Retrieval of Snow Grain Size over the Tibetan Plateau: Preliminary Cross-Validation Between Optical and Satellite Altimetry Data

Snow grain size is important in albedo calculation, mass balance, and climate research. Critically, in situ measurements of snow grain size on the Tibetan Plateau remain scarce. As a broad, continuous, and multiscale measurement method, remote sensing has become the primary means of sourcing data for calculating snow grain size, and the Asymptotic Radiative Transfer (ART) model is the most popular retrieval model. In this research, three-band data from MODIS and point data from the ICESat/GLAS L2A campaign were adopted to retrieve snow grain size based on the ART model. Snow grain size data from 2003 to 2024 were obtained using the Snow Grain Size and Pollution (SGSP) algorithm, and point snow grain size data from September 2003 to November 2003 were acquired using a 1-band algorithm. Cross-validation showed a stronger correlation between snow grain sizes retrieved using different methods in stable snow-covered areas. The correlation coefficients in the three areas are around 0.8. For other areas, especially those affected by seasonal snows, the snow grain sizes that retried by two methods have a lower correlation. Affected by global warming and the Karakoram anomaly, the trends in snow grain size in glaciers near the Karakoram ranges differ from those in other regions. Point-to-point cross-validation showed consistency between the MODIS and ICESat/GLAS retrieval results, offering a new way of estimating snow grain size.