CoAuthors

Andrew Shepherd (University of Leeds, United Kingdom); Inès Otosaka (University of Leeds, United Kingdom); Thomas Slater (University of Leeds, United Kingdom)

Satellite altimeters have continuously observed surface elevation changes across the Greenland Ice Sheet surface for the past three decades. Improvements made in processing these observations and in the development of new sensors during this time, have culminated in high resolution instruments, which are able to provide new insights into the physical processes and changes that the Greenland Ice Sheet experiences as the climate warms.

Here, we compare elevation changes and trends in elevation change observed over the Greenland Ice Sheet, by the CryoSat-2 and ICESat-2 satellite altimeters, between October 2018 and March 2022. We quantify the agreement between estimates from the two altimeter missions across the entire Greenland Ice Sheet and within its’ principal drainage basins. In addition, we assess seasonal variations in elevation observed by both instruments, largely driven by snowfall accumulation in the winter and surface melting in the summer. Significant changes in these processes have been observed across Greenland as the climate has warmed in the recent decades; comparing the elevation changes observed by the radar and laser instruments on-board CryoSat-2 and ICESat-2, respectively, has the potential to improve our understanding of these surfaces processes due to the differences in how these two frequencies interact with the physical properties of near-surface snowpack. We also assess elevation differences within the predominantly dry ice sheet interior in order to improve understanding of the differences in penetration depth of the different wavelengths of the two signals. As an example, in Northwest Greenland, we estimated the trends in elevation change to be -25.93 cm/yr and 20.86 cm/yr from CryoSat-2 and ICESat-2, respectively. We process the satellite radar and laser altimetry data over grids of different spatial resolution in order to statistically identify the optimum spatial and temporal sampling for each mission. Our assessment provides a detailed, multi-year comparison of radar and laser altimeter observations across the entire Greenland Ice Sheet, allowing us to examine the suitability of combining these datasets or where appropriate, computing a correction for surface depth penetration, providing a basis for improved estimates of ice sheet mass balance from satellite altimetry. Our Ice Sheet wide comparison here is an advancement on previous comparisons of radar and laser altimetry, which were based on surveys from airborne laser altimetry like NASA’s Operation IceBridge, thus limiting the spatial extent to the margins of the Greenland Ice Sheet, where majority of the surveys were carried out.