The International GPS Service (IGS) has provided GPS orbit products to the scientific community with increased precision and timeliness. Many users interested in geodetic positioning have adopted the IGS precise orbits to achieve centimeter level accuracy and ensure long-term reference frame stability. Positioning with GPS can be performed by either of two ways: point positioning or differential (relative) positioning. GPS point positioning employs one GPS receiver, while differential positioning employs two (or more) GPS receivers simultaneously tracking the same satellites. Surveying works with GPS have conventionally been carried out in the differential positioning mode. This is mainly due to the higher positioning accuracy obtained with the differential positioning mode compared to that of the GPS point positioning. A major disadvantage of GPS differential positioning, however, is its dependency on the measurements or corrections from a reference receiver; i.e. two or more GPS receivers are required to be available. New developments in GPS positioning show that a user with a single GPS receiver can obtain positioning accuracy comparable to that of differential positioning (i.e., centimeter to decimeter accuracy). This work details a post-processing approach that uses un-differenced dual-frequency pseudorange and carrier phase observations along with IGS precise orbit products, for stand-alone precise geodetic point positioning (static or kinematic) with centimeter precision. This is possible if one takes advantage of the satellite clock estimates available with the satellite coordinates in the IGS precise orbit products and models systematic effects that cause centimeter variations in the satellite to user range. This paper will describe the approach, summarize the adjustment procedure and specify the earth and space based models that must be implemented to achieve centimeter level positioning in static mode. Results obtained using existing control as case studies are also presented.
Journal of the Nigerian Association of Mathematical Physics, Volume 19 (November, 2011), pp 499 – 512