3aUW11. Impact of the environment on energy spreading loss in shallow water at high frequencies.

Session: Wednesday Morning, December 4

Time: 10:32

Author: Akira Tanaka
Location: Dept. of Oceanogr., Naval Postgrad. School, Spanagal Hall, Monterey, CA 93943
Author: James H. Wilson
Location: Neptune Sci., Inc., San Diego, CA 92123
Author: Robert H. Bourke
Location: Naval Postgrad. School, Monterey, CA 93943


Energy spreading loss (ESL) is qualitatively defined as reduction in peak echo level due to time spreading of the transmitted acoustic pulse. An analysis of the impact of shallow water propagation on ESL was performed using a time domain propagation loss program to compute the spreading of the received pulse due to multipath propagation. Typical sound speeds and a Hamilton geoacoustic model of Area Foxtrot off the U.S. eastern seaboard was used. ESL's impact on sonar performance was determined as a function of range, depth, sound speed and geoacoustic properties. The impact of shallow water propagation on the correlation of the propagated pulses through the quantitative definition of mismatch loss (MML) was also discussed. Strong ESL existed over a reflective bottom and was generally invariant with range. ESL was correlated with TL. ESL was not as large over absorptive bottoms due to increased absorption of the bottom refracted path, and thus, reduction in the number of multipath modes. Broadband pulses were found to exhibit fewer fluctuations than narrowband signals, and the total TL loss was larger than a single cw case. To overcome the ESL, integration techniques based on an accurate prediction model are required with high temporal resolution of the echo energy.

ASA 132nd meeting - Hawaii, December 1996