Applications of GPR Technology to Humanitarian Demining Operations in Cambodia: Some Lessons Learned Jean-Daniel Nicoud LAMI-EPFL, CH-1024 Lausanne Tel. +41 21 693 2642 email:
[email protected] http:\\diwww.epfl.ch/lami/detec
John W. Brooks Brooks Enterprises International, Inc. 1509 Locust Circle, S.E. Huntsville, AL 35801, USA Tel: +1-256-539-0148 email:
[email protected] [email protected]
Background:
Abstract: This paper describes the activities of the Demining Technologies (DeTec) team from the École Polytechnique Fédérale de Lausanne (EPFL), and personnel of Brooks Enterprises International, Inc., Huntsville, Al, USA, while testing the prototype DeTec-2 Ground Penetrating Radar (GPR) in Cambodia. The team, under the direction of Prof. J. D. Nicoud, tested the prototype radar from 18-21 November 1997 in the village of Thmar Pouk, near the Thai border. A test minefield had been prepared by personnel from Hazardous Areas Life-support Organization (HALO Trust). The minefield represented several different soil types and contained hundreds of false targets and a few selected antipersonnel (AP) mines which had been deactivated. A significant amount of useful GPR data was collected and is currently being processed. A description of current demining operations is presented, describing the incredibly tedious prodding method, and we propose guidelines for the use of GPR in the field. Lessons learned, specifically recommendations for equipment validation are presented.
Discussions with HALO Trust in Cambodia, in November 1996, led to the design of a hand-held antenna to be used by a kneeling deminer (or in prone position). The DeTec-1 system (Figure 1) was tested in Karlovac, Croatia, in July 1997, in a military field in which live mines had been planted the same morning. The test was quite instructive and demonstrated that the head of a hand-held device must not weigh more than 1 kg. In addition, it was determined that, for good data, the mines must be planted in the ground several months prior to the tests; Otherwise, the disturbance around the mine creates a severe clutter environment. From Figure 1, it can be seen that the hand-held antenna, used in the kneeling position, results in a rather erratic scan pattern. The operator will tend to increase the distance between consecutive scans as the antenna moves farther from the body, and the scans become clustered as the antenna comes closer to the body. This results in uneven sampling of the target area, and can creates problems in interpretation of data. Nonetheless, any final design will most likely involve a hand-held system, so these issues must still be addressed.
1. INTRODUCTION This paper describes the activities of the DeTec team in the village of Thmar Pouk in Cambodia, from 17-21 November 1997. The purpose of the visit was to test the prototype DeTec-2 Ground Penetrating Radar (GPR) under realistic operational and environmental conditions.
An additional factor is that the operator tends to raise the antenna off the ground slightly when a real mine possibly lies beneath the surface; the variation in height also creates data anomalies. The particular antenna used in all our tests (ERA Technologies, Ltd. SPR-Scan, 1GHz nominal bandwidth) was designed originally for civil engineering applications and normally requires contact with the surface of the ground.
Section 2 describes the current practices of searching for the mine with a metal detector and subsequent prodding. Section 3 provides details of the DeTec-2 equipment operation in the field, and provides some perspective on the data collected. Section 4 provides a candidate methodology for the development and validation of new mine detection/classification equipment. A brief list of references is included in Section 5.
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Figure 1. Detec-1 in Croatia, and example of hand scanning pattern on ground.
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The system was redesigned with all equipment inside the same box, supporting a moving arm which included a simple mechanism for doing the regular scanning ([1][5]), resulting in much improved data quality. DeTec-2 (Figure 2) weighed 25kg and was reasonably easy to
carry and position. The distance between consecutive scans is held constant at 1.0 cm by a mechanical ratchet system, described in detail at the DeTec-2 Homepage, http://diwww.epfl.ch/w3lami/detec/detec2.html
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Figure 2. Detec-2 System and typical scanning pattern over ground Arrival in Cambodia: Prof. Nicoud and Frédéric Guerne of EPFL-LAMI met with John Brooks and Douglas Ludolph of BEI, Inc. in Phnom Penh on 17 November 1997 for the flight to Battambang. We were accompanied by Halo personnel who were to drive us from Battambang, via Sisophon, to Thmar Pouk (Figure 3). Due to the extremely poor condition of the roads in Cambodia, the trip required 4 hours for the 120km trip.
Road travel in the target area of Cambodia is very difficult. Movement should take place only during daylight hours. Travelers should consult their respective governmental agencies for any travel restrictions. In addition, there are no good medical facilities outside the major cities, so care should be exercised to minimize the risk of injury on the road. Avoid those areas in which elements of the Khmer Rouge may be active. Three factors are vital when considering transporting gear; dust, heat and the size/weight of any vehicle. All electronic equipment and other instruments should be packed in resealable plastic bags. Dust will penetrate
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Figure 3. Map of Cambodia showing main locations involved
Figure 4. View of Bridge on the Way to Minefield everything that is not completely sealed. This is particularly important for laptop computers, floppies and the like. The heat will affect the operation of sensitive electronics in the field; we had to protect DeTec-2 from direct sunlight with a large umbrella. Finally, the bridges in the area are in extremely poor condition. The bridge in Figure 4 is just west of Thmar Pouk. It consists of handlaid logs with large gaps between. The man in the photo is preparing to adjust one of the wooden planks to the correct position for the wheels of the Land Rover. 2. CURRENT DEMINING PRACTICES The manual demining methods employed by HALO Trust follow very strict standing operational procedures (SOPs). Safety and thoroughness are top priorities. Each deminer wears a protective flak vest and polycarbonate face shield as shown in Figure 5. The configuration which protects only the torso and face is a compromise; the intense heat in Cambodia precludes the use of heavier protective gear. During our visit, daytime temperatures ranged to 32 degrees Celsius. The operators normally work in half-hour shifts to minimize fatigue; the act of prodding for landmines is very stressful and the concentration of the deminer must not be compromised.
the sensitivity and ergonomic criteria.
A deminer works within a narrow lane about 1 meter wide, the leading edge of which is indicated by a wooden stick. Figure 6 shows that the detector head of the Ebinger metal detector is placed as close to the ground as possible. HALO SOP requires calibrating the sensitivity of the head to detect a small (approx. 1mm x 5mm) piece of metal 10cm from the detector head, while minimizing false alarms. This is to ensure reliable detection of a minimum-metal mine such as the Chinese T72. According to HALO personnel on site, the Ebinger detector is considered superior to other detectors from
In Figure 7, J. Brooks is shown in the process of locating a mine which had been previously laid by HALO Trust personnel. Following a familiarization with the Ebinger equipment and training on the scanning/prodding methods, he was instructed to attempt to find a PMN-2 located in what is now called “Field 4”. The ground was dry on the surface, but moist a few cm below, and there was a small amount of ground cover, such as twigs, stones, small roots, etc. Per SOP, an area the length of one detector head in front of the guide stick, and one head length to either side of the stick, is scanned. All
Figure 5. Cambodian Deminer
Figure 6. Details of Ebinger Metal Detector in Operation intervening twigs/grass must be manually removed prior to scanning, as the detector head must barely touch the ground for maximum effectiveness. The procedure is painstakingly slow; one realizes that an undetected mine such as a T72 will find itself directly under the knee of the operator. This presents an extremely stressful environment for the individual deminer, in addition to the physical stresses. The kneeling position, coupled with the operation of the metal detector, hasten operator fatigue. It is clear that the protective gear will provide no protection for the arms or legs. Figure 7(a) shows the scanning with the metal detector. The head is placed flat on the surface. When an audio tone indicates the presence of a metal object, the detector head is tilted so that the edge of the head can provide a better localization of the metal piece. Clearly, if a GPR head would be fixed to the metal detector, any movement to optimize metal detector operation would defeat the operation of the GPR. Such issues impact “sensor integration”. Figure 7(b) shows the method of prodding with a locally-made prodder. When a suspect area is indicated, the operator slides the prodder into the ground at about a 20-30 degree angle, to the length of the prodder. Rocks, roots and other intervening objects can mask the presence of a mine. One does not aggressively ram the prodder into the ground; the possibility of a mine which is tipped toward the operator is great, and such prodding could detonate the mine. Therefore, the prodded area is carefully excavated with a small scoop, as shown in Fig-
ure 7(c). The prodded soil has been made somewhat easier to excavate. When the mine is discovered (Figure 7(d)) the operator announces “Mine!” and the team chief will verify the discovery. The mine is most often detonated in situ using a 250 gram charge of TNT. Per HALO SOP, EVERY suspected alarm must be resolved; each alarm must be prodded to a depth of about 15 cm. If the metal detector still indicates the presence of any metal, the area is cordoned off and marked as suspect. This attention to safety and thoroughness results in what appears to be an unreasonable rate of clearance. The estimate of the personnel on site was that a 40m x 40m area would require about 3 weeks to clear, using 2-3 deminers at a time. Each demining lane must be separated by about 20-25 meters to minimize the danger to an adjacent deminer in case one should detonate a mine. Some Personal Thoughts: Even though the PMN-2 mine above was deactivated, the process of manual demining by prodding was still quite stressful. Several “false alarms” were encountered prior to the real mine. In each case, all SOPs had to be followed, and each false alarm had to be verified and the offending metal removed from the ground. Any of those false alarms could have been a mine. Any mistake could be deadly in a real minefield.
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(d) Figure 7. Scanning With Ebinger Detector
The challenge for any technological tool such as GPR is clear: When the manufacturer of the tool is willing to let his own children play in a field demined with his/her equipment, we can safely assume that it works as well as the current manual method. Now, if that tool can speed up the process sufficiently to warrant the additional cost while maintaining the current level of deminer employment, it will be a winner.
obvious that we could spend a very great amount of time searching for the mines, we were permitted access to the map which showed the locations of the mines. By then, we had collected over 40 data files which contained nothing but false alarms. After locating the mines with the aid of the map, we were able to collect good GPR data on the real mines. DeTec-2 Operations:
3. THE FIELD TESTS WITH DETEC-2 Layout: Six months prior to our arrival, the HALO Trust personnel had prepared seven distinct test sections within a 40m by 40m field next to their compound in Thmar Pouk. This was done to ensure that the soil would be well-weathered, and also to give the vegetation time to grow back, providing a realistic test environment. Several deactivated AP mines ranging from all-metal to minimum-metal types, had been laid at varying depths from about 5cm to 22cm. The test area represented varying soil conditions ranging from a relatively dry, rocky area beneath a large tree, to a silty, wet area. One additional field, Field 8, was located a few km west of Thmar Pouk and was used on the final day of tests. It was characterized by very hard, dry soil and numerous roots, rocks and additional vegetation. Initially, we had no knowledge of the location of the AP mines; only the HALO site supervisor had access to that information. However, as time progressed, and it was
The DeTec-2 equipment suffered some difficulties the first day due to the 32 degree (90 degree F), but these problems were fixed by applying toothpaste to an aluminum plate which served as an additional heat sink. From then on, the equipment could operate for about 2-3 hours, permitting good data collection. The first day (18 November) was mostly devoted to equipment set-up and check-out, solving our heat problems and explaining to the deminers how to proceed ; we collected only 4 files. On the second day we conducted 7 hours of data acquisition (22 files). On the third day we obtained 21 files, including 4 mines. The last half-day took place in “Field 8” in the countryside (12 files), far from the “comfort” of the compound. In all, about 500MB of data was collected, and is posted at the DeTec website. Power supply for recharging DeTec-2 was provided at this field by an additional car battery connected to a 220V converter. The heat and level of discomfort were high, but we had asked for this, after all. HALO Trust had allocated a team of 6 deminers to assist
us during our tests. The chief of the platoon spoke English quite well. One deminer was in charge of the equipment. Two pairs of deminers were doing the vegetation removal, metal detection and prodding. Metal detector alarms were indicated on the ground by means of wooden triangles, and DeTec-2 was then put in position for the scanning. Positioning took 1-2 minutes, scanning 2-3 minutes. In operation, the normal SOP was followed by a deminer first scanning the ground with the metal detector. When a suspect area was found, the deminer would report that to the DeTec-2 operator, who would then move into position within the demined lane and adjust the GPR head position to be a few centimeters off the ground as shown in Figure 8. Note the lane markers as described earlier; the end of the cleared lane is indicated by the stick, and the trailing white straps indicate the sides of the lane.
points. This was enough for 4 days of operation. However, to ensure that no data would be lost due to equipment malfunctions, it was copied onto a streamer tape and also backed up on a laptop PC every evening. Recharging the DeTec-2 system was a problem since the 220V generator provided only about 160V. BEI, Inc. provided a laptop Pentium PC which was 110V-220V compatible. It was equipped with an external backup hard drive with three disks, each capable of storing 250MB of data. Every evening, data was transferred from Detec-2 to the laptop (Figure 9), and the collected data was verified to be of good quality. In addition, some preliminary processing of the data was possible, and suggestions could be made to the DeTec-2 operator, if necessary, for the activities for the following day.
Following initial setup, the DeTec-2 is positioned such that the antenna is just ahead of the lane limit. Final adjustments are made to the antenna height, and then the scan commences. A 40cm-by-40cm swath (Figure 4) was scanned over the suspected area.
Figure 9. Laptop PC with Extra Drive; Detec-2 in Background
Figure 8. F. Guerne Setting up Detec-2
Records of each scan were made by F. Guerne, including comprehensive diagrams and pictures of the environment and detected objects. Figure 11 shows an example of scan results with a PMN-2 mine. Figure 10 shows an example of the detail applied to a scan involving numerous metallic false alarms. At this time, the differences between the false alarm image and the PMN-2 image are not obvious. Work is currently underway to more clearly define various discriminant features which may be used in an automatic classification algorithm.
Data Storage and Processing The local DeTec-2 disk had sufficient capacity for 50 acquisitions, due to the high spatial density of data
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Figure 11. Example of GPR scan of metallic false alarms, with picture of removed objects and detailed field notes 4. CONCLUSIONS AND RECOMMENDATIONS
maintaining the established level of reliability.
All of the objectives of the trip to Cambodia were met; we were able to successfully demonstrate that a manportable GPR could be integrated with the SOPs of an operational demining group. A wealth of good data was collected, and is now being processed for the development of target classification algorithms. The DeTec program objectives of building and demonstrating a prototype GPR under field conditions by the end of 1997 were met. All data collected has been published on the World Wide Web at http://diwww.epfl.ch/w3lami/detec/ detec2cambodia.html and is freely available to any interested researcher.
Suggestions for Program Development and System Validation:
Cambodia offered some very unique perspectives for a group of scientists and engineers. First, it was important for the engineers to understand the actual operations in a demining unit, so that subsequent system design can accommodate the operational environment. Second, it was important for the on-site personnel to witness visitors who took an active interest in their daily operations, and not just trying to sell another technical solution to their problems. In general, personnel in the field are extremely skeptical of technological solutions, and rightfully so. No technical solution exists which will guarantee the level of accuracy which is demonstrated daily be the individual deminers. Few, if any system development programs are designed to focus, from the outset, on developing equipment which is totally “idiot-proof”, rugged and reliable. It must also be inexpensive. On-site personnel were adamant that any GPR must be able to provide a “significant” reduction in the time spent demining, while
With a new mine detection/classification system, the first casualty resulting from an undetected mine will simply make the product disappear from the market, and a similar technology may not be proposed again for many years. It is therefore especially long and difficult to validate demining equipment. Tests in the laboratory will never be considered sufficient. We need a reference procedure to evaluate demining equipment. The SOP's documented and followed by each demining team is the only reference trusted by the demining team. It specifies how to remove the vegetation, how to check, adjust and use the metal detector, how to prod, what to do when a dangerous object is found. For the few places that may have non-metallic mines, or where the soil does not allow the use of a metal detector, systematic prodding as deep as required is the reference procedure. Any new demining equipment must be tested in the field against the reference procedure in use. Validation at a military proving ground will never be accepted by humanitarian deminers. The test procedure must be performed by the demining teams themselves. Due to the dangers in the field, engineers will not be allowed near the deminer with the equipment, and this complicates the test procedures. In the initial phases of the test, the developers need to check the operation and verify the quality of the data.
They have of course done this abundantly in the lab and in different fields, but the situation in a real minefield introduces many new parameters. A solution has to be found to be able to give the deminers the equipment to be tested. Its operation has to be inserted into the SOP, without removing any step, and not adding difficult or dangerous operations. Either the new sensor is used after removing vegetation (40cm at a time on the 1m wide lane), or the sensor is used on the potentially dangerous spots indicated by the metal detector. Then the usual prodding is performed and the cause of the alarm can be determined. For the system developers, the work is then to check the data given by the detector against the alarms, and see if a correct prediction could have been done. In the case a complete scan is performed, one could dream about a sensor able to find mines the metal detector would not detect; in this case, it would be necessary to prod the entire area to the depth specified by the SOP's. Figure 12 below shows a candidate validation methodology for any new hi-tech mine detection/classification system. The interaction with the working deminers in the field (NOT representatives from NGO headquarters, etc.) is essential from the very beginning of the project. Their active participation will ensure that ridiculous designs do not make it off the paper, and will also lend credibility to the design when the developers eventually bring the equipment into the field.
About the Authors:
John W. Brooks is the President of Brooks Enterprises International, Inc., a Huntsville, AL-based firm which specializes in GPR signal processing and humanitarian demining research. His work in the field of radar spans 30 years, and includes practical field experience as well as laboratory research.
5. REFERENCES [1]
F. Guerne, B. Gros, M. Schreiber, J.D. Nicoud, “DETEC1 and DETEC-2: GPR Mine Sensors for Data Acquisition in the Field,” Proceedings SusDem'97, Zagreb, Sept. 29Oct 1, 1997, pp. 5.34-5.39. [2] J.-D. Nicoud, “Detec1 - GPR system designed for acquisition of real mine data,” Report on the tests in Karlovac (Croatia), July 3, 1997, 6p. [3] J.-D. Nicoud, "Detec2 - Report on the tests in Thmar Pouk (Cambodia)", November 18-21, 1997, 6p. [4] K. Tsipis, “Report on the Landmine Brainstorming Workshop of Aug. 25-30, Nov. 96,” Report No. 27, Program in Science and Technology for International Security, MIT, Cambridge, MA, USA, Nov. 1996.Web: http://mcnutt.mit.edu/PSTIS/minereport/minereport.html [5] D. Toews, “Land Mine Detector Evaluation Trials,” SusDem'97, 1997, pp 5.62-5.68. [6] C. Bruschini, et al, "Ground Penetrating Radar and Induction Coil Sensor Imaging for Antipersonnel Mines Detection", Proceedings of the Conference GPR'96, Sendai, Oct 1997, pp. 211-216. [7] (http://diwww.epfl.ch/lami/detec/ detec.html#Detec_projects) [8] C. Borgwardt, “High-precision Mine Detection with Realtime Imaging,” Detection and Remediation for Mines and Minelike Targets, Conference Proceedings, 1996, SPIE 2765, pp. 301-309. [9] D.J. Daniels, “Surface Penetrating Radar,” IEE Radar, Sonar, Navigation and Avionics Series 6, Institute of Electrical Engineers, London, 1996, ISBN 0 85296 862 0. [10] J.W. Brooks, “A Survey of Modern Signal Processing Methods and their Application to Sustainable Humanitarian Demining,” SusDem97 Proceedings, Zagreb, Croatia, pp. S5.40-S5.47 [11] C. Bruschini, B. Gros, “A Survey of Current Sensor Technology Research for the Detection of Landmines,” Proceedings SusDem'97, Zagreb, Sept. 1997, pp. S6.18S6.27.
Prof. Jean-Daniel Nicoud (Shown here reviewing papers at night in Cambodia) is the Director of the LAMI (Laboratoire de Micro-informatique), which is a lab mostly concerned with microprocessor systems, sensors and interfaces. Expertise and interest exist for building small and potentially low cost systems. The team masters microcontrollers, DSPs, neural network dedicated circuits, mobile robots, sensors, positionning devices, as well as the associated software tools.
Deminer Inputs
Start Program?
Yes
Get informations on mines, fields and requirements Develop or buy the sensor Test for feasibility in Lab
Deminer Inputs
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Redesign, Additional Studies or Program Termination
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Specifications of the operational prototype Design and construction Test on a proving ground (specially prepared field)
Deminer Inputs
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Redesign if necessary Tests in the field Acceptance tests by deminers Final validation
Commercialize?
No
Other Demining/UXO Application
Yes
Commercial Markets
Figure 12. Candidate validation process for new mine detection system
