Measuring local spacetime curvature using GPS and GRACE

In this thesis the sensitivity of GPS and GRACE satellites to the local spacetime curvature was examined. Annual oscillations in a perturbation variable, β, in the Schwarzschild metric, as measured by GPS, used to express local position invariance (LPI) of fundamental constants was studied [15]. In this thesis these annual variations are modeled by extraterrestrial potentials. It was found that the solar tidal potential was the dominant effect and the influence of other planets was negligible. Looking at the contributions in the Fourier domain, it was seen that there were similarities in the periodicities of peaks at 180 and 365 days. The yearly peaks were found to coincide within 61.1% in amplitude. This is suggestive that the yearly and 180 day periods in are attributed to the solar tidal potential. Plotting the predicted β versus the measured β shows there is a linear correlation between the two with Râ� = 0.8980 and a slope of 0.7978. This shows evidence that GPS is sensitive to the local spacetime curvature. Since the solar tidal potential was left unfiltered from β, this thesis must reach the preliminary conclusion that GPS currently does not have sufficient accuracy for geopotential mapping of the earth's surface. To support ongoing efforts for the use of GPS for geodesy, geopotential mappings of the earth's surface were made using GRACE spherical harmonic coefficients. These were created using harmonics up to degree and order 50 and 100. The mappings represent a baseline for which to compare furture GPS mappings against. Weekly GRACE data was averaged and analyzed in the time and Fourier domains, as well as a function of longitude and lattitude, resulting in peaks that agreed favorably with the solar potential in periodicity, but not in amplitude. On average these peaks were found to be roughly one order of magnitude smaller than the solar tidal potential for GRACE. It is assumed this is due to the handling of the solar tidal potential in GRACE, but further study is needed.