衛星重力データによる精密重力測定の環境補正

抄録

We propose a practical method and discuss some problems related to corrections for the gravity effects of fluid envelope of the Earth, i. e., the atmosphere, the ocean and/or land water using coming satellite gravity data . Recent progress of precise gravity measurements using superconducting gravimeters (SG) and/or absolute gravimeters (AG) enables us to study thevery weak signals (less then a few micro gals) of long-term gravity changes due to polar motion effects, post-glacial rebounds, crustal movements, sea level changes, and other various phenomena. Besides these, mass redistribution of the fluid envelope causes global gravity changes mainly in the seasonal frequency band . Since the gravity changes observed by the gravimeters are the integrated sum of all these signals, we need to extract a desired signal or to correct unnecessary signals depending on the purpose of the study. A new satellite gravity mission GRACE will be expected to provide a time series of global gravity fields coefficients with an interval of about one month. Hence, we will be able to use the coefficients for the correction of the gravity changes due to the global mass redistribution. Conversely, we may use the surface gravity measurements as a validation tool ofthe satellite data. The principle of the correction is rather simple; 1) calculate equivalent surface mass changes from the observed gravity coefficients, and 2) calculate the gravity changes at a station with Green's functions for loading effects and attraction . However, there are some practical problems related to the selection of the green functions, high frequency aliasing, local effects, zero definitions, and so on . We will discuss these problems by simulation studies using gravity coefficients estimated from reanalysis and model data sets of the fluid envelope.