Assessment of Ka-Ku Altimetric Snow Depth on Sea Ice during Arctic and Austral Winters

Snow depth on sea ice is a key parameter of climate change. For instance, it plays an isolating role which regulates sea ice growth and accelerates the melting. As it will be shown in this presentation, snow depth is mandatory to compute sea ice thickness (SIT). Nevertheless, there currently doesn't exist reliable snow depth products for sea ice. Nearly all SIT estimations in Arctic are computed using the Warren climatology (Warren et al, 1999) which has been constructed from in-situ data of the last century, prior to the first sensible impacts of the climate change. In addition, meteorological re-analyses have difficulties to faithfully reproduce snow falls in polar regions.
Recently, Guerreiro et al, 2016 has demonstrated the ability to retrieve the snow depth over sea ice from the difference of penetration between the CryoSat-2 Ku frequency radar, which reflects at the snow/ice interface and the Saral/AltiKa Ka frequency radar, which reflects on the top of the snow pack. Following this study, an Altimetric Snow Depth (ASD) product, covering the 2013-2019 winter periods in Arctic, is developed at the LEGOS as part of the ESA CryoSeaNice and Polar+ Snow on Sea Ice projects . The main objective of this presentation is to show and assess this dataset. In addition, in the context of the ESA Antarctica+ project, an equivalent snow depth product is also under process for the Austral sea ice. First results will be presented here.

In this presentation, the ASD data will be compared with 2 Advanced Microwave Scanning Radiometer 2 (AMSR-2) snow depth products. The first version (Meier et al, 2018) available on the NSIDC website () has the inconvenience of being only available over First Year Ice. The Bremen AMSR-2 v1.0 product (Rostosky et al, 2018) is calculated over Multi Year Ice but only for March and April (during the Operation Ice Bridge campaigns). In the southern hemisphere, only the NSIDC product is available. This data set covers the entire southern region considering all sea ice as First Year Ice around Antarctica.

We will also assess the relevancy of the ASD data compared to these 2 AMSR-2 products, the Warren W99 climatology and the PIOMAS v2.1 model reanalyze. For this purpose we will present extensive comparisons with: 1) several Operation Ice Bridge (OIB) campaigns, 2) the 2017 ESA-CRYOsat Validation EXperiment (CryoVex) campaign which includes the Ka band KAREN altimeter and 3) the Beaufort Gyre Exploration Project (BGEP) data. Finally, impact of the various dataset (ASD, PIOMAS, AMSR-2) on SIT estimations will be presented.

The results presented here will also underline the interest and relevance of the data that should be obtained during the future CRISTAL mission