Abstract's details
Waiting for CRISTAL: evaluation of a snow depth product using Ka/Ku dual-frequency altimetry. Impacts on sea ice thickness estimation
CoAuthors
Event: 2022 Ocean Surface Topography Science Team Meeting
Session: Science IV: Altimetry for Cryosphere and Hydrology
Presentation type: Type Oral
Contribution: PDF file
Abstract:
Snow on the sea ice is an element that is still very poorly known and poorly observed. However, it plays an important role in climate change due to its albedo, and in the dynamics of the sea ice due to its insulating properties. This lack of knowledge is also one of the main factors limiting the measurement of sea ice thickness by altimetry.
A method to measure this snow depth was first proposed in [Guerreiro et al. 2016]. It is based on the comparison of two altimetry frequencies, the Ku frequency on board CryoSat-2, and the Ka frequency from Saral. Indeed, these frequencies have different snow penetration properties. This observation was one of the reasons for adding a second frequency to the Copernicus CRISTAL polar altimeter project.
Following this study, an Altimetric Snow Depth (ASD) product was developed in the Arctic as part of the ESA CryoSeaNice project. In the framework of the ESA CS+AO project, an equivalent snow depth product has also been computed in Antarctica.
The first objective of this presentation is to show the relevance of this approach and the contribution of these data to the measurement of sea ice thickness.
To do so, the ASD data are compared with different datasets from different sources: space data obtained with the AMSR-2 passive radiometer, model data and in-situ data.
The AMSR-2 data are currently the only other snow depth observations that provide monthly estimates of snow depth on the polar ice pack. The first version (Meier et al, 2018) available on the NSIDC website (https://nsidc.org/data/AU_SI12/versions/1) has the disadvantage that it only covers first-year ice. The Bremen AMSR-2 v1.0 product (Rostosky et al, 2018) is calculated on multi-year ice but only for the months of March and April (during the Operation Ice Bridge campaigns). Only the NSIDC product covers the Southern Hemisphere, but this is complete because in this region the pack ice is mostly first-year ice.
Furthermore, in the Arctic, we will compare the ASD data with the Warren99 modified climatology (Arctic only), the PIOMAS model, the NESOSIM model (Arctic only) and the CMEMS LIM-3 sea ice model. The performance of these snow depth solutions will be evaluated by comparison with: 1) several Operation Ice Bridge (OIB) airborne campaigns, 2) the 2017 ESA-CRYOsat Validation Experiment (CryoVex) campaign that includes the KAREN Ka-band airborne altimeter, and 3) Beaufort Gyre Exploration Project (BGEP) data. Finally, the impact of different snow depth solutions on sea ice thickness estimates will be presented.
Finally, the important potential of these results for the monitoring of sea ice evolution by the future Copernicus CRISTAL mission will be discussed.
Acknowledgements: This work was supported by the ESA CryoSeaNICE project, the ESA CryoSat+ Antarctica project and the CNES TOSCA CASSIS project.
A method to measure this snow depth was first proposed in [Guerreiro et al. 2016]. It is based on the comparison of two altimetry frequencies, the Ku frequency on board CryoSat-2, and the Ka frequency from Saral. Indeed, these frequencies have different snow penetration properties. This observation was one of the reasons for adding a second frequency to the Copernicus CRISTAL polar altimeter project.
Following this study, an Altimetric Snow Depth (ASD) product was developed in the Arctic as part of the ESA CryoSeaNice project. In the framework of the ESA CS+AO project, an equivalent snow depth product has also been computed in Antarctica.
The first objective of this presentation is to show the relevance of this approach and the contribution of these data to the measurement of sea ice thickness.
To do so, the ASD data are compared with different datasets from different sources: space data obtained with the AMSR-2 passive radiometer, model data and in-situ data.
The AMSR-2 data are currently the only other snow depth observations that provide monthly estimates of snow depth on the polar ice pack. The first version (Meier et al, 2018) available on the NSIDC website (https://nsidc.org/data/AU_SI12/versions/1) has the disadvantage that it only covers first-year ice. The Bremen AMSR-2 v1.0 product (Rostosky et al, 2018) is calculated on multi-year ice but only for the months of March and April (during the Operation Ice Bridge campaigns). Only the NSIDC product covers the Southern Hemisphere, but this is complete because in this region the pack ice is mostly first-year ice.
Furthermore, in the Arctic, we will compare the ASD data with the Warren99 modified climatology (Arctic only), the PIOMAS model, the NESOSIM model (Arctic only) and the CMEMS LIM-3 sea ice model. The performance of these snow depth solutions will be evaluated by comparison with: 1) several Operation Ice Bridge (OIB) airborne campaigns, 2) the 2017 ESA-CRYOsat Validation Experiment (CryoVex) campaign that includes the KAREN Ka-band airborne altimeter, and 3) Beaufort Gyre Exploration Project (BGEP) data. Finally, the impact of different snow depth solutions on sea ice thickness estimates will be presented.
Finally, the important potential of these results for the monitoring of sea ice evolution by the future Copernicus CRISTAL mission will be discussed.
Acknowledgements: This work was supported by the ESA CryoSeaNICE project, the ESA CryoSat+ Antarctica project and the CNES TOSCA CASSIS project.