DE3124881A1 - "RADAR SYSTEM FOR DETERMINING UNDERGROUND DISTANCES" - Google Patents

Description

HOEGER,

PATEN "i Ä ^: W * W Ä L 'Τ * Ε ·> UHLANDSTRASSE 14 c · D 7000 STUTTGART 1

A 44 725 u Applicant: ENSCO, Inc.

UO - 168 5408A Port Royal Road

6/22/1981 Springfield, Virginia, U.S.A.

Description

Radar system for determining underground distances

The invention relates to a radar system for determining underground Distances according to the preamble of the main claim.

Many mining activities require precise knowledge of the size and location of various underground possessing geological features. For example, the operator of a drill working in underground mining occupied by coal, the boundaries of the coal seam can accurately determine when moving the drill through the seam should be guided correctly. In addition, geological discontinuities, such as sand channels, when Drilling may be encountered; it is necessary to determine the coal extension on the other side of the sand channel, in order to be able to decide whether further drilling beyond the canal is economically justified. In such Situations, a compact, portable and self-contained bore guide system is of great benefit, which makes use of the proven Rad'artec'hnologie and provides accurate and reliable measurements of the thicknesses to the top and bottom of the coal seam.

Various methods of surveying the boundaries of a coal seam are known. U.S. Patent 3,823,787

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a borehole guide system is described in which the radiation of a radiation source, for example Cesium 137 is scattered back from the rock wall that surrounds a coal seam. This radiation is from a Radiation counter detected, which then generates a control signal. A hole is then drilled a certain distance from the top or bottom of the seam. In the U.S. Patent 3,961,307 describes another device by which the boundaries of an underground coal seam are described be determined. Here is the time between the emission of monochromatic, coherent sound waves of an underground test station and the reception of the sound waves after their reflection at a discontinuity elapses in the seam as an indication of the distance between the reflective discontinuity and the test station used. Regardless of the merits of these systems, there is nothing of note in the aforementioned prepublished patents testified about the use of radar to survey coal seams «j

Various factors need to be considered when using radar technology are to be used successfully for bore guide systems in coal mining. Boreholes in coal seams usually only 3 or 4 inches in diameter; the radar components including the antenna structure and associated electronics must be reduced in size to fit in the wellbore. Geophysical exploration systems, which electromagnetic Using waves to locate geological formations is in the technical field of borehole surveying has been developed. Such systems contain numerous elements that are specially designed to be within

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of a borehole can work. For example, in US Pat. No. 3,449,657, a spiral antenna is reduced Described diameter, which is fitted into a borehole of conventional size and underground earth formations with electromagnetic energy is irradiated in a plane transverse to the axis of the borehole.

Despite the compactness achieved by this device, much of the radar control circuitry must still be external of the borehole. A measuring cable, which connects the antenna to the external circuit, is used for transmission the control signals to the antenna in the borehole are necessary. Changes in both the size of the borehole and however, the electrical properties of the surrounding earth create variations along the length of the borehole in the antenna impedance, which are detected by the transmitter and receiver electronics of the borehole radar system. As a result Elongated radar control cables, as required in the devices described above, carry false impedances; overshoots or post-oscillations occur due to reflections within the antenna structure itself.

It is of course impossible to use control wires for downhole radars to build which are perfectly matched to the varying impedance of a borehole radar antenna. Nevertheless the ringing problems caused by imperfect impedance determinations can be minimized if the control cables are kept as short as possible. An embodiment in U.S. Patent 3,412 shows a borehole radar device in which the energy supply and the time systems are arranged within the device itself are. While doing so, some undesirable properties

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which are connected to elongated control cables eliminated; nevertheless this configuration is for the measurement of coal seams not suitable.

The distances between the borehole and the top and the borehole and the bottom of the coal seam are often relatively short, between 6 and less than 1 foot. The transit times between the borehole and the upper or lower interface are correspondingly short. Reflected pulses often arrive at the receiver while pulses are still being transmitted by the transmitter. The transmitting and receiving device must therefore be active _s the result that send control signals overlap receive control signals. The transmit and receive circuit cables, which are appropriately energized, then tend to act as RF antennas themselves. This leads to an electromagnetic coupling phenomenon between the transmitter and the receiver and to interference in the receiving electronics. The above-mentioned embodiment of US Pat. No. 3,412,815 contains nothing that could eliminate these indirect coupling problems in radar components operating in wells

Other embodiments in the same US patent use a dielectrically charged horn directional antenna Transmission of electromagnetic energy pulses and a separate, dielectrically charged horn directional antenna for reception of the reflected impulses. The existence of separate transmitting and receiving antennas in a radar guidance system, which should work even at short distances, leads to further coupling problems. When the reflective interface is relatively close to the transmitting antenna must also

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the receiving antenna must be close to the transmitting antenna if it is to detect reflected pulses. However, if the If the receiving antenna is placed close to the transmitting antenna, this easily leads to over-steering of the receiver as a result direct electromagnetic radiation from the transmitter. It is thus difficult to find a radar guidance system for short . Bringing distances with separate receiving and transmitting antennas for receiving reflected pulses.

An attempt to solve the problem caused by short reflection distances and causing correspondingly short electromagnetic propagation times, is in the US patent 3 806 795. Here a single broadband antenna is used to both receive electromagnetic energy to send out as well as to receive. This system emits impulse-excited short-lasting electromagnetic impulses, their rise times on the order of one nanosecond and their frequencies are up to 400 MHz. The antenna is attenuated quickly after the transmission, which causes the system is made ready to receive the reflections. The combination of small pulse widths and the antenna attenuation makes acceptable measurements possible with reflective interfaces, that are 4 to 5 feet away from the antenna.

Electromagnetic impulses of short duration (a detailed description of these impulses known as "short pulse radar" form known radar is in U.S. Patent 4,008 can enhance the ability to measure within short distances in a radar well guidance system. Frequently however, mineral boundaries and other geological discontinuities should be within 1 foot or more

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less are measured from the detection device. The device described in US Pat. No. 3,806,795 cannot make such measurements accurately. For example, the speed of electromagnetic energy propagation in coal is approximately 0.5 feet / nsec. When the operator of a drill tries to orient his drill against a coal seam line exactly 1 foot from the borehole, a search electromagnetic pulse from. The downhole antenna broadcast _{3 takes} approximately 4 nanoseconds to travel from the antenna to the interface and back. Even when short pulse radar is used, the transmitted and received pulses often overlap; then it is difficult, if not impossible, to attenuate a single antenna configuration enough to detect the returning signal. In addition, high-frequency pulses in a single transmit / receive antenna structure often result in ringing or overshooting. Accordingly, in the case of electromagnetic measurements, preferably separate transmitting and receiving antennas are used, which are designed so that electromagnetic coupling between them is avoided.

In US Pat. No. 3,440,523 in particular it is recognized that it is not practical to have the same antenna there both for the To use both emission and reception of electromagnetic energy where one is reflected by a geological discontinuity Echo pulse arrives at the antenna before the transmitter has stopped emitting pulses and during the receiver is still saturated with energy from the transmitter. The method described in this patent specification uses a rectilinear. transmitter with a Receiving frame, which is mounted in such a way that it

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vertical axis tangential to the cylinder surface of the rotation the axis of the transmitter can be rotated. In this way there is a device which prevents the Radiated radiation saturates the receiver. In this process, the direct electromagnetic The problem created by coupling between the transmitting and receiving antennas is eliminated; the problem of indirect coupling between the transmission control cables and the receiving antenna is not addressed in this publication. In addition, the known device must be controlled from the outside of the borehole, whereby the above-described Impedance problems also occur.

The object of the present invention is to provide a radar system the type designated in the preamble of the main claim so that it is used to measure the interfaces of a Mineral seam is suitable.

This object is achieved by the invention described in the characterizing part of the main claim; advantageous further training are specified in the subclaims.

The radar system according to the invention uses a radar device which is inserted into the borehole drilled along a coal seam is introduced. High frequency electromagnetic pulses are broadcast from the device and back to a receiving antenna from the coal-shale interface at the top or bottom Reflecting underside of the coal seam. The transit times of the reflected pulses are measured continuously while the device is moved through the borehole. This gives an indication of the distances between the boreholes and the top and the borehole and the bottom of the

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Seams preserved. The radar is approximately 5 feet long and 2 3/4 inches in diameter. It contains a high-frequency electromagnetic pulse generator, a directional transmitting antenna, a directional receiving antenna, control electronics and a battery as a power source. The components of the circuit are designed so that they fit into the small diameter of the device. The control circuit carries out all control, transmission and reception functions in the device itself. In this way, control transmission lines into the hole are superfluous, as a result of which ringing and overshooting processes due to incorrect impedance adaptations within the circle are kept very small. By arranging the transmitting antenna at a point between the control circuit and the receiving antenna, the indirect electromagnetic coupling between the antennas can be reduced. Circuit isolators are used to further reduce RF crosstalk between the control circuit and the receiving antenna. The insulators are made of coaxial cable that is coiled in a spiral. This provides a maximum length in a minimum of space. The isolators are each connected in series with the sections of the control cables that lead to the transmitting and receiving antennas. A metallic shielding is attached to the inside of the device and can also be used to direct the ₅ passage of electromagnetic waves to prevent between the transmitting and the receiving antenna.

With the system according to the invention, geological discontinuities that are less than 1 foot away.

An embodiment of the invention is presented below

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hand of the drawing explained in more detail; show it

Fig. 1 is a diagram in which the basic operation of the radar device in a coal seam borehole is shown;

Fig. 2 schematically shows the various high-frequency electromagnetic Pulses transmitted and received by the radar;

3 shows a cross section through the radar device itself;

4A shows the plan view of the radar device, with the arrangement a metal foil shield is shown;

Fig. 4B is a side view of the device showing the arrangement of the metal foil shield;

5 shows the scissor diagram of the radar device electronics.

The general functioning of the radar drill guide system is shown in FIG. A coal seam, as indicated by the reference number 2, is often made of slate surround. This creates a coal-shale interface 4 at the top of the seam and another coal-shale interface 6 at the bottom of the seam. A borehole 8 is drilled in the coal seam; Information, which affect the orientation of the borehole relative to the top and bottom of the seam, are thereby obtained that the total provided with the reference numeral 10 radar device is introduced into the borehole. A Directional transmitter 12 inside the device emits electromagnetic

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table energy in the form of short pulses in the range of radar wavelengths through the coal onto one of the coal-shale interfaces, as indicated by path A. Some of the electromagnetic energy is returned afterwards to a directional receiver 14 reflected in the tool, is arranged adjacent to the transmitter. The time that elapses between the transmission and reception of the radar pulses, is then determined and used to provide a measure of the distance between the borehole and the interface submit.

Since transmitter 12 and receiver 14 have a directional effect, the radar pulses can only propagate in a single direction; the device can therefore only measure an intermediate surface at a certain time. In Fig. 1 the distance between the borehole 8 and the coal-shale interface 4 is measured at the top of the seam. If the distance measurement between the borehole and the coal-shale interface 6 is to be carried out on the underside of the seam, the device 10 must be rotated; in the process, the transmitter 12 and receiver 14 are aligned with the intermediate surface on the underside of the seam.

Not all of the electromagnetic energy emitted by transmitter 12 travels along path A to Receiver 14. On the contrary, the pulses can traverse a number of paths between the two units. Some of the impulses move, for example, from the transmitter to the receiver through the coal on the wall of the borehole. These pulses follow the path denoted by B ′ in FIG. 1 is. Other impulses can travel directly through the air from the transmitter to the receiver along path C.

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The different transmission media and distances involved create a multiple pulse pattern on the Receiver 14, as shown idealized in FIG. At a certain time t, the transmitter 12 sends a Energy burst of 1 or 2 nanoseconds. The energy impulses that move along path C through the air, first reach the receiver 14 at time t. Path B is slower than path C because of the speed of propagation electromagnetic energy in coal (about 0.5 feet / nsec) about half the speed of propagation of electromagnetic energy is in air. Thus, the impulses that follow path B reach the Receiver 14 at a time t, after t. Path A, i.e. the path taken from the distance between borehole 8 and the coal-shale surface 4, also runs through coal, but is longer than path B. As a result, the impulses come which traverse the path A, at the receiver 14 at a time t after t. at.

The pulse pattern shown in Fig. 2 is seldom realized in practice. This is due to the multitude of transmission paths which are available to the electromagnetic erercjie. Changes in the electrical properties of the coal seam themselves also reflect a certain amount of energy just before the coal-shale interface. irregularities lead in the borehole wall together with limits in the construction of the transmitting and receiving antenna to pulses that are not as short or well defined as those of FIG. As a result, it is not possible to check the pulse pattern on the receiver and to clearly distinguish one reflected pulse from the other.

The data interpretation of the received pulses must instead be based on changes in the pulse pattern.

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the _s when the transmitter and receiver in the radar device are moved along the borehole. Paths B and C remain constant regardless of the position of the device; Irregularities in the coal-shale interface 4 at the top of the seam lead, however, to variations in the dimensions of the path A and thus in the path times of the corresponding reflected pulses. It is thus possible to identify the pulses received from path A by paying attention to that portion of the pulse pattern which changes with respect to the rest of the pulse pattern as the device moves. Pulses identified in this way can then be used to carry out the desired measurements of the distances between the borehole and the top and the borehole and the underside of the seam.

A section through the borehole radar device 10 is shown in FIG. The radar device 10 includes a tubular housing 16 with threads 18 at one end, with which the device can be attached to a conventional drill rod. The housing, which is made of impact-resistant plastic or another durable material, is approximately 5 feet long and 2 3/4 inches in diameter. An electronic control device 20 powered by batteries 22 and a power supply circuit 24 is located within the housing. The control device 20 leads off all control functions that are necessary for the sending and receiving processes in the device. Be that way both the transmission of control signals into the hole and the associated elongated control cables are avoided. The fact that no elongated control cables are required, in turn, minimizes the problem of harmonics and post-oscillation, which are based on wrong impedances. These arise

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in that the impedances between the receiving electronics and the receiving antenna, as explained above, not can be adjusted properly.

The transmitter 12 is located at a point between the controller and the receiver 14 and includes a .loop-shaped dipole transmitting antenna 26, which is in the vicinity of the housing 16 is arranged. A capacitively coupled resistive load may be used at each end of the antenna 26 will. This allows the broader bandwidths to be used, which are normally the broadband frequency spectrum accompany short radar wave impulses. A transmitting antenna reflector 28 is located under the transmitting antenna 26 and ensures that electromagnetic energy from the Front of antenna 26 with double intensity as radiated from the rear. The energy that at the front of the receiver 14 is thus four times as large as that at the rear. To this Way, the directional effect is achieved, which is necessary for the measurement of top or bottom interfaces is required.

Pulses with frequencies in the range between 200 MHz and 1 GHZ are sent to the transmitting antenna 26 by an electromagnetic High-frequency pulse generator 30 placed. This is done in response to time signals from the control device and the pulse generator 30 via a control line 32 can be entered. A transmission insulator 34 is made of wound Coaxial cable constructed and in series with the control cable 32 between the control device 20 and the pulse generator 30 switched. The function of the isolator 34 is described below explained in detail.

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The receiver 14 contains a loop-shaped dipole reception antenna 36, which is also arranged in the vicinity of the housing 16 and oriented in the same way as the Transmitting antenna 26. A receiving antenna reflector 38 gives the receiving antenna 36 has a directional effect which is similar to the directional effect of the transmitting antenna and reflector combination 26, is equivalent to. The receiving circuit 40, which is connected to the receiving antenna 36, is actuated in response to clock signals, which are generated by the control device 20 and fed to the receiving circuit via the control line 42. A Reception isolator 44 made of coiled coaxial cable is in series with the control cable 42 between control device 20 and Receiving circuit 40 switched.

The special configuration of the components in the radar device, which has just been described is intended to reflect the effects of electromagnetic coupling between the transmitting and receiving antennas keep it as small as possible. The control cable 32, which the electromagnetic pulse generator 30 with the electronic control device 20 connects, tends to itself to act as an RF antenna when it is controlled by the control device is acted upon with tent signals. When the coal-shale interface being surveyed gets close is located on the radar device 10, both the transmitting and receiving antennas are active at the same time; the time signals on Transmitters then often overlap the function of the receiver. The correspondingly energized control cable 32 would thus be closed Interference in the active receiver would result if the control cable 32 were anywhere in the vicinity of the receiver. Through this, that the transmitting antenna 26 and its associated control cable 32 at a point between the control device 20 and receiving antenna 36 are positioned, however, these coupling

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reduced effects. The control cable 32 is turned off away from the receiving antenna.

Coupling effects are further enhanced by the transmit isolator 34 and reduce the receiving isolator 44, which act as RF chokes and attenuate any RF signals of the same mode, which run along the control cable 32 and the control cable 42. The insulators 34 and 44 prevent the cables 32, 42 act as antennas when they are energized by control signals are. The outside of the insulators can be covered with an absorbent material, for example with the material ECCOSORB ™ SC-100 from Emerson & Cummings, where the diameter of the housing 16 is more closely approximated - In this way, the RF attenuation in the isolators is increased and at the same time the passage of electromagnetic waves along the inside of the device directly between Sending and receiving antenna blocked.

A shield can also be used to create a direct To prevent transmission of electromagnetic energy between the transmitting antenna 26 and the receiving antenna 36. As can be seen schematically in FIGS. 4A and 4B, a cylindrical shielding element 46 is made of copper foil or some other suitable metal around the inside diameter of the housing 16. The shielding element covers the entire surface of the device 10 with the exception of openings 48, 50 in which the transmitting antenna 26 or the Receiving antenna 36 are housed. This enables the antennas to function unimpeded. If If desired, the control cable 42 can be connected between the outside of the shielding element and the inside of the housing 16 to be ordered; in this way a coupling of

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Prevents energy from entering the cable 42 from the transmitting antenna.

The circuit configuration of the radar device 10 is shown in the block diagram of FIG. The electronic Control device 20 contains a sampler control 52, which generates timing signals to control the radar scan sequence. The sampler controller 52 is conventional Sampling timing circuit which is similar in design and function to the Tektronic 7S11 model. If the radar is correct is positioned in the borehole, the operator operates outside the borehole the on-off switch 54 and thus initiates the scanning sequence. The scanning speed is usually preset in the range between 10 and 30 Hz, however, it can be adjusted by the operator before the tool is inserted into the borehole.

After initiating the scanning sequence, the sampler control device begins 52 time signals with a frequency of 200 kHz through the control cable 32 and the transmission isolator 34 to the electromagnetic pulse generator 30 to send. 200 kHz is the preferred time signal frequency; it can, however other time signal frequencies in the range between 50 and 250 kHz can be used with a satisfactory result. The electromagnetic pulse generator responds to the time signals 30 to the transmitting antenna 26 from bursts of electromagnetic pulses, which characteristically have a frequency in of the order of 100 MHz to 2 GHz. These high frequency electromagnetic pulses are generated by the transmitting antenna 26 broadcast into the surrounding coal and from a coal-shale interface back to the receiving antenna reflected as described above. The received pulses are fed into the receiving circuit 40, the one

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RF amplifier 56 and an RF sampler 58 under the control of sampler controller 52. The RF sampler 58 is an analog sample-and-hold circuit which follows the incoming pulses and capacitively controls representative pulses in response to a clock signal generated by the sampler control device 52 and the RF sampler 58 through the control cable 42 and the receiving isolator 44. The first clock signal after the initiation of the sampling sequence coincides with the first time signal of the sequence. Then the frequency of the clock signals follows the frequency of the time signals; however, the time period between successive clock signals is progressively increased by increments of 0.25 nsec; in this way a progressively increasing delay period is created between each clock pulse and each timing signal. For example, if the initial timing signal occurs in a particular sampling sequence at time t ₁ , the initial clock signal also occurs at time t 1. The second time signal occurs at time t «; however, the second clock signal does not occur until time t ₂ +0.25 nsec. The third time signal occurs at time t 1, while the third clock signal occurs at time t 1 + 0.50 nsec. The delay between the time signal and the clock signal continues to grow through the entire sampling sequence, although the effective frequency of the clock signals and the corresponding sampling rate remain the same as the frequency of the time signals. In this way, the RF sampler 58 can examine received pulses sequentially at progressively increasing time intervals that follow the transmission of the pulses from the transmitting antenna 26.

The pulses stored in the sampler 58 are transmitted via the Cable 60 to the audio frequency operational amplifier 62 in FIG

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electronic control device 20 supplied. The amplifier 62 is controlled by a control signal from the sampler controller 52 triggered at the same time as the scan sequence is initiated. It amplifies the stored impulses, so that they can be transmitted to the outside of the wellbore via a surface cable 64.

After completing a scan sequence, the sampler controller returns 52 back to the exit; another scan sequence is initiated. The pulses generated by the RF sampler 58 stored during a single scan sequence and sent from amplifier 62 and surface cable 64 to the outside of the Boreholes are transmitted from a single data set, which in a conventional oscilloscope-like visual Display or in another monitoring circuit.

The scan sequences last _s while the radar device 10 is moved along the borehole. Changes in the pulse patterns as detected in the data sequences or data sets, serve to ιdentifizieren those pulses stored the _s-shale interface carbon was reflected at the top or bottom of the coal seam at the. The pulses identified as reflected pulses can in turn be used as a measure of the distance between the borehole and the reflective interface.

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Claims (1)

HOEGER, LEGAL LAW & PARTNER3 1 2488 PATEN I A N WÄ w T E £ UHLANDSTRASSE 14 ο · D 7000 STUTTGART 1 Ä 44 725 u Applicant: ENSCO, Inc. UO - 168 5408A Port Royal Road o6 »1981 Springfield, Virginia, U.S.A, Claims 1. Radar system for determining underground distances with a source of electromagnetic pulses; a transmitting device, which is connected to the source of electromagnetic Impulse is connected and transmits the electromagnetic impulses into the earth; a receiving device, which receives electromagnetic energy after reflection from various geological discontinuities in the Earth returns to the receiving facility; a control device, which both the emission of the electromagnetic Pulses from the transmitting device as well as receiving the electromagnetic energy from the Receiving device controls, characterized in that the source of electromagnetic pulses (30) which Control device (20), the transmitting device (12) and the Receiving device (14) within a housing (16) are mounted such that the transmitting device (12) within the housing (16) between the control device (20) and the receiving device (14) is positioned, whereby an electromagnetic coupling between the Control device (20) and the receiving device (14) is prevented, the transmitting device and the receiving device each having directional antennas (26, 36) within the Housing (16) included. 2. Radar system according to claim 1, characterized in that the transmitting device (12) has a first, loop-shaped Dipole directional antenna (26) and the receiving device (14) a second, loop-shaped directional dipole antenna (36) -2- * * Ct t 1 · • It «* SI T »1 A 44 725 u UO - 168 - 2 - June 22, 1981 contains. 3. Radar system according to claim 2, characterized in that a first reflection device (28) is arranged below the first loop-shaped dipole antenna (26) and thereby gives the transmitting device (12) a directivity, and that a second reflection device (38) is arranged below the second loop-shaped dipole antenna (36) and thereby the receiving device (14) gives directivity. 4. Radar system according to claim 1, characterized in that the electromagnetic pulses emitted by the source electromagnetic pulses (30) are generated, have a frequency in the range between 100 MHz and 2 GHz. 5. Radar system according to one of claims 1 to 4, characterized characterized in that the housing (16) includes a shield member (46) which surrounds its inner surface is mounted and a direct electromagnetic coupling between the transmitting device (12) and the receiving device (14) prevented. 6. Radar system according to claim 5, characterized in that the shielding element (46) is formed from metal foil. 7. Radar system according to one of "Claims 1 to 6, characterized in that that a first RF choke (34) in series between the control device (20) and the transmitting device (12) is switched and. Common mode RF signals attenuates along the connection (32) between -3- A 44 725 u UO - 168 - 3 - June 22, 1981 the control device (20) and the transmission device (12) run, and that a second RF choke (44) in series is connected between the control device (20) and the receiving device (14) and RF signals are more common Mode weakens which along the connection (42) between the control device (20) and the receiving device (14) run. 8- radar system according to claim 7, characterized in that the first RF choke (34) consisting of a first cylindrically spirally wound coaxial cable and the second RF choke (44) is formed from a second cylindrically spirally wound coaxial cable. 9. Radar system according to claim 8, characterized in that the housing (16) has a cylindrical cross section, wherein the diameter of the two cylindrically wound coaxial cables (34, 44) equal to the inner diameter of the cylindrical housing (16). 10 «radar system according to one of claims 1 to 9, characterized that the control device (20) time signals to the transmitting device (12) and clock signals to the Receiving device (14) during a scanning cycle outputs, wherein the receiving device (14) is a sampling device (58), which is connected so that it detects the received electromagnetic energy and stores in response to a clock pulse from the control device (20), the control device (20) during of a sampling cycle, a progressively increasing delay period between successive timing and clock pulses generated. -4- A 44 725 u UO - 168 - 4 - June 22, 1981 11. Radar system for determining underground distances with a source of electromagnetic pulses; with a transmitting device connected to the source of electromagnetic Impulse is connected and transmits electromagnetic impulses into the earth; with a receiving device, which receives electromagnetic energy after the reflection of electromagnetic pulses at various geological discontinuities in the earth return to the receiving facility; with a control device, which both the emission of electromagnetic pulses from the transmitting device and the Receipt of the electromagnetic energy by the receiving device controls, characterized in that a first RF choke (34) in series between the controller (20) and the transmitting device (12) is switched and RF signals of a common mode attenuates which run along the connection between the control device (20) and the transmitting device (12), and that a second RF choke connected in series between the control device (20) and the receiving device (14) and attenuates RF signals of a common mode, which along the connection between the control device (20) and the receiving device (14) run. 12. Radar system according to claim 11, characterized in that the first RF choke (34) consisting of a first spiral wound coaxial cable and the second RF choke (44). consists of a second spiral-wound coaxial cable. 13. Radar system according to claim 12, characterized in that the transmitting device (12) has a first loop-shaped -5- A 44 725 u UO - 168 - 5th May 22, 1981 Dipole antenna (26) and the receiving device (14) contains a second loop-shaped dipole antenna (36). 14 ,, radar system according to claim 13, characterized in that that a first reflection device (28) is positioned under the first loop-shaped dipole antenna (26) and gives the transmitting device (12) directivity, and that a second reflection means (38) under the second loop-shaped dipole antenna (36) arranged and gives the receiving device (14) directivity.