Earth tides observed by gravimeter and GPS in Juneau, Southeastern Alaska

We have analyzed the gravity data obtained at the Egan Library of University of Alaska, Southeast (UAS) and the GPS data obtained at a PBO site in Juneau, and we compared the obtained tidal amplitudes and phases with those estimated from the predicted tides including both effects of the body tide and ocean tide. To improve the accuracy in prediction, we also computed the regional ocean tide model in Southeastern Alaska (SE-AK). Our comparison results suggest; (1) By taking into account the ocean tide effect including the regional ocean tide model, the amplitude differences between the observation and the predicted body tide is remarkably reduced for both the gravity and displacement tides (e.g. for the M2 constituent, 8.04 microGal to 0.02 microGal (1 microGal=1E-8 m/s/s), and 2.43 cm to the order of 0.01 cm for the vertical displacement), (2) The PPP method (Zumberge et al., 1997) used to extract the tidal signals from the original GPS time series works well to recover the tidal signals. Although the GPS analysis results still contain the noises which may be considered to be the meteorological effects, we may conclude that the GPS observation surely detects the tidal signals with the sub cm accuracy or better for some of the tidal constituents. The viscoelastic effect in gravity tides is estimated to be the order of 0.05 ?Gal for the M2 constituent in Juneau. The magnitude is equivalent to the analysis error for our gravity data. Increasing the accuracy of calibration of the gravimeter and the regional ocean model in SE-AK is needed to constrain the Earth's viscoelastic response to the tidal force tightly.