Inferring Lake Ice Status Using ICESat-2 Photon Data

Lake ice phenology is a temporally integrated response to the seasonal cycles of meteorology, and its study results in obtaining the periods of ice growth and melt process. The recently launched spaceborne laser altimetry satellite called Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) hosts a single sensor titled Advanced Topographic Laser Altimeter System (ATLAS) is equipped with photon-counting technology. In this research, we have investigated the applicability of a data product, namely ATL03 from the ICESat-2 to infer the state of alpine lake ice. Three alpine lakes situated in the Himalayan region, which are above 4200 m ASL and exhibit annual freeze–thaw cycles were studied to understand the interaction of ICESat-2 photons with the lake surface during various phases of the ice growth and decay process. Elevation profiles were generated from the photon beams of ICESat-2 over these lakes during various stages of its surface cover like meltwater conditions, ice thickening stage, frozen state, and ice breakup period. These elevation profiles besides giving the lake surface height, the pattern of photons in the profile has contributed to envisage the status of the ice surface over the lake. Photons from ICESat-2 during meltwater conditions can penetrate the subsurface, and this feature helps in distinguishing meltwater from frozen ice cover over the lake surface. Further, it was observed that during the stage of ice thickening stage, a certain number of photons have penetrated up to a depth of ~ 35 m but the number of photons that penetrated is significantly less when compared with that of penetrating photons during meltwater conditions. Similarly, during the ice breakup periods, the photon data of ICESat-2 are proven to identify the exposed water columns in the ice sheet. The results obtained from this study prove that the photon data from ICESat-2 over alpine lakes can result in advance the understanding of the lake ice phenology.