Direct spectral measurements with a Brewer spectroradiometer: absolute calibration and aerosol optical depth retrieval
S. Kazadzis, A. F. Bais, M. Blumthaler, N. Kouremeti, E. Gerasopoulos, B. Schallhart, A. Cede, K. Garane
[περίληψη] We present three different methods for the absolute calibration of direct spectral irradiances measured with a Brewer spectroradiometer, which are shown to agree to within ±2%. Direct irradiance spectra derived by a Brewer and a Bentham spectroradiometer agree within 4±3 %. Good agreement was found also in comparing the aerosol optical depth and Angstrom exponent retrieved by the two instruments and a multi-filter rotational shadowband radiometer. The spectral aerosol optical depth (300-365 nm) derived from six years of direct irradiance measurements at Thessaloniki shows a distinct seasonal variation, averaging to ~0.3 at 340 nm in winter and ~0.7 in summer.
[keywords] direct irradiance, aerosol optical depth, spectroradiometer
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