Robotic And Remotely Operated Geophysical Platforms For Terrestrial And Marine UXO Detection
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Noel T. Rogers, Geophysical Solutions, Inc., Albuquerque, NM
Stewart K. Sandberg, University of Southern Maine, Gorham, ME
George Prince, U. S. EPA Environmental Response Team Center, Edison, NJ
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Abstract
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Two remotely operated geophysical platforms were deployed for terrestrial and marine unexploded ordnance (UXO) detection. The terrestrial system is a fully robotic system and the marine system is a remotely towed platform. The remotely operated geophysical UXO explorer (ROGUE) is a semi-autonomous robotic platform equipped with a Geonics Ltd. EM-61™ time-domain electromagnetic metal detector, a pair of GEM Systems, Inc. GSMP-30™ potassium magnetometer sensors, pan and tilt video camera and, tracked with real-time kinematic GPS (±2 centimeter accuracy). Both magnetometer and EM data, video, and GPS are simultaneously collected and transmitted via radio modems to a remote data acquisition center. Once the extents of the survey are input into the ROGUE command and control system the robot autonomously collects the geophysical data and transmits the data back to the command center in real-time. The marine geophysical system (ROHICA) consists of a non-magnetic vessel equipped with a magnetometer and differential GPS (± 0.5 meter accuracy) and a moored offshore barge for towing the geophysical vessel. The offshore barge has a set of four winches, two winches control the on-line positioning of the barge and two winches control the transport of the geophysical vessel down lines. Navigation for all marine vessels is controlled from the remote data acquisition system. The geophysical and positional data from the marine system are transmitted in real-time via radio modems to the remote data acquisition system.
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Introduction
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Remotely operated terrestrial and marine systems were developed in order to reduce the potential risk associated with UXO. The systems were designed for UXO detection in semi rugged terrain and shallow marine environments. Both systems can be remotely operated at distances in excess of 3,000 feet under optimal conditions.
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The robotic platform (ROGUE) was designed to detect ferrous and non-ferrous ordnance as small as 40 millimeter (mm) projectiles in semi rugged terrain. The ROGUE is a comprehensive and cost effective solution to unmanned semi-autonomous detection of UXO. The system is equipped with magnetometer and EM-61 sensors, video, and GPS and all these data are collected concurrently (Figure 1). The ROGUE is capable of fairly rugged terrain with limitations.
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Figure 1. ROGUE semi-autonomous robotic platform (photo courtesy of OAO Robotics).
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The marine platform (ROHICA) was designed to detect only ferrous ordnance 40 mm projectiles or larger in the shallow water with depths of zero to less than seven feet. The ROHICA is a 100% non-metallic barge that is towed between the shore and an offshore control barge (Figure 2). The survey vessel was equipped with a pair of magnetometer sensors for the detection of the ferrous ordnance. The ROHICA can withstand rough seas and is capable of being towed up onto a beach to the edge of the tidal zone.
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Figure 2. ROHICA remote marine geophysical platform and BOHICA offshore control barge.
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Procedure
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The initial phase of design criterion for both systems involved selection of materials that would have as little magnetic and electromagnetic interference (EMI) as possible. Non-metallic materials were used everywhere possible and instrumentation and electronics were physically placed as far as possible from the geophysical systems. A "buck-out" coil was incorporated into the ROGUE to remove the EMI associated with the EM-61. With the buck-out the EM-61 and magnetometer could be run concurrently without interference.
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| ROGUE Design |
The ROGUE was designed, engineered, and manufactured by OAO Robotics from specifications and requirements stipulated under subcontract. Stringent requirements were placed on the design of the ROGUE to eliminate as many metal components and EMI as physically possible. The ROGUE robotic chassis is made of a carbon composite material and the electronics and battery were strategically placed in order to minimize interference to the geophysical instrumentation. Once the initial design and layout was completed magnetic and electromagnetic measurements were taken around the robotic system to quantitatively map the signature of the system. The completed ROGUE has a zero EM-61(Figure 3) and magnetic signature (Figure 4) eight feet either side of the robot. Based upon these measurements the center of EM-61 coil was placed at a distance of eight feet behind the chassis. The EM-61 trailer is also the mounting platform for the magnetometer sensors.
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Figure 3. Electromagnetic signature of the ROGUE robotic geophysical platform with the various instrumentation on and off.
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Figure 4. Magnetic signature of the ROGUE with the various instrumentation on and off.
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The potassium magnetometer was chosen because of its sensitivity (0.001 nT/and the ability of the GSMP-30 to operate concurrently with the EM-61. In order to remove the large electromagnetic field associated with the EM-61 (see Figure 3) and allow simultaneous operation with the magnetometer a buck-out coil was designed with the assistance of Geonics, Ltd. and GEM Systems. Geonics, Ltd. designed the buck-out coil such that the electromagnetic field magnitude and slope was identical and opposite to that of the induced electromagnetic field from the EM-61 primary coil. Based on the optimal distance of the buck-out coil the magnetometer sensors were rigidly mounted in a "stinger fashion" 1.5 meters to the rear of the EM-61 coils. With the buck-out coil present the interference associated with the EM-61 was reduced to less than 2 nanoTesla (nT) on either sensor.
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Funding for the project described in this article has been provided in full or in part by the U.S. Environmental Protection Agency. This abstract has not been reviewed by the Agency, therefore, no official endorsement should be inferred.
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