No abstract

DED produces towed line sonar arrays for a large number of U.S. Navy applications. The fact that the performance of these arrays is very tightly specified and that DED produces hydrophones for these arrays by the tens of thousands each year has forced the development of production oriented hydrophone calibration systems meeting the following requirements: parameters measured—free field voltage sensitivity, relative phase; frequency range—1 Hz to 2 kHz; measurement repeatability—±0.2 dB max., ±0.5 dB degrees max.; measurement correlation with Navy's standard facility (NRL/USRD)—±0.2 dB max.; temperature/pressure—ambient. Automated measurement systems have been developed where the above hydrophone parameters are measured within closed, rigid air chambers. Measurements are made by comparison against acoustical standards which are built into each chamber. These systems provide a well behaved, repeatable measurement over a wide frequency range. These measurement systems meet or exceed the above requirements and have been in use for approximately ten years.

DED has developed a facility for the accurate calibration of towed line sonar arrays which is small and noise immune enough that it can be installed at any site requiring such measurements. The facility consists of a series of cylindrical transducers submerged in a water tank. The array under test is pushed through the transducers and the free field voltage sensitivity of each channel is measured one-at-a-time by comparison against some of the transducers. The remaining transducers project acoustical energy into the water. This facility is an outgrowth of a concept developed by NRL/USRD [J. F. Zalesak and W. J. Trott, J. Acoust. Soc. Am. 62, 91–101 (1977)]. Within limits, the accuracy of this facility meets the requirements of the Navy's towed line arrays. Typically, between 20 Hz and 2 kHz, measurements are repeatable within ±0.7 dB and correlate with the Navy's measurements within ±0.7 dB. During the past three years, the facility has performed over 3000 measurements and is presently under development as a product line.