Towards combined spectrodirectional reflectance measurements and detailed snow microstructure studies

The knowledge of spectrodirectional reflectance properties is significant for the characterization of natural surfaces. Furthermore it is a prerequisite to fully understand surface property processes, which are responsible for anisotropic reflectance characteristics. In the case of snow, the derivation of the sources of reflectance patterns allows conclusions on properties, such as snow grain size, impurity concentration, liquid water content, etc., which affect snow stratigraphy, snow pack stability, atmosphere interaction processes and the radiation budget.
First directional reflectance studies of snow have already been performed three decades ago. With the development of accurate and flexible systems such as ASG (Automated Spectro-Goniometer), snow reflectance characteristics were determined in a more comprehensive way (Painter et al. 2004). In particular a surplus of information has resulted through the combination of spectral data with additional relevant snow data, such as grain size, specific surface area or optically equivalent diameter of snow. However, only few investigations have been done so far following this combined approach (Painter et al. 2007, Matzl et al. 2006). Consequently, explicit estimations of the abovementioned relationship are still critical (Odermatt et al. 2005).
In this study we present an innovative measurement setup and a novel approach for combined exploration of spectrodirectional reflectance properties of snow with an exhaustive study of snow microstructure. Spectrodirectional reflectances and microstructure data of various snow types are collected during a field campaign in Davos (Switzerland, 1560 m a.s.l.) in winter 2007/08.
Bidirectional reflectance factors (BRF) are then retrieved from spectrodirectional field measurements using the established dual view goniometer system FIGOS (Schopfer et al. 2007, Sandmeier et al. 1995), implementing the approach described by Martonchik (Martonchik 1994). Simultaneously, a micro computer tomographer (μ-CT) from the Swiss Federal Institute for Snow and Avalanche Research (SLF) is used to examine the respective snow microstructure. Results from the μ-CT offer the possibility of 3D-reconstruction of the respective snow stratigraphy.
Preliminary results show the importance of combining snow BRF and μ-CT data and the potential for accurate estimation of fundamental snow properties and snow pack characteristics.