TRANSFORMATION BETWEEN SLR VLBI AND WGS-84 REFERENCE FRAMES/

In geodetic and geophysical applications of GPS, it is important to re alize the ephemerides of the GPS satellites and the coordinates of sta tion positions in a consistent reference system. At present, more than one reference system is being used by various GPS users depending on their specific applications. The WGS-84 and various reference frames b ased on satellite laser ranging (SLR), very long baseline interferomet ry (VLBI), or a combination of SLR and VLBI are the most commonly used in high precision geophysical applications. The WGS-84 is widely used in applications which rely on the GPS broadcast ephemeris. Station co ordinates estimated in one system may have to be transformed to anothe r for further use or for evaluation/comparison purposes. This paper pr esents a seven-parameter transformation between the WGS-84 and SLR/VLB I reference frames. The GPS double-differenced phase measurements for two consecutive weeks from a set of five Defense Mapping Agency (DMA) sites (defined in the WGS-84 frame) and from an augmented set of fifte en CIGNET sites (defined in the SLR/VLBI frame) were processed in a le ast squares estimation scheme to determine station coordinates, from w hich the transformation parameters were determined. A scale difference bf about 0.2 ppm and an orientation difference in longitude of about 31 milliarcseconds were found to be the only parameters of significanc e between the adopted SLR/VLBI and the WGS-84 frames. Transformation b etween WGS-84 and the ITRF90 is also included, in which the scale diff erence is the same as before but the longitude rotation is about 16 ma s.