Abstracts Geography

Analysis of low frequency transmission loss in the shallow Timor Sea

by Stuart M. Taylor

The objectives of this study were to enhance understanding of the parameters affecting transmission loss in the shallow waters of the Timor Sea and to conduct a performance analysis of the range dependent acoustic PE model, RAM. The study utilized transmission loss data (from 10-1600 Hz) collected by DSTO and NAWC during the SWISS 1 experiment held in the Sahul Shelf area in early March 1994 in waters ranging from 60 to 120 m depth. In addition, transmission loss data from a similar experiment conducted in 1990 in the same area was used as a comparison to the SWISS 1 data. The analysis revealed that the acoustic environment over the Sahul Shelf exhibits a high degree of lateral variability which is primarily dependent on the geological composition of the shelf region. Of particular interest was the north/south oriented SWISS 1 transmission loss data which displayed characteristics associated with shear wave coupling. RAM was able to accurately simulate the SWISS 1 transmission loss for regions unaffected by shear wave coupling but failed to simulate portions of the north/south track where transmission loss data was excessive. A version of RAM which incorporates shear wave effects, RAMS, was used to simulate the north/ south transmission loss data. Due to the high range dependence of the geoacoustic parameters, coupled with inadequate availability of geoacoustic data for this region, only limited success was achieved using RAMS