The InfraSnow device measures the specific surface area (SSA) of snow with an optical sensor. The method consists of diffuse near-infrared reflectance measurements using a compact integrating sphere setup to derive SSA. Diffuse reflectance is measured at a NIR wavelength, where impurities have only a weak influence on the reflectance of snow. 

For a sufficiently thick snow block, there exists a unique correlation between diffuse hemispherical reflectance and SSA according to multiple-scattering radiative transfer theory.

The correlation between snow SSA and reflectance is calculated by applying Monte-Carlo ray tracing to a 3D implementation of the measurement geometry. Snow density is required as second input parameter to the SSA analysis and can be measured e.g. by means of the SLF snow sensor.