360 OCEANOGRAPHIC INVESTIGATIONS 



BOTTOM-ROUGHNESS POWER SPECTRUM 



The power spectrum of bottom roughness is a function needed as an environmental input 

 for statistical theories of sound scattering from sea bottoms. Since no such data exist for 

 real ocean bottoms at Sealab II depths, it was desirable to attempt measurement of bottom 

 roughness, using a technique which has been tested at shallow depths and sandy bottoms in the 

 Gulf of Mexico. This technique involves establishing a reference baseline about 3 in. above 

 the bottom in the form of a tightly stretched nylon line; measurements from this baseline to 

 the bottom are then made at preselected equispaced intervals, yielding a series of data points 

 from which variance of the bottom topography as a function of space frequency can be calcu- 

 lated. A suitable area of bottom was located near the visibility range, about 30 m (100 ft) 

 upslope from Sealab II. The general appearance of the bottom revealed random irregularities 

 in the form of depressions and bumps (with relief of approximately 1 to 2 in) probably caused 

 by biological activity, and weak, highly irregular ripples (with relief of approximately 1/2 to 

 1 in.) probably caused by waves and currents. These features appeared to be isotropic and 

 homogeneous over the area considered. Unfortunately, on the first attempt to make measure- 

 ments as described above, it was found that the presence of the thin layer of easily disturbed 

 fine silt at the bottom was a critically limiting factor. Invariably and unavoidably, as the two 

 divers adjusted themselves and moved equipment into position to get data, enough silt was 

 stirred into suspension to completely occult the field of view where measurements were being 

 made. For this reason, and for lack of time to adequately modify the measurement techniques, 

 this experiment was not successful, and no useful data were obtained. Modified techniques to 

 get around this problem are being worked on, so that in future work it will be possible to make 

 measurements of bottom roughness in both sandy and silty regions. 



DIFFUSION STUDIES OF BOTTOM BOUNDARY LAYER AND NEAR-BOTTOM TURBULENCE 



It was planned to photograph dye and/or neutrally buoyant particle movement near the bot- 

 tom in order to study turbulence in and above the bottom boundary layer. This work was not 

 successful for a combination of reasons. 



1. Primarily, as with the bottom- roughness power- spectrum study, presence of the layer 

 of fine silt which was unavoidably stirred into suspension prevented effective use of cameras 

 and dye drops near the bottom. 



2. This experiment would have been much more time consuming than others in the plan, 

 so that relative to the limited amount of diving time available (at suitable distances from Sea- 

 lab) it was felt this study should be of relatively low priority. 



3. It proved much more difficult than anticipated to provide accurate and reliable movie 

 coverage for experiments such as this; again, available diving time was a limiting factor. 



ULTRAVIOLET FLUORESCENCE STUDY 



Sealab II offered a unique opportunity to observe, both at night and in weak daylight, the 

 effect of exposing marine organisms and bottom sediments to ultraviolet light. However, since 

 such a study would be completely qualitative and exploratory, it was considered to be low in 

 importance relative to many others planned. A speciaUy waterproofed ultraviolet light was 

 constructed for use from Sealab II. As it turned out, the difficulty of getting sufficient time in 

 the water to do experiments was such that this experiment, along with several others planned, 

 was never attempted. The desirability of conducting this type of experiment, however, remains 

 for future Sealabs for which, hopefully, there will be a larger ratio of outside-to- inside time. 



WAVE -INDUCED BOTTOM MOTION 



It was planned that motion of near-bottom particles resulting from passage of surface 

 swells would be photographed in such a manner as to correlate with a simultaneous pressure 

 record from the same swells, thus allowing direct measurement of pressure- velocity phase 

 relationships in or above the wave- induced boundary layer. This experiment was not success- 

 fully completed for the simple reason that surface waves were never of sufficient height to 



