Results from the Fourth WMO Filter Radiometer Comparison for aerosol optical depth measurements

Abstract

Abstract. This study presents the results of the Fourth Filter Radiometer Comparison that was held in Davos, Switzerland, between 28 September and 16 October 2015. Thirty filter radiometers and spectroradiometers from 12 countries participated including reference instruments from global aerosol networks. The absolute differences of all instruments compared to the reference have been based on the World Meteorological Organization (WMO) criterion defined as follows: 95% of the measured data has to be within 0.005 ± 0.001∕m (where m is the air mass). At least 24 out of 29 instruments achieved this goal at both 500 and 865 nm, while 12 out of 17 and 13 out of 21 achieved this at 368 and 412 nm, respectively. While searching for sources of differences among different instruments, it was found that all individual differences linked to Rayleigh, NO2, ozone, water vapor calculations and related optical depths and air mass calculations were smaller than 0.01 in aerosol optical depth (AOD) at 500 and 865 nm. Different cloud-detecting algorithms used have been compared. Ångström exponent calculations showed relatively large differences among different instruments, partly because of the high calculation uncertainty of this parameter in low AOD conditions. The overall low deviations of these AOD results and the high accuracy of reference aerosol network instruments demonstrated a promising framework to achieve homogeneity, compatibility and harmonization among the different spectral AOD networks in the near future.

Ozone—climate interactions and effects on solar ultraviolet radiation

“…129 Finally, in an intercomparison campaign held in Davos, Switzerland in autumn 2015, most of the instruments measuring the AOD at visible wavelengths (500 and 865 nm) agreed to within 0.005 units of AOD, while two thirds of the instruments reporting AOD in the UV-A (368 and 412 nm) achieved that goal. 130 Such improvements in instrumentation and methods will facilitate clearer separation of the effects of ozone and aerosols on UV-B radiation.…”

Single Scattering Albedo’s Spectral Dependence Effect on UV Irradiance

“…The most commonly used variable for monitoring aerosols in the atmosphere is the aerosol optical depth (AOD), which is retrieved by ground-based [11,12] and satellite instruments [13]. AOD varies a great deal at different parts of the spectrum and the variable of the Angström exponent is used to quantify the extinction's spectral behavior, which influences incident irradiance.…”

Improving the mean and uncertainty of ultraviolet multi-filter rotating shadowband radiometer in situ calibration factors: utilizing Gaussian process regression with a new method to estimate dynamic input uncertainty

“…AERONET CIMELs have a FOV of 1.2 • while the UV-MFRSR has a larger FOV (e.g., ∼ 6.5 • ; reported by Kazadzis et al, 2018). AODs obtained from instruments with larger FOVs are associated with greater AOD uncertainty due to larger contributions of scattered light to the direct irradiance measurement (Kim et al, 2005).…”

“…Periodic soiling and cleaning of the UV-MFRSR diffuser can result in spurious increases and decreases in AOD, respectively. The frequency of on-site maintenance (e.g., cleaning of the UV-MFRSR dome) as well as rainfall events may therefore account for some of the AOD difference (Kim et al, 2005(Kim et al, , 2008. 4.…”