Abstract
ICESat-2 altimeter data could be used to estimate sea ice freeboard and thickness values with a higher measuring accuracy than that achievable with data provided by previous altimeter satellites. This study developed an improved algorithm considering variable lead proportions based on the lowest point method to derive the sea surface height for the retrieval of Antarctic sea ice freeboard and thickness values from ICESat-2 ATL-07 data. We first collocated ICESat-2 tracks to corresponding Sentinel-1 SAR images and calculated lead (seawater) proportions along each track to estimate the sea surface height in the Antarctic Ocean. Then, the Antarctic sea ice freeboard and thickness were estimated based on a local sea surface height reference and a static equilibrium equation. Finally, we assessed the accuracy of our improved algorithm and ICESat-2 data product in the retrieval of the Antarctic sea ice thickness by comparing the calculated values to ship-based observational sea ice thickness values acquired during the 35th Chinese Antarctic Research Expedition (CHINARE-35). The results indicate that the Antarctic sea ice freeboard estimated with the improved lowest point method was slightly larger than that estimated with the ICESat-2 data product algorithm. The root mean squared error (RMSE) of the improved lowest point method was 35 cm with the CHINARE-35 measured sea ice thickness, which was smaller than that determined with the ICESat-2 data product algorithm (65 cm). Our improved algorithm could provide more accurate data on the Antarctic sea ice freeboard and thickness, thus supporting Antarctic sea ice monitoring and the evaluation of its change under global effects.
Highlights
Antarctic sea ice plays a significant role in the Earth’s system, affecting changes in the global climate and environment [1,2]
These results demonstrated that SAR images with a short time interval could reflect the overall consistent sea ice conditions of the corresponding ICESat-2 data
Since the SAR images obtained in our study could be inaccurate for distinguishing thin sea ice from seawater, our algorithm may overestimate the lead proportions in the lowest point method, resulting in overestimated sea surface height values and underestimated sea ice freeboard and thickness values according to Equation (1) [33]
Summary
Antarctic sea ice plays a significant role in the Earth’s system, affecting changes in the global climate and environment [1,2]. The sea ice freeboard and thickness are important parameters reflecting the exchange of mass and energy between the atmosphere and ocean [3,4]. Satellite altimetry has been demonstrated to constitute an effective method of retrieving the sea ice freeboard and thickness at the basin scale [5,6]. Through the application of satellite altimeter data derived from the ICESat and CryoSat-2 [7,8,9,10], researchers have obtained information on Arctic and Antarctic sea ice thickness levels and explored the response of the sea ice thickness to climate change [11,12]. The new-generation altimeter satellite of the ICESat-2 (Ice, Cloud, and Land Elevation Satellite-2) provides a new direction for follow-up research.
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