Doom Bar Targets
The geophysical survey found sixteen targets that would be worth further investigation. The chart shows the main targets as large blue circles with smaller targets as small blue circles. The magenta circles mark the positions of keep pot buoys that were in the area during the survey.
Two small targets to the south were detected by the magnetometer with estimated masses of 11 and 14 tons. To the north was a single magnetometer target close to the estimated position for the Whiting. East of this was a 78 ton magnetometer target that also showed on the side scan sonar trace. North of this was a line of targets in the range 12 to 32 tons.
Target 15 was first found because it showed as a prominent object on the side scan sonar trace. The side scan sonar showed this as a target approximately 23m long by 18m wide with no shadow suggesting that the target was not far proud of the seabed. The position of the sonar target was added to the survey plan so that it could be investigated using the magnetometer and sub-bottom profiler.
The magnetometer detected a significant target when it was first run over this area. The target measured 911 nT and gave an estimated mass of 78 tons. The shape of the trace (Image A below) confirmed that the magnetometer had been run directly over the target and that the target was not buried.
The boat was then run over the target from all directions (Image B below) so we could collect more information about the magnetic field around the target. When plotted as a 3D model (Image C below) it shows a large bipole target about 40m wide and 50m long with a positive deflection to the south-west and a smaller negative deflection to the north-east.
From the estimates of size and shape this target appeared to be a small wreck about 23m long.
The next phase of the project was to investigate the high priority targets using divers. Even though it was not the right size for Whiting, Target 15 was made a priority target because it was likely to be a wreck and needed to be investigated.