65 



S (Seafloor Surveillance Sy stem) - The University of Georgia's S^ was 

 inspired and designed after RUFAS II. The distinction between the two vehi- 

 cles is that the S-^ is designed for Outer Continental Shelf oil and gas 

 lease surveys and deep water mineral exploration. Functional capabilities 

 of S-^ include: detailed video-tape recordings of manganese nodules including 

 readout of nodule density per unit area, seafloor micro-bathymetry, high- 

 resolution sub-bottom profiling and underway seafloor sample retrieval. 



DIGITOW - The Jet Propulsion Laboratory's Advanced Ocean Technology Develop- 

 ment Platform (AOTDP) or DIGITOW is designed to provide JPL with a capability 

 for testing and demonstrating new or advanced instruments, technology and 

 concepts under operational (deep sea) conditions. The DIGITOW system is 

 designed for adaptability, flexibility and future growth potential to accom- 

 modate new developments over an extended period of years. Patterned after 

 the Marine Physics Laboratory's DEEP TOW, it consists of a cylindrical 

 pressure hull containing the electronics and an external structure providing 

 protection and mounting areas for instrumentation. One objective of JPL 

 is to apply technology and expertise - developed under the aegis of the 

 space program - to aid in the solution of non-space problems, and to transfer 

 this technology and know-how, where appropriate, to an ultimate developer 

 or user. At present JPL is field testing an experimental towed, sub-bottom 

 profiling system referred to as the "Chirp" sonar. The system is intended 

 to demonstrate improved performance in resolution and depth of penetration 

 over conventional techniques and employs advanced transmission and signal 

 processing using a frequency modulating or "chirp" technique. The system 

 recently completed its fifth in a series of field applications. In March 

 1979 NOAA's Office of Ocean Engineering supported an at-sea evaluation of 

 the advanced chirp sonar in conjunction with NOAA's National Ocean Survey, 

 to track and delineate a portion of the San Andreas fault. 



2.3.2 Operating Depth 



Vehicle operating depth ranges from 400m to 6,096m (650 ft to 20,000 ft), the 

 average being 4,712m (15,459 ft). Significantly, of the 19 vehicles listed in 

 Table 2.6, 13 are capable of operating to depths of 6,000m (19,685 ft) and greater. 

 This extended operating depth reflects the commercial interest in manganese nodule 

 deposits. From a military viewpoint, 5,096m provides a search capability which 

 includes approximately 98 percent of the ocean bottom. 



2.3.3 Construction 



Towed vehicle configuration is generally cylindrical. Unlike tethered, free- 

 swimming ROVs, almost half are enclosed by fairings to reduce hydrodynamic 

 drag, the remainder are unfaired and are open metallic framework construction. 



The dry weight of the vehicles varies according to their operational depth and 

 the instrumentation they carry. The lightest vehicles, BATFISH, weighs approxi- 

 mately 71kg (156 lbs); the heaviest, MANKA 01, weighed 4,500kg (9,921 lbs or 

 approximately 5 tons). The average weight is 1,488kg (3,058 lbs). 



At depths of 6,000m the weight of cable (approximately 1.5 x water depth in 

 length) overrides the weight of the fish. DEEP TOW's 9,144m (30,000 ft) of cable, 

 for example, weighs 10,750kg (23,700 lbs or approximately 12 tons) in air, some 

 12 times the dry weight of the fish. 



