A dam had possible areas of seepage and an inspection was required. Visibility in the water was very poor and a scanning and profiling sonar survey was recommended.

To produce finely detailed data it was proposed that the profiling sonar head be lowered 150’ to 20’ above the bottom - this would keep the sound footprint small. When a profile was taken the sonar head had to be held steady and directly below the prism used by the Robotic Total Station.

The area was approximately 100 by 200 metres, centered on an old river bed.