High-frequency acoustic phase stability measurement system

During March and April 1995 the Naval Research Laboratory (NRL) conducted a series of high-frequency acoustic phase stability measurements to determine the limits that the shallow-water (20-40 ft) environment places on synthetic aperture (SAS) sonar system. The paper describes the acoustic systems and experiments that took place in the shallow-waters off Panama City, Florida. The instrumentation consisted of several linear arrays mounted on three stable towers that were deployed on the shallow-water ocean bottom. These arrays were designed at the Applied Research Laboratory/Penn. State University and had vertical beamwidths that ranged from 1 to 3 degrees with 28 dB sidelobe suppression. Direct path phase stability measurements were taken as a function of frequency (20-200 kHz), path length, and environmental conditions. Several examples of the instantaneous signal phase versus small scale thermal variabilities are shown