Benthic 4800 BITS/S Acoustic Telemetry

In June, 1981, continuous 4800 bits/s digital data was acoustically telemetered in 15,000-foot deep water from a near-bottom instrumentation package to a surface platform. As the platform drifted from overhead to an offset angle greater than 45° from the vertical, over 1.0×10⁷ bits of pseudo-random digital data were transmitted with a total of 10 received errors, yielding an average bit error rate of 1×10^-6. For the same experimental conditions 2.6×10⁶ bits of 1200 bits/s data were transmitted downward without making a single error. In addition to the digital data, voice, pings, tones and slow-scan television were transmitted. All transmissions were at a transducer input power level of 33 Watts and were between 8 and 14 kilohertz. The modulation technique used was dual independent sideband with an injected pilot tone to provide for Doppler correction. Within each independent sideband, the pseudo-random digital data was transmitted using quad differential phase shift keying and slow-scan television data was transmitted using non-orthogonal frequency shift keying. These results are the culmination of a 5-year effort to determine the limitations on high data rate telemetry imposed by the near vertical (~0°-45°) acoustic channel. The pop-up instrumentation package BUMP (Benthic Untethered Multipurpose Platform) was used throughout these tests as an acoustic source and receiver. The main features of this package and accomplishments of earlier tests will be discussed along with the aforementioned results.