In situ effective snow grain size mapping using a compact hyperspectral imager
Christopher Donahue, S. McKenzie Skiles, Kevin Hammonds
Abstract
Abstract Effective snow grain radius ( r e ) is mapped at high resolution using near-infrared hyperspectral imaging (NIR-HSI). The NIR-HSI method can be used to quantify r e spatial variability, change in r e due to metamorphism, and visualize water percolation in the snowpack. Results are presented for three different laboratory-prepared snow samples (homogeneous, ice lens, fine grains over coarse grains), the sidewalls of which were imaged before and after melt induced by a solar lamp. The spectral reflectance in each ~3 mm pixel was inverted for r e using the scaled band area of the ice absorption feature centered at 1030 nm, producing r e maps consisting of 54 740 pixels. All snow samples exhibited grain coarsening post-melt as the result of wet snow metamorphism, which is quantified by the change in r e distributions from pre- and post-melt images. The NIR-HSI method was compared to r e retrievals from a field spectrometer and X-ray computed microtomography (micro-CT), resulting in the spectrometer having the same mean r e and micro-CT having 23.9% higher mean r e than the hyperspectral imager. As compact hyperspectral imagers become more widely available, this method may be a valuable tool for assessing r e spatial variability and snow metamorphism in field and laboratory settings.