Typical tasks performed by such vehicles include general site survey, 
debris clearance and detailed inspection of the underwater structure of 
platforms, pipelines and other associated installations. In the case of 
structures, Such as platforms, the inspection will include debris surveys, 
scour assessment, estimation of marine growth thickness, wastage of 
protective anodes and detailed examination of damaged (corroded, pitted or 
cracked) parts of the structure. For pipelines, the survey will examine 
scouring and spanning of pipes, wastage of anodes and damage to the 
concrete weightcoat of the pipe. Continuous video coverage is a feature 
of these surveys and is supplemented by an observer's spoken commentary 
which will include visual estimates of the depth of scour, height of span, 
the amount of damage etc. In addition, still photographs are taken to 
obtain more permanent hard copy of items of particular interest and data is 
logged from other sensors on board. All the data generated during a dive 
is subsequently merged with the navigational data through a time 
referencing system. 
Street (1977) estimated that, by 1984, there would be some 100 production 
platforms operating in the North Sea with innumerable pipelines, flowlines 
and wellhead installations. This has proved to be a conservative estimate 
and, by September 1981, there were already 103 production platforms 
operating in 34 oil and gas fields with a further 35-45 platforms either 
under construction or proposed for fields under development. Over 2700 km 
of main oil and gas pipelines have been constructed to date, with a further 
700 km under construction, and a further 700 km of smaller diameter 
interfield lines. It is estimated that some 10-20% of these installations 
will be due for survey in any one season. Viewing this on a global basis, 
the problem of adequate underwater inspection and maintenance is huge and 
will continue to grow both in amount and complexity as work is carried out 
in increasing water depths and under increasingly adverse conditions. 
UNDERWATER PHOTOGRAPHY 
Several underwater cameras suitable for operation from a manned submersible 
are available using both 35mm and 70mm format. The most widely used of 
these cameras appear to be those manufactured by the Rebikoff, Benthos and 
Photosea companies of the United States and Underwater and Marine Equipment 
Limited (UMEL) of the United Kingdom. Many of the 35mm cameras use water 
corrected 28mm Nikkor lenses (approximately 37mm in water) with a plane 
front port, focal plane shutter and preset exposure time.  UMEL manufacture 
an underwater housing for the Hasselblad SWC 500 70mm camera, fitted with a 
38mm Zeiss Biogon lens and a corrective domed front port, giving a focal 
length of approximately 49mm in water. Many of today's underwater cameras 
feature internal rechargeable power units, automatic film advance and some 
form of internal data chamber. A11 the cameras are housed in a water tight 
and pressure resistant housing. 
For use in this project, British Oceanics Limited undertook to provide a 
pair of Benthos 35mm cameras (model 370-2) and a pair of UMEL Hasselblad 
70mm cameras. The principal characteristics of these cameras are 
summarised in Table I and the cameras are illustrated in Figures 2 and 3. 
To the photogrammetrist, the most significant difference between the two 
camera systems is that the UMEL camera will readily allow a film flattening 
device to be incorporated into the camera. This takes the form of a glass 
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