The Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) mission has; collected global surface elevation measurements for over three years.; ICESat-2 carries the Advanced Topographic Laser Altimeter (ATLAS); instrument, which emits laser light at 532 nm, and ice and snow absorb; weakly at this wavelength. Previous modeling studies found that melting; snow could induce significant bias to altimetry signals, but there is no; formal assessment on ICESat-2 acquisitions during the Northern; Hemisphere melting season. In this work, we performed two case studies; over the Greenland Ice Sheet to quantify volumetric scattering in; ICESat-2 signals over snow. Elevation data from ICESat-2 was compared to; Airborne Topographic Mapper (ATM) data to quantify bias. We used snow; optical grain sizes derived from ATM and the Next Generation Airborne; Visible/Infrared Imaging Spectrometer (AVIRIS-NG) to attribute altimetry; bias to snowpack properties. For the first case study, the mean optical; grain sizes were 340±65 µm (AVIRIS-NG) and 670±420 µm (ATM), which; corresponded with a mean altimetry bias of 4.81±1.76 cm in ATM. We; observed larger grain sizes for the second case study, with a mean grain; size of 910±381 µm and biases of 6.42±1.77 cm (ICESat-2) and 9.82±0.97; cm (ATM). Although these altimetry biases are within the accuracy; requirements of the ICESat-2 mission, we cannot rule out more; significant errors over coarse-grained snow, particularly during the; Northern Hemisphere melting season.
