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Detection of Uxo In Marine Environments With Towed Array Ip Measurements
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 18th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, Apr 2005, cp-183-00086
Abstract
During World War II, scientists at the Naval Ordnance Laboratory (NOL) based the development<br>of the RX-1 Beach Mine Locator on “Induced Electrical Potential” (IEP), the phenomenon we now call<br>IP. Although deployed briefly in Okinawa just before the end of the war, there is no record of any<br>further development of the IP method for locating metal objects in the marine environment.<br>In this paper, we describe a research project undertaken jointly by Zonge Engineering and Multi-<br>Phase Technologies, LLC with the objective of demonstrating that IP is a practical method for detecting<br>metallic objects such as sea mines and UXO. The Strategic Environmental Research and Development<br>Program (SERDP) funded the project. During the project, we performed IP measurements in the<br>laboratory using a small metal target immersed in both fresh water and in salt water (30,000ppm NaCl).<br>These experiments provided us with an indication of the amplitude of the IP response that we can expect<br>from a target and the dependence of response amplitude on salinity of host medium. We used the<br>laboratory measurements to calibrate numerical models used to study electrode arrays for deployment in<br>full-scale experiments. Using results from our modeling, we assembled an electrode array and we<br>conducted experiments at the Mare Island Naval Shipyard in San Francisco Bay.<br>Our results confirm the presence of measurable IP responses associated with metallic targets.<br>The responses are 3-5 times larger in salt water than they are in fresh water. We estimate the intrinsic<br>response of metallic object in salt water is 100-200 ms (Newmont IP units). Detection range is<br>intimately tied both to the characteristic size of an object and to the size of the electric dipole used to<br>measure it. We conclude that measurement dipoles should have a length that is on the order of a<br>characteristic dimension of the object to be detected. Detection range is on the order of 3-5 dipole<br>lengths. Detection range is still an issue that can only be resolved with further research. Practical<br>exploitation of IP for UXO detection will require a submerged electrode platform with measurement<br>dipoles scaled to detect both small and large targets.