Some comparative results for the Benthos and UMEL cameras are presented 
in Tables II and III. Table II shows the precision of the projective 
transformation for various numbers of parameters obtained using 15 control 
points. For both cameras, a significant increase in the precision is 
obtained by the inclusion of the systematic error compensation terms, with 
the standard error of the photograph residuals being reduced to that of the 
observations. The standard error of unit weight computed for each 
photograph is comparable for each camera for a solution involving the same 
number of parameters. Table III compares the accuracy of the computation 
of object space points for the two cameras using the same transformations 
as Table II. For both cameras, there is a significant improvement 
obtained with the addition of distortion parameters. Further, the 
improvement is more significant for the UMEL camera which produces results 
superior to the Benthos camera by a factor of up to x3. It is suggested 
that the UMEL camera's superior performance is largely due to the 
incorporation of a film flattening device into its focal plane. On this 
basis further work with the Benthos cameras has been abandoned. 
At the time of writing, further trials are under way using the UMEL cameras. 
The emphasis is on determining the optimum amount and distribution of 
control, optimum distortion function and camera orientation. 
CONCLUSIONS 
The offshore based system for underwater photogrammetry from a manned 
submersible discussed in this paper has yet to be fully implemented. 
Initial investigations carried out in a shallow water tank have produced 
encouraging results and it is hoped to mount a full trial of the system 
under normal operational conditions during the 1982 offshore inspection 
season in the North Sea. 
This is just one of several systems for underwater photogrammetry under 
trial at the present time. It is hoped that these will demonstrate that 
photogrammetry can produce acceptable results when used in the underwater 
environment. There is little doubt that if this is so then photogrammetry 
will become a very important technique in underwater inspection and 
maintenance work as the quest for oil and gas continues in this hostile 
environment. | 
ACKNOWLEDGEMENTS 
The authors wish to acknowledge the support given throughout the project 
by British Oceanics Limited and the Science and Engineering Research 
Council (SERC).