Snow grain size is a primary control on albedo and snowmelt.Compact imaging spectrometers and lidars mounted on uncrewed aerial systems (UAS) now offer flexible, high-resolution observations, but their relative performance for optical snow property retrievals has not been assessed.We compared grain size retrievals from two UAS-mounted imaging spectrometers (925-1700 nm, 900-2500 nm) and two lidars (905 nm, 1550 nm) against field spectroscopy over snow covered terrain (Mores Creek Summit, ID in March 2024).The compact imagers and 905 nm lidar retrieved grain sizes within ~10% of field reference values, with little sensitivity to flight altitude (40-120 m).The 1550 nm lidar showed large negative bias (>90% error) due to strong shortwave-infrared absorption by ice.Results demonstrate that affordable, lightweight UAS sensors can accurately map grain size, with 905 nm lidar offering flexibility, notably in conditions unsuitable for passive optical measurements.
Ackroyd et al. (Thu,) studied this question.