Retrievals of precipitable water vapor and aerosol optical depth from direct sun measurements with EKO MS711 and MS712 spectroradiometers

• Published in: Atmospheric measurement techniques 2023-03, Vol.16 (6), p.1539-1549
• Main Authors: Qiao, Congcong, Liu, Song, Huo, Juan, Mu, Xihan, Wang, Ping, Jia, Shengjie, Fan, Xuehua, Duan, Minzheng
• Format: Article
• Language: English
• Subjects: Absorption bands; Absorption spectra; Accuracy; Aerosol optical depth; Aerosols; Algorithms; Atmosphere; Atmospheric physics; Circumsolar radiation; Coefficients; Comparative analysis; Continuous spectra; Correlation coefficient; Correlation coefficients; Elevation angle; Global positioning systems; GPS; Instruments; Inversion; Irradiance; Irradiance measurements; Optical analysis; Optical thickness; Photometers; Physical instruments; Physics; Precipitable water; Radiation; Radiative transfer; Spectroradiometers; Standard deviation; Sun; Water depth; Water vapor; Water vapour
• ISSN: 1867-8548; 1867-1381; 1867-8548
• DOI: 10.5194/amt-16-1539-2023

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 direct sun irradiance measurements. The attenuated direct irradiance from 300 to 1700 nm was measured by a pair of grating spectroradiometers, MS711 and MS712 produced by EKO Instruments, located at the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing (39.98∘ N, 116.38∘ E), from June 2020 to March 2021. Compared with regular sun photometers such as CE-318 and POM, EKO instruments can measure a wider range of continuous spectra, but their field of view (FOV) is also relatively large. In the PWV inversion of this work, a strong water vapor absorption band around 1370 nm is introduced to retrieve PWV in a relatively dry atmosphere. The circumsolar radiation (CSR) of the EKO instruments is corrected to reduce the influence of scattering from a relatively larger FOV on the AOD inversion. The PWV and AOD inversion results obtained by MS711 and MS712 are compared with the synchronous data of the CE-318 sun photometer. The two retrieval results are highly consistent. The correlation coefficient, mean bias, and standard deviation of PWVEKO and PWVCIMEL are 0.999, −0.027 cm (−2.42 %), and 0.054 cm (3.93 %), respectively, and the relative deviations of the differences between the two are slightly larger for drier air (PWV