Comparison and Uncertainty of Aerosol Optical Depth Estimates Derived from Spectral and Broadband Measurements

Abstract

Abstract An experimental comparison of spectral aerosol optical depth τa,λ derived from measurements by two spectral radiometers [a LI-COR, Inc., LI-1800 spectroradiometer and a Centre Suisse d'Electronique et de Microtechnique (CSEM) SPM2000 sun photometer] and a broadband field pyrheliometer has been made. The study was limited to three wavelengths (368, 500, and 778 nm), using operational calibration and optical depth calculation procedures. For measurements taken on 32 days spread over 1 yr, the rms difference in τa,λ derived from the two spectral radiometers was less than 0.01 at 500 and 778 nm. For wavelengths shorter than 500 nm and longer than 950 nm, the performance of the LI-1800 in its current configuration did not permit accurate determinations of τa,λ. Estimates of spectral aerosol optical depth from broadband pyrheliometer measurements using two models of the Angstrom turbidity coefficient were examined. For the broadband method that was closest to the sun photometer results, the mean (rms) ...