The compressional-wave velocity in the uppermost sediments near the sea floor has been measured with high resolution, in deep water, by a variable-offset technique in which source and receiver are at the sea floor. The receiver is a single hydrophone connected through a 300-m length of seismic cable to an STD wire leading to a shipboard winch. The source is a 3.5-kHz pinger clamped to the STD wire and transmitting 1-ms pulses at 1-s intervals. With the phone on the sea floor together with the piled-up cable, the pinger drifts with the ship, moving away from the hydrophone until the cable comes taut, thus ending the run. Maximum offset is of the order of a few hundred meters (the length of the cable) and velocity structure can be obtained to depths of 100 or 200 m into the sediment. Interval velocities in layers as thin as 7 m in water depths in excess of 5000 m have been resolved by the method.
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George M. Bryan (1980) studied this question.