Comparison of GRACE Data With a Superconducting Gravimeter Data at Syowa Station, Antarctica

We have been conducting several precise geodetic measurements such as gravity measurement with a superconducting gravimeter, measurements of crustal movements by VLBI, GPS, DORIS, and sea level measurements in and around Syowa Station, Antarctica. Data obtained from these measurements can provide validation data of the Gravity Recovery and Climate Experiment (GRACE) satellite mission. In this study, we employed gravity data obtained by a superconducting gravimeter (SG) CT-043 at Syowa Station to compare with the data of GRACE Level-2 data. Observation by the SG has been carried out since April 2003, and the trend of gravity change whose length is about two years is available. After eliminations of Earth tides, atmospheric pressure effect, effect of polar motion, and linear component of instrumental drift, we obtained gravity change greater than 10 micro-gal for the period from April 2003 to January 2005. On the other hand, we used monthly anomaly of equivalent water mass change data given by the University of Colorado GRACE Data Analysis Website - http://geoid.colorado.edu/grace/grace.php to calculate expected gravity change induced by mass change yielding on Antarctic region whose south latitude is greater than 60 degree. The expected maximum gravity difference induced by the equivalent water mass on the region during the period from January 2003 to January 2005 is approximately 1 micro-gal. Amount of the both gravity changes are quite different. We infer the difference is mainly caused by insufficient corrections in obtaining the SG trend such as influences of atmospheric density re-distribution and non-tidal sea level change, and non-linear instrumental drift.