Retrievals of Precipitable Water Vapor and Aerosol Optical Depth from direct sun measurements with EKO MS711 and MS712 Spectroradiometers

Based on the strict radiative transfer algorithm, a new method is developed to derive the Precipitable Water Vapor (PWV) and Aerosol optical depth (AOD) from the ground-based measurements of direct sun irradiance. The attenuated direct irradiance from 300 nm to 1700 nm with FWHM of 6.5 nm are measured by a pair of grating spectroradiometers MS711 and MS712, located at the Institute of Atmospheric Physics, Chinese Academy of Sciences (39.98° N, 116.38° E), from June 2020 to March 2021. Compared to that of regular sun photometers such as CIMEL and POM, a strong water vapor absorption band near 1370 nm is introduced to derive PWV for the relatively dry atmosphere. The PWV and AOD inversion results obtained by EKO are compared with the synchronous data of CIMEL, and the two are highly consistent. The correlation coefficient, mean bias and standard deviation of PWVEKO and PWVCIMEL are 0.999, -0.027 cm (-3.57 %) and 0.054 cm (3.93 %) respectively, and the relative deviations of the differences between the two are slightly larger for drier air (PWV<5 mm) and lower solar elevation angle. The correlation coefficients of AODEKO and AODCIMEL at 380, 440, 500, 675, 870, 1020 nm are greater than 0.99, and the relative deviations are between -13.59 % and 9.37 %.