sounding techniques from the water surface are deficient for surveys for 

 seafloor structures. This deficiency was demonstrated by the survey con- 

 ducted with the Alvin.* 7 The echogram aboard the surface support vessel 

 Lulu indicated a gentle rise over a particular area where as the Alvin actually 

 determined a 200 meter (650 feet) near vertical cliff existed. Other similar 

 situations can be demonstrated with the use of submersibles. 



An improvement over the above technique involves the use of 

 submersibles near the bottom with depth profilers and a local positioning 

 system. At least one submersible has the capability to collect data in this 

 fashion to later develop contour charts of the area. However, both the sub- 

 merged and the surface technique are based on the propagation of sound 

 emitted from a source; in some cases in a cone-shaped spectrum as large as 

 60 degrees. I n many instances because of the wide cone of emission, the 

 first echo (usually considered to be the bottom) may not be the depth to 

 the bottom directly under the recorded surface position. Thus, a better 

 system for mapping the seafloor is required. 



The need for a better system for mapping the seafloor has stimulated 

 the U.S. Naval Oceanographic Office (NAVOCEANO) to develop the photo- 

 grammetric technique for ocean applications. Initial phases of this development 

 using a diver-operated vehicle were reported by Pollio. 48 The results obtained 

 using this technique are satisfactory for application to structures on the seafloor. 

 It was possible to draw contours to 1 decimeter (about 4 inches) with the col- 

 lected data. Application of this technique to deep water using manned 

 submersibles presents additional problems. These problems, as outlined in 

 Pollio's paper, include improving camera systems, positioning systems, and 

 submersible performance. In addition to NAVOCEANO, another organization 

 pursuing the development of photogrammetric methods is NURDC, San Diego. 



The photogrammetric technique, at the moment, appears to be the 

 most promising to develop contour charts for application to structures on the 

 seafloor. However, imaging techniques and laser techniques being developed 

 may also prove fruitful. 



Systems for Measuring Physical and Chemical Parameters 



Instruments for assessing the physical and chemical oceanographic 

 parameters of significance to ocean structures are listed in Table B-5. 

 Included in this table under each manufacturer are the various instruments 

 for determining water depth, salinity, temperature, dissolved oxygen, pH, 

 sound velocity, and currents. A number of instruments have the capability 

 to assess two or more parameters at the same time. For example, the Litton 

 STD probe measures conductivity (salinity), depth, and temperature. There 



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