Differential GPS (DGPS) is a technique for reducing the error in GPS-derived positions by using additional data from a reference GPS receiver at a known position. The most common form of DGPS involves determining the combined effects of navigation message ephemeris and satellite clock errors [including the effects of selective availability (SA), if active] at a reference station and transmitting pseudorange corrections, in real time, to a user's receiver. The receiver applies the corrections in the process of determining its position [63] | Global Positioning Systems Inertial Navigation and Integration Mohinder S. Grewal Lawrence R. Weill Angus P. Andrews Copyright 2001 John Wiley Sons Inc. Print ISBN 0-471-35032-X Electronic ISBN 0-471-20071-9 9 Differential GPS INTRODUCTION Differential GPS DGPS is a technique for reducing the error in GPS-derived positions by using additional data from a reference GPS receiver at a known position. The most common form of DGPS involves determining the combined effects of navigation message ephemeris and satellite clock errors including the effects of selective availability SA if active at a reference station and transmitting pseudorange corrections in real time to a user s receiver. The receiver applies the corrections in the process of determining its position 63 . This results in the following Some error sources are canceled completely a selective availability and b satellite ephemeris and clock errors. With other error sources cancelation degrades with distance a ionospheric delay error and b tropospheric delay error. Still other error sources are not canceled at all a multipath errors and b receiver errors. 265 266 DIFFERENTIAL GPS LADGPS WADGPS AND WAAS Description of Local-Area DGPS LADGPS LADGPS is a form of DGPS in which the user s GPS receiver receives real-time pseudorange and possibly carrier phase corrections from a reference receiver generally located within the line of sight. The corrections account for the combined effects of navigation message ephemeris and satellite clock errors including the effects of SA and usually atmospheric propagation delay errors at the reference station. With the assumption that these errors are also common to the measurements made by the user s receiver the application of the corrections will result in more accurate coordinates 81 . Description of Wide-Area DGPS WADGPS WADGPS is a form of DGPS in which the user s GPS receiver receives corrections determined from a network of reference stations .
