Improving the Estimation of Lake Ice Thickness with High-Resolution Radar Altimetry Data

Author:

Mangilli Anna1ORCID,Duguay Claude R.23ORCID,Murfitt Justin3,Moreau Thomas1,Amraoui Samira14,Mugunthan Jaya Sree3,Thibaut Pierre1,Donlon Craig5ORCID

Affiliation:

1. CLS, 11 Rue Hermes, 31520 Ramonville, France

2. Department of Geography and Environmental Management, University of Waterloo, Waterloo, ON N2L 3G1, Canada

3. H2O Geomatics, Kitchener, ON N2L 1S7, Canada

4. Bioceanor, 06560 Nice, France

5. European Space Agency/European Space Research and Technology Centre, 2201 AZ Noordwijk, The Netherlands

Abstract

Lake ice thickness (LIT) is a sensitive indicator of climate change, identified as a thematic variable of Lakes as an Essential Climate Variable (ECV) by the Global Climate Observing System (GCOS). Here, we present a novel and efficient analytically based retracking approach for estimating LIT from high-resolution Ku-band (13.6 GHz) synthetic-aperture radar (SAR) altimetry data. The retracker method is based on the analytical modeling of the SAR radar echoes over ice-covered lakes that show a characteristic double-peak feature attributed to the reflection of the Ku-band radar waves at the snow–ice and ice–water interfaces. The method is applied to Sentinel-6 Unfocused SAR (UFSAR) and Fully Focused SAR (FFSAR) data, with their corresponding tailored waveform model, referred to as the SAR_LIT and FFSAR_LIT retracker, respectively. We found that LIT retrievals from Sentinel-6 high-resolution SAR data at different posting rates are fully consistent with the LIT estimations obtained from thermodynamic lake ice model simulations and from low-resolution mode (LRM) Sentinel-6 and Jason-3 data over two ice seasons during the tandem phase of the two satellites, demonstrating the continuity between LRM and SAR LIT retrievals. By comparing the Sentinel-6 SAR LIT estimates to optical/radar images, we found that the Sentinel-6 LIT measurements are fully consistent with the evolution of the lake surface conditions, accurately capturing the seasonal transitions of ice formation and melt. The uncertainty in the LIT estimates obtained with Sentinel-6 UFSAR data at 20 Hz is in the order of 5 cm, meeting the GCOS requirements for LIT measurements. This uncertainty is significantly smaller, by a factor of 2 to 3 times, than the uncertainty obtained with LRM data. The FFSAR processing at 140 Hz provides even better LIT estimates, with 20% smaller uncertainties. The LIT retracker analysis performed on data at the higher posting rate (140 Hz) shows increased performance in comparison to the 20 Hz data, especially during the melt transition period, due to the increased statistics. The LIT analysis has been performed over two representative lakes, Great Slave Lake and Baker Lake (Canada), demonstrating that the results are robust and hold for lake targets that differ in terms of size, bathymetry, snow/ice properties, and seasonal evolution of LIT. The SAR LIT retrackers presented are promising tools for monitoring the inter-annual variability and trends in LIT from current and future SAR altimetry missions.

Funder

European Space Agency

Publisher

MDPI AG

Reference30 articles.

1. World Meteorological Organization (2022). The 2022 GCOS ECVs Requirements (GCOS-245), World Meteorological Organization.

2. Ghiasi, Y., Duguay, C., Murfitt, J., van der Sanden, J., Thompson, A., Drouin, H., and Prévost, C. (2020). Application of GNSS interferometric reflectometry for the estimation of lake ice thickness. Remote Sens., 12.

3. The fate of lake ice in the North American Arctic;Brown;Cryosphere Discuss.,2011

4. 50 years of lake ice research from active microwave remote sensing: Progress and prospects;Murfitt;Remote Sens. Environ.,2021

5. Sensitivity of AMSR-E brightness temperatures to the seasonal evolution of lake ice thickness;Kang;IEEE Geosci. Remote Sens. Lett.,2010

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