Sub bottom profilers work on the same principle as simple echosounders, but use much lower frequency acoustic energy. The acoustic pulses penetrate below the seabed and into the sediment. Returning echoes from sub bottom features such as geological stratas or buried material create a trace on paper and in the digital record.
A number of different sub bottom profiling systems are available. These are categorised by the frequency content of transmitted pulses.
Low frequency systems, often called boomers achieve high ground penetration at low resolution, while higher frequency systems, called pingers, achieve high resolution but only limited ground penetration.
For the 2003 fieldwork, Wessex Archaeology employed an Applied Acoustics boomer plate. The survey sought to determine the geological setting of the wreck sites and to detect pieces of buried wreckage that were not visible in magnetometer, sidescan or multibeam results.
The data was processed using Coda software and then interpreted. Typical sub bottom profiler data, acquired from wreck site 5010 can be seen here.