Acoustic propagation experiments in a deep lake

Abstract

Acoustic propagation experiments were conducted at Lake Pend Oreille, a deep (350 m) lake in northern Idaho. The goal of the experiments was to quantify the level and seasonal variability of transmission loss fluctuations of acoustic pulses propagated along wholly refracting paths in the lake. Continuous measurements of transmission loss at mid‐depth were recorded for approximately 1‐week periods during 5 months in 1988‐1989. Most measurements were made in the 10‐ to 40‐kHz range, using a fixed bottom‐moored projector and bottom‐moored hydrophones at ranges of 1 and 2 km. In May 1989, a series of temperature profiles was acquired concurrently with acoustic data over a 5‐day period. Acoustic transmission in this short‐range, high‐frequency regime is subject to weak scattering due to thermal microstructure. The mean temperature at mid‐depth is near 4°C with superimposed microstructure. During some periods, the temperature gradients were strong enough to cause several dB of short‐term acoustic fluctuations. The acoustic data have been processed to produce numerous received signal statistics including the mean, standard deviation and variance of the received signal level, intensity, logarithmic variance of the received intensity, and intensity scintillation index. This paper will present selected results from the experiments and provide a comparison with stochastic (weak scattering theory) and deterministic modeling approaches. [Work supported by DARPA.]