A New GrainSize Lookup Table for the Airborne Snow Observatory

The Airborne Snow Observatory (ASO) is a coupled lidar and imaging spectrometer system developed by NASA-JPL to more accurately quantify important snowpack properties. Along with snow depth and water equivalency, ASO has the ability to drastically improve measurements of snow albedo, a major factor regulating the absorption of solar radiation and consequently snowmelt. Snow grain size is one of the primary parameters controlling the broadband albedo of a snowpack. Imaging spectrometry has provided the ability to examine snow grain size over basin-wide scales. Nolin and Dozier (2000) developed a method using imaging spectrometer data to estimate the optical grain size of a snow surface by relating the reflectance centered around an ice absorption feature at 1030 nm to optical grain size. Due to the operational demands of product delivery (24-hour turnaround time), the Nolin-Dozier approach to grain size retrievals has not yet been implemented in the CASI processing pipeline. Additionally, the CASI imaging spectrometer only covers a portion of the grain size absorption feature, requiring an updated relationship between the ice absorption feature and the grain size. Here, we created a look up table for the CASI spectral range and resolution using two methods, and compare grain size retrievals to current operational methodology. (KEYWORDS: snow hydrology, snow melt, snow energy balance, optical grain size, remote sensing)