In situ measurement of geoacoustic sediment properties: An example from the ONR Mine Burial Program, Martha’s Vineyard Coastal Observatory

In support of the Office of Naval Research’s Mine Burial Program (MBP), in situ acoustic and resistivity measurements were obtained using ISSAP, a device developed and built by the Center for Coastal and Ocean Mapping. One of the field areas selected for the MBP experiments is the WHOI coastal observatory based off Martha’s Vineyard. This area is an active natural laboratory that will provide an ideal environment for testing and observing mine migration and burial patterns due to temporal seabed processes. Seawater and surficial sediment measurements of compressional wave sound speed, attenuation, and resistivity were obtained at 87 stations. The ISSAP instrument used four transducer probes arranged in a square pattern giving acoustic path lengths of 30 and 20 cm with a maximum insertion depth of 15 cm. Transducers operated at a frequency of 65 kHz. The received acoustic signal was sampled at a frequency of 5 MHz. A measurement cycle was completed by transmitting 10 pulses on each of the five paths and repeating three times for a total 150 measurements. Resistivity measurements were obtained from two probes mounted on ISSAP following completion of the acoustic measurements. [Research supported by ONR Grant Nos. N00014‐00‐1‐0821 and N00014‐02‐1‐0138.]