MEASUREMENTS OF THE SPECTRAL AEROSOL OPTICAL DEPTH USING A SUN PHOTOMETER

A sun photometer fitted with 9 narrowband interference filters from 36 8 nm to 1024 nm was used to determine the aerosol optical depth at 8 m easuring stations in Europe. Of the 9 filters, 3 were not included in the standard equipment of the sun photometer. Given the temporal insta bilities of the calibration Factors of these 3 filters, meaningful res ults for the aerosol optical depth can be achieved only if calibration and measurements follow each other closely. Calibration was performed using the Langley plot method. For wavelengths < 500 nm, the measured aerosol optical depths were compared with the results of a high resol ution spectrometer. Broadband aerosol optical depths, centred at 427 n m, were determined with an actinometer and were also used for comparis on. Generally, there was good agreement of the results. To characteriz e the aerosol optical depths, the Angstrom parameters alpha and beta w ere used. The individual measuring stations showed a clustered distrib ution of a and beta values.