137 



b. Doppler Sonar: The Doppler Sonar continuously measures the speed of 

 the vehicle in relation to the longitudinal and transversal axis. 

 This measurement when integrated with time and a gyro compass thus 

 enables the distance run by the vehicle to be knov^n with high accuracy 

 in relation to a specific reference points. 



c. Pipetracker: The pipetracker enables the submersible to locate and 

 follow a buried pipe to a depth of burial of 3m ± 10cm (10 ft i 4 in.) 

 depending upon the size of the pipeline. The system induces eddy 

 currents in the metallic mass of the pipe and measures the resulting 

 field which gives the location of the pipe both vertically and laterally. 



d. Continuous Seabed Profiler: The continuous seabed profiler, which 

 combines an Echo Sounder and a Pressure Sensor, uses the surface sea 

 level to give a continuous seabed profile related to absolute depth. 



e. Trench Profiler: The continuous sector scanning trench profiler 

 produces a profile of the seabed every 25m (82 ft) at a normal survey 

 speed of about one knot (1.8km/hr). The 140 degree sector scan cycle 

 lasts about 60 seconds which includes data recording. The effective 

 scan width is about 20m (66 ft) with the profiler 4m (13 ft) above 

 the seabed. 



f. Current Density: The INTERSUB Current Density System measures the 

 D.C. currents produced by the anodes which vary between 25mA/m2 and 

 500mA/m2. This gives a curve showing current density along the pipeline 

 whether it is buried or not. 



g. Cathodic Potential Readings: This system using Ag/agCl reference 

 cells achieves either direct measurement in contact with the bare 

 metal areas or indirect measurement using two separated reference cells. 



h. Leak Detection: This system, which is not yet fully proven at sea, 



includes a fluorometer leak detector system that continuously measures 

 the hydrocarbon content of the seawater. The system, combined with 

 an acoustic hydrophone to monitor the noise level, allows very small 

 leaks to be accurately pin-pointed. 



i. Optical Systems: The vehicle is fitted with three Sub Sea Systems 

 CMS Newvicon cameras, two of them are located in the front of the 

 vehicle (one on pan and tilt, one on tilt) while the third one, placed 

 on pan and tilt on the rear of the vehicle, allows a visual control of 

 the umbilical and pipe tracker. The cameras have two functions: one 

 allows the surface controller to see where the vehicle is going; the 

 second provides a visual record of the inspection. 



For detailed photographic work on specific areas of interest, color 

 stills are taken using a benthos 372 still camera. 



j. Computer System: Figure 5.1 shows the inter-relationship of the 

 instrumentation. The sensors continuously transmit information to 

 the computers on the surface. This information is collected at the 



