Correction of albedo measurements due to unknown geometry

Abstract

The diurnal albedo variation of glaciers on clear sky days can be relatively high due to geometric effects induced by tilt errors. In the present paper, these tilt errors of albedo measurements are corrected in cases where tilts of both, the sensors and the slopes are not accurately measured. For this method of correction, a nearby reference measurement with a horizontally levelled sensor is needed to determine atmospheric parameters. Based on that a model is developed that is fitted to the measured data to determine tilts and directions of sensors and slopes, which vary daily due to changing atmospheric conditions and snow cover. Once these parameters are determined, the albedo, the radiative balance and the energy balance can be corrected. The differences between measured and corrected values show an obvious under- or overestimation of albedo, depending on the direction of the slope. It is also demonstrated that the difference between measured and corrected albedo is highest for high solar zenith angles.