Abstract
Abstract. Geometric effects induced by the underlying terrain slope or by tilt errors of the radiation sensors lead to an erroneous measurement of snow or ice albedo. Consequently, artificial diurnal albedo variations in the order of 1–20 % are observed. The present paper proposes a general method to correct tilt errors of albedo measurements in cases where tilts of both the sensors and the slopes are not accurately measured or known. We demonstrate that atmospheric parameters for this correction model can either be taken from a nearby well-maintained and horizontally levelled measurement of global radiation or alternatively from a solar radiation model. In a next step the model is fitted to the measured data to determine tilts and directions of sensors and the underlying terrain slope. This then allows us to correct the measured albedo, the radiative balance and the energy balance. Depending on the direction of the slope and the sensors a comparison between measured and corrected albedo values reveals obvious over- or underestimations of albedo. It is also demonstrated that differences between measured and corrected albedo are generally highest for large solar zenith angles.
Highlights
The energy balance of snow and ice surfaces is strongly determined by its short-wave surface reflectivity
To determine the described parameters that depend on the composition of the atmosphere, the data of the Suntracker are compared to the model of TOA for each location, in this case the roof of ZAMG in Vienna and the Sonnblick Observatory
In both cases the ranges of ε and V are within the same intervals, shown in Tables 2 and 3
Summary
The energy balance of snow and ice surfaces is strongly determined by its short-wave surface reflectivity (albedo). Once the underlying snow/ice is isothermal, the surface energy balance of a seasonal snow cover or glacier defines the amount of energy available for melt (Warren and Wiscombe, 1980) Depending on their directions, tilted radiation sensors and terrain slopes alter albedo measurements. The underlying terrain slope may change due to differential melt or changing glacial morphology and ice dynamics, tilting the radiation sensors within periods of days or weeks and altering the direction of these tilts. This means that the geometry of the measurement site is unknown and changes with time. The use of a dual axis inclinometer to automatically determine the sensor tilts and directions is only possible if the azimuthal direction of the (tilted) radiation sensors were constant with time, which is not the case
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