RU2451954C1 - Mobile georadar for remote search of location of underground communication main lines and determination of cross dimensions and depth thereof - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to radar techniques and apparatus for detecting subsurface objects, which enable to search the route of underground pipelines, determine their cross dimensions and their depth in the ground, and also detect points of leakage of oil and gas from underground pipelines. The mobile georadar has an aircraft 1, a transmitting 2 and a receiving 3 antenna, a clock, an antenna control unit, a high-frequency pulse generator, a receiver, a multitapped delay line, an adder, a processor with software and a monitor.

EFFECT: high azimuthal resolution by synthesising the aperture of the receiving antenna.

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Description

The proposed device relates to the field of instrumentation, in particular to radar methods and non-destructive testing, allowing remotely, for example from an aircraft, to search for the trajectory of laying the routes of the main trunk underground pipelines (oil and gas pipelines, gas pipelines, fiber optic and metal cables) made of metal and non-metallic materials, determine their transverse size and depth of occurrence of tracks in the ground, and also detect m stopolozhenie oil and gas leaks from the main underground pipeline.

Known mobile georadars for remote determination of the trajectory of laying an oil and gas pipeline route and its depth in the ground (ed. Certificate of the USSR No. 1.287.680, 1.810.859; RF patents No. 2.046.378, 2.119.680, 2.202.812, 2.206. 106, 2.207.588, 2.256.941; US patents Nos. 4,905.008, 6.087.883, 6.252.588; patent WO No. 01 / 38.902 V. Dikarev et al. Water, oil, gas and pipes in our lives St. Petersburg, 2005 and others).

Of the known devices, the closest to the proposed one is "Mobile georadar for remote search for the location of underground trunk communications and determine their transverse size and depth in the ground" (RF patent No. 2.256.941, G01V 3/17, 2004), which is chosen as prototype.

In this case, the georadar antennas are made in the form of collimating arrays pivotally mounted externally, for example, on the bottom of the aircraft fuselage with the possibility of synchronous swinging of each antenna in the plane of the fuselage cross section at an angle of 1-5 °. Antennas are focused towards the surface of the earth. The duration of the probe electromagnetic pulses is fixed within the range of 10-0.2 ns.

However, the known mobile georadar has a relatively low resolution in azimuth.

An object of the invention is to increase the resolution in azimuth by synthesizing the aperture of the receiving antenna.

The problem is solved in that a mobile georadar for remote search for the location of underground trunk lines and determining their transverse size and depth in the ground, containing, in accordance with the closest analogue, an aircraft, a high-frequency pulse generator and a transmitting antenna of high-frequency electromagnetic pulses sequentially connected, the second the input of which is connected to the first output of the antenna control unit, the high frequency receiving antenna connected in series of electromagnetic pulses, the second input of which is connected to the second output of the antenna control unit, and the receiver, a processor with software and a monitor connected in series, while the antennas are made in the form of collimating gratings pivotally mounted outside on the bottom of the fuselage of the aircraft with the possibility of synchronous swinging of each antenna in the plane of the cross section of the fuselage at an angle of 1-5 ° relative to the vertical and regardless of the roll of the aircraft and focused on the surface of the earth whether, the duration of the probe electromagnetic pulses is fixed and assigned within the range of 10-0.2 ns, and the data of the dependence of contrast on the electrophysical properties of fractions of soils and materials of pipeline communications are entered into the processor software, differs from the closest analogue in that it is equipped with a synchronizer, multi-tap a delay line and an adder providing synthesis of the aperture of the receiving antenna, and the control inputs of the antenna control unit, a high-frequency generator pulses and the receiver are connected to the corresponding outputs of the synchronizer, a multi-tap delay line and an adder are connected to the output of the receiver, the control input of which is connected to the output of the receiver, and the output is connected to the input of the processor with software, the control input of which is connected to the fourth output of the synchronizer.

Topographic and geodetic fragment of the relative position of the mobile GPR and the underground highway route is shown in figure 1. The structural diagram of the equipment placed on board the aircraft is presented in figure 2. The principle of the formation of the synthesized aperture of the receiving antenna 3 is shown in Fig.3. The geometric side view of the synthetic aperture radar is shown in Fig.4.

Mobile georadar contains an aircraft 1, transmitting 2 and receiving 3 antennas of high-frequency electromagnetic pulses (figure 1).

The equipment located on board the aircraft 1 contains a synchronizer 4 connected in series, a high-frequency pulse generator 6 and a transmitting antenna 2, the control input of which is connected to the first output of the antenna control unit 5, serially connected to the receiving antenna 3, the control input of which is connected to the second output of the block 5 antenna control, the control input of which is connected to the third output of the synchronizer 4, multi-tap delay line 8.i (i = 1, ..., n), an adder 9, the control input of which is connected output from the receiver, the processor 10 with the software, which control input is connected to the output of the synchronizer with quarter 4 and the monitor 11 (Figure 2).

Antennas 2 and 3 are made in the form of collimating arrays pivotally mounted outside on the bottom of the fuselage of the aircraft with the ability to synchronously swing each antenna 2, 3 in the plane of the cross section of the fuselage at an angle of 1 ... 5 ° relative to the vertical and regardless of the roll of the aircraft and focused to the side the surface of the earth. Collimation of antenna arrays allows you to form the necessary aperture of the radiated and reflected electromagnetic beam.

The duration of the probe electromagnetic pulses is fixed, the value of which is assigned within the range of 10 ... 0.2 ns and is selected depending on the actual geology and type of bulk soil fractions, pipeline material and the database of the dependence of contrast on the electrophysical properties of bulk soil fractions recorded in the processor memory. The maximum number of points in each implementation is 2048, the minimum time between samples is 2.5 ns, and the maximum is 1 ns.

It should be noted that fractions of backfill soils into the channel along which the route is laid, as a rule, are small-sized (sand, peat, light loam, sandy loam) compared with the transverse dimensions of extended pipelines, and large fractions such as stones and cobblestones are not used when filling the channel.

The high-frequency generator 6 is designed to emit short high-frequency pulses into the ground through the airspace through the transmitting antenna 2. The reflected high-frequency pulses from the ground and the interfaces between fractions and other objects in the ground are received by the antenna 3.

Georadar provides spatial information about the geological characteristics of the translucent medium, in particular, the presence of various fractions in the soil that differ in physical and electrical properties, geometric shape, depth from the surface of the soil, and the type and condition of soils in the section, which affects the electromagnetic parameters pulses (propagation velocity V of the radio waves in the ground and absorption coefficient α).

The radar control method used in GPR is based on the study of the parameters of the emitted and reflected short high-frequency pulses, i.e. in time t the delay between the probing and reflected pulses, the velocity V of the propagation of radio waves in the ground [cm / ns]:

V = C / ε _rel

and the depth of the reflecting pulse:

h = (Vt) / 2,

where C is the speed of light in vacuum, equal to 30 cm / ns;

ε _rel - the complex relative dielectric constant, calculated from the expression

ε _rel = ε ^∗ / ε ₀ ,

where ε ^∗ is the dielectric constant of the investigated medium;

ε ₀ - dielectric constant in vacuum.

When studying the nature of the propagation of electromagnetic waves in the soil for cases when the wavelength is substantially less than the depth to the reflected interfaces of fractions in the soil, which is typical for practice, it is possible to model the physics of the interaction of the electric field with the medium with a known degree of approximation on the capacitor diagram. Since the value of ε _rel depends mainly on the quantitative moisture content and mineral composition of the soil, the relative permittivity ε _rel shows how many times the capacitance of the capacitor increases if this soil is placed instead of air.

According to the degree of absorption of electromagnetic waves, soils are divided into three groups:

- weakly absorbing - unpopulated soils, glass, sands, peat (α = 0.3 ... 7.0 dB / m);

- intermediate - light loam, sandy loam (α = 7.0 ... 14 dB / m);

- highly absorbing - clays, heavy loams, metals (α = 14 ... 26 and more dB / m).

It follows that with an increase in the attenuation of the electromagnetic signal in the soil, the depth of research by the non-destructive testing by the radar method varies from 25 ... 30 m for sand and up to 3 ... 8 m for clay rocks. But this minimum depth limit (clayey rocks) is enough for reliable control of the parameters of the pipeline, since the depth of the pipeline communications in the soil in practice does not exceed 1.5 ... 2 m.

The georadar processor is designed to process the information parameters of incoming reflected signals, comparing them with a database entered into the software. The software consists of two parts: primary (signal registration, its accumulation and creation of files) and secondary information processing. Providing secondary processing is implemented in the form of the package "Geo-data for Windows", which provides the operator with the following features:

- reading data, storing and indicating in the form of a cut of the soil or individual implementations;

- selection of color gamut in the image of a slice of soil;

- data filtering by low and high frequency filters;

- data transformation (scaling, interpolation, decimation and subtraction), aperture synthesis, Hilbert transform;

- logging conversions per session;

- data printing.

Since the data of the dependence of contrast on the electrophysical properties used to fill the channels under the soil pipeline are stored in the processor memory, when comparing the information data with the database, it is possible for the operator to improve the image quality on the monitor screen by rational selection of the duration of the electromagnetic signal probing the soil.

The video monitor is designed to visually monitor the current information coming from the processor.

As an aircraft, there can be an airplane, a helicopter, a glider, a probe, etc.

The principle of operation of a synthetic aperture radar can be explained as follows.

The trajectory of an aircraft (aircraft), whether it be an airplane, a helicopter or an artificial satellite, can be considered straightforward at short time intervals (of the order of several seconds), and the speed along the trajectory can be considered constant. Accordingly, the on-board receiving antenna of the EVA moves uniformly and rectilinearly.

The directional pattern of the antenna array (BOTTOM) is formed as a result of coherent addition of oscillations received by its individual elements. So, if the antenna system consists of n adjacent identical antennas of size d (linear array) and the signals received by each antenna are coherently summed, the antenna array has the same narrow radiation pattern as an antenna of size D = dn (Fig. 3).

The synthesized aperture in the radar uses a small receiving antenna 3, whose wide radiation pattern (BOT) is directed perpendicular to the trajectory, i.e. provides a side view of the space. When the aircraft is flying, the receiving antenna 3 sequentially occupies in space various positions 1, 2, 3, etc. (Fig. 4) in a straight line (flight path of the aircraft), thereby forming an artificial (synthesized) antenna array.

где V_c - скорость ЛА, последовательно принимаемые антенной 3 в каждой точке траектории, и когерентно их суммируя, можно получить узкую диаграмму направленности искусственно сформированной антенной решетки. Размер решетки, т.е. размер синтезированной апертуры приемной антенны 3, равен длине L участка траектории, на котором когерентно суммируются сигналы, принятые в разные моменты времени в разных последовательных точках траектории.Holding signals for a while

where V _c is the speed of the aircraft sequentially received by antenna 3 at each point of the trajectory, and summing them coherently, a narrow radiation pattern of an artificially formed antenna array can be obtained. Lattice size i.e. the size of the synthesized aperture of the receiving antenna 3 is equal to the length L of the path section on which the signals received at different points in time at different consecutive points of the path are coherently summed.

The maximum possible (potential) angular resolution of the radar in azimuth is determined by the width of the radiation pattern of the synthesized antenna

,

,

where L is the size of the portion of the aircraft trajectory on which the received signals are processed and the aperture is synthesized. When a side view of the radar information is formed in a strip of terrain, the boundaries of which are parallel to the trajectory of the aircraft (figure 4).

When the radar moves along the trajectory, the frequency f _{0 of the} signal reflected by the line differs from the frequency of the probing signal f _s by the value of the Doppler signal

,

,

where θ is the angle between the direction to the object and the lateral direction.

GPR operation is as follows.

When the aircraft 1 takes off, the GPR blocks are included in the on-board electrical network, and when the device 1 enters the proposed topographic route, the routes begin to scan the earth's surface with antennas 2 and 3, and synthesize the aperture of the receiving antenna 3.

Synchronizer 4 is intended for the formation of triggering, controlling and blanking video pulses. It provides coordination of the work of all functional units of the GPR in time. The start pulses of the generator 6 pulses coming from the synchronizer 4, determine the moments of radiation of the probe pulses. The short electromagnetic pulses probing the earth's surface, penetrating through the soil, are reflected back from the earth's surface, the boundaries of the fractions of the soil medium and the extended pipeline artificially inserted into the soil, and through the receiving antenna 3 and receiver 7 enter the adder 9 directly and through the n-branch delay line 8 .i (i = 1, ..., n). The latter form a synthesized aperture of the receiving antenna 3 with a narrow radiation pattern. The amplitude of the received radio pulses varies during the irradiation of the earth's surface in accordance with the directivity pattern of a real antenna in azimuth with a synthesized aperture. The phase of the radio pulses changes in accordance with the Doppler frequency offset determined by the ground speed of the aircraft and the current azimuth of the trunk. Based on the reflected signals, a soil profile picture with a massive extended object is formed. The boundaries between the fractions of the soil and the pipeline are displayed on the screen of the video monitor 11 in the form of bright dark lines, the homogeneity of the medium is the same color of even tonality, the degree of which depends on the electrophysical properties of the soil structure. The higher the absorption coefficient, the darker the tonality. The presence of the pipeline and its transverse size are judged by the difference in the contrast of the sections, their dimensions and sharp bright dark boundaries displayed on the monitor screen 11, and by the time of arrival of the corresponding reflected signals from the ground surface of the earth and the interface between the pipeline fractions of the soil and antenna 3 judge the depth of the pipeline in the ground.

Thus, the proposed mobile GPR in comparison with the prototype provides an increase in resolution in azimuth. This is achieved by synthesizing the aperture of the receiving antenna.

It is believed that using the synthesis method it is possible to increase the resolution of a mobile GPR in azimuth by 100 times or more compared with the resolution of panoramic radars and a prototype. According to the potential characteristics of the resolution, the proposed mobile georadar with a synthesized aperture of the receiving antenna approaches the resolution characteristic of optical instruments.

The size of the synthesized antenna, i.e. the portion of the path on which the signals are processed can be changed so that the width of the synthesized radiation pattern decreases in proportion to the increase in range. This effect allows to obtain radar images with a constant resolution regardless of the remoteness of the viewed area.

A positive result of the proposed mobile georadar is enhanced functionality (simultaneous search for a route, determination of its transverse size and depth in the ground), high noise immunity and image quality on a video monitor due to the selected parameters of the probe pulses, synchronization of antenna scanning and the operation of all georadar functional blocks in time, the presence of a database stored in the processor memory, the dependence of contrast on the electrophysical properties of the fraction th soil and high resolution in azimuth due to the formation of an artificial (synthesized) antenna array. Using the latter, a detailed and accurate map of the translucent medium can be constructed. The quality of such a radar survey is comparable to the quality of images in the optical range. But the weather and lighting conditions, which significantly affect the use of optics, practically do not interfere with conducting radar surveys.

Claims (1)

A mobile georadar for remote search of the location of underground trunk communications and determination of their lateral size and depth in the ground, comprising an aircraft, a high-frequency pulse generator in series, and a high-frequency electromagnetic pulse transmitting antenna, the second input of which is connected to the first output of the antenna control unit, the receiving an antenna of high-frequency electromagnetic pulses, the second input of which is connected to the second the course of the antenna control unit, and the receiver, a processor with software and a monitor connected in series, while the antennas are made in the form of collimating arrays pivotally mounted outside on the bottom of the fuselage of the aircraft with the possibility of synchronous swinging of each antenna in the plane of the fuselage cross section at an angle of 1-5 ° relative to the vertical and regardless of the roll of the aircraft and focused towards the surface of the earth, the duration of the probe electromagnetic pulses is fixed and called It starts within the range of 10-0.2 ns, and the data of the dependence of contrast on the electrophysical properties of fractions of soils and materials of pipeline communications are entered into the processor software, characterized in that it is equipped with a synchronizer, a multi-tap delay line and an adder that synthesizes the aperture of the receiving antenna, moreover, the control inputs of the antenna control unit, the high-frequency pulse generator and the receiver are connected to the corresponding outputs of the synchronizer, to the output of the receiver RAKE sequentially connected delay line, and an adder whose control input is connected to the receiver output, and an output connected to the input of the processor with software, which control input is connected to the fourth output of the synchronizer.

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