A New Index for Snow/Ice/Ice‐Snow Discrimination Based on BRDF Characteristic Observation Data

Abstract The field observation data of ice‐snow (the ice covered by snow) is scarce, causing a poor understanding of its characteristics and some uncertainty in ice process simulation. Using a multi‐angle observation instrument, we conducted a field investigation and measured the snow/ice/ice‐snow Bidirectional Reflectance Distribution Function. Both snow and ice have the typical feature of forwarding scattering, and the scattering intensity is governed by their properties (i.g., snow grain size, liquid water content, and transparency). The characteristics of ice‐snow are similar to snow when a small amount of fresh snow is deposited on the ice surface, but will change significantly when the surface snow is metamorphic (melt or refreezing). This change can affect the monitoring accuracy of snow and ice using remote sensing data. In this study, a Normalized Difference Ice‐Snow Index (NDISI) was developed using two bands (i.e., 1,080–1,120 nm and 1,760–1,800 nm). We applied spectra from different regions to verify the ability of NDISI and its application for distinguishing ice‐snow. This work should be helpful for the fine classification between snow, ice, and ice‐snow. It can support a more accurate simulation of ice phenology.