CA2237972C - Apparatus and process for clearance of unexploded ordnance - Google Patents

Abstract

A two-step process for clearing unexploded ordnance ("UXO") from the ground. First a high power electromagnetic transmitter sweeps the ground area to be decommissioned. Secondly a lower-power time-domain electromagnetic transmitter or metal detector sweeps the same area to locate UXO. The high power transmitter employs a waveform of having the same frequency and pulse duration as that of the metal detector but does so with at least twice the power. Firstly, when the higher power waveform is applied to the ground, UXO which does not trigger and detonate or "function" is proved as non- functioning at subsequent and lower detection power. Subsequently, the ground area can then be safely scanned by human personnel with impunity, applying the more accurate, lower power metal detector. The detected locations of unexploded ordnance are recorded for subsequent manual removal.

Description

1 "APPARATUS AND PROCESS FOR

2 CLEARANCE OF UNEXPLODED ORDNANCE"

3

4 FIELD OF THE INVENTION
The present invention is related to apparatus and method for 6 clearing unexploded ordnance having triggering mechanisms capable of being 7 functioned by magnetic fields or induced electric currents.

It is known that in order to decommission land used for military 11 purposes and return it to a safe, habitable environment, all unexploded ordnance 12 (UXO) remaining in the ground must be removed safely and efficiently. This 13 needs to be accomplished with painstaking and hazardous hand work.
14 Current technology provides both passive and active systems for the detection of subterranean unexploded ordnance. The passive systems measure 16 variations in the earth's magnetic field and are the safest to human personnel as 17 they do not result in the triggering and detonation or "functioning" of unexploded 18 ordnance. They do not, however, provide an accurate, sensitive scan as they are 19 subject to environmental interference, such as anomalous magnetic soils, and are unable to detect non-ferrous metals.
21 Active "time domain" metal detectors are more accurate, detect non-22 ferrous metals, and probe deeper than do the passive systems. An 23 electromagnetic transmitter produces a pulsed primary magnetic field in the earth, 24 which induces eddy currents in nearby metallic UXO. The eddy current decay produces a secondary magnetic field measured by the receiver coil. The 26 measurement is taken at a relatively long time after the start of the decay to allow 1 the current induced in the ground to fully dissipate. In this way, only the current 2 produced by the secondary magnetic field is detected by the receiver coil.
The 3 responses from the receiver coil are recorded and displayed by an integrated data 4 logger.
Time domain metal detectors are most efficient when operated by 6 human personnel as their location on the ground must be precisely controlled in 7 order to relocate UXO once the data collected by the data logger is evaluated.
8 The electrical current and resulting magnetic field produced by the 9 active metal detecting devices also induces an electrical current in nearby metallic UXO. This current may be sufficient to trigger fuses of unexploded ordnance that 11 employ electronic fuses, with catastrophic results for the person conducting the 12 search.
13 Other inventors have attempted to clear UXO, and more specifically 14 mines, by triggering electronic fuses with electromagnetic signals. Because the nature of a signal that will trigger a fuse is unknown, a variety of signals are tried.
16 For example, US patent 5,361,675 to Specktor describes a land-based invention 17 wherein a magnetic mine detonation apparatus is mounted on a vehicle and 18 utilizes varying waveform configurations for the purposes of detonating all 19 magnetic mines within the scan area.
US patent 4,220,108 to Burt describes a multi-sweep method in an 21 underwater environment. While minesweeping ships are constructed with a very 22 low magnetic signature, modern magnetic detection systems have advanced to 23 the point where even these small magnetic signatures can be detected. Burt 24 teaches use of a permanent magnet which produces a large magnetic signal, greater than the magnetic signature of a following minesweeping ship. This 1 permanent magnet is towed ahead of the following minesweeper with the 2 objective of actuating substantially all magnetically triggered mines in its path. As 3 is virtually impossible to duplicate the exact magnetic signature characteristics of 4 a minesweeper, the field strength of the first magnetic signal is varied by allowing the magnet to move zigzag back and forth transverse to the course and clear a 6 channel. The minesweeper follows relatively safely in the de-mined channel.
7 Additional minesweeper or additional passes may be used to actuate mines in an 8 ever- widening channel.
9 To function UXO, two aspects must be satisfied: one, a signal must be produced which is capable of triggering functioning of the UXO; and second, 11 the signal must be generated in the location of the UXO. Note that each UXO
is 12 unique in terms of its design, historical trauma and environmental effects, and as 13 such, signal characteristics which are capable of triggering functioning of the UXO
14 are unknown.
The prior art minesweepers address a similar problem with 16 magnetically-activated mines. As part of the solution, they vary the waveform as 17 they traverse a mined area. One of the risks with a moving system and a variable 18 waveform is that there is no assurance that waveform being applied at any instant 19 is the one which would trigger the fuse in mine being scanned.
The prior art minesweepers further seek to actuate or function as 21 many of the mines as possible and, for safety, space the mine-triggering device 22 some distance from the personnel-carrying vehicle.
23 The prior art operate on a macro scale for clearing a path through a 24 field for passage of additional minesweeping or other military vehicles and are not concerned with accurate, detailed detection of UXO. The problem remains that 1 for decommissioning of land subsequently intended for human use, there is a 2 demonstrated need to be able to safely remove all 1.1X0, utilizing the precision 3 which is only possible using human-operated detecting equipment or extremely 4 expensive, remote vehicle-navigation systems such as inertial guidance and sub-s cm differential global positiorring systems.
G
7 SUMMARY OF 'THE INVENTION
8 The present invention employs both armoured vehicle-conveyed and 9 human-towed apparatus in a two-step process to provide a safe, efficient means of removing all unexploded ordnance and returning land to a habitable state.
11 In the preferred embodiment, a r~atcfi of ground, in which it is known 12 that at least some of l:he UXO present are electronically fused, is first swept using 13 a high-powered electromagnetic transmitter, called a proving transmitter, having a 14 known waveform. Any UXO sensitive to that waveforrn will either detonate or function at that power or it is proven that it will not function under the influence of 16 that waveform. The patch of ground is then swept again using a human personnel 17 operated UXO detector having a lower-powered electromagnetic transmitter, 18 called a detection trar~snoitter, emitting the same waveforrn only at a lower power.
19 The detection transmitter will not function any electronically fused UXO in the proven patch of ground. Accordingly, the detection transmitter can be safely 21 conveyed and accurately operated using human-personnel without fear of injury.
22 The detection transmil.ter induces an electromagnetic field in the non-functioning 23 UXO which is detected by a receiver the detector for locating the UXO.

1 Accordingly, in one broad aspect of the invention, apparatus for 2 safely locating UXO is provided comprising:
3 ~ a first transmitter and a first receiver, preferably a hand-4 operated metal detector being capable of detecting ferrous and non-ferrous metals, said first transmitter producing a first 6 electromagnetic waveform; and 7 ~ a second transmitter, preferably towed by an armored vehicle, 8 which produces a second electromagnetic waveform having 9 the same characteristics as the first electromagnetic waveform excepting that the second electromagnetic 11 waveform is produced at a greater amplitude so that, when 12 the second transmitter is swept over the patch, any 13 unexploded ordnance which does not function is proved non-14 functioning by either waveform, and so that the patch can be subsequently and safely swept by the hand-operated metal 16 detector locating UXO.
17 Preferably, the first and second waveforms comprise a series of 18 electrical pulses wherein the pulses of the first waveform and second waveforms 19 have the same duration and the same frequency but the amplitude of the pulse of the second waveform is greater than the amplitude of the pulse of the first 21 waveform.
22 The above apparatus is amenable to application to a patch of 23 ground in a unique two-step sweeping method comprising:
24 ~ firstly transmitting a proving waveform into the patch at a power greater than that required to induce an electromagnetic

5 1 field in UXO wherein any UXO in the patch which is sensitive 2 to that proving waveform will either function or be proved non-3 functioning;
4 ~ secondly transmitting a detection electromagnetic waveform into the patch and receiving an electromagnetic field induced

6 in the unexploded ordnance by the detection waveform for

7 locating UXO, the transmitted detection waveform having the

8 same characteristics as the proving waveform except that the

9 detection waveform has an amplitude which is less than that of the proving waveform.

13 Figure 1 is a perspective view of the personnel-conveyed metal 14 detector, operated in accordance with one embodiment of the invention, more specifically being operated after the passage of a higher-powered EM
transmitter.
16 The metal detector is shown traversing one of a series of rectilinear paths;
17 Figure 2 is a top view of the human personnel-conveyed time 18 domain metal detector following in the path proved by the higher-powered EM
19 transmitter;
Figures 3a and 3b illustrate the similarity in the characteristics of the 21 nature of the waveforms produced by the detection transmitter (Fig. 3a) and the 22 second EM transmitter (Fig. 3b);
23 Figure 4 is a flow chart illustrating sequential UXO functioning and 24 UXO detection steps; and 1 Figure 5 is a perspective view illustrating positioning ofi the proving 2 transmitter as a loop when obstacles prevent access by a vehicle.

Generall G Having reference to Fig. 1, a human operator 1 is shown towing trailer 2 7 carrying an active electromagnetic metal detector 3. The detector 3 employs a first 8 electromagnetic (EM) transmitter 4, called a detection transmitter, which is used for 9 detecting unexploded ordnance (UXO) 5 buried in the ground. The UXO 5 is subsequently neutralized for decommissioning a defined area G of the ground (typically by 11 manual excavation). t~egarding safety issues, a persoro of skill in the art would 12 understand that, where an area G is to be swept by an unshielded human operator 1 13 using the present invention, the area G is either known to be free of antipersonnel mines 14 and the like or has been rendered free of mines using corwentional means.
At least some of the UXO 5 are of the type employing electronic fuses.
16 Having reference to I=ig. 2, ar leading vehicle 7 employs a second EM
17 transmitter 8, called a proving transmitter. Tloe operator 1 and metal detector 3 follow the 18 leading vehicle 7 at a safe distance (typically 250 m for most ordnance, excluding larger 19 aircraft bombs and missiles). Alternatively, the operator 1 and metal detector 3 can follow much later in time. The leading vehicle 7 and proving transmitter 8 reader a path 9 safe 21 for the following operator 1 and detection transmitter 4.

23 The Detection Transmitter 24 More particularly and referring again to Fig. 1, the metal detector 3 comprises a main coil 10 incorporating the detection transmitter 4 and a first 26 receiver coil 11 a. The detector 3 further comprises a focussing or second receiver 1 coil 11 b. The detection transmitter 4 is coincident with the first receiver coil 11 a.
2 The detection transmitter 4 and receiver coils 11 a,11 b are spaced from the 3 ground. A controller 12 and first signal generator 13 produce a pulsed electric 4 signal 14 and is applied to the detection transmitter 4 through connector 15.
During the pulse of signal 14, current is produced in the detection transmitter 4 6 and creates a magnetic field which extends into the ground. The magnetic field 7 produced is of sufficient strength to induce eddy currents in metal, including metal 8 UXO 5. The end of the signal's pulse represents cessation of current to the 9 detection transmitter 4. The decay of the eddy current sets up a secondary magnetic field which is ultimately detected by receivers 11a, 11 b.
11 The second receiver 11 b is spaced above the main coil 10. Both 12 first and second receiver coils 11 a,11 b receive the secondary magnetic field. The 13 spacing between the first and second receiver coils 11 a,11 b enable determination 14 of the depth of detected UXO 5.
An example of such a metal detector is model EM61 time domain 16 metal detector available from Geonics Ltd., Mississauga, Ontario.
17 Having reference to Fig. 3a, the first signal generator 13 produces a 18 signal 14 comprising a waveform having a series of pulses 16. The pulses 16 are 19 part of the unique characteristics of the signal's waveform including:
pulse amperage or amplitude A1, pulse duration D, and pulse frequency F. Power of 21 the signal 14 is related to the square of the pulse amplitude A1.
22 For the known EM61 detector, a pulse amplitude A1 of 8 amperes is 23 produced with a pulse duration D of 3.33 ms and a frequency F of 75 Hz.
24 The frame of trailer 2 is constructed of a non-conducting material so as to isolate the detection transmitter 4 from other structure.

1 The Proving_ Transmitter 2 The second EM proving transmitter 8 comprises a proving 3 transmitter coil 20 connected to a controller 21 and a second signal generator 22 4 with connector 23. As shown in Fig. 3b, the second signal generator 22 produces a second signal 24 and waveform having similar characteristics to the first signal 6 generator's signal 14 except in one respect; the second signal 24 has an 7 amperage or amplitude A2 which is higher than the amplitude A1. Signal power of 8 about 2 times or greater (amperage A2 being 1.414 times greater that A1 ) is 9 sufficient.
Typically an EM61 detection transmitter 4 produces a peak signal 11 amperage A1 of 8 amps. A large factor of safety is achieved through use of A2 of 12 40 amps. The amperage increase is 5 times (40/8) or a power increase of 25 13 times.
14 The second signal 24 has pulses 25 having the same duration D and frequency F as does the first signal 14.
16 First signal 14 is capable of functioning a small, but clearly 17 hazardous, number of UXO 5. As previously stated, whether UXO 5 will function 18 is dependant upon the state of its fuse. To avoid the hazard and expense of 19 functioning all UXO, it is desirable to function, or prove non-functioning, only UXO
which are sensitive to signal 14. As demonstrated by the prior art, individual UXO
21 5 will function under different electromagnetic fields (i.e. different pulse duration 22 and different frequency).
23 Accordingly, UXO 5 is first subjected to a higher-power signal 24 24 from the proving transmitter, the signal 24 having the same pulse duration and frequency characteristics as the first signal 14. Signal 24 is applied to the ground 1 and buried UXO. Eddy currents are induced in the UXO 5. The specific eddy 2 current induced may or may not function the UXO 5. If the UXO 5 does not 3 function, that UXO is proved that it will also not function when subjected to the 4 lower-powered signal 14.
Note that one can see that, as described above, the proving 6 transmitter 8 is not associated with an electromagnetic receiver and therefore is 7 not capable of detecting UXO, nor is the proving step capable of collecting 8 measurements or data.
9 To ensure safety of personnel operating the proving transmitter 8, it is mounted on a trailer 30 having wheels 31 which is towed behind the leading 11 vehicle 7 which is armoured. Such vehicles include an armored personnel carrier, 12 a main battle tank chassis, or a truck with added armour. The leading vehicle 13 could be a remote controlled vehicle.

In Operation 16 Having reference to Fig. 4, and beginning at block 40, to clear and 17 area 8 of UXO, the proving transmitter 8 is towed over the area 6 to be 18 decommissioned. An efficient ground track pattern is utilized. One, such pattern, 19 amenable to uncomplicated terrain is to employ a sequence of rectilinear paths (9,9a,9b,9c . . .).
21 The trailer-mounted proving transmitter 8 preferably covers a larger 22 area than does the human-conveyed detection transmitter 4. As the proving 23 transmitter 8 need only prove non-functioning of UXO and not pin-point it, its 24 accuracy need not be as great as that required of the detection transmitter 4.

1 UXO 5 in area 6 are either functioned by the second signal 24 (Block 2 42) or are proven to be non-functioning at the specific characteristics of signal 24 3 and more particularly at the specific characteristics of first signal 14.
4 As a result (Block 43), the metal detector 3 can be towed (Block 44) by human operator 1, without fear of inducing functioning, over the same 6 sequence of rectilinear paths (9,9a . . .), proved safe by the proving transmitter 8.
7 The positioning of the metal detector 3 is precisely controlled by the 8 human operator 1. The secondary magnetic field induced in the metal UXO by 9 signal 14 (Block 45) and received by the first and second receivers 11 a, 11 b (Block 46) is stored in a data collecting device integrated with the controller 12 11 and first signal generator 13, carried by the human operator 1. The wheels of the 12 trailer are fitted with an odometer and outputs traversed distance data which is 13 collected for measured intervals. The measured length of the path (9,9a . .
.) 14 traversed, typically 50 meters, is compared against the odometer distance.
The locations of UXO are normalized (measured/odometer) and more accurate 16 locations of the detected UXO 5 are calculated. The location of UXO 5 is 17 recorded (Block 47) and can be re-located later for neutralization.
18 In another embodiment of the invention, a plurality of detection 19 transmitters are towed side by side to increase the path width swept with each pass. The detection transmitters are towed closely behind an all-terrain vehicle.
21 In yet another embodiment of the invention, where as shown in Fig.
22 5, terrain is too rough to be traversed by vehicle or contains too many obstacles, 23 the higher-power proving transmitter 8 is formed using electrically conductive 24 cables laid out directly on the irregular ground surface to form loops 50.

1 In yet another embodiment of the invention, as illustrated in phantom 2 lines in Fig. 2, a plurality of trailer-mounted proving transmitters are towed side by 3 side to increase the path width swept with each pass. Further, the signal pulses of 4 each of a plurality of proving transmitters may be synchronized.

Claims (19)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN
EXCLUSIVE PROPERTY OR PRIVILEGE IS BEING CLAIMED IS DETAILED
AS FOLLOWS:

1. A method of sweeping a patch of ground for unexploded ordnance, at least some of which are of the type employing electronic fuses, said method comprising the steps of:

providing a detector having a detection transmitter and a detection receiver, the detection transmitter producing a detection waveform having sufficient detection amplitude to induce an electromagnetic field in unexploded ordnance for detection by the detection receiver;
providing a proving transmitter which produces a proving waveform having the same characteristics as the detection waveform except that the proving waveform has a proving amplitude which is greater than the detection amplitude;

firstly sweeping the patch with the proving transmitter while transmitting the proving waveform into the patch using the proving transmitter to prove that any unexploded ordnance in the patch with function or be proved non-functioning in response to either the proving waveform or the detection waveform;
and secondly sweeping the proved patch while transmitting the detection waveform and receiving any induced electromagnetic field at the detection receiver so as to safely establish the location of non-functioning unexploded ordnance with the detection receiver.

2. The method as recited in claim 1 wherein:
the detection waveform comprises a series of electrical pulses having a duration, a frequency, and the detection amplitude; and the proving waveform comprises a series of electrical pulses having the same duration and the same frequency as the detection waveform and having the proving amplitude which is greater than the detection amplitude.

3. The method as described in claim 2 wherein the proving transmitter is mounted on a trailer and is towed by an armored vehicle for traversing the patch.

4. The method as described in claim 3 wherein the detection transmitter and detection receiver are a time domain metal detector.

5. The method as described in claim 2 wherein after the patch has been swept by the proving transmitter, the patch is then swept by towing the detection transmitter and detection receiver by human personnel.

6. The method as described in claim 2 wherein the patch is then swept by towing the detection transmitter and detection receiver sequentially along an array of rectilinear paths within the proved patch.

7. The method as recited in claim 2 wherein the location of unexploded ordnance detected by the metal detector is marked for manual neutralization.

8. The method as recited in claim 2 wherein the patch has a terrain which is irregular, the method further comprising deploying electrically conductive cables over the patch to produce one of more irregular-shaped electromagnetic transmitters on the patch.

9. Apparatus for safely detecting the location of unexploded ordnance, at least some of which are the type employing electronic fuses, in a patch comprising:
a first transmitter and a first receiver, said first transmitter producing a first electromagnetic waveform; and a second transmitter being towed by a vehicle and which produces a second electromagnetic waveform having the same characteristics as the first electromagnetic waveform excepting that the second electromagnetic waveform is produced at a greater amplitude so that, when the second transmitter is swept over the patch, any unexploded ordnance which does not function is proved non-functioning by either first or second waveforms, and so that the patch can be subsequently swept by the first transmitter and the first receiver for safely locating unexploded ordnance.

10. Apparatus as recited in claim 9 wherein the first transmitter and the first receiver are a hand-operated metal detector capable of detecting ferrous and non-ferrous metals.

11.Apparatus as recited in claim 9 or 10 wherein:
the first and second electromagnetic waveforms comprise a series of electrical pulses;
the pulses of the first waveform and second waveforms have the same duration and the same frequency; and the amplitude of the pulse of the first waveform is less than the amplitude of the pulse of the second waveform.

12. Apparatus as recited in claim 10 wherein the hand-operated metal detector is mounted on a trailer and is towed by human personnel.

13. Apparatus as recited in claim 12 wherein the hand-operated metal detector is electrically isolated from the wheels and axle of the trailer.

14. A system for sweeping a patch of ground for unexploded ordnance, at least some of which are the type employing electronic fuses, comprising:
proving means for transmitting a proving waveform into the patch using a proving transmitter to prove non-functioning of the unexploded ordnance, wherein the proving waveform has substantially the same characteristics as a detection waveform except that the proving waveform has an amplitude higher than that of the detection waveform; and detecting means for transmitting the detection waveform into the proved patch wherein unexploded ordnance is detected by the detection receiver without functioning the unexploded ordnance.

15. The system as recited in claim 14 wherein:
the detection waveform comprises a series of electrical pulses having a duration, a frequency, and a detection amplitude;
the proving waveform comprises a series of electrical pulses having the same duration and the same frequency as the detection waveform and having a proving amplitude which is greater than the detection amplitude.

16. The system as described in claim 15, wherein the proving means is mounted on a trailer and is towed by an armored vehicle.

17. The system as described in claim 15, wherein the detection means is a time domain metal detector.

18. The system as described in claim 17, wherein the patch is subjected to an electromagnetic field by towing the detecting means sequentially over an array of rectilinear paths having been previously rendered safe by the proving means.

19. The system as recited in claim 14, wherein the proving means includes electrically conductive cables deployed over the patch and configured to produce a non-regular shaped electromagnetic transmitter.