Characterizing laser radar snow reflection for the wavelengths 0.9 and 1.5 μm

This article describes measurements of snow reflection using laser radar. There seem to be few publications on this subject. This article reports measurements on reflection from different kinds of snow, including the angular reflection properties. Reflectance information obtained from two commercial scanning laser radars working at the wavelengths 0.9 and 1.5 µm is shown and discussed. Data are mainly be presented at the eye-safe wavelength 1.5 µm, but some measurements were also performed at 0.9 µm. We have measured snow reflection during a part of a winter season that gave us opportunities to investigate different types of snow and different meteorological conditions. The reflection values tend to decrease during the first couple of hours after a snowfall. The structure of the snow seems to be more important for the reflection than its age. In general the reflection at 1.5 µm is rather low; the reflectivity can vary between 0.5% and 10% for oblique incidence, depending on the structure of the snow, which in turn depends on its age, the air temperature, the humidity, etc. The reflectivity at the 0.9-µm wavelength is much higher: more than 50% for fresh snow. Images of snow-covered scenes are shown together with reflection data, including bidirectional reflectance distribution functions.