Altimetry-derived marine gravity anomaly and its impact to the geoid of Norway

Marine Free-Air Anomalies (FAA) around Norway including some parts of the North Sea, the Norwegian Sea and the Barents Sea are computed from satellite altimetry data. 84 cycles of ERS2 along track data, 25 cycles of ENVISAT along track data and high density ERS1 data during its geodetic mission are used. The new geopotential model from the Gravity Recovery and Climate Experiment (GRACE) mission (GGM02S) is used to compute long wavelengths contributions of geoid and FAA. To correct data for mean dynamic topography, the available Levitus climatology model is used.Corrected data are then used to compute along track gradients in each cycle-pass to suppress the orbital and the atmospheric errors below the noise level of the altimeter. Resulted gradients are then stacked and the east-west and the north-south components of the deflection of verticals are computed where ascending and descending tracks meet each other. Finally, inverse Vening-Meinesz formula is implemented on the gridded deflections to compute FAA.