UNDERWATER WEATHER STATION .381 



Diver Observations 



Observations by divers were made in the vicinity of Sealab and from within Sealab through 

 three of the 24-in. portholes. The first two days' observations were made outside the habitat 

 because the porthole protective covers were in place; but once removed, the forward port, the 

 laboratory space port, and the starboard portholes were chosen for routine observations. The 

 underwater weather station was not set up, and operational until the seventh day of occupation. 



On the first two days of occupation a swimmer survey of the lab site was made with Mk-VI 

 mixed-gas equipment. The two relatively higher ridges of sand that extended from the port 

 quarter and starboard bow were explored. Divers carried a safety line attached to Sealab and 

 used underwater sonar that was tuned to a "pinger" frequency previously placed on the Sealab 

 conning tower. 



An area on the port quarter 165 ft from Sealab was selected for the underwater weather 

 station, and current observations were made here during each inspection. The weather station 

 platform and its equipment were placed on a sand slope near the rim of the submarine canyon. 

 Anchor and nylon safety line were mainted between the Sealab shark cage and the underwater 

 weather station at all times. Sediment stirred up by the divers during inspection dives was a 

 problem both for the instruments as well as for safety and visibility. The distance between 

 Sealab and the underwater weather station (165 ft) and the capacity of the MK-VI mixed-gas 

 diving apparatus limited the time outside to 70 minutes, or about two round trips to the weather 

 station. A very large part of installation time was spent placing the cables that led from Sea- 

 lab to the weather station. Once sensors and cables were in place, daily routine cleaning and 

 inspection trips were initiated. 



During the first four days it was possible to "hear" or feel pressure changes caused by 

 the passage of surface waves. Simultaneous observations on the surface and in the habitat 

 showed that occupants were able to sense on the surface and in the habitat showed that occu- 

 pants were able to sense crests and troughs of waves passing on the surface. 



Observation of fish that set up permanent occupancy near Sealab portholes showed they 

 definitely oriented with the current. Migratory fish appeared independent of the direction of 

 current and surge. Usually the orbital motion of surface waves is not apparent from the tra- 

 jectory of small particles at this depth. 



During the first three to five days of occupancy, surface waves were low, and tides were 

 near their spring range (about 5 ft). Bottom currents, as indicated by particle trajectories, 

 did not show good agreement with tidal fluctuations. Erratic fluctuations from onshore to off- 

 shore currents were commonly observed. On the sixth day of occupancy, the height of the sur- 

 face waves increased to about 60 to 8 ft, and the waves continued to be high through the tenth 

 day. The high waves were followed on the eleventh day by a strong, steady offshore current. 

 This current was also measured by the sensors on the underwater weather station, which 

 showed maximum velocities of 1 knot and 2 knots on the lower and upper sensors respectively. 

 During the first teams occupancy, each period of high surface waves was followed by: (a) an 

 increased tendency for offshore current, (b) increase in water temperature, (c) increase in 

 numbers of plankton, and (d) appearance of large, migratory fish. Observations over longer 

 periods are necessary to determine if this is a common trend. 



REFERENCES 



1. Inman, D. L., "Areal and Seasonal Variations in Beach and Near-shore Sediments at La 

 Jolla, California", Corps of Engrs., Beach Erosion Board Tech. Memo. No. 39, 1953 



2. Shepard, F. P., Curray, JrR., Inman, D. L., Murray, E. A., Winterer, E. L., and Dill, R. F., 

 "Submarine Geology by Diving Saucer," Science, 145:3636:1042-1046 1964 



3. Chamberlain, T. K., "Mechanics of Mass Sediment Transport in Scripps Submarine Canyon, 

 California," dissertation for Ph.D. degree. University of California, Los Angeles, 1960 



