Improving Langley calibrations by reducing diurnal variations of aerosol Ångström parameters

A. Kreuter, S. Wuttke, M. Blumthaler
2013 Atmospheric Measurement Techniques  
<p><strong>Abstract.</strong> Errors in the sun photometer calibration constant lead to artificial diurnal variations, symmetric around solar noon, of the retrieved aerosol optical depth (AOD) and the associated Ångström exponent &amp;alpha; and its curvature &amp;gamma;. We show in simulations that within the uncertainty of state-of-the-art Langley calibrations, these diurnal variations of &amp;alpha; and &amp;gamma; can be significant in low AOD conditions, while those of AOD are negligible.
more » ... OD are negligible. We implement a weighted Monte Carlo method of finding an improved calibration constant by minimizing the diurnal variations in &amp;alpha; and &amp;gamma; and apply the method to sun photometer data of a clear day in Innsbruck, Austria. The results show that our method can be used to improve the calibrations in two of the four wavelength channels by up to a factor of 3.6.</p>
doi:10.5194/amt-6-99-2013 fatcat:ngpaako36fhenjl2whufb5b3iq