Ship navigation using Navstar GPS - An application study

Ocean current measurement applications in physical oceanography require knowledge of inertial ship velocity to a precision of 1-2 cm/sec over a typical five minute averaging interval. The navigation accuracy must be commensurate with data precision obtainable from ship borne acoustic profilers used in sensing ocean currents. The Navstar Global Positioning System is viewed as a step in user technological simplification, extension in coverage availability, and enhancement in performance accuracy as well as reliability over the existing systems, namely, Loran-C, Transit, and Omega. Error analyses have shown the possibility of attaining the 1-2 cm/sec accuracy during active GPS coverage at a data rate of four position fixes per minute under varying sea-states. This paper is intended to present results of data validation exercises leading to design of an experiment at sea for deployment of both a GPS y-set and a direct Doppler measurement system as the autonomous navigation system used in conjunction with an acoustic Doppler as the sensor for ocean current measurement.