Preprints
https://doi.org/10.5194/tc-2020-371
https://doi.org/10.5194/tc-2020-371

  06 Jan 2021

06 Jan 2021

Review status: this preprint is currently under review for the journal TC.

A Bayesian approach towards daily pan-Arctic sea ice freeboard estimates from combined CryoSat-2 and Sentinel-3 satellite observations

William Gregory1, Isobel R. Lawrence2, and Michel Tsamados1 William Gregory et al.
  • 1Centre for Polar Observation and Modelling, Earth Sciences, University College London, UK
  • 2Centre for Polar Observation and Modelling, University of Leeds, UK

Abstract. Observations of sea ice freeboard from satellite radar altimeters are crucial in the derivation of sea ice thickness estimates, which in turn inform on sea ice forecasts, volume budgets, and productivity rates. Current spatio-temporal resolution of radar freeboard is limited as 30 days are required in order to generate pan-Arctic coverage from CryoSat-2, or 27 days from Sentinel-3 satellites. This therefore hinders our ability to understand physical processes that drive sea ice thickness variability on sub-monthly time scales. In this study we exploit the consistency between CryoSat-2, Sentinel-3A and Sentinel-3B radar freeboards in order to produce daily gridded pan-Arctic freeboard estimates between December 2018 and April 2019. We use the Bayesian inference approach of Gaussian Process Regression to learn functional mappings between radar freeboard observations in space and time, and to subsequently retrieve pan-Arctic freeboard, as well as uncertainty estimates. The estimated daily fields are, on average across the 2018–2019 season, equivalent to CryoSat-2 and Sentinel-3 freeboards to within 2 mm (standard deviations < 5 cm), and cross-validation experiments show that errors in predictions are, on average, within 3 mm across the same period. We also demonstrate the improved temporal variability of a pan-Arctic daily product by comparing time series of the predicted freeboards, with time series from CryoSat-2 and Sentinel-3 freeboards, across 9 sectors of the Arctic. The mean of predicted and CryoSat-2 or Sentinel-3 time series are generally consistent to within 3 mm, except for the Canadian Archipelago and Greenland, Iceland and Norwegian Seas, which show discrepancies greater than 1 cm due, in part, to biases between CryoSat-2 and Sentinel-3 observations in these locations.

William Gregory et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on tc-2020-371', Alan Muir, 07 Jan 2021
    • EC1: 'Reply on CC1', John Yackel, 08 Jan 2021
  • CC2: 'Comment on tc-2020-371', Alan Muir, 08 Jan 2021
    • AC1: 'Reply on CC2', William Gregory, 08 Jan 2021
  • RC1: 'Comment on tc-2020-371', Alessandro Di Bella, 08 Feb 2021
  • RC2: 'Comment on tc-2020-371', Rachel Tilling, 10 Feb 2021

William Gregory et al.

William Gregory et al.

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Short summary
Satellite measurements of radar freeboard allow us to compute the thickness of sea ice from space, however attaining measurements across the entire Arctic basin typically takes up to 30 days. Here we present a statistical method which allows us to combine observations from three separate satellites to generate daily estimates of radar freeboard across the Arctic basin. This helps us understand how sea ice thickness is changing on shorter time scales and what may be causing these changes.