Quality control in DGPS separation vector systems

Quality control and the computation of relative positions of multiple remote objects are key elements of a marine seismic streamer tracking system. NCS International and Pulsearch Navigation Systems have developed a separation vector system that has undergone extensive testing in the Gulf of Mexico and the North Sea. Each remote object, or in this case a tail buoy, is equipped with a controller board, GPS receiver and radio modem. Raw GPS measurements are collected and transmitted to the vessel where they are processed and stored on an IBM compatible computer using a Windows operating system. Differential GPS corrections are received by the vessel and used in the real-time vessel solution, if available. Processing includes using a series of eight-state Kalman filters for position and velocity determination for the vessel and each buoy. The detection and identification of measurement blunders are performed along with the computation of precision estimates in the form of confidence regions. Reliability measures are computed in real-time giving a measure of the strength of the solution. With these latter estimates, the computed positions are said to be repeatable when reliability measures lie within the precision confidence regions. The paper describes the variety of textual and graphical display screens available for the operator, including items such as range residuals, range corrections, satellite constellation information, quality assurance parameters and statistics on communications. The hardware for the system and the method of operation is described. Experience to date with the system is highlighted