Acoustic testing dockside and at sea of the last American SASS

The US Navy Multibeam Bathymetric Sonar known as the Sonar Array Survey System, SASS, was installed and successfully operated by NAVOCEANO on the USNS Wyman since 1989. This paper describes unique testing dockside at Souda Bay Crete, and also at sea in the Mediterranean prior to its final SURVOPS the latter part of 1996. A special test frame, allowing acoustic evaluation dockside of individual hydrophones and projectors was designed, fabricated on board, and positioned by divers during the testing at various points along the array domes on the Wyman´s hull. The purpose of the tests was to determine if any possible deterioration of the transducers had taken place over the years, because although the latest hardware and software designs were always incorporated into the SASS electronics, the transducers stayed the same. A calibrated NRL Test Transducer was used as both a hydrophone, and as a projector to measure the Transmitted Voltage Response (TVR), and the Sensitivity of the projector and hydrophones respectively, and the effect any excess attenuation caused by possible debris in the domes and growth on the windows may have had. The special test frame, constructed of plywood and 2×3´s, was designed to straddle the projector dome and hold the NRL test transducer about 1 meter away from the projectors. The transducer was located at the end of a moveable arm which could be pinned in position at 0, 30, 45, and 60 degree angles from the projectors. Tests at sea were aimed at investigating the effect losing several hydrophone channels had on the wide swath coverage of SASS, and if improvements in coverage could be effected through installation of recently designed noise reduction software. The theory behind the software design is discussed, and the results of both the dockside and at sea testing is presented. Although there is currently no American SASS, the system is alive and well with the latest improvements aboard the UK´s HMS Scott