RU2447464C1 - Geophysical radar set - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: geophysical radar set has a processing and control unit 1, an interface 2, a transmitter 3, a transmitting antenna 4, a first mixer 5 of a stroboscopic converter, a first strobe former 6, a receiving antenna 7, a receiver 8, a second strobe former 9, a second mixer 10 of a stroboscopic converter, a correlator 11, a flip flop 12, a switch 13, a digital-to-analogue converter 14, a first amplifier 15, an analogue-to-digital converter 16, an audio indicator 17, a liquid crystal display 18, a delay line 19, a substracter 20, an integrator 21, a divider 22, a reference voltage generator 23, a comparator 24, a controlled delay unit 25, a multiplier 26, a low-pass filter 27, a second amplifier 28, a decoder 29 and an indicator 30 of the depth of a subsurface object.

EFFECT: high accuracy and sensitivity of automatic measurement of the depth of subsurface objects by using a correlation function derivative

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Description

The proposed radar relates to geophysics, in particular to devices for geoelectrical exploration using electromagnetic waves of high frequency, and can be used in mineral exploration, as well as for the search for utilities and other hidden heterogeneities in the investigated subsurface layer of the earth's surface.

Known devices for geoelectrical exploration (ed. Certificate of the USSR No. 397.877, 455.307, 746.370, 817.640, 1.100.603, 1.151.900, 1.247.805, 1.300.396, 1.420.574, 1.553.933, 1.721.566; RF patents No. 2.044.331, 2.105.330, 2.194.292, 2.234.112, 2.256.941, 2.375.729; US patents No. 5.819.859, 6.677.201; Petrovsky N.D. Radio wave methods in underground geophysics .-- M., 1971 and others).

Of the known devices, the closest to the proposed one is "Geophysical radar" (RF patent No. 2.375.729, G01V 3/12, 2008), which is selected as a prototype.

The principle of operation of this radar is based on the method of ultra-wideband radar sensing, which assesses the change in the unsteady electromagnetic field formed by electromagnetic waves reflected from a subsurface object after it is received by a sounding radio signal, which uses a sequence of radio pulses with a small number of periods of high-frequency oscillations in each of them (up to to one). In this case, the separation of the transceiver channels on the air is carried out using two antennas (transmitting and receiving), which form a two-antenna unit.

To exclude direct transmitter radiation and reflections from the air-ground surface and from layers with different depths in the known radar, "vertical gating" is used.

In addition, the known radar provides automatic measurement of the depth of the subsurface objects by correlation processing of the probing and reflected signals.

To accurately measure the depth of subsurface objects, it is necessary to more accurately determine the value of the adjustable delay τ _s corresponding to the maximum of the correlation function R (τ). However, in the region of the maximum, the correlation function has a very small slope and changes insignificantly with changes in τ (Fig. 2, a). The form of the derivative of the correlation function dR (τ) / dt is much more favorable for the search for the maximum. At the point τ = τ _{s, the} derivative has a significant steepness and, in addition, changes sign depending on the position relative to the point τ = 0.

Thus, finding the maximum of the correlation function (the maximum principle is an extreme problem) is replaced by the minimum measurement principle - stabilization of the zero value of the controlled variable. This principle can significantly increase the accuracy and sensitivity of the meter.

An object of the invention is to increase the accuracy and sensitivity of automatic measurement of the depth of subsurface objects by using the derivative of the correlation function dR (τ) / dt.

The problem is solved in that the geophysical radar, containing, in accordance with the closest analogue, sequentially connected processing and control unit, interface, transmitter, which is used as a shock excitation generator and to the second output of which a transmitting antenna is connected, the first mixer of the stroboscopic converter, the second whose input through the first gate driver is connected to the second output of the interface, and the trigger, the second input of which is connected to the second output of the unit is adjustable the first delay, the receiving antenna in series, the second mixer of the stroboscopic converter, the second input of which is connected to the third output of the interface through the second gate driver, the key, the second input of which is connected to the trigger output, the first amplifier, the second input of which is connected to the fourth output of the interface through the digital-to-analog converter , to the fifth, sixth and seventh outputs of which a processing and control unit, sound and liquid crystal indicators are connected, respectively, ki, a subtraction unit, the second input of which is connected to the output of the first amplifier, an integrator, a division unit, the second input of which is connected to the output of the subtraction unit, a comparison unit, the second input of which is connected to the eighth output of the interface through a voltage generator, and an analog-to-digital converter, the output of which is connected to the second input of the interface, the adjustable delay unit, multiplier and low-pass filter, connected in series to the first output of the transmitter, differs from the closest analogue in that it abzhen the second amplifier, differentiator, and an indicator of the depth of the subsurface objects, the second input of the adjustable delay unit through the second amplifier connected to the output of the low-pass filter, the second input of the multiplier through the differentiator connected to the output of the second mixer, the indicator of the depth of the connected to the second output of the adjustable delay unit subsurface objects.

The structural diagram of the proposed radar is presented in figure 1. An exemplary form of the correlation function R (τ) and its derivative dR (τ) / dτ are shown in Fig. 2 (a, b).

The geophysical radar contains serially connected processing and control unit 1, an interface 2, a transmitter 3, which uses a shock excitation generator and to a second output of which a transmitting antenna 4 is connected, the first mixer 5 of the stroboscopic converter, the second input of which is connected to the first shaper 6 of the gate the second output of interface 2, and a trigger 12, the second input of which is connected to the second output of the adjustable delay unit 25, the receiving antenna 7 connected in series, the second with a mixer 10 of the stroboscopic converter, the second input of which is connected through the second gate driver 9 to the third output of the interface 2, key 13, the second input of which is connected to the output of the trigger 12, the first amplifier 15, the second input of which is connected via the digital-to-analog converter 14 to the fourth output of the interface 2, the fifth, sixth and seventh outputs of which are connected to the processing and control unit 1, the audio 17 and the liquid crystal 18 indicators, respectively, the delay line 19, the subtraction unit 20, the second input of which is connected n with the output of the amplifier 15, the integrator 21, the division unit 22, the second input of which is connected to the output of the subtraction unit 20, the comparison unit 24, the second input of which is connected to the eighth output of the interface 2 through the generator 23 of the reference voltage, and the analog-to-digital converter 16, the output which is connected to the second input of the interface 2, a variable delay unit 25, a multiplier 26, the second input of which is connected through a differentiator 29 to the output of the second mixer 10 of the stroboscopic transducer, connected in series to the first output of the transmitter 3 the browser, a low-pass filter 27 and a second amplifier 28, the output of which is connected to the second input of the adjustable delay unit 25, to the second output of which an indicator 30 of the depth of subsurface objects is connected. The adjustable delay unit 25, the multiplier 26, the low-pass filter 27 and the second amplifier 28 form a correlator 11.

Geophysical radar operates as follows.

The main mode of operation is the "Search" mode. This mode is set automatically when the device is turned on and is used when searching and recognizing subsurface objects.

When applying power to the radar unit 1, the processing and control initiates the installation of the initial modes of all nodes of the radar. At the command of the processing and control unit 1, the shock excitation generator 3 generates a probe pulsed ultra-wideband signal in the form of a single sinusoid period with an amplitude of 25 V and a duration of 1 ns, emitted by the transmitting antenna 4 in the direction of the Earth's surface.

The detection of subsurface objects in the "Search" mode is carried out by the operator by moving the antenna unit mounted on the rod in front of him right and left and moving forward in a given direction. In this case, it is necessary to ensure that the antenna unit moves parallel to the surface being examined at a fixed distance (no more than 5 cm from it). The speed of movement of the antenna unit is selected depending on the search conditions and should be within 0.1 ÷ 1.0 m / s. In the search process, it is necessary to alternate the transverse and longitudinal displacements of the antenna unit so that after each swing from right to left or left to right, the antenna unit moves forward up to 20 cm (by the size of its linear size). In this case, it is necessary to ensure that the entire checked area is examined.

An electromagnetic wave reflected from a subsurface object acts on the receiving antenna 7. This antenna is also affected by interfering direct radiation of the transmitter 3 and the reflected signal from the air-ground interface. Moreover, large amplitudes will have a direct signal and a signal reflected from the air-ground interface.

Part of the energy of the probe signal from the reference output of the transmitter 3 is supplied to the first input of the first mixer 5 of the stroboscopic converter, the second input of which is supplied with a short strobe pulse from the shaper 6 of the strobe. The pulse generated in the mixer 5, which is the instantaneous value of the probing periodic signal, is fed to the installation input of the trigger 12. The trigger 12 is transferred to the first (zero) state, in which a negative voltage is generated at its output.

The reflected signal containing information about the interface between the media and the subsurface object comes from the output of the receiving antenna 7 to the first input of the second mixer 10, the second input of which is supplied with a short strobe pulse from the output of the gate former 9.

Part of the energy of the probe signal from the reference output of the transmitter 3 simultaneously enters through the adjustable delay unit 25, with a variable time delay τ, to the first input of the multiplier 26, to the second input of which a reflected signal is supplied through the differentiator 29 from the output of the second mixer 10 of the stroboscopic converter, the delay time of which defined by the expression:

,

,

where h is the depth of the subsurface object;

C is the propagation velocity of radio waves.

. Усилитель 28, предназначенный для поддержания нулевого значения производной корреляционной функции

и подключенный к выходу фильтра 27 нижних частот, воздействует на управляющий вход блока 25 регулируемой задержки и поддерживает вводимую им задержку τ, равной нулю, что соответствует минимальному значению производной корреляционной функции

.The voltage obtained at the output of the multiplier 26 is passed through a low-pass filter 27, at the output of which a derivative of the correlation function is formed

. Amplifier 28, designed to maintain a zero value of the derivative of the correlation function

and connected to the output of the low-pass filter 27, acts on the control input of the adjustable delay unit 25 and maintains the delay τ introduced by it equal to zero, which corresponds to the minimum value of the derivative of the correlation function

.

The scale of the adjustable delay unit 25 is associated with an indicator 30 of the depth of the subsurface objects, which allows you to directly read the measured value of the depth of the subsurface object in the ground:

.

.

The pulse generated at the second output of the adjustable delay unit 25, corresponding to the time delay τ = τ _s , is supplied to the second input of the trigger 12. The latter is transferred to the second (single) state, in which a positive voltage is generated at its output. This voltage is supplied to the control input of the key 13 and opens it. In the initial state, the key 13 is always closed. The correlator 11 automatically determines the depth of the subsurface object and performs "vertical gating", which provides a sequential view of the subsurface space from the air-ground interface to layers of different depths.

“Horizontal gating” allows against the background of electromagnetic field variations not related to the electromagnetic wave reflected from the subsurface object, to reliably select subsurface objects in the subsurface layers.

To exclude the influence of periodic quasi-stationary variations of the Earth’s electromagnetic field, a periodic measurement of the field strength and the normalization of the difference signal of two successive measurements are performed, integrate the difference signal, divide the difference signal into the integrated difference signal. The operation of comparing a normalized signal with a given threshold value allows you to make a decision about the presence or absence of a subsurface object.

To do this, the pulse generated in the mixer 10, which is the instantaneous value of the received periodic signal reflected from the subsurface object, or the pulse due to variations in the electromagnetic field, through the open spike 13 is fed after amplification in the amplifier 15 to the subtraction unit 20 directly and through the delay line 19. Moreover, at each observation point, at least two consecutive measurements of these pulses are made. Then, the operation of subtracting two consecutive measurements is performed. For this, the pulse corresponding to the previous measurement is delayed by the delay line 19 until it is compared with the subsequent pulse in the subtraction unit 20.

The operation of integrating the difference signal and dividing the difference signal by the integrated difference signal is performed in blocks 21 and 22. In block 24, the normalized signal is compared with the threshold value of the signal set by block 23. If the threshold level is exceeded, the signal is input to the analog-to-digital converter 16, where it is converted into a digital formula and transmitted through interface 2 to special computer 1, and then to the screen of the liquid crystal indicator 18, on the screen of which in real time a flat brightness pattern of subsurface objects is observed.

The maximum amplitude of the received signal is compared with the set threshold value, above which the sound indicator 17 turns on.

The appearance of sound and visual signals requires the operator to stop and indicates that an object is located in the coverage area of the antenna unit, the origin of which should be established, and if necessary, specify its location and shape.

The “Scan” mode and the formation of a vertical cut of soil with an object. It is carried out by switching from the “Search” mode by pressing the “Scan” button. 20 seconds after the signal is processed, a radar image of the subsurface object appears on the screen of the indicator 18, giving an idea of the shape and size of the object.

To identify the detected object with the available standards, the operator must turn to the trained algorithm, and the corresponding name is displayed on the screen (for example, “object 2”). In case of discrepancy, the message “object not recognized” is displayed.

To determine the material of the detected object, the operator starts the basic algorithm by pressing the Scan button. The screen displays a message about the type of material: “Metal”, “Composite” or “Plastic”.

The interaction of the processing and control unit 1 with the other nodes of the radar, as well as the organization of the operation control, is carried out through the interface circuit 2.

.Thus, the proposed geophysical radar in comparison with the prototype provides increased accuracy and sensitivity of automatic measurement of the depth of subsurface objects. This is achieved using the derivative of the correlation function

.

The method of measuring the depth of subsurface objects by minimizing the derivative of the correlation function (passing through zero), along with high accuracy and sensitivity, has another very significant advantage of the zero method, namely: the amplitude of the input signals and its fluctuations do not affect the measurement result.

Claims (1)

A geophysical radar comprising a processing and control unit, an interface, a transmitter, which uses a shock excitation generator and a transmit antenna connected to a second output, a first stroboscopic mixer, the second input of which is connected to the second output of the interface through the first gate driver, and trigger, the second input of which is connected to the second output of the adjustable delay unit, a receiving antenna connected in series, the second mixer a stroboscopic converter, the second input of which is connected to the third output of the interface through the second gate driver, the key, the second input of which is connected to the trigger output, the first amplifier, the second input of which is connected via the digital-to-analog converter to the fourth output of the interface, to the fifth, sixth and seventh outputs of which are connected processing and control unit, sound and liquid crystal indicators, respectively, delay line, subtraction unit, the second input of which is connected to the output of the first amplifier I, the integrator, the division unit, the second input of which is connected to the output of the subtraction unit, the comparison unit, the second input of which is connected to the eighth output of the interface through the voltage generator, and the analog-to-digital converter, the output of which is connected to the second input of the interface, connected in series to the first the output of the transmitter is an adjustable delay unit, a multiplier and a low-pass filter, characterized in that it is equipped with a second amplifier, a differentiator and an indicator of the depth of the subsurface objects, the second input of the adjustable delay unit through the second amplifier connected to the output of the low-pass filter, the second input of the multiplier through the differentiator connected to the output of the second mixer, the depth indicator of subsurface objects is connected to the second output of the adjustable delay unit.

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