Two-Way Hydroacoustic Communications Link for an Ocean-Bottom Seismograph

An underwater acoustic telemetry system was developed to provide a two-way communications link between an ocean-bottom seismograph and a ship overhead. Four data channels are transmitted from the instrument on IRIG Channel 12 (10.5 kc/s). Commands to the instrument are transmitted in the form of a simple pulse position code using a 14 kc/s carrier, and provide for such functions as gain change, calibration, instrument leveling, and uncaging. A mercury battery pack provides sufficient power for 15 days of continuous operation. Acoustic power output is approximately 2.5 watts at an overall efficiency of 20 percent. Instrumentation and batteries are housed in two spherical pressure vessels designed to withstand depths in excess of 2500 fathoms. The system was successfully operated in May, 1964, off Bermuda.