Abstract
Accurate values of ship’s heading, usually obtained from a gyrocompass, are vital in calculating absolute currents from ship-mounted acoustic Doppler current profilers (ADCPs). This note presents a straightforward method of calibrating a ship’s gyro by comparing two independent estimates of ship’s absolute velocity: one from bottom-track ADCP data (in combination with gyro data), and the other from differential global positioning satellite data. From a dataset collected in June 1993, 5-min-averaged data were isolated having these two estimates of ship’s velocity. These data showed that the speed estimates agreed within 0.2% but that the direction estimates varied by ±5° (standard deviation 2.4°) in a manner that was strongly a function of ship’s gyro heading. Correcting the data for this relationship reduced the standard deviation of the components of the ship-velocity differences by a factor of 2 and removed clear biases in their means.
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