Buffington, Hamilton, and Moore 



sound cones from any given echo-sounder transducer. These angles 

 are usually taken from a standard transducer calibration curve. 

 Simple geometry has been developed and graphic solutions found. 

 Acknowledging that the solutions almost certainly improve the situa- 

 tion, there is still no way to check the absolute error without empiri- 

 cal data on the slopes being measured. This empirical data can be 

 provided by lead-line sounding, but inherent errors in this method 

 give a very low level of confidence. This leaves only " in situ " mea- 

 surements,' made directly on the spot with submersibles, as the best, 

 and perhaps the only, basis for absolute comparison or calibration. 



One might expect that the measurement of a bottom slope from a 

 submersible to be a simple matter, and indeed it is if one is content 

 with accuracies which vary 2 or 3 degrees. Simple gravity- dependent 

 instruments, such as pendulum or bubble inclinometers can be instal- 

 led within the pressure-proof sphere in which the pilot and the obser- 

 vers ride. From these, inclinations can be measured to fractions of 

 degrees. However these instruments still permit only an approxi- 

 mate measurement of the sea-floor slope on which a submersible 

 rests because the pilot can only visually estimate that the horizontal 

 plane of symmetry of the submersible, to which the interior inclin- 

 ometers are adjusted and referred, is parallel to the plane of the sea 

 floor. 



In the past three years, slope measurements have been made in 

 16 dives with the Cousteau Diving Saucer and the Westinghouse DEEP- 

 STAR 4000. All dives were made where the sea floor had rugged 

 relief. The largest concentration of dives was made off the town of 

 San Clemente, California, where specific features had been echo 

 sounded under good navigation control, and a large number of slopes 

 calculated from echograms. These calculated slopes ranged from 

 7. 5° to 31. 0° on the simple basis of a tangent resolved from depth 

 differential, ship's speed, and time. In the same area, the same 

 slopes, directly measured, ranged from 7. 5 to a maximum of 43 . 

 The accuracy of these latter measurements was circumscribed by 

 the limitation mentioned previously; namely, the pilot's ability to 

 estimate that the horizontal plane of the submersible was parallel to 

 the sea floor. Even so, the difference was most striking, and under- 

 lined immediately the need for precise measurements and carefully 

 controlled experiments. 



A device for permitting a submersible to measure accurate slopes 

 has been developed at the U. S. Navy Electronics Laboratory (NEL), 

 and tested with DEEPSTAR 4000. It has proved successful enough so 

 that a series of dives, designed specifically for direct and precise 

 slope measurement and comparison with echo-sounding records under 

 rigorously controlled conditions, is planned for the coming dive ser- 

 ies which will get underway when DEEPSTAR is recertified. 



The device is basically optical, and permits the pilot of a sub- 

 mersible to adjust its attitude around both a fore-and-aft and a verti- 

 cal axis while heading upslope and watching two light spots projected 



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