WO2010151125A1

WO2010151125A1 - Improved ground penetrating radar

Info

Publication number: WO2010151125A1
Application number: PCT/NL2010/050388
Authority: WO
Inventors: Paulus Benedictus Van Der Roest
Original assignee: Monshouwer Beheer B.V.
Priority date: 2009-06-23
Filing date: 2010-06-23
Publication date: 2010-12-29
Also published as: EP2446297A1; NL1037058A; NL1037058C2

Abstract

The invention relates to an improved ground penetration radar and method for using such. In particular the invention relates to a ground penetrating radar (GPR) having a base plane for facing the ground when in use, said GPR comprising a transmit antenna for transmitting a signal into the ground, a receive antenna for receiving a reflected signal from the ground, and an electromagnetic shielding, the transmit and/or receive antenna being located substantially between the base plane and the electromagnetic shielding,wherein the GPR further comprises an electrode conductively connectable with the electromagnetic shielding and having a tip arranged for extending to and/or past said base plane for conductively contacting the ground when in use.

Description

Improved ground penetrating radar

BACKGROUND

The invention relates to an improved ground penetrating radar (GPR) . Ground penetrating radars have been used successfully in the past for finding underground discontinuities. Using GPR, archeological sites have been investigated without excavating the site or otherwise damaging underground structures, construction sites have been checked for underground anomalies that might interfere with construction, and utility companies have pinpointed underground pipes and cables for which the locations were inaccurate or unknown. US patent 3,831,173 discloses a ground radar system for locating underground objects, such as pipes, utility lines, culverts, ledges and like kinds of underground discontinuities, including voids to depths in excess of 10 feet (ca. 3.05 m) , the system including a basic radar having a special antenna design which launches radiation that penetrates the earth and receives reflections from underground discontinuities for recordation in a moving vehicle.

Several factors play a role in obtaining a good radar resolution. First of all there is the problem of getting the radar radiation into the ground as opposed to directly reflecting off the ground. Typically lower frequency signals penetrate deeper into the ground, however at a cost of a lower display resolution. Secondly, a ringing effect in which energy still present in the transmitting antenna interferes with the signals received is detrimental to the resolution of a ground penetrating radar.

It is an object of the present invention to provide a ground penetrating radar capable of providing improved readings .

SUMMARY OF THE INVENTION

According to a first aspect, the present invention provides a ground penetrating radar (GPR) having a base plane for facing the ground when in use, said GPR comprising a transmit antenna for transmitting a signal into the ground, a receive antenna for receiving a reflected signal from the ground, and an electromagnetic shielding, the transmit and/or receive antenna being located substantially between the base plane and the electromagnetic shielding, wherein the GPR further comprises an electrode conductively connected or connectable with the electromagnetic shielding and having a tip arranged for extending to and/or past said base plane for conductively contacting the ground when in use. Surprisingly it was found that penetration depth and/or resolution of a survey using the GPR according to the invention, when the electrode is conductively connected to the electromagnetic shielding, is considerably increased. Even when used at notoriously difficult soil structures, such as clay or loess, detailed surveys with increased penetration depth were possible. Furthermore, an attenuation of the ringing effect is observed, sometimes the ringing effect is substantially absent.

In an embodiment the GPR comprises one or more additional electrodes conductively connectable with the electromagnetic shielding and having a tip arranged for extending to and/or past the base plane for conductively contacting the ground when in use. In an embodiment the electrode tips are arranged substantially symmetrically around the transmit and/or receive antenna. These measures have proven especially advantageous when the electrode tips are arranged substantially symmetrically around and near the transmitting antenna when contacting the ground, further improving the readings by the GPR.

In an embodiment the GPR has a preferred direction of movement during use, and, at least during contact with the ground, the electrode tips are arranged substantially next to the transmit antenna without contacting the antenna, wherein an intersecting line through the electrode tips is substantially perpendicular to the preferred direction of movement .

In an embodiment the electromagnetic shielding is arranged between the one or more electrode tips and the transmit and/or receive antenna.

In an embodiment the one or more of the electrode tips are arranged outside the transmit range of the transmit antenna. The transmit range of the transmit antenna may be dependent on the shape of the antenna and/or of the electromagnetic shielding. In this embodiment the electrodes substantially do not interfere with the transmitted signal.

In an embodiment one or more of the electrode tips are arranged within the transmit range of the transmit antenna. In this embodiment the electrodes can be placed under or next to the antennas, allowing a more compact GPR to be constructed.

In an embodiment one or more resistors conductively connect the transmitting and/or receiving antenna with the shielding. The resistors may aid in reducing oscillation of the transmitted pulse within the ground radar. Additionally the antennas of this embodiment may thus function as broadband antennas. In an embodiment the electrode or electrodes are spring-mounted on the GPR. The springs aid in maintaining contact between the electrode tips and the ground, especially when the GPR is dragged across the ground. In an embodiment the electromagnetic shielding is substantially covered with a non-conductive material. For example, the entire surface of the shielding that faces away from the antennas may be covered with a non conductive material. This may protect operators from electrical shock and further isolate the GPR from external influences.

In an embodiment the GPR further comprises a non- conductive contact surface for contacting the ground and forming an outer surface of the GPR. This surface preferably comprises a wear-resistant and substantially non-static material.

In an embodiment the contacting surface comprises a material which provides for a low friction when dragged along the ground.

In an embodiment the contact surface comprises a non-conducting sheet material, preferably a synthetic or plastic material. In an embodiment the sheet material is removable connected to the GRP, and can be replaced by a new sheet when worn.

In an embodiment the non-conductive outer surface covers substantially all of the GPR, except for the electrode tips.

In an embodiment the GPR further comprises potential difference measuring means conductively connectable to selected electrodes of the two or more electrodes and configured for measuring a potential difference there between, and selection means adapted for establishing and or breaking conductive connections between individual electrodes of the two or more electrodes with the potential difference measuring means and/or the electromagnetic shielding. A GPR of this embodiment may be used to measure potential differences in the soil between the electrodes, when at least one of the electrodes is not conductively connected to the shielding. It has been found that the potential differences between two electrodes may also provide information about subsurface discontinuities as disclosed in an earlier patent application NL2002124 by the applicant. The electrodes of the GPR of this embodiment can be switched to a first configuration wherein they provide grounding to the electromagnetic shielding for use with the radar, or to a second configuration wherein the electrodes are conductively connected to potential difference measuring means for measuring a potential difference between the electrodes .

In an embodiment the GPR comprises potential difference measuring means conductively connected said two or more electrodes, for measuring a potential difference between two of said electrodes when at least one of these two electrodes is not conductively connected to the electromagnetic shielding. When moved across the ground, changes in the measured potential differences can be used to detect subsurface discontinuities, such as contours of electrical cables, in an alternative manner without the use of the radar. The information obtained by measuring potential differences and obtained by radar can be complementary.

According to a second aspect the present invention provides a method for detecting underground structures using a GPR according to the invention wherein the one or more electrodes are conductively connected to the electromagnetic shielding, said method comprising the steps of: placing the one or more electrodes in conductive contact with the ground, moving the GPR across the ground while maintaining contact between the electrode and the ground, transmitting a signal into the ground using the transmit antenna and receiving reflected signals. According to a third aspect the present invention provides a method for detecting underground structures using a GPR according to the invention having potential difference measuring means conductively connected to said electrodes, said method comprising the steps of: placing the two or more electrodes in conductive contact with the ground, moving the GPR across the ground while maintaining contact between the electrodes and the ground, selecting one of the two or more electrodes as a measuring electrode and selecting at least one of the other electrodes of said two or more electrodes as a reference electrode, measuring a potential difference between the measuring electrode and the reference electrode. This method may be used to determine differences in potential in the soil that might indicate underground discontinuities. In an embodiment the transmit antenna is operated to transmit a signal having characteristics dependent on a potential difference measured between the two or more electrodes. For instance, the frequency of the signal transmitted by the transmit antenna may be adapted based on the potential differences measured between the electrodes.

In an embodiment the selection means are operated to establish or break contact between electrodes and the shielding and/or potential difference measuring means dependent on a reflected signal received by the receive antenna. In this case, the configuration of the measuring and reference electrodes is dependent on the signal received by the receive antenna.

The various aspects and features described and shown in the specification can be applied, individually, wherever possible. These individual aspects, in particular the aspects and features described in the attached dependent claims, can be made subject of divisional patent applications .

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be elucidated on the basis of an exemplary embodiment shown in the attached drawings, in which:

Figures IA and IB show a schematic bottom view and a schematic side view respectively of an embodiment of a GPR according to the invention, figure 2 shows a schematic perspective bottom view of an embodiment of a GPR according to the invention with the bottom plate removed figure 3 shows the GPR of figure 2, with the bottom plate attached, figure 4 shows a detail of a spring mounted electrode as may be used in a GPR according to the invention, figure 5 shows a schematic view of a second embodiment of the GPR according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

A schematic bottom view of a ground penetrating radar 100 according to the invention from which the bottom plate has been removed is shown in figure IA. It comprises a transmit antenna 102a, 102b and a receive antenna 103a, 103b adapted for transmitting a signal and receiving reflections of that signal respectively. The antennas are arranged transverse to direction D in which the GPR may typically be dragged during use. The GPR may be dragged behind a motorized vehicle such as a quad, tractor and the like or may be manually moved across an area of interest. During use of the GPR, differing reflective properties of underground discontinuities for the signal emitted by the transmit antenna result in differing signals received at the receive antenna. Information about underground structures may be inferred from the received signals.

Electromagnetic shielding 101 is provided at least at the side of the antennas 102,103 facing away from a base plane which in use faces the ground surface. In use, the antennas and their electromagnetic shielding are arranged at a distance from the ground. This shielding may shield the receive antenna 103a, 103b from external electromagnetic radiation, and may also direct the signal emitted from transmit antenna 102a, 102b in the desired direction, in particular into the ground. The antennas may be connected to the shielding through resistors (not shown) as is known in the art, for instance for making the antennas broadband. Two electrodes 105a, 105b having associated electrode tips 106a, 106b are provided at the sides of the GPR, and are arranged for conductive contact with the electromagnetic shielding 101. In the embodiment shown the two electrodes are directly conductively connected with the shielding at mount points 104a, 104b.

A side view of one of the mount points is given in figure IB. The GPR has a base plate 108 facing a ground surface 120 and, in this case, substantially contacting and supported by the ground surface. The base plate 108 is made from a non-conductive, wear-resistant material, such as Nylon 6,6. Instead of a base plate 108, also a substantially circumferential edge can be used as support element of the GPR when placed on the ground. Said base plate 108 or circumferential edge defines a base plane of the GPR. Though the GPR is shown facing a ground surface it will be obvious to a person skilled in the art that the GPR of the invention may used facing walls, ceilings etc., as long as the base plane faces the volume that is to be investigated. The electrode tips 106a, 106b are arranged substantially symmetrically around the transmit antenna 102a, 102b, preferably substantially symmetrically around the transverse axis 110 which goes through the transmit antenna. The spring coil 107a and electrode 105a are adapted for pushing the electrode tip 106a towards and/or slightly past the base plane 108 to ensure substantially continuous contact with the ground when the GPR is dragged in direction D. In this exemplary embodiment the angle α between the electrode 105a and the ground 120 is preferably a sharp angle, opening in the direction D. This allows the electrode some freedom of movement when it is dragged in direction D, while preventing the electrode from digging into the ground.

Figure 2 shows a schematic perspective bottom view of a GRP according to the invention, from which the bottom plate has been removed. Electrode 105a is spring mounted to the GPR at mount point 104a, in this case by enclosing the spring coiled end of the electrode in a substantially enclosing holder. The spring coiled end is thus kept conductively connected to the shielding 101. During use, the tip of the electrode 105a is arranged substantially in the base plane of the and symmetrical around the transverse axis of the transmit antenna 102a, 102b. Transmit antenna 102a, 102b is connected to transmission lines 141a, 141b which are adapted to supply a signal to be transmitted. The transmit antenna is spaced apart from the electromagnetic shielding 101 by spacers 130 and 140, comprising for instance non-conductive foam. At the corners away from the transmission lines, the transmit antenna 102a, 102b is connected through resistors 142a, 143a and 142b, 143b respectively to the electromagnetic shielding 101. Likewise, the receive antenna 103a, 103b is connected through resistors 132a, 133a and 132b, 133b respectively to the electromagnetic shielding. The GPR further comprises a side surface 150 on the outer side of which mount points 104a, 104b are provided for the electrodes 105a, 105b respectively. Preferably the side surface is made from a non conductive material, to prevent direct electrical contact between the ground and the antennas. Alternatively the side surface 150 is may be comprise an electrically conductive material, essentially extending the electromagnetic shielding and aiding in shielding the antennas from external radiation. In the latter case, a non-conductive bottom plate 108 as shown in figure 3 may prevent direct electrical contact between the antennas and the ground. The non-conductive bottom plate preferably comprises a non-static material, preferably wear- resistant as well, to prevent static build up from interfering with the signals, and to protect the GPR from damage. A typical GPR construction would comprise, from bottom to top, a layer of non-conductive, non-static material such as plastic, a layer of air, another layer of the non-conductive, non-static material, a circuit board comprising both antennas, another layer of air, the electromagnetic shielding and finally another layer of the non-conductive, non-static material. Additionally the layers comprising air may also be partly filled with a non conductive foam for absorbing shocks. Though the GPR will typically be used outside watery environments, it may further comprise extra weight to allow it to sink to the bottom of for instance a water filled trench. When the outside of the GPR is substantially covered with a non- conductive material, except of course for the electrode tips, it is less likely to act as a battery when submerged in water, reducing signal corruption.

Figure 4 shows a detail of a mounted electrode 105a as may be used in the invention. The spring-coiled end 107a of the electrode 105a is enclosed in a restraining structure 104a which allows some deformation of the coil and thus some freedom of movement of the electrode tip in a vertical direction. Advantageously, the electrodes may be easily replaced, without the need for special tools, as might be desired when surveying different kinds of soil or when electrodes are worn out. Figure 5 shows an embodiment of a GPR comprising potential difference measuring means 211 adapted for measuring a potential difference between electrodes 205a and 205b. The electrodes are connectable to the potential difference measuring means 211 or the electromagnetic shielding 201.

The electrodes are isolated from the electromagnetic shielding by isolators 207a, 207b. The electrodes 205a, 205b are conductively connected to switching members 210a, 210b, which switching members 210a, 210b, in a first configuration as shown in figure 5, connect the electrodes 205a, 205b to the potential difference measuring means 211. In a second configuration, as indicated by the dotted lines in the switching members in figure 5, the electrodes 205a, 205b are conductively connected to the electromagnetic shielding 201. The switching means may be operated to select two different modes of operation of the embodiment of the GPR shown in figure 5.

The electrodes 205 of the GPR of this embodiment can be switched to a first configuration wherein they provide grounding to the electromagnetic shielding 201 for use with the radar 202,203, or to a second configuration wherein the electrodes 205 are conductively connected to potential difference measuring means 211 for measuring a potential difference between the electrodes.

It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the invention. From the above discussion, many variations will be apparent to one skilled in the art that would yet be encompassed by the spirit and scope of the present invention .

Claims

C L A I M S

1. Ground penetrating radar (GPR) having a base plane for facing the ground when in use, said GPR comprising a transmit antenna for transmitting a signal into the ground, a receive antenna for receiving a reflected signal from the ground, and an electromagnetic shielding, the transmit and/or receive antenna being located substantially between the base plane and the electromagnetic shielding, characterized in that the GPR further comprises an electrode conductively connectable with the electromagnetic shielding and having a tip arranged for extending to and/or past said base plane for conductively contacting the ground when in use .

2. GPR according to claim 1, comprising one or more additional electrodes conductively connectable with the electromagnetic shielding and having a tip arranged for extending to and/or past the base plane for conductively contacting the ground when in use.

3. GPR according to claim 2, wherein the electrode tips are arranged substantially symmetrically around the transmit and/or receive antenna.

4. GPR according to any one of the preceding claims, the GPR having preferred direction of movement during use, wherein, at least during contact with the ground, the electrode tips are arranged substantially next to the transmit antenna without contacting the antenna, an intersecting line through the electrode tips being perpendicular to the preferred direction of movement.

5. GPR according to any one of the preceding claims, wherein the electromagnetic shielding is arranged between the one or more electrode tips and the transmit and/or receive antenna.

6. GPR according to any one of the preceding claims, wherein the one or more of the electrode tips are arranged outside the transmit range of the transmit antenna.

7. GPR according to any one of the preceding claims, wherein one or more of the electrode tips are arranged within the transmit range of the transmit antenna.

8. GPR according to any one of the preceding claims, wherein one or more resistors conductively connect the transmitting and/or receiving antenna with the shielding.

9. GPR according to any one of the preceding claims, wherein the electrode or electrodes are spring- mounted on the GPR.

10. GPR according to any one of the preceding claims, wherein the electromagnetic shielding is substantially covered with a non-conductive material.

11. GPR according to any one of the preceding claims, further comprising a non-conductive contact surface for contacting the ground and forming an outer surface of the GPR.

12. GPR according to claim 11, wherein the non- conductive outer surface covers substantially all of the

GPR, except for the electrode tips.

13. GPR according to any one of the claims 2-12, further comprising: potential difference measuring means conductively connectable to selected electrodes of the two or more electrodes and configured for measuring a potential difference there between, selection means adapted for establishing and or breaking conductive connections between individual electrodes of the two or more electrodes with the potential difference measuring means and/or the electromagnetic shielding.

14. Method for detecting underground structures using a GPR according to claim 13, said method comprising the steps of: placing the two or more electrodes in conductive contact with the ground, moving the GPR across the ground while maintaining contact between the electrodes and the ground, selecting one of the two or more electrodes as a measuring electrode and combining the other electrode or electrodes for providing a reference, determining a potential difference between the measuring electrode and the reference.

15. Method for detecting underground structures using a GPR according to claim 14, said method comprising the steps of: placing the two or more electrodes in conductive contact with the ground, moving the GPR across the ground while maintaining contact between the electrodes and the ground, selecting one of the two or more electrodes as a measuring electrode and selecting at least one of the other electrodes of said two or more electrodes as a reference electrode, measuring a potential difference between the measuring electrode and the reference electrode.

16. Method according to claim 15, further comprising the steps of: cyclically selecting each of the other electrodes as a reference electrode, measuring for each of the selected reference electrodes a potential difference between said reference electrode and the measuring electrode, determining an average of the measured potential differences for said measuring electrode.

17. Method according to claim 14, 15 or 16, further comprising the step of cyclically selecting each of the two or more electrodes as a measuring electrode.

18. Method according to claim 17, further comprising the step of determining an average potential of the other electrodes for providing an average reference potential .

19. Method according to any one of the claims 14- 18, wherein the transmit antenna is operated to transmit a signal having characteristics dependent on a potential difference measured between the two or more electrodes.

20. Method according to any one of the claims 14- 19, wherein the selection means are operated to establish or break contact between electrodes and the shielding and/or potential difference measuring means dependent on a reflected signal received by the receive antenna.

21. Method for detecting underground structures using a GPR according to any one of the claims 1-12, wherein the one or more electrodes are conductively connected to the electromagnetic shielding, said method comprising the steps of: placing the one or more electrodes in conductive contact with the ground, moving the GPR across the ground while maintaining contact between the electrode and the ground, transmitting a signal into the ground using the transmit antenna and receiving reflected signals.