The reconnaissance area is divided into two topographic entities by a northeast - 

 southwest trending steep hveak in slope. This scaip separates the shallow water of 

 the eastern half of the area from the deeper water to the west where the probable 

 range area is located. 



Note that in Figure 2 certain portions of several tracks are marked as having been 

 analyzed. These portions of the individual runs were subjected to a simple statistical 

 analysis of bottom slope. The portions of the runs selected for analysis all fall to the 

 west of the scarp and approximately within the probable range area. This area was 

 selected partially on the basis of the existence of the scarp and it is for this reason 

 that we have confined our slop)e analysis to the portions of the runs which fall in the 

 area of operational significance. 



EQUIPMENT AND METHOD OF OPERATION 



The MPL deeply -towed echo sounder consists of an instrumented vehicle which is 

 towed in proximity to the ocean bottom by means of a well -logging type cable. The 

 actual echo sounding is done from this vehicle, and travel times are measured both to 

 the bottom and to the surface. The downward -looking echo sounder is a narrow -beam 

 system with a beam width of about 2 degrees by 5 degrees. The upward -looking sys- 

 tem has considerably less directivity and is used to monitor the depth of the "fish" at 

 all times. In rugged topography such as that west of Kauai proximity of the fish to the 

 bottom can only be maintained by paying out or reeling in wire as needed. It is for 

 this reason that the upward -looking system is so important, for it provides the means 

 by which the changing fish depths are continuously monitored. 



All control of the echo -sounding equipment remains at the ship. Power and com - 

 mands for the electronics in the fish are sent down the coaxial conductor of the well - 

 logging cable and echo -sounding infoimiation is returned via the same wire. All 

 sounding information is recorded in conventional fashion on die ship on an Alden Pre- 

 cision Graphic Recorder. 



A typical record is shown in Figure 3. The upper half of the record shows the 

 trace of the upward-looking system and the trace of the conventional surface ship echo 

 sounder. Since the ship is always ahead of the fish, the topography can be monitored 

 at all times to prevent disastrous surprises. The lower half of the record shows the 

 trace of the narrow -beam dovmward -looking system. At any given instant the sum of 

 the travel times from the upward -looking system and the downward -looking system is 

 the time equivalent of the surface -to -bottom distance. 



It is from data of this sort that our study was made and upon which our conclu- 

 sions are based. 



It is interesting to note that most of this work was done in roug^ weather with sea 

 state 4 prevailing most of the time. This made the handling of equipment from a small 

 ship such as^e;R/;V^ OCDNOSTOTA rather Jiazardousjespeciailly ddring laanching and 

 retrieval of the fish. 



212 



