A MEASUREMENT OF OCEAN-BOTTOM SLOPE

The slope of the deep ocean bottom is calculated by measuring the bottom reverberation from active sonar transmissions. Knowledge of this slope is required to localize a target detected by bottom bounce echo-ranging. The method is based on the fact that reverberation has a space-time coherency; that is, bottom reverberation has a directionality that changes with time, and the rate of this change is a function of bottom slope. A sea test was conducted to measure one coordinate of bottom slope. The test consisted of transmitting on sequential target bearings, then tape recording the resulting reverberation as seen at the output of a vertically split array. The tapes were reduced in the laboratory by playing the split-beam signals into a bearing deviation indicator (BDI) and recording the output on an optical oscillograph. For short transmission lengths, the data showed that the expected coherency is present; however, the measurements of the bottom slopes were not in close agreement with fathometer measurements. It is believed that the discrepancy is a result of the interfering surface reflection of the bottom reverberation. (Author)