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Radio occultation events recorded on 28–29 July 2004 by a GPS receiver aboard the GRACE‐B satellite are analyzed. The stability of the receiver clock allows for the derivation of excess phase profiles using a zero difference technique, rendering the calibration procedure with concurrent observations of a reference GPS satellite obsolete. 101 refractivity profiles obtained by zero differencing and 96 profiles calculated with an improved single difference method are compared with co‐located ECMWF meteorological analyses. Good agreement is found at altitudes between 5 and 30 km with an average fractional refractivity deviation below 1% and a standard deviation of 2–3%. Results from end‐to‐end simulations are consistent with these observations.
Beyerle et al. (2005) studied this question.