Gravity Effects of Sea Level Variation at the Superconducting Gravimeter Sites, Estimated from ERS-1 and TOPEX/Poseidon Altimeter Data

Abstract

The effects of sea level variation on the observations of superconducting gravimeters (SG) have been evaluated at 18 SG sites over the world. As for the data of sea level variation, 1 degree x 1 degree mean sea surface heights were prepared for 2 to 75 repeat cycles of TOPEX/Poseidon satellite altimeter data, and then the loading effects of the sea level variation were calculated. The results show that (1) the gravity effects vary in peak-to-peak amplitudes from 1.5 to 4 micro Gals according to the site locations, and (2) they have a same dominant frequency of about 1 CPY (Cycle Per Year) but differing phases. This fact suggests that the sea level variation should be taken into account for the long period SG observations, and it inversely suggests that precise SG observations have a potential to detect not the thermal expansion of seawater but the actual mass changes which could not be observed by satellite altimetry.