ASA 127th Meeting M.I.T. 1994 June 6-10

4pEA10. A 350-m depth capable, air-compensated baffled transponder for the deep water portable tracking system.

R. K. Menoche

R. J. Reid

Naval Undersea Warfare Ctr., Range Development Div., Newport, RI 02841

P. J. Stein

Scientific Solutions, Inc., Nashua, NH 03062

Here we describe a novel baffled central up-link subsurface link (SSL) for the deep water portable tracking system. The central SSL is deployed at depths up to 350 m and collects the acoustic information from bottom moored tracking transponders. These transponders can be deployed to depths up to 6000 m. Degradation of the up-link SSL performance is generally due to support ship radiated noise and surface generated ambient noise. The sources of interference can be suppressed with a downward looking receiver. This receiver must have a wide beamwidth (140 deg) and its response must fall off rapidly outside the beam to reject ambient noise. The device built consists of a hydrophone and projector mounted on the face of a steel signal conditioning plate (SCP). The plate is designed to have low vibration sensitivity and edge diffraction. Behind the plate, and extending beyond the SCP edges is a fiberglass air chamber. To prevent crushing, it is fed by an air-compensation bag. Extension of the air-backing beyond the SCP is important to ambient noise rejection. This soft surface helps to reject noise which diffracts around the edge of the baffle. The air-chamber design was chosen over material solutions because it was uncertain if, at the deeper depths, the latter could provide the pressure release surface required. Both theoretical and experimental results of baffle performance are presented.