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M r KellandAs a result of the operational success of the prototype Rangemeter and the relative positional accuracy( k 20 cm)achieved by 10s during an underwater study of the mobility of a sand wave crest, the British Petroleum Co. Ltd purchased the first production model for an underwater survey in its West Sole gas field. The new Rangemeter incorporates a 4 digit visual display and operates with up to five transponders.57. The transponders were deployed in special frames on the sea bed near Platform WB at West Sole, and the distances between each pair were determined using the Rangemeter. Ranges were then established to each transponder from a number of survey points approximately 5 m apart along the sea lines adjacent to the platform.Measurements were also taken from positions above buried sections of sea line. In this case the measuring points were established with the diver-operated Pipelock system developed by Mobell (Marine) Ltd. Ranges were also determined from the platform legs. All the results were logged on a tape recorder mounted in a BP designed underwater housing. A computer program was written to calculate the optimum position of each survey point, and its relative accuracy, and a map was constructed to show the distribution of the sea lines relative to the platform. Provided ranges are measured to more than three transponders, the program will eliminate a range value which gives an accuracy outside a predetermined value. The ranges measured during the survey varied between 60 and 450 m, and the relative positioned accuracy of most of the survey points was calculated to be within +20 cm. Dr R. L. Cloet, Scientist, The Institute of Oceanographic Sciences I should like to congratulate Mr Kelland on his achievement in making measurements in the North Sea.59. I was pleased when he joined the Institute of Oceanographic Sciences (10s) at Taunton to find that he would undertake the trials with this position system himself because for some years I had gradually been becoming more and more disturbed by the way in which people took measurements at sea. I have seen a water intake for a power station designed on the basis of two depth soundings near to each other with the history of the level of that particular point worked out on the basis of half a dozen soundings spread over a hundred years.60. This situation made me feel it was essential to get to grips with site investigations and positioning as distinct from navigational positioning. This is precisely what Mr Kelland has done. In the event the movements of sand waves were so small that they nearly always fell within the positioning errors of the surface navigation systems. Work on these is still continuing and I have great confidence that both for diver work

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