Integrating Marine Navigational Systems in Post Cruise Processing

Abstract

The R/V ROBERT D. CONRAD uses a mix of systems for mid-ocean navigation during geological and geophysical research cruises: GPS, Transit Satellite, Rho-Rho Loran-C, Two-Axis Doppler Speed Log, and Gyro Compass. These systems have complementary error-spectra characteristics. GPS has high long period (>10 minute) accuracy, but can show unrealistic ship velocities when consecutive one-minute readings are used. The infrequent transit satellite fixes have only long period accuracy. Loran-C has high medium period accuracy (< hours). The speed log and Gyro show high short period (< hour) accuracy, but currents and wind introduce long period errors.

The information from all systems is combined to achieve the best possible navigation over all time scales. A group of transit fixes establishes average Loran-C station ranges. Short period GPS and Loran-C errors are diminished by smoothing difference navigation formed by subtracting speed log/Gyro dead reckoning positions from GPS and Loran-C navigation points. Comparison of raw gravity and the Eotvos correction provide a check on this procedure.