Light reflection and transmission by a temperate snow cover

Abstract

An understanding of the reflection and transmission of light by snow is important for snow thermodynamics, hydrology, ecology and remote sensing. Snow has an intricate microstructure replete with ice/air interfaces that scatter light. Spectral observations of light reflection and transmission, from 400 to 1000 nm, were made in temperate snowpacks, under cold and under melting conditions. The optical observations were made using a dual-detector spectroradiometer. One detector was placed above the snow surface to monitor the incident and reflected solar irradiance, and the second detector was placed at the base of snow cover to measure downwelling irradiance. The optical measurements were supplemented by a physical characterization of the snow, including depth, density and an estimate of grain size. In general, transmitted light levels were low and showed a strong spectral dependence, with maximum values between 450 and 550 nm. For example, a 10 cm thick snow layer reduced visible transmission (500 nm) to about 5 % of the incident irradiance, and infrared transmission (800 nm) to less than 1 %. Extinction coefficients were in the range 3-30 m-1, and tended to decrease slightly as the snow aged and increase as snow density increased.