JPS60173486A - Survey device for underground buried body - Google Patents

Abstract

PURPOSE:To perform good inspection of S/N with low peak transmitting electric power by performing correlation processing by using encoded pulses when detecting the depth of the underground buried body on the basis of the time delay of a receive reflected pulse. CONSTITUTION:A pulse generator 2 generates a pulse train with constant length which has clear autocorrelation in response to an encoded sequence generator 1, and sends out electromagnetic pulses to a transducer 4. Then, a reflected wave from the underground buried body is received by a transducer 4 and a receiver 5 and the received pulse train is supplied to a correlator 6 for autocorrelation processing, so that the depth of the underground buried body is detected from the time delay of receive reflected pulses. Then, N pulses in the pulse sequence with constant length are compressed in a constant-length code section by N-pulse autocorrelation to increase its amplitude N time, and noises in the receive signals are added at random to decrease the output of the correlator 6. Consequently, the underground buried body is surveyed at an excellent S/N with low peak transmitted electric power.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an underground object exploration device that radiates a pulse signal into the ground and searches for a buried object using reflected pulses from the underground object.

BACKGROUND OF THE INVENTION Conventional devices of this type detect buried objects by focusing only on one transmitted wave and one received wave obtained thereby, and detect reflected waves from the underground objects. Therefore, in order to increase the detection distance of buried objects, it is necessary to increase the transmission peak power. Furthermore, in order to improve the distance resolution of buried objects, it is necessary to use pulses with a narrow pulse width. However, increasing the transmission peak power is limited by physical constraints such as circuit components of the transmitter and receiver.

For this reason, conventional underground buried object exploration devices have the disadvantage of a poor signal-to-noise ratio. Moreover, because of the high attenuation characteristics of soil, reflected waves from buried objects are received with significant attenuation, making the above-mentioned drawbacks even more pronounced.

OBJECTS OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional drawbacks and to provide an underground buried object exploration device capable of obtaining a good signal-to-noise ratio with low transmission peak power.

Structure of the Invention The underground buried object exploration device of the present invention radiates the output of a pulse generator into the ground and receives the pulse A reflected by the underground buried object,
In an underground buried object exploration device that detects the depth of underground buried objects by a time delay of a received pulse, a coded sequence generator that drives the pulse generator with a code sequence of a certain length encoded at a certain code interval; , and a correlator that performs correlation processing on received signals, and underground objects are searched based on the processing results of the correlator.

Note that the same effect can be obtained by providing an encoder that encodes the received signal without encoding the transmitted pulse, and by calculating the correlation of the output of the encoder (No. 8).

Furthermore, if a receiver is provided that samples the received signal at a time interval slightly longer than the fixed period, the output of the receiver can generate a signal obtained by expanding the received signal within the fixed period to a time that is an integral multiple of the fixed period. Since it can be obtained, it is possible to perform frequency conversion isometrically.

Embodiments of the Invention Next, the present invention will be described in detail with reference to the drawings.

Figure i'51 is a block diagram showing a first embodiment of the present invention. ? The ternary sequence generator 1 generates a code sequence (sequence length N), such as an M sequence or a bar code "-", for example.

t) interval Tc and repetition period T), and supplies the pulse generator 2 with a tri-force pulse train having a polarity corresponding to each code of the code sequence. The No. 91 sequence is a code sequence in which autocorrelation clearly appears and has a high pulse compression rate. The pulse generator 2 is driven by a trigger pulse train inputted from the encoded sequence generator 1, generates a pulse having a predetermined shape and a polarity corresponding to the polarity of the trigger pulse, and generates a pulse having a predetermined shape and a polarity corresponding to the polarity of the trigger pulse, and generates a pulse having a predetermined shape and transmitting the pulse to the directional coupling circuit 3 and the I/transducer 4. radiates into the ground as an electromagnetic pulse according to the shape of the excitation pulse. The transducer 4 uses an antenna to send out the dj:ω pulse, or converts the output pulse of the pulse generator 2 into a wave such as an ultrasonic wave and radiates it into the interior. Also good.

A portion of the electromagnetic waves reflected by the underground target returns to the transducer 4 and is input to the receiver 5 via the directional coupling circuit 3. The output accuracy of the receiver 5 is inputted to a correlator 6, which uses the output IJ3 of the receiver 5 to indicate the beginning of the encoded sequence supplied from the waiting sequence generator l. Correlation processing is performed using the 1-rigger signal and a trigger signal (period Tc) that reduces the start of each number 1.

For example, by accumulating received signals for -periods T, a signal obtained by inverting the polarity of the -1-th received signal according to the encoding polarity of the first code, and a signal obtained by inverting the polarity of the -1-th received signal according to the encoding polarity of the second code are stored. A signal obtained by inverting the polarity of the received signal described above and shifting it by l code interval Tc, and a signal obtained by inverting the polarity of the received signal described in 3. ..., if we detect the peak position of the signal obtained by sequentially adding the polarity inversion process according to the polarity of the Nth code and the signal shifted by l code interval Tc at corresponding time points. , this peak position corresponds to the delay time of the reflected wave. Moreover, this peak is N times the peak value of each received pulse, as will be described later.

Now, each code of the encoded sequence is converted to Kl and 2 in turn.

......, KN, the correlation value Pi is expressed as, for example, when the sequence code is a bar code, i=0
For , PO=N, and for i Hong O, Pi−±
It becomes 1.0. Therefore, N
Each pulse can be pulse compressed into one code interval (Tc), and its amplitude can be N times the amplitude of each pulse. Therefore, the aforementioned peak will be N times the peak value of the individual received pulse. Further, since the noise in the received signal is randomly added in the correlation processing, the noise in the correlator output is extremely small. Therefore, the signal-to-noise ratio is improved, and it is possible to detect small reflected waves that are attenuated in the upper part.
More than two reflected waves can also be easily identified. The processing results of the correlator 6 are stored in the storage device 8, and can be displayed in the form of a waveform or burial depth in accordance with the display format of the display device 7 to present the state of electromagnetic wave reflection to the measurer. .

Further, in the second embodiment of the present invention, the coded sequence generator l sends a timing signal to the receiver 5 shown in FIG. (for example, α-T1512), the received signal is sampled and held and output. Therefore, the receiver 5 is capable of enlarging the received signal of -period T to a time width of T/α (for example, 512 times) and outputting it. That is, isometric frequency conversion can be performed. Then, the correlator 6 performs correlation processing on the output signal of the receiver 5 using, for example, 512Tc as a time unit.

FIG. 2 is a block 1Δ showing a third embodiment of the present invention. In this case, the pulse generator 2 is driven by a trigger pulse generator 9 that generates a trigger pulse at a constant period T. Then, reflected waves from objects buried in the ground are input to the receiver 5 via the transducer 4 and the directional coupling circuit 3. The encoder 14 has a received wave storage function and a multiplication function, and uses N received signals for one period T output from the receiver 5, and delays each by a fixed code interval Tc. The resulting signals are converted into polarities corresponding to the respective codes of the N code sequences, and the polarities are added and output as one signal. Then, by correlating the output signals of the encoder 14 with the correlator 6, buried objects can be detected in the same manner as in the first embodiment described above. In this case as well, the amplitude of the received pulse is multiplied by N by the correlation process, and the noise is completely randomized. Therefore, the same effects as the first embodiment are achieved.

In the fourth embodiment, a timing signal synchronized with the trigger pulse of the constant period T is supplied from the trigger pulse generator 9 to the receiver 5 of FIG. A rather long period T + α (α is T151, for example)
2), and the sampled value is held and output. In this case, the output signal of the receiver 5 is a signal for one cycle T which is expanded to a time width of 512T, for example. That is, the frequency is converted. Then, the encoder 14 converts the output signal of the receiver 5 into 512
Encoding is performed at a code interval of Tc, and the output of the encoder 14 is subjected to correlation processing by a correlator 6.

Effects of the Invention As shown in 1, in the present invention, the 4i5' method for detecting underground objects by receiving reflected waves of transmitted pulses
3. In the acquisition process, the pulse signal is converted into a code sequence on the transmitting side or the receiving side, and a correlator is provided to perform correlation processing on the code sequenced received signal, and underground objects are detected based on the processing result of the correlator. With this configuration, pulse compression can increase the pulse amplitude and improve the signal-to-noise ratio. In other words, there is an effect that a decrease in search accuracy due to reception noise can be prevented. Also, since the amplitude value increases due to correlation processing, the larger S
This is equivalent to searching using a transmitter with a small peak power, and the search distance can be increased even with a small transmission peak power.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing first and second embodiments of the invention, and FIG. 2 is a block diagram showing third and fourth embodiments of the invention. In the figure, 1: 'TI type resistance series generator: pulse generator, 3: Force plane P1 coupling circuit, 4 Nidorance duplex, 5: Receiver 4. 6: correlator, 7: display device, 8: storage device, 9 pulse generator, 14: encoder. Person 11 Representative of City Telephone and Telephone Public Corporation Patent attorney Resident Ell Toshimuneo 1 Figure

Claims (1)

[Claims] (1) The output of the pulse generator is emitted into the ground, the pulse reflected by underground objects is received, and the received pulse II! A coded sequence generator that drives the pulse generator with a code sequence of a constant length encoded at a constant code interval in a buried object exploration device that detects the depth of an underground buried object by a delay of f time; An underground buried object exploration device characterized by comprising a correlator that performs correlation processing on received signals, and searches for underground objects based on the processing results of the correlator. In an underground buried object exploration device, the received signal is sampled at a time interval slightly longer than the repetition period of the code sequence of the certain length, and the received signal within the repetition period is expanded to a width that is an integral multiple of the repetition period and output. The correlator is characterized in that the correlator performs correlation processing on the output signal of the receiver. (3) The output of the pulse generator is radiated underground and reflected by underground objects. In an underground buried object exploration device that receives pulses and detects the depth of underground objects based on the time delay of the received pulses, the device includes a trigger pulse generator for driving the pulse generator at a constant cycle, and a trigger pulse generator for driving the pulse generator at a predetermined period. It includes an encoder that converts the polarity of a signal delayed by a code interval and outputs the signal in accordance with each code of a code sequence of a fixed length, and a correlator that performs autocorrelation processing on the output signal of the encoder. hand,
An underground buried object exploration device characterized in that underground buried objects are explored using the output of the correlator. (4) In the underground buried object exploration device according to claim 3, by sampling the received signal at time intervals slightly longer than the certain period, the received signal within the certain period is an integer multiple of the certain period. The encoder is characterized in that the encoder encodes the output even of the −1−th receiver.