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The ROGUE also may also be used in shallow water operations where water depths are 1.5 feet or less. This was accomplished by placing the electric wheel motors in a waterproof housing with ventilation ports for heat dissipation. The chassis for the ROGUE is completely waterproof and is ventilated through a snorkel-type of apparatus under the GPS antenna that cools the electronics.
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The ROGUE has limitations associated with mobility, overhead canopy (trees, buildings, etc.) that may block GPS satellite transmissions, line of sight of data link antennae, and severe weather. Due to the length of the robotic platform (13 feet) some steep walled ravines or ditches may cause the magnetometer sensors to become in contact with the ground and possibly cause the robot to get stuck. The robot is capable of pulling the towed platform over curb-sized structures but slopes greater than 25 degrees may cause problems. As with the use of any GPS receiver if there is not sufficient view of the sky some GPS transmissions may be impinged causing a loss of adequate position. The ROGUE has a built in safeguard that when the positional accuracies are less that 0.5 meters the robot will cease semi-autonomous operation. Once good GPS position has been lost the robot can still be operated with the joystick to retrieve the vehicle. The robot needs to be within line-of-sight of the base station antennae except for short distances primarily because of the attenuation of the video signal. The system can be operated without video but the likelihood of hitting an obstruction is greatly increased. Severe weather such as heavy rain, hurricanes, tornados and extreme solar activity could also cause the system to be inoperable for obvious reasons.
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ROHICA Marine Geophysical Platform
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An example of magnetic data collected during an actual survey is presented in Figure 5. On this particular survey a total of 130,000 linear feet (approximately 25 linear miles) of data were collected with an average line spacing of approximately five feet and data were collected on average every 1.5 feet along each transect. On a typical field day an average of 20,000 linear feet of geophysical data were collected. Using a ten-foot line spacing with the dual magnetic sensor configuration near 100% coverage attained.
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Figure 5. Example of data collected during an actual survey.
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Data quality is very good with an observed near zero horizontal magnetic gradient indicating no induced noise was present from either the electronics or ship-to-shore data transmissions.
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Several inert projectiles of various dimensions were placed in the water the ROHICA was towed over those ordnance to determine their magnetic signatures. The delineation of UXO types of anomalies was based upon magnetic signatures of the "dummy rounds". Magnetic data were collected over a 155 mm projectile, two 105mm projectiles, a 90mm projectile and, a 57mm cluster bomb. The magnetic signature of these ordnance are depicted in Figure 7.
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Figure 6. Magnetic signature of submerged "dummy rounds" (~3.0 feet) collected with the ROHICA geophysical platform.
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The system was capable of withstanding winds in excess of 20 knots and waves greater than 3 feet. There were some limitations related to the distance (approximately 2,000 feet) that data from the radio modems could be received at the remote command post and the battery life of the electronics which was approximately seven hours of continuous data collection. In very high waves the pitching and rolling of the ROHICA may cause some degradation of the GPS position due to the tilting of the GPS antenna.
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Conclusions
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Both systems proved to be very robust for the remote detection of UXO. The ROGUE is a prototype system that incorporates the use of a Geonics Ltd. EM-61™ and GEM Systems GSMP-30 potassium magnetometer that until this program has never been accomplished. The buck-out coil sufficiently reduces the large EMI associated with the EM-61 to less than two nanoTesla at either sensor. As expected with any wheeled platform there are some limitations associated with mobility and lack of GPS coverage.
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The marine platform proved to be a very viable system for collection of geophysical data in the near shore setting even for non-hazardous scenarios. Once the system was set up data collection was very fast with an average data collection rate of four miles per day. With the 100% non-metal design of the ROHICA there was zero magnetic noise induced by the platform. With the exception of troubleshooting radio modem difficulties and lack of GPS coverage the system worked flawlessly.
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Acknowledgements
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This paper was funded as a subcontract under the U.S. Environmental Protection Agency Contract No. 68-C99-223 and an Interagency Agreement (IAG) between the U.S. Army Department of Safety, Health, and Environment and EPA.
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Security Clearance
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This document has been classified as an UNCLASSIFIED document by the U.S. Army OPSEC office in Aberdeen Proving Ground, Maryland as authorized under clearance number 3617-A-6.
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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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