Experimental Use Of The Induced Polarization Method To Map And Characterize The Shallow Sea-Floor

We have developed a new high-resolution sea floor mapping system, based on the<br>induced polarization (IP) principle. This system uses a weighted streamer, designed to be towed<br>directly on the sea floor at speeds up to 3 knots. Signal injection is achieved by means of a pair<br>of titanium transmitter electrodes that force 2+ amps in the form of a 4 Hz square-wave into the<br>sediments. Two staggered receiver dipole arrays are used to detect polarizing materials in the top<br>5+ meters below the sediment-water interface. Using this system, we can continuously<br>characterize the sea floor at two different depths by means of a geophysical acquisition and<br>processing system (providing resistivity and phase for two different depths) and a GPS receiver<br>positioned on a ship. Data acquisition and control are via a laptop computer, and the entire<br>system is highly portable and battery-powered. We have demonstrated that the array can detect<br>ilmenite (a titanium-bearing heavy placer mineral) to concentrations at or below 1% by volume,<br>and can also characterize lithologic changes beneath an overlying veneer of sand. We believe<br>that the system has additional potential applications, including rapid characterization of<br>anthropogenic materials (including urban waste), identification and mapping of buried cables,<br>unexploded ordnance (UXO), and possibly even to map buried archeological sites. Theoretically<br>we can acquire more IP measurements in a week at sea than have been acquired historically on<br>land over the past 50 years.