A Dual-Threshold Algorithm for Ice-Covered Lake Water Level Retrieval Using Sentinel-3 SAR Altimetry Waveforms.

Area of Science:

• Earth Observation
• Hydrology
• Remote Sensing

Background:

• Satellite altimetry, particularly Sentinel-3A's SRAL, offers precise inland water level measurements.
• Ice cover on lakes at middle/high latitudes complicates accurate water level estimation due to altimeter footprint non-uniformity.
• Standard SAR waveform retracking algorithms struggle with ice-covered lakes, leading to abnormal readings.

Purpose of the Study:

• To develop and validate a novel dual-threshold algorithm for precise water level measurements of ice-covered lakes.
• To improve surface type classification for inland water bodies using backscattering coefficients and brightness temperature.
• To enhance the accuracy of Sentinel-3A SRAL data for winter lake monitoring.

Main Methods:

• A modified method was developed to classify lake surface types by analyzing backscattering coefficients and brightness temperature, validated with ground observations.
• A dual-threshold algorithm was introduced to identify multiple peaks in altimeter waveforms without requiring elevation correction, overcoming limitations of previous methods.
• Water level data from nine North American ice-covered lakes (2016-2019) were retrieved and compared using the dual-threshold algorithm and the SAMOSA-3 algorithm against in situ data.

Main Results:

• The dual-threshold algorithm demonstrated significantly higher precision compared to the SAMOSA-3 algorithm for ice-covered lakes.
• Root mean square errors (RMSE) for the dual-threshold algorithm were substantially lower across studied lakes, with reductions up to 87% compared to SAMOSA-3.
• The new algorithm achieved RMSEs as low as 5.01 cm for Lake Erie, showcasing its effectiveness.

Conclusions:

• The dual-threshold algorithm accurately estimates water levels in ice-covered lakes during winter conditions.
• This method provides a promising approach for long-term, continuous, and high-precision water level monitoring of lakes in middle and high latitudes.
• The findings support enhanced understanding and management of freshwater resources in seasonally frozen regions.