Sentinel-3 FRM for Sea ice

The main objectives of sea ice observation with satellite altimetry are to reconstruct the topography of the sea ice and its evolution, particularly under the impact of climate change, at basin scale.

Satellite altimetry products provide two essential parameters:

  • The Surface Type Classification over Sea Ice (leads/floes);
  • The Radar Sea Ice Freeboard.

The surface type classification is essentially used to calculate the freeboard by difference in altimeter heights between leads and floes, but it also allows to characterize the fracturing ratio of the sea ice. The freeboard is the main proxy of the sea ice thickness and allows reconstituting the thickness of the sea ice.

This conversion can only be achieved after two successive steps: the conversion of the radar freeboard measured by the altimeter into an ice freeboard, and then the conversion of the ice freeboard into an ice thickness thanks to the hydrostatic equilibrium equation of the ice in the water. The first conversion depends on the snow depth and the speed of propagation of the radar wave in snow (assuming that the radar wave passes through the snow). The second conversion, from ice freeboard to thickness, requires knowledge of snow depth and of densities of water, ice and snow.

In the St3TART project, the Sea Ice team will provide an extensive literature review of existing methodologies and techniques to measure these parameters and support proper validation of the Copernicus Sentinel-3 STM Land sea ice products and associated geophysical measurements within the requirements for Fiducial Reference Measurements (FRM). Existing methods and lessons learnt from previous FRM campaigns will be investigated to identify suitable solutions in terms of sensors, validation sites, sampling strategy, sensor stability and uncertainty budget.

Based on these analyses and on the identification of existing permanent or semi-permanent measurements, the Sea Ice team will draw a roadmap for the provision of Copernicus Sentinel-3 FRM for sea ice, considering the most relevant and cost-effective methods to be maintained, supported as far as possible or implemented, and identifying the parameters that are missing or are insufficiently covered or precise.

A Copernicus Sentinel-3 FRM campaign in sea ice covered regions will be planned and executed during the St3TART project, based on the recommendations that will be gathered in the roadmap.

This campaign will combine well tested techniques and new novel techniques, which should provide a unique combination of data beneficial for the validation of the Copernicus Sentinel-3 sea ice products.

Partners involved:

  • DTU Space
  • NPL