The geodetic reference frame, which is consistently used in the PATHFINDER reprocessing of all altimetric satellite data, is the International Terrestrial Reference Frame (ITRF). The ITRF definition and other current modeling recommendations of the International Earth Rotation Service are documented in their ``IERS Conventions,'' [D. D. McCarthy, IERS Technical Note 21, July 1996].

In the context of reference systems and station positioning, it is interesting to note the special case of Geosat, which was tracked only by the TRANET Doppler system. Were it not for the Seasat mission, which employed both TRANET and SLR tracking, it would be very difficult to adjust Geosat's TRANET tracking sites into the ITRF. Thus, Seasat is important not only for its altimetry, but also for its tracking data. Appropriate use of those data allows Geosat to be tied into the same geodetic reference system as TOPEX/POSEIDON. Work is still in progress to strengthen this tie. A consistent geodetic reference frame is crucial to climate-related studies.

The reference ellipsoid used for all Pathfinder altimeter products is consistent with the official TOPEX/POSEIDON Geophysical Data Records. It is defined by: