DGPS is assumed to be accurate within 1-2 meters.
Standard GPS is assumed accurate within 5-10 meters.
99% of the positional data is DGPS. Unless noted, all
GPS/DGPS data is referenced to WGS84 (NAD83). Slant-range
distance is recorded between the sidescan-sonar tow vehicle
and a sidemount rigged with an acoustic transponder. Offset
between the sidemount and GPS antennae is measured.
Basic trigonomic calculations use the slant-range offset
to calculate a 'fish' (tow-vehicle) navigation. An assumption
in these calculations is that the tow-vehicle is traveling
directly behind the vessel; movement to port or starboard
is not accounted for within 'fish' navigation. Thus, the horizontal
accuarcy of the sidescan-sonar tow-vehicle is +/- 15 meters. The
horizontal positioning of the seismic systesm did not account for source and
receiver offsets and offset the GPS antennae and the
boomer source and streamer. It is estimated that these
offsets could lead to inaccuracies of about 30 m.
Interpretive products are based on the evaluation of sidescan-sonar,
seismic-reflection, and sample data. Therefore, the horizontal
accuracies of these systems will carry through to the interpretive
products. As such, the horizontal accuracy of these data is assumed
to be within +/- 30 meters.