Day 4

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Paper title Monitoring of Surface Melt Processes in Greenland and Antarctica using Sentinel-1 SAR and Metop ASCAT backscatter time series
Authors
  1. Jan Wuite ENVEO IT GmbH Speaker
  2. Thomas Nagler ENVEO IT GmbH
  3. Helmut Rott ENVEO IT
  4. Stefan Scheiblauer ENVEO IT GmbH
  5. Anne M. Solgaard GEUS
  6. Manu Holmberg Finnish Meteorological Institute (FMI)
  7. Kimmo Rautiainen Finnish Meteorological Institute (FMI)
Form of presentation Poster
Topics
  • A9. Polar Science and Cryosphere
    • A9.04 Mass Balance of the Cryosphere
Abstract text 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. Surface melting has a significant impact on the surface energy budget of snow areas, as wet and refrozen snow typically have a relatively low albedo in the visible and near-infrared spectral regions. Moreover, enhanced surface meltwater production may drain to the bed and raise the subglacial water pressure, which can have a strong impact on glacier motion. Surface melt also plays an important role for the stability of ice shelves, as the intensification of surface melting as precursor to the break-up of ice shelves in the Antarctic Peninsula has shown.

Passive and active microwave satellite sensors are the main data sources for products on melt extent over Greenland and Antarctica. In particular, passive microwave data has been widely used to map and monitor melt extent on ice sheets. C-band SAR has several advantages over passive microwave radar, including the ability to detect wet snow below a frozen surface and more sensitivity to the melting state of the snow volume. The better sensitivity of C–band to the physical properties of internal snow and firn layers on ice sheets and glaciers is of relevance for modelling of meltwater production and energy fluxes in the snow volume. The limited availability of SAR data over the ice sheets, that existed in the past, has been overcome with the launch of the Copernicus Sentinel-1 (S-1) mission. S-1 SAR data are now regularly acquired every 6 to 12 days, allowing for detailed time series analysis at a high resolution.

To evaluate snowmelt dynamics and melting/refreezing processes in Greenland and Antarctica, we have developed and implemented an algorithm for generating maps of snowmelt extent based on multitemporal S-1 SAR and METOP-A/B/C ASCAT scatterometer data. The detection of melt relies on the strong absorption of the radar signal by liquid water. The dense backscatter time series yields a unique temporal signature that is used, in combination with backscatter forward modelling, to identify the different stages of the melt/freeze cycle and to estimate the melting intensity of the surface snowpack. The high-resolution S-1 SAR data are complemented by daily lower resolution backscatter maps acquired with ASCAT to cover the complete time period from 2007 onwards. The melt maps form the main input for deriving value-added products on annual melt onset, ending and duration. Intercomparisons with in-situ weather station data and melt products derived from regional climate models (RCMs) and passive microwave radiometers confirm the ability of the algorithm to detect short-lived and longer melt events.

Our results demonstrate the excellent capability of the S-1 mission in combination with ASCAT for operational monitoring of snowmelt areas in order to produce a consistent climate data record on the presence of liquid water and snow properties in Greenland and Antarctica for studying surface melt processes.