The contemporary GIA has been measured by several different methods and data sets individually, such as GPS (Milne et al., 2001), combining tide gauge and altimetry records (Braun et al., 2008), satellite altimetry over land (Lee et al., 2008) and absolute gravimetry (Lambert et al., 2001). All of these data sources suffer from limited availability in remote areas, inhomogeneous accuracy, and sensitivity to localized non-GIA effects. On the other hand, each method is more sensitive to a specific type of movement, and therefore, appropriate integration of geodetic methods is desirable to study a geodynamic process comprehensively. As an example, although GPS is more sensitive to horizontal displacement, precise levelling can only reveal vertical displacement. In conformity with, while GPS and the precise levelling are both sensitive to surface deformations, gravity data are sensitive to lower mantle viscosity (Velicogna and Wahr, 2002).
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Lambert, A., Courtier, N., Sasagawa, G., Klopping, F., Winester, D., James, T. S., and Liard, J. O. (2001). New constraints on Laurentide postglacial rebound from absolute gravity measurements. Geophysical Research Letters, 28(10), 2109. American Geophysical Union. doi:10.1029/2000GL012611.
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Velicogna, I., and Wahr, J. (2002). Postglacial rebound and Earth’s viscosity structure from GRACE. Journal of Geophysical Research, 107(B12), 2376. doi:10.1029/2001JB001735.