Study on calibration method of sky radiometer and aerosol optical properties in Xi'an region

On the base of Langley method, a more reliable instrument calibration coefficient was obtained after the expected average and fitting average method were used, and the spatiotemporal characteristics of aerosol optical depth(AOD) and Ångström wavelength exponent were analyzed using observations of sky radiometer at Xi'an University of Technology from 2015 to 2018. Results revealed that: (1) Only the Langley method is used to calibrate the instrument. The error is large. After the introduction of the expected average method and the fitted average method, the instrument calibration value obtained is more reasonable, effectively solving the problem of large fluctuations in the legal value of the Langley legal calibration value; (2) the diurnal variation of aerosol optical depth has 5 types: flat type, ascending type, descending type, convex type, and concave type, respectively. The frequency of flat type is lowest, 3.55%, and concave type is highest, 34.25%; (3) the seasonal variation of aerosol optical depth at 550 nm wavelength showed spring and summer are lower, and autumn and winter are higher, with the average values: 0.60±0.36, 0.59±0.33, 0.62±0.40, 0.68±0.36, respectively. Moreover, Ångström wavelength exponent have a highest value in summer (1.06±0.33), and have a lowest value in spring (0.81±0.32).espectively. Moreover, Ångström wavelength exponent have a highest value in summer (1.06±0.33), and have a lowest value in spring (0.81±0.32).al variation of aerosol optical depth at 550 nm wavelength showed spring and summer are lower, and autumn and winter are higher, with the average values: 0.60±0.36, 0.59±0.33, 0.62±0.40, 0.68±0.36, respectively. Moreover, Ångström wavelength exponent have a highest value in summer (1.06±0.33), and have a lowest value in spring (0.81±0.32).