Speaker
Description
The area extent and duration of surface melt on ice sheets are important parameters for climate and cryosphere research and key indicators of climate change. The surface melting / refreezing condition is essential information for modelling glacier hydraulics and the surface energy budget. Data on surface meltwater production are also crucial for estimating changes in the subglacial water pressure, a main parameter for glacier speed-up. Surface melt plays an important role for the stability of ice shelves, as the amplification of surface melting as precursor to the break-up of ice shelves on the Antarctic Peninsula has shown.
In the frame of the ESA Polar Cluster projects 4DGreenland and 4DAntarctica we developed an algorithm for generating maps of snowmelt extent based on multitemporal Sentinel-1 SAR and METOP-A/B/C ASCAT scatterometer data. The detection of melt relies on the strong absorption of the C-band radar signal by the presence of liquid water in the snowpack. The proposed algorithm exploits dense backscatter time series to identify the different stages of the melt/refreeze cycle. Using ASCAT data with about 5 km pixel spacing we generated time series with daily maps of melt / refreeze area at low spatial resolution providing an insight into the dynamics of changing surface conditions in Antarctica and Greenland. These products are intercompared to surface energy balance models in order to check the model performance in respect to the melting and surface refreezing conditions. On confined outlet glaciers the resolution of ASCAT is not suitable for detecting spatial details such as changes in melt conditions with elevation. For these glaciers we use time series of high resolution Sentinel-1 C-band SAR data, available in 6 to 12 days timesteps. In order to estimate the evolution of the increasing thickness of refrozen snow layers on top of wet snow, we use an approach based on backscatter modelling integrating C-band SAR data of Sentinel-1 and L-band SAR data of SAOCOM. In the presentation we will show time series of ASCAT melt products for Greenland and Antarctica and their relation to climate model output. Additionally, examples of the newly developed refreezing depth product, derived from Sentinel-1 and SAOCOM data, will be presented.
