Augmentation of GPS for Ship Navigation in Constricted Water Ways

Vessels navigating in constricted water ways require reliable and accurate positions. In these water ways, the line-of-sight GPS signals are often masked by obstructions, resulting in degraded geometry and accuracy at best, and unavailability or unreliable positions at worst. The use of combined GPS-GLONASS results in a dramatic increase in the number of satellites available above the horizon. Simulation analysis was used to show the improvement achievable by augmenting DGPS with single point GLONASS, differential GLONASS, and height constraint. By running the simulation over a 24 hour period the complete GPS constellation was analyzed. To validate the results from the simulation, field trials were conducted under various GPS and GPS-GLONASS masking angles. Two Ashtech GG24™ receivers were used for these trials. For both the simulation and field trials the availability and reliability performance were analyzed as a function of signal obstruction elevation and the types of augmentation that were implemented. These results clearly demonstrate the advantage of augmenting GPS with GLONASS and a height constraint, especially for ship navigation in constricted water ways.