A framework for evaluating ice sheet altimetry uncertainty estimates

Abstract. For three decades, ice sheet elevation records from satellite radar altimetry have provided new insight into the state of the cryosphere and its contribution to global sea-level rise. The availability of robust, consistent and traceable uncertainties alongside ice sheet elevation data is crucial for combining measurements across missions and enabling their use in reconciling estimates of ice sheet mass balance and constraining numerical ice sheet models. At present, such uncertainties are largely absent from existing Level 2 ice sheet elevation products, and for the subset of products where uncertainties are provided, there is neither a standardised approach to uncertainty generation nor a method to evaluate their robustness. Here, we develop a novel uncertainty evaluation framework and provide a comprehensive assessment of uncertainty generation for altimetry-based ice sheet elevations. Overall, we find that calculating uncertainty as a parameterisation of topographic complexity (characterised by surface slope and roughness) and measurement quality (characterised by backscattered power and coherence) improves performance relative to solutions that use fewer co-variates. Ultimately, the framework presented here will enable the systematic characterisation of ice sheet elevation uncertainties associated with historical, current and future polar radar altimeter missions, including the Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL). Such information will aid the successful combination of altimetry measurements across missions, improve the constraint of numerical ice sheet models, and enable more certain estimates of current and future ice sheet mass balance and global sea-level rise.