Détermination de l'albédo de surface des glaciers à partir de photographies terrestres
Résumé
The use of terrestrial photography to determine snow surface albedo has been developed by J. Corripio in 2002. This method allows an easy determination of spatio-temporal variability of this parameter which is decisive in glacier mass balance. Two digital cameras have been settled for this intent on the Saint Sorlin glacier (Alps, France) in order to complement meteorological and glaciological monitoring instruments. Corripio's method has been applied on Saint Sorlin glacier and improved using a database of Bidirectional Reflectance Distribution Function (BRDF) of snow in order to take into account anisotropy of snow radiative transfer. This database has been built using BRDFs of different types of snow measured in laboratory. Spatial and temporal evolution of glacier albedo has been derived during summer 2006 using terrestrial photography and surface albedo measurement on one point of the glacier; these data show that the original method improved with reflected radiation anisotropy processing allows coherent retrieval of albedo values. Nevertheless, the original method requires an albedo reference point (measured) on glacier. A new method based on Corripio's original method has been also developed in order to avoid the necessity of an albedo reference point. This method includes several improvements, spectral processing of incident and reflected radiation, narrow-to-broadband conversion, anisotropy treatment and so allows absolute retrieval of surface albedo value without the necessity of an albedo reference point. This study described the results obtained during summer 2006 with the original method but also the principles of this new method.