Correction of broadband snow albedo measurements affected by unknown slope and sensor tilts
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 t...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-04-01
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| Series: | The Cryosphere |
| Online Access: | http://www.the-cryosphere.net/10/775/2016/tc-10-775-2016.pdf |
| Summary: | 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. |
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| ISSN: | 1994-0416 1994-0424 |