Articles | Volume 10, issue 2
The Cryosphere, 10, 613–622, 2016
https://doi.org/10.5194/tc-10-613-2016
The Cryosphere, 10, 613–622, 2016
https://doi.org/10.5194/tc-10-613-2016

Research article 15 Mar 2016

Research article | 15 Mar 2016

Tilt error in cryospheric surface radiation measurements at high latitudes: a model study

Wiley Steven Bogren1,a, John Faulkner Burkhart2,3, and Arve Kylling1 Wiley Steven Bogren et al.
  • 1NILU – Norwegian Institute for Air Research, P.O. Box 100, 2027 Kjeller, Norway
  • 2Department of Geosciences, University of Oslo, Oslo, Norway
  • 3Sierra Nevada Research Institute, University of California, Merced, California, USA
  • anow at: NIBIO – Norwegian Institute of Bioeconomy Research, P.O. Box 115, 1431, Ås, Norway

Abstract. We have evaluated the magnitude and makeup of error in cryospheric radiation observations due to small sensor misalignment in in situ measurements of solar irradiance. This error is examined through simulation of diffuse and direct irradiance arriving at a detector with a cosine-response fore optic. Emphasis is placed on assessing total error over the solar shortwave spectrum from 250 to 4500 nm, as well as supporting investigation over other relevant shortwave spectral ranges. The total measurement error introduced by sensor tilt is dominated by the direct component. For a typical high-latitude albedo measurement with a solar zenith angle of 60°, a sensor tilted by 1, 3, and 5° can, respectively introduce up to 2.7, 8.1, and 13.5 % error into the measured irradiance and similar errors in the derived albedo. Depending on the daily range of solar azimuth and zenith angles, significant measurement error can persist also in integrated daily irradiance and albedo. Simulations including a cloud layer demonstrate decreasing tilt error with increasing cloud optical depth.

Download
Short summary
The magnitude and makeup of error in cryospheric radiation observations due to small sensor misalignment in in situ measurements of solar irradiance is evaluated. It is shown that relatively minor sensor misalignments give significant errors in irradiance and hence albedo measurements. The total measurement error introduced by sensor tilt is dominated by the direct component. Significant measurement error can also persist in integrated daily irradiance and albedo.