Preprints
https://doi.org/10.5194/egusphere-2024-179
https://doi.org/10.5194/egusphere-2024-179
06 Mar 2024
 | 06 Mar 2024
Status: this preprint is open for discussion.

Assessing the sea ice microwave emissivity up to submillimeter waves from airborne and satellite observations

Nils Risse, Mario Mech, Catherine Prigent, Gunnar Spreen, and Susanne Crewell

Abstract. Upcoming submillimeter wave satellite missions require an improved understanding of the sea ice emissivity to separate atmospheric and surface microwave signals under dry polar conditions. This work investigates hectometer-scale airborne sea ice emissivity observations between 89 and 340 GHz combined with high-resolution visual imagery from two Arctic airborne field campaigns in summer 2017 and spring 2019 northwest of Svalbard, Norway. We identify four distinct sea ice emissivity spectra through K-Means clustering, which occur predominantly over multiyear ice, first-year ice, young ice, and nilas. Nilas features the highest, and multiyear ice features the lowest emissivity among the clusters. Each cluster exhibits similar nadir emissivity distributions from 183 to 340 GHz. To relate hectometer-scale airborne to kilometer-scale satellite footprints, we quantify the reduction of airborne emissivity variability with increasing footprint size. At 340 GHz, the emissivity interquartile range decreases by almost half from the hectometer scale to a footprint of 16 km, typical for satellite instruments. Furthermore, we collocate the airborne observations with polar-orbiting satellite observations. After resampling, the absolute relative bias between airborne and satellite emissivities at similar channels lies below 3 %. Additionally, spectral nadir emissivity variations on the satellite scale are low, with slightly decreasing emissivity from 183 to 243 GHz, which occurs for all hectometer-scale clusters except for predominantly multiyear ice. Our results will enable the development of microwave retrievals and assimilation over sea ice from current and future satellite missions such as Ice Cloud Imager (ICI) and European Polar System (EPS) Sterna.

Nils Risse, Mario Mech, Catherine Prigent, Gunnar Spreen, and Susanne Crewell

Status: open (until 25 Apr 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-179', Tim Hewison, 03 Apr 2024 reply
Nils Risse, Mario Mech, Catherine Prigent, Gunnar Spreen, and Susanne Crewell

Model code and software

nrisse/si-emis: Code related to: Assessing the sea ice microwave emissivity up to submillimeter waves from airborne and satellite observations Nils Risse https://doi.org/10.5281/zenodo.10533864

Nils Risse, Mario Mech, Catherine Prigent, Gunnar Spreen, and Susanne Crewell

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Short summary
Satellite passive microwave observations are crucial for monitoring the Arctic's sea ice and atmosphere. To do this effectively, it's important to understand how sea ice emits microwaves. Through unique Arctic sea ice observations, we've improved our understanding, identifying four distinct emission types and expanding current knowledge towards higher frequencies. These findings will enhance our ability to monitor the Arctic climate and provide valuable information for new satellite missions.