Browsing by Author "Tsali, Iliana"

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    Land Ice Monitoring via GRACE and Satellite Altimetry in the Canadian Arctic Archipelago
    (2017) Tsali, Iliana; Sideris, Michael George; Marshall, Shawn; Collins, Michael J; Yackel, John J.; Forsberg, Rene
    The Canadian Arctic Archipelago (CAA) was remarked as the third most significant contributor to the global sea level rise between 2003 and 2009, containing one third of the world’s freshwater as land ice (Gardner et al., 2011). Continuous monitoring of the long-term mass variability of the CAA is essential knowledge for gaining insight about their forthcoming impact due to climate change. The scope of this thesis is to determine independent mass balance estimates from GRACE gravity and ICESat laser altimetry data for both the Northern and the Southern Canadian Arctic (NCA; SCA), compare both estimates and assess them with respect to previous studies, while discussing the reasons of the potential discrepancies existing. GRACE data are available as spherical harmonic coefficients (Level-2) express the gravity field and they are expanded up to a certain degree and order. This hampers the recovery of regional scale mass anomalies, which need knowledge of higher spatial detail. The proposed approach reconstructs spatial averaging basin functions that mask the glaciated areas of the NCA and SCA and fits GRACE-Stokes coefficients to isolate the ice-signal. This methodology has been applied to large river basins and ice sheets, however the present algorithm is applied for the first time to ice caps and glaciers. Due to the basins’ nature of signal leaking outside the basin, an estimate of the basin leakage error is accounted as well. High correlation in the Stokes coefficients of shorter wavelengths produces artificial noise which has to be filtered. Four different filters were tested and assessed with respect to geophysical signal attenuation they induced. The impact of the different filtering has been neglected for ice applications up to now, however this thesis highlights mass trends differences up to 8 Gt/yr. The GIA and hydrology reduced GRACE mass balance was -27.5 ± 4.1 Gt/yr for the NCA and -19.8 ± 2.5 Gt/yr for the SCA from 2003 to 2009. 5-year-intervals were estimated between 2003 and 2014 and accelerating mass losses of 50-55 Gt/yr for the NCA and 20-25 Gt/yr for the SCA were noticed. ICESat repeat tracks are not repeated exactly, while the elevation sampling is relatively sparse for glaciers, ICESat operated 2-3 times/yr. The ICESat mass changes derivation involved the retrieval of elevation changes by fitting elevations into boxes, and the conversion to volume changes using Ordinary Kriging and mass changes assuming a constant ice density. The GIA-free ICESat mass changes of -39.4 ± 10.4 Gt/yr for the NCA and -23.9 ± 6.1 Gt/yr for the SCA showed greater mass losses compared with GRACE in the same period. The potential causes are discussed analytically and justified sufficiently in this thesis.