Arctic sea ice freeboard heights from satellite altimetry

The Arctic sea ice cover is most sensitive to climate change and variability, mainly due to the ice-albedo feedback effect. With an increase in the average temperature across the Arctic during the past few decades, sea ice has been melting rapidly. The decline in the sea ice extent was estimated as 10% per decade since satellite observations began in 1979. Sea ice thickness is an important parameter that moderates the heat exchange between the ocean and the atmosphere, extent of sea ice deformation and sea ice circulation in the Arctic Ocean. In addition, sea ice thermodynamics and dynamics depend on the thickness of the sea ice cover. In order to estimate the trend in the sea ice volume, both the extent and thickness must be known. Hence, it is important to measure the sea ice freeboard (a representative fraction of the thickness) distribution in the Arctic Ocean.;In order to improve the accuracy of the freeboard estimation, an accuracy assessment of the ocean tide models (one of the component models in the sea surface height estimation) in the Arctic Ocean was performed. The Arctic Ocean Tide Inverse Model (AOTIM-5) was found to have the best accuracy in the Arctic Ocean and was, therefore, used in the sea ice freeboard estimation. It was also shown that the present generation of ocean tide models have ignored the ice-tide interaction processes in the model parameterization, as they are not constrained by observations from sea ice covered regions.;A sensitivity analysis of the freeboard estimation procedure indicates an uncertainty of ∼0.24 m over a length scale of 100 km. The estimated total ice freeboards were compared with freeboard measurements from other methods (e.g. 'lowest level'), and a good agreement was found between the two methods at regional scales. The sea ice thickness, in the multi-year ice region north of Greenland and Ellesmere Island, was also derived from the total ice freeboard heights by assuming a hydrostatic equilibrium condition. The estimated thicknesses were compared with the thickness measurements from a Helicopter-borne Electromagnetic Induction technique. The difference between the means of the two thickness distributions was ∼0.53 m, which is well below the accuracy of the thickness estimates of ∼0.98 m.;The sea ice freeboard estimation procedure, demonstrated in this study, can also be applied to upcoming laser and radar altimetry missions, such as Cryosat-2 and ICESat-2, to continuously monitor the regional, seasonal and inter-annual changes in the Arctic sea ice freeboard (and thickness) distribution.;In this thesis, the total ice freeboards (height of the snow/ice surface above the sea level) were derived from satellite laser altimetry. NASA's Ice Cloud and Land Elevation Satellite (ICESat) carries a Geoscience Laser Altimetry System (GLAS) onboard, and provides dense coverage of snow (or sea ice) surface heights in the Arctic Ocean up to 86° N. The total freeboard height at each ICESat footprint location was computed by removing the instantaneous sea surface height from the ice/snow surface height. In this study, the instantaneous sea surface heights were modeled using a combination of geodetic and oceanographic models.