Ocean Surveying from Manned Submersibles

Abstract

The performance of the bathyscaphes and second generation manned submersibles has generated considerable speculation concerning the merits of these platforms as undersea surveying tools. Although a wide variety of tasks have been successfully performed, the manned submersible is still too new a tool to have firmly established its role in oceanographic/engineering surveys. Undersea navigation, launch/retrieval methods and surveying sensors designed for submersible use are, in the main, unsatisfactory, but their development is being pursued. Preliminary observations indicate that the following surveying missions could benefit most highly through employment of a Deep Ocean Survey Vehicle, (DOSV): (1) Site Surveys of small ocean bottom areas for installation of hardware or habitats; (2) Bottom Truth Surveys of representative areas for verification of surface-obtained data; (3) Route Selection Surveys of prospective cable or pipeline routes; (4) Biological Surveys for quantitative and qualitative assessment of marine biota; and (5) Geological Surveys of bottom sediments, structures and depositional/erosional processes. Although little, if any, ocean surveying per se has been performed from submersibles, sufficient observations exist to indicate that surface-conducted surveying may produce an erroneous impression of the bottom and near-bottom environment. Wide beam (60° cone) echo-sounding in the Bahamas completely missed 3 to 150 meter (10-500 ft.) high near-vertical cliffs and outcrops which have been observed from submersibles. Near-bottom current speeds have been observed to vary from essentially zero to 20 cm/sec (0.5 kns.) within a lateral distance of less than 1 meter. Zonation of currents along the bottom was observed in the Straits of Florida which would have been virtually impossible to observe and interpret with conventional measuring techniques. Abrupt changes in bottom sediment grain sizes have been observed which would lead to erroneous impressions if sampled from the surface. Preliminary tests have indicated that sediment bearing strengths measured from surface-collected cores may be in error by several orders of magnitude from measurements taken by manned submersibles in situ.