Abstract
The use of pressure- and temperature-controlled tanks for calibration of Navy projectors is a cost-effective alternative to open-water or at-sea measurements. The Underwater Sound Reference Division (USRD) of the Naval Undersea Warfare Center maintains a large closed tank which is temperature and pressure controlled. This tank, like all closed vessels, suffers from a major drawback: it is highly reverberant, especially at low-frequency operation, which precludes the possibility of making steady-state projector response measurements (especially for highly resonant projectors with low-frequency resonances) as would be possible in a large body of open water. This presentation surveys the techniques developed at USRD to ensure that measurements made in the tank are traceable to those that would be made for the same projector in open water. Three broad categories of approaches will be presented: (1) estimating the steady-state response using a model that represents only the pre-echo portion of the received data (transient modeling), (2) estimating the echo-free steady state using a multiple-arrival model that accounts for echoes in the received data (multipath modeling), and (3) characterizing the wave field using multiple hydrophones to separate the direct wave field from the wave field due to echoes (spatial processing). [Work supported by ONR.]
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