Conference Agenda

Snow water equivalent (SWE) is a critical parameter of seasonal snow cover for meteorology and hydrology in northern China and other high-latitude or high-altitude regions with abundant snow resources. However, our ability to accurately measure and monitor SWE change from satellite remote sensing remains a challenge. Traditional passive microwave remote sensing provides daily and large-scale SWE observations, but is limited by its coarse spatial resolution, which is typically tens of kilometers in scale. Repeat-pass Interferometric Synthetic Aperture Radar (InSAR) offers a promising approach to obtaining SWE change at high spatial resolution and accuracy. For this technique, low-frequency (e.g., L-band) radar signals and shorter revisit times are essential for minimizing temporal decorrelation in frequent snowfall regions. This technique has been available until recently due to its limited observations with the optimal radar frequencies and temporal repeat intervals.

This study presents the first demonstration of spaceborne repeat-pass L-band InSAR observations from the Chinese Lutan-1 mission for retrieving SWE changes at Altay, Xinjiang Province, during the winter of 2023–2024. Consecutive 4-day and 8-day repeat-pass interferometric pairs were processed to phase changes, and then related to SWE variations. An InSAR processing chain was developed, including atmospheric phase delay correction (both ionospheric and tropospheric effects), orbital error removal, filtering parameter optimization, and phase calibration. These procedures establish a comprehensive workflow for time-series InSAR SWE retrieval using L-band Lutan-1 data.

The retrieved SWE change shows a good agreement with in-situ SWE observations during the dry snow period (January 12 to February 9, 2024), yielding a root mean square error (RMSE) of 9 mm and a correlation coefficient (R) of 0.48 for the 4-day temporal baselines (p-value << 0.05). However, the accuracy decreases significantly for the 8-day baselines (February 17 to March 28, 2024), mainly due to temporal decorrelation associated with snowfall and snowmelt events. A heavy snowfall observed from February 9 to 17, 2024, induced severe decorrelation, leading to phase unwrapping errors and preventing the retrieval of SWE. This finding emphasizes the necessity of using shorter temporal baselines, such as 4 days, in regions characterized by rapid snow accumulation and ablation processes.

Overall, this study demonstrates the capability of spaceborne repeat-pass L-band InSAR with short revisit intervals to effectively retrieve SWE change under appropriate snow cover conditions. The results also highlight the potential and challenges of operational SWE monitoring from existing and upcoming L-band SAR missions, such as JAXA’s ALOS-4, NASA’s NISAR, and ESA’s ROSE-L, which feature short repeat cycles, wide swath coverage, and high spatial resolution. Future work will focus on improving SWE retrieval accuracy by investigating the impacts of meteorological and environmental factors on InSAR phase.