GPS MARINE KINEMATIC POSITIONING ACCURACY AND RELIABILITY

Abstract

Positioning accuracy and reliability are two parameters of major concern to GPS marine users. GPS limitations and error sources are analyzed from a user’s point of view. The coverage limitations inherent to the (18 + 3) satellite constellation are discussed and related outages inherent to specific geographical areas are described. Receiver and antenna characteristics are described in relation to their effect on positioning accuracy and reliability. Antenna requirements for shipborne applications are discussed. The effect of the troposphere and ionosphere on GPS measurements is quantified for various cases. Multipath and imaging effects on both P and CIA code and carrier phase measurements are discussed. A variety of user accuracy and reliability enhancements are described. These include the use of seven-channel receivers and that of height and time constraints to increase redundancy and limit poor geometry effects, the use of differential methods to reduce satellite and propagation medium errors, the integration of code and carrier phase measurements to increase positioning accuracy, and the use of external sensors such as pitch and roll sensors, and inertial navigation systems. It is concluded that GPS is capable of achieving the one metre accuracy level for marine applications provided that error sources specific to shipborne applications can be effectively controlled.