Note: Descriptions are shown in the official language in which they were submitted.
CA 02237972 2001-10-15
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.
8
9 BACKGROUND OF THE INVENTION
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
CA 02237972 2001-10-15
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
2
CA 02237972 2001-10-15
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
3
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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.
4
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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
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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.
11
12 BRIEF DESCRIPTION OF THE DRAWINGS
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
6
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1 Figure 5 is a perspective view illustrating positioning ofi the proving
2 transmitter as a loop when obstacles prevent access by a vehicle.
3
4 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
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.
22
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
7
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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.
8
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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
9
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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.
14
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.
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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.
11
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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.
12
