Global sea level is rising. The globally averaged sea level is now widely recognized to have risen since 20th century withvarying amount, between 1 to 2 mm/yr ( Gornitz, 1995; Douglas, 1997; Peltlet and Tushingham, 1989; Church & White, 2006,2011; Jevrejeva et al., 2008; Nicholls and Cazenave, 2010; Hay et al., 2015). Between 1900 and 2012 it rose about 25 cm.
For the last two to three decades the sea level has also been accelerating, coincide with the mass flux from e.g. Greenlandicesheet with a tapestery of observational evidence. Priori to the satellite altimetry era, this global averaged sea level isprimarily estimated from a set of secular tide gauge records relative to coastal benchmarks. However, the tide gauge recordsare influenced by a superposition of various contributions of earth processes, with different time space characteristics. Thisinclude the influence of post glacial rebound or glacial isostatic adjustment (GIA) concomitant with changes (decay) in icesheet (Peiltier 2002, 2004; Tamisiea et al.
2001; King et al. 2012), the effects of active tectonics and solid earth deformation(Woppelman and Marcos, 2016), the changes in the eustatic sea surface height due to the expansion of the warming oceanwaters (and density changes) ( Cazenave and Cozannet, 2013), wind stress (Merrifield and Maltrud, 2011), recent melting ofglaciers and land water reservoir (freshwater fluxes to the ocean) (IPCC, 2007; Elliott et al. 2010), ice-ocean contact melt(Rignot et al. 2010), geoid (equipotential surface) changes due to large-scale mass redistribution (Dahlen, 1976; Tamisieaet al. 2011; Frederikse et al. 2017) , anthropogenic effects such as ground water usage and drought (Borsa et al.
2014) andthrough atmopsheric air pressure in the form of inverted barometric effect (Dangendorf et al. 2013). To estimate the eustatic sealevel change, the tide gauge records should be corrected for earth processes that have nothing to do with world ocean, such asfor present day GIA, tectonics, geoid changes, all the other aforementioned earth processes. Pre-satellite era, the correctionwere mainly comes from geological data (Gornitz, 1995; Church et al. 2004) or GIA (Peltier 2001; 2004; Ray and Douglas,2011; Spada and Galassi, 2012; Hay et al., 2015; Hamlington and Thompson, 2015).
The glacial isostatic adjustment andgeological (saltmarsh sedimentary sequences) vertical land motion estimate chiefly show long term geophysical motion that arenot adequate to represent short term geophysical motion linked to non-GIA response (e.g. Emery and Aubrey, 1991; Carter etal. 1989; Woodworth 2006 ) and also show large discrepancy compared to global positioning system (GPS) derived verticalland movement (vlm)(Snay et al. 2007) and error in the GIA model – such as the uncertainty in mantle rheology (Argus andPeltier, 2010). In spite of this limitation and in the absence of other accurate technique to measure vlm, GIA has been themodel of choice.
More recently measurements using GPS has been demonstrated as another tool as direct estimate of the rateof vertical land motion induced by both long and short term geophysical process in a absolute (geocentric) reference frame