Observations of gravity field variations from ground and satellite data

Abstract

The Earth's gravity field consists of several constituents of geophysical nature. By using geodetic observations techniques to observe gravity field variations, it is possible to monitor these geophysical processes.

This thesis tries to analyse how Earth's gravity field varies on a global and on a local scale. In addition, attempts have been made to offer geophysical explanations to the variations observed. Observational material gathered through terrestrial gravimetry from three different locations in Norway, as well as satellite data from GRACE, has been used to study Earth's gravity field.

Performing an analysis covering several years using terrestrial gravimetry data, shows how Norway is influenced by glacial isostatic adjustment (GIA). The GIA induced vertical displacement was estimated to be 8.7 mm for \AA s and 8.0 mm for Trysil. The Trysil observations also reveal severe amounts of seasonal gravity variations, ranging from $\pm$ 4 microgals to $\pm$ 8 microgals. These seasonal gravity variations are correlated with the local hydrology cycle.

Using monthly GRACE solutions, this thesis shows how GIA influence Fennoscandia, northern parts of North America and Antarctica by increasing the regional mass distribution. Seasonal hydrology variations in the Amazon and southern parts of Africa can be detected by GRACE as well.

Finally, this thesis shows how GRACE and terrestrial data can detect some of the same gravity field variations. However, due to some methodology differences, the different gravity field signals behave differently.