Testing the Validity of the Equivalence Principle via Noon-Midnight Doppler Compensation in the GPS System

We propose an experiment based on GPS sattelite clock data to probe the validity of the Equivalence Principle. A particular focus is on the apparent absence of a classical first order Doppler effect due to the geocentric systems acceleration in the solar gravitational field. This missing effect is potentially to be compensated by a gravitational redshift arising from a uniform external field. This compensation parallels that of the Pound Rebka experiment sugesting that the observed null result may not reflect coordinate cancellation, but a physical effect. We argue that if the Doppler contribution should exist objectively in both GCRS and BCRS , then its absence in observation implies a real gravitational influence.