Precise Marine Positioning Using the Global Positioning System (GPS).

The development of the Global Positioning System GPS has led to the possibility of positioning marine platforms with great accuracy. This report describes position computations made from GPS observations aboard a ship and the evaluation of the accuracy and precision of a Texas Instruments TI-4100 GPS Receiver at sea in a low dynamic mode. The observed pseudoranges were corrected and smoothed by Doppler count, and then were used to compute position using an eight-state Kalman filter. A comparison is made between the ships position obtained by GPS receiver and by Del Norte Trisponders. Data covering a period of 3600 s were processed and compared, yielding a total of 3171 s of data points from both positioning systems, which consisted of 2740 s of data with four satellites present and 431 s of data with three satellites. The mean of the root-mean-square differences between launch positions determined by mean of GPS satellites and by Trisponder was found to be or - 11 m when four satellites were available and or - 21 m when only three were presents. Some 29 percent of the time, the GPS positions and Trisponders positions had similar accuracy. Author.