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The Critical Sea Test (CST) is an empirical Navy program which collects low‐frequency (100–1000 Hz) environmental acoustics measurements in order to provide a diverse, high‐quality database for sonar performance prediction. During the course of its experiments in direct path bottom reverberation, CST has observed frequency, grazing angle, and waveform behaviors which differ significantly from those assumed in commonly available bottomscattering strength models. For empirical programs, deviations from standard models are significant because they limit the ability to extrapolate survey measurements into sonar performance scenarios. The most controversial aspect of the coherent source experiments has been the observation of a pulse length dependence in the scattering strength measurements beyond the linear term normally associated with ensonified area. This paper discusses CST’s bottomscattering strength measurement technique and summarizes the pulse length ‘‘anomaly’’ results for a variety of geographic areas. Because these results run counter to standard modeling assumptions, this paper will also discuss the data quality procedures used to reach these conclusions. [Work supported by SPAWAR.] |
