depth of his in situ observations with the 

 utmost accuracy. To obtain more accurate 

 pressure/depth measurements vibrating wire 

 transducers and quartz capacitance pressure 

 transducers have been constructed in ocean- 

 ographic instruments and provide greater 

 accuracy than the instruments described 

 heretofore. 



In June 1967 the Marine Technology Soci- 

 ety sponsored the symposium "Precise De- 

 termination of Pressure/Depth in the 

 Oceans." Selected papers presented at this 

 symposium are contained in reference (9), 

 which describe the limitations, construction 

 and testing of specific pressure/depth sen- 

 sors. 



Seemingly incidental but quite important 

 to a variety of missions, is the method or 

 device used to present and/or record vehicle 

 depth during a dive. On many missions the 

 only importance attached to depth is that of 

 safety and in this case the operator need 

 know nothing beyond what the depth is at 

 any given time. However, in surveying, envi- 

 ronmental studies and cable inspections 

 depth is a critical parameter and is the basis 

 to which all observations are related. In such 

 cases a record of depth versus time is invalu- 

 able in reconstruction of the dive and relat- 

 ing observations to their proper depth cate- 

 gory. One can always record the time and 

 depth with each observation, but in the small 

 confines of submersibles this is not always 

 convenient and many times the observer 

 may simply forget to do so. Strip chart re- 

 corders of the Rustrak variety are available 

 which are small and trace an imprint on a 

 paper scroll; these require electric power to 

 operate. BEIS FRANKLIN used a Swiss-built 

 ink recorder which traced on a depth/time 

 calibrated paper strip and was powered by a 

 wind-up-motor, 8-day clock (Haenni S.A. 

 Model 89RE, Jegenstorf). The recorder was 

 invaluable in post-dive reconstruction relat- 

 ing events to time and depth. 



Sonic Devices — Depth measurements from 

 submersibles using sonic devices are ap- 

 proached in the same manner as a surface 

 ship measures bottom depth, but instead of 

 measuring the round trip time interval of an 

 acoustic impulse from surface to bottom, it 

 measures the round trip time interval from 

 vehicle to surface. A number of submers- 



ibles, thus, have upward-looking sonar trans- 

 ducers for this purpose. The accuracy of such 

 measurements can be better than many of 

 the pressure sensors, but this accuracy de- 

 pends upon the accuracy with which the time 

 between the outgoing and returning im- 

 pulses is measured, and the accuracy with 

 which sound velocity in the overhead water 

 column is known. The time measurement 

 accuracy is the instrument error and in con- 

 temporary echo sounders is considered negli- 

 gible. The sound velocity error, however, can 

 be considerable and is the controlling factor 

 in accuracy. An indication of the errors 

 brought about by seawater sound velocity 

 variation can be seen from Figure 10.12 (con- 

 structed by Mr. J. Berger, U.S. Naval Ocean- 

 ographic Office), which shows the corrections 

 versus depth which are required for a stand- 

 ard sound velocity of 1,500 m/sec (4,920 ft/sec) 

 off the west coast of Greenland and off Gi- 

 braltar. 



In most instances the sonic devices are 

 used during ascent for safety purposes to 

 monitor closure rate with the surface rather 

 than depth. The reason is quite simple: 



GREENLAND 



_L 



b OFF GIBRALTAR 



50 



DEPTH CORRECTION IMETERSI 



Fig, 10 12 Depth corrections tor echo sounder (1,500 meter/sec). 



484 



