about the saturation of the amplifier 22. Therefore, when a sampling section 30 samples each reflected wave transmitted from the amplifier, the reflected waves from a reflected body 3b separated from the ground surface 2 can be amplified with a high amplification factor and accurately amplified reflected waves can be sampled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar-type underground exploration apparatus for exploring an underground object such as an underground gas pipe, and more particularly, to a transmission for emitting a pulse wave into the ground at a predetermined repetition period. Unit, a receiving unit that receives the reflected wave returned from the underground, an amplifying unit that amplifies the received reflected wave at an amplification factor changed according to the repetition period, and the amplified reflected wave The present invention relates to a radar type underground exploration device including a sampling unit for sampling with a time gate displaced for each repetition period, and a signal processing unit for processing a sampling signal sampled for each repetition period to restore a reflected wave. .

[0002]

2. Description of the Related Art An underground exploration apparatus of the type described above is known, for example, from JP-A-63-120271. In this apparatus, a transmission radio wave is periodically emitted, and a reflected reception radio wave is sampled at a sampling cycle that is sequentially longer than a transmission repetition cycle of the transmission radio wave, and the sampled signals are combined to form one reception signal. The radio waves are reproduced on the stretched time axis. At that time, since the attenuation of radio waves propagating in the ground is large, when sampling a signal reflected from a region distant from the origin of the time axis, that is, a position distant from the ground surface,
By performing larger amplification by an amplifier before sampling, the received radio wave reflected by the reflector with the same reflection characteristic is displayed at the same level as possible regardless of the distance from the ground surface .

[0003]

However, the attenuation of radio waves in the ground may be 1/10 at 1 m depending on the location, and the attenuation increases exponentially with distance. When sampling a reflected radio wave from an area 2.3 m below the ground, it is necessary to amplify the signal by 50 to 60 dB more than when sampling a reflected radio wave near the ground surface. The amplifier receives not only the reflected radio waves from the area 2.3 m underground, but also the reflected radio waves near the ground surface. If the amplification factor is large, the amplifier will be saturated by the reflected radio waves near the ground surface. In this case, the reflected radio wave from a deep area cannot be amplified with reliability. SUMMARY OF THE INVENTION It is an object of the present invention to provide a radar-type underground exploration apparatus capable of accurately amplifying and processing a reflected wave from a region distant from the ground, despite the presence of a reflected wave near the ground.

[0004]

SUMMARY OF THE INVENTION In order to overcome the drawbacks of the prior art and achieve the above object, a radar type underground exploration apparatus according to the present invention emits a pulse wave into the ground at a predetermined repetition period. A transmitting unit, a receiving unit that receives a reflected wave returned from the underground, an amplifying unit that amplifies the received reflected wave with an amplification factor changed according to the repetition period, and the amplified reflected wave. Sampling at a time gate displaced at each repetition period, a signal processing unit for processing a sampling signal sampled at the repetition period to restore a reflected wave, and exceeding a predetermined level at the amplification unit. And blocking means for blocking a part of the reflected wave entering the amplifying section in order to prevent a signal from entering.

In this configuration, when a reflected wave having a signal level that saturates the amplification section at a large amplification factor is input, during a time domain having the large signal level,
The signal is prevented from entering the amplification unit from the transmission unit. This prevents saturation of the amplification section, for example, by amplifying the reflected wave from near the ground surface with a large amplification rate, and even in the ground where the radio wave attenuation is severe such as clay, the underground extends from the near surface to the deep area. Good exploration of buried objects becomes possible.

In this device, the possibility of saturation of the amplifier is:
This occurs when the reflected wave from near the ground surface is amplified with a large amplification factor, so when the amplification factor of the amplifier is large, the signal flow from the receiver to the amplifier is cut off only in the time domain where the reflected wave near the ground enters the amplifier. By doing so, saturation of the amplification unit can be prevented. Therefore, in one of the preferred embodiments of the present invention, the cutoff means is configured to be activated when the amplification factor of the amplification section exceeds a predetermined value. Since the amplification factor of this amplifier changes in accordance with the transmission repetition period, the amplification factor is checked, and when the amplification factor exceeds a predetermined value, the reception unit receives the reflected wave from near the ground into the amplification unit for the time interval. The connection between the amplifier and the amplifier is cut off. When the amplification factor is large, it is time to sample a reflected wave from a position distant from the ground surface. Therefore, the cutoff between the receiving unit and the amplifying unit does not affect the sampling of the reflected wave.

[0007] As such blocking means, a high-frequency switch provided between a receiving section and an amplifying section, a pulse generator for generating a control pulse for controlling the high-frequency switch, and a high-frequency switch for transmitting the control pulse to the high-frequency switch , And a comparator that controls the analog switch according to the amplification factor of the amplifying unit. In this configuration, a control pulse is generated with a time axis aligned with a large-level signal, that is, a reflected wave from near the ground, and when the comparator detects that the amplification factor of the amplification unit has exceeded a predetermined value, the analog switch is turned on. ON to allow the control pulse to pass. The control pulse that has reached the high-frequency switch turns off the high-frequency switch for a time interval corresponding to the pulse width of the high-frequency switch, thereby blocking the passage of the reflected wave. By adjusting the time position and time width of the control pulse, it is possible to cut only a region having a large level of the reflected wave.

[0008] In another preferred embodiment of the present invention,
The shutoff means is configured to operate at predetermined time intervals. In this device, the amplification unit sequentially samples the reflected waves over a desired time region while increasing the amplification factor from low to high at each transmission repetition period, so that the amplification ratio of the amplification unit is set at the set period. It is very low and high. Therefore, only by operating the blocking means at predetermined time intervals, it is possible to cut a reflected wave reflected from near the ground surface only when the amplification unit is set to a high amplification factor.

[0009] Such a blocking means includes a high-frequency switch provided between a receiving unit and an amplifying unit, a pulse generator for generating a control pulse for controlling the high-frequency switch, and a high-frequency switch for transmitting the control pulse to the high-frequency switch. , And a timer that controls the analog switch at predetermined time intervals.
In this configuration, the time until the amplification factor of the amplification unit rises from low to a predetermined height is set in the timer, and the amplification unit reaches the amplification factor that is saturated by the reflected wave from near the ground surface. After that, the analog switch is turned on to allow the control pulse to be sent to the frequency switch. When the amplification factor of the amplification unit decreases again, the timer is reset, the analog switch is turned off, and the counting of a predetermined time until the amplification factor increases next starts. By adjusting the time position and time width of the control pulse to the time region with the large level of the reflected wave, only the region with the large level of the reflected wave that saturates the amplifier operating at a high amplification factor Can be cut. Other features and advantages of the present invention will become apparent from the following description of embodiments of the present invention with reference to the drawings.

[0010]

FIG. 1 is a schematic functional block diagram of one embodiment of a radar-type underground exploration apparatus according to the present invention. The main components of the radar-type underground exploration device 1 radiate a pulse-like radio wave in the microwave region toward the ground surface 2 at a predetermined repetition frequency, and use a reflecting object 3 such as a buried object existing in the ground. A transmitting / receiving unit 10 for receiving the reflected wave that has been reflected back, an amplifying unit 20 for amplifying the received reflected wave, a sampling unit 30 for sampling the sequentially received and amplified reflected wave while shifting the sampling point, A signal evaluation unit 40 that combines the sampled signals to restore the reflected wave and evaluates and displays the restored reflected wave, and a blocking unit 50 that controls the signal flow between the transmission / reception unit 10 and the amplifier 20. It is.

The transmission / reception unit 10 includes a transmission trigger generator 11 for generating a transmission trigger pulse in accordance with a set repetition frequency, and a transmitter for emitting a pulsed radio wave from the transmission probe 13a in response to the transmission trigger pulse. And a receiving unit 14 for receiving the reflected wave reflected by the underground reflecting object 3 and returning by the receiving probe 13b and sending the reflected wave into the apparatus.

The amplifying section 20 has an STC (Sensitivity Time C).
ontol (sensitivity time control) A signal generation unit 21 and an amplifier 22 are provided, and the STC signal generation unit 21 generates an STC signal that increases every period of the transmission trigger pulse,
The amplifier 22 increases the amplification factor by the C signal. For example, a full-range 100 dB amplification factor of 1000
It is increased step by step in each cycle of the transmission trigger pulse. In this case, when receiving 1000 transmission trigger pulses, the amplification factor is returned to the lowest level again, and a similar increase in the amplification factor is started. In such automatic gain control of the amplifier 22, the ST changes in every cycle of the transmission trigger pulse.
This is done by the C signal. Therefore, this STC
By adjusting the signal, any time-varying amplification factor can be created.

The sampling section 30 includes a sampler driving section 31 for determining a sampling timing in response to a transmission trigger pulse, and a sampler 32 for sampling a reflected wave amplified by a command from the sampler driving section 31 at a predetermined time point. It has. The sampling unit 30 samples each reflected wave sent from the amplifying unit 20 in the repetition cycle using a sampling gate whose sampling point is sequentially shifted on the time axis. That is, sampling is performed at one sampling point from the reflected wave received by the first transmitted wave, and is sampled at a sampling point slightly delayed from the reflected wave received by the next transmitted wave. By performing this operation twice, sampling of the entire reflected wave in a desired time region is completed. That is, a sampling signal of one entire reflected wave is obtained from the 1000 reflected waves sequentially received. Signal evaluation unit 40
Is a signal processing unit 41 for restoring a reflected wave from the signal sampled by the sampling unit 30 and evaluating the underground exploration
And a display unit 42 for displaying the restored reflected wave.

The shut-off means 50 includes the receiving unit 14 and the amplifier 22
A high-frequency switch 51 interposed in the signal line between the high-frequency switch 51 and a pulse generator 52 that generates a control pulse having a desired pulse width for the high-frequency switch 51 at the same period as the transmission trigger pulse; A delay circuit 53 for delaying the control pulse on the time axis to determine the position of the time axis on which the reflected wave should be cut, and comparing the STC signal level with the reference level to determine whether the level of the STC signal is the reference level A comparator 54 that sends out a control signal when it exceeds
And an analog switch 55 that allows a control pulse from the delay circuit 53 to flow to the high-frequency switch 51 in response to a control signal from the control circuit. The cut-off means sends a control pulse to the high-frequency switch 51 when the level of the STC signal exceeds a predetermined reference level.
The reflected wave in a predetermined time region flowing to the second filter 2 is cut.

The operation of the radar type underground exploration apparatus 1 having the above configuration will be described with reference to the time chart of FIG. The transmission trigger generator 11 generates a transmission trigger pulse at a period of 1 μs. Therefore, the repetition frequency of the transmission radio wave radiated from the transmission probe 13a is 1 Mz. The propagation speed of radio waves in the ground depends on the geology, for example, 10 cm
/ Ns, the time required for the reflected wave from the depth of 5 m to return is 100 ns. Usually, the exploration area such as a gas conduit is about 5 m underground, so a repetition frequency of 1 Mz is sufficient.

The control pulse generated by the pulse generator 52 in response to the transmission trigger pulse is sent to the analog switch 55 by the delay circuit 53 with a predetermined time delay from the rise of the transmission trigger pulse. The delay time of the control pulse is set to a time region where the reflected wave is desired to be cut, and is set to a time region where a reflected wave from the reflector 3a near the ground surface 2 normally occurs.

The STC signal is a signal that increases stepwise with the count of the transmission trigger pulse. In this embodiment, the signal returns to the lowest level after the count of the transmission trigger pulse is 1,000 times. Since the gain of the amplifier 22 changes in accordance with the signal level of the STC signal, the amplifier 22 repeats from the lowest gain to the highest gain in a cycle of 1 ms.

In FIG. 2, regarding the temporal change of the analog switch, the ON state is represented by a low level and the OFF state is represented by a high level, and the level of the STC signal exceeds a reference value (threshold level) which can be set in advance. , From the low level to the high level to allow the control pulse of the high frequency switch to pass from the delay circuit 53 to the high frequency switch 51. The high-frequency switch 51 is turned off (open) while receiving the control pulse, more specifically, the high-level signal, so that the reflected wave passes from the receiving unit 14 to the amplifier 22 for a time corresponding to the pulse width of the control pulse. Cut off.

The reflected wave A shown in FIG. 2 indicates the waveform of the reflected wave at the receiving unit 14, the first peak waveform indicates the reflection from the reflector 3a near the ground surface 2, and the second peak waveform
Represents the reflection from the reflector 3b away from the ground surface 2. The drawing of the reflected wave emphasizes legibility, and does not show an accurate shape with respect to its time axis or signal strength axis. This reflected wave is obtained every time the transmission trigger pulse is repeated.

The reflected wave B shown in FIG. 2 shows the waveform of the reflected wave after being amplified by the amplifier 22, and is amplified as the level of the STC signal increases. However, STC
When the signal level exceeds the reference value (threshold level), the time domain in which the first peak wave occurs is cut off by the operation of the high-frequency switch 51 by the control pulse adjusted to the first peak wave. This prevents a reflected wave having a strong signal level from near the surface at a high amplification factor from entering the amplifier 22, and prevents the amplifier 22 from saturating.

Sampling is performed by one sampling gate for one reflected wave reception signal received at a repetition period of 1 μs. The time position of the first sampling gate is set at the position on the time axis corresponding to the ground surface 2, and thereafter sampling is performed at a point delayed by 0.1 ns every repetition cycle of the transmission radio wave. That is, the n-th sampling is 1 μm from the (n−1) -th sampling.
Performed after s + 0.1 ns. The sampling returns to the first sampling point every 1000 times.
This means that a time region of 100 ns was sampled by sampling 1000 times, which corresponds to a region having a depth of 5 m from the ground surface 2 and is a sufficient region for exploring a gas conduit or the like. If the sampling interval is 0.1 ns, the micro can satisfactorily restore the waveform of the reflected wave in the region. FIG. 3 shows a reflected wave restored by synthesizing signals sampled one by one from 1000 reflected waves, and the display period of the reflected wave is 1 μs * 10.
00 = 1 ms, and the time axis is expanded to 1000 times, and can be displayed on the display unit 42 with low resolution. Both the reflected wave reflected from the reflector 3a near the ground surface 2 and the reflected wave reflected from the reflector 3b remote from the ground surface 2 have the same time as the STC signal despite the large attenuation rate of the radio wave in the ground. Due to the change of the dependent amplification factor, the values are displayed at almost the same level, facilitating the exploration evaluation.

Here, the point which should be particularly emphasized is the ground surface 2
In order to sample the reflection from the reflector 3b away from the ground, it is necessary to perform the sampling on the reflected wave amplified with a high amplification factor. In this case, as is clear from FIG. Since the time region in which the signal from the reflector 3a occurs is cut by the action of the blocking means 50, the amplifier 22
Does not have to be saturated, and it is possible to sample the reflected wave amplified with high accuracy.

The present invention is not limited to the values such as the repetition frequency and the sampling interval used in the above description, and it goes without saying that the present invention can be implemented with various values as needed. In the above-described embodiment, the comparator 54 that compares the reference value and the level of the STC signal is employed as control means for controlling the analog switch 55. Instead, as shown in FIG. It is also possible to control ON / OFF of the analog switch 55 by a time gate, that is, a timer or a counter 154. Since the level of the STC signal is increasing with time, the time to reach the reference value is predicted. Accordingly, the same control can be performed by turning on the analog switch 55 by counting the estimated time or the number of transmission trigger pulses by the timer or the counter 154. In FIG. 4, other members are the same as those in FIG. 1, and those having the same functions are designated by the same reference numerals, and description thereof is omitted.

The transmission probe 3a and the reception probe 3
Although b is provided separately, a configuration may be adopted in which the transmission probe 3a and the reception probe 3b are shared by one probe, and the path between the transmission unit 12 and the reception unit 14 is branched by a biplexer or the like.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing an example of a radar type underground exploration device according to the present invention.

FIG. 2 is a time chart showing the operation of the radar type underground survey device shown in FIG. 1;

FIG. 3 is an explanatory diagram showing a restored reflected wave.

FIG. 4 is a functional block diagram showing another example of a radar type underground exploration device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Transmitting part 14 Receiving part 20 Amplifying part 30 Sampling part 41 Signal processing part 50 Blocking means

Claims (5)

[Claims] 1. A transmitting unit for emitting a pulse wave into the ground at a predetermined repetition period, a receiving unit for receiving a reflected wave returned from the ground, and making the received reflected wave correspond to the repetition period. An amplifying unit that amplifies the amplified reflected wave at a changed amplification factor, a sampling unit that samples the amplified reflected wave with a time gate displaced at each repetition cycle, and processes a sampling signal sampled at the repetition cycle. And a signal processing unit for restoring the reflected wave by means of a radar underground exploration apparatus, wherein a part of the reflected wave entering the amplification unit is cut off to prevent a signal exceeding a predetermined level from entering the amplification unit. A radar-type underground exploration device comprising a blocking means. 2. The apparatus according to claim 1, wherein said cut-off means operates when an amplification factor of said amplification section exceeds a predetermined value.
2. The radar type underground exploration device according to 1. 3. The high frequency switch provided between the receiving unit and the amplifying unit, a pulse generator for generating a control pulse for controlling the high frequency switch, and The radar type underground exploration apparatus according to claim 1, further comprising: an analog switch to be sent to the switch; and a comparator that controls the analog switch according to an amplification factor of the amplification unit. 4. The radar type underground exploration apparatus according to claim 1, wherein said blocking means operates at predetermined time intervals. 5. The high frequency switch provided between the receiving section and the amplification section, a pulse generator for generating a control pulse for controlling the high frequency switch, The radar type underground exploration apparatus according to claim 1, further comprising: an analog switch to be sent to the switch; and a timer for controlling the analog switch at the predetermined time interval.