OCEANOGRAPHIC INVESTIGATIONS 355 



Sonar Conditions— An important problem from the point of view of naval applications is 

 that of short-range acoustic transmission variability as related to the oceanographic environ- 

 ment. In order to study this problem from Sealab II, tape recordings were made of sonar re- 

 turn, from several fixed targets, for later correlation with environmental parameters obtained 

 from both the NAVMINDEFLAB instrumentation and the SIO weather station. The sonar 

 chosen for this task was the AN/PQS-IB, a diver-held, continuous- wave, frequency- modulated 

 (55 to 85 kc) unit that is, and will be, commonly used in Sealab type operations. Sonar runs 

 were made by pointing the sonar at two preselected, fixed, strong targets which were reliably 

 reidentifiable. By carefully bracing himself against Sealab, the operator could hold the sonar 

 steadily on each target for three to five minutes, during which time a tape recording was made 

 of the sonar's audio output. After this time, the sonar was held pointed upward at the surface 

 and a three-minute recording made. In all, six such runs were made over three days, cover- 

 ing times of day from 1000 to 2145. There were noticeable differences in both target and sur- 

 face signals from day to day and from morning to night. The tape recordings will be analyzed 

 for relative energy content as a function of frequency, and correlated with oceanographic data. 

 Although the analysis technique will obviate the need for knowing absolute acoustic levels, care 

 was taken during data collection to insure that sonar and tape-recorder gains were constant 

 and/or known, so that comparison of actual signal levels can be made. 



General Bottom Conditions and Settlement of Sealab II — A general survey of bottom type 

 and topography was made in the immediate vicinity of Sealab II. Sediment in this area was a 

 dark gray, micaceous, very fine silty sand with few marine shells and a trace of clay. The 

 upper one or two centimeters of sediment contained a large proportion of relatively loose fine 

 silt which was easily disturbed and placed in suspension, with generally a drastic loss of visi- 

 bility for divers. Analysis of a surficial sediment sample obtained in the vicinity of Sealab II 

 yielded 81 percent sand, 19 percent silts and clays, with a median diameter of 0.095 mm. Lab- 

 oratory tests of soil-engineering properties of this sample were made giving the following 

 results: angle of internal friction, 22 degrees; cohesion, 976 kg per square meter (200 lb per 

 sq ft); unit buoyant weight, 833 kg per cubic meter (52 lb per cu ft). From these data it was 

 calculated that Sealab should have a safety factor of about three against footing settlement of 

 as much as 61 cm (two feet). 



At the Sealab II site the bottom generally sloped up to the southeast at about 8 degrees. 

 Small-scale bottom relief was of the order of one to four inches and was of irregular appear- 

 ance, consisting largely of mounds and depressions of biological origin. Occasionally seen 

 were scattered debris consisting mostly of remains of sea grasses and kelp from shallower 

 depths; also seen were fragments of shells and echinoderms. Within about 15 m (50 ft) of 

 Sealab, the bottom appearance had been drastically modified and scarred by the presence of 

 Sealab and divers; many of these scars persisted throughout the duration of the experiment. 



Measurements of the angles of roll and pitch made inside Sealab with a plumb bob indicated 

 a port list of 6.54 degrees and a bow-up pitch of 5.96 degrees. Similar measurements made 

 during Team I occupancy indicated that these angles had not appreciably changed over a period 

 of three weeks. It was thus apparent that Sealab was stably sitting at a lesser slope than that 

 of the outside bottom, implying a differential footing settlement at its four corners. In order 

 to check this, the writers made careful measurements of footing settlement; the results were 

 as follows (data are with respect to bottom of main footing I-beams to which spades were at- 

 tached): starboard aft, 23.1 cm (9.1 in.); starboard fwd, 40.1 cm (15.8 in.); port aft, 23.3 cm 

 (9.2 in.); port fwd, cm. Thus the starboard forward corner was dug in more than the others, 

 while the after end settled evenly. These measurements were repeated after an interval of 

 several days, yielding the same data; thus from these settlement data and from the inclination 

 data one concludes that essentially all of the settlement occurred on impact or very shortly 

 thereafter. 



General Observations of Near Bottom Underwater "Weather" and Biology — A number of 

 general and somewhat unrelated observations of the undersea weather and the behavior of 

 various marine organisms were made by the writers during Team 2's occupancy of Sealab, 

 which, because of the uniqueness of the situation, should be documented. 



Porthole watching became the favorite pastime of the entire crew, and many hours were 

 spent observing the antics of our outside neighbors. Although at 62.5 m (205 ft) the light level 



