Hydrological effects on the superconducting gravimeter observation in Bandung

Gravity observation using the superconducting gravimeter (SG: GWR TT-70#008) in Bandung has been carried out since December 1997. The SG station in Bandung (BA) is the only station existing near the equator in the Global Geodynamics Project (GGP) Network and belongs to a tropical climatic zone. In the rainy season, there are heavy rainfalls of over 30 mm/h by the passage of a squall line. In order to estimate the peculiar hydrological effects of the gravity observation to the tropics, we installed a groundwater level meter in January 2000, and soil moisture meters and the rain gauge in November 2002. We investigated the gravity variation for the short period before and after each heavy rainfall. As a result of the comparison between gravity residuals and the rain gauge data, a heavy rainfall caused gravity changes in the order of 1 μGal. The model of soil moisture can explain about 80% of the variations in gravity.