Enhancement of shipboard ADCP data with DGPS position and GPS heading measurements

Navigation errors contribute substantially to errors in shipboard ADCP data. Position measurement errors require long averaging intervals to reduce their effect, and heading errors produce systematic bias in underway data. With Differential GPS (DGPS) position fixing and GPS attitude measurement, each of these errors can be reduced to 1 cm/s for 10-min ACDP data. DGPS pseudorange corrections produced almost continuous coverage with 4-m rms errors at a range of 2000 km from a reference station; even at 4500 km from a reference station the data were worthwhile. GPS heading measurements were used to reveal the deficiencies in a gyrocompass over a 24-h period. Although coverage was not quite continuous, linear interpolation of gyrocompass error was sufficient to fill the gaps.