Global Surface-Based Sun Photometer Network for Long-Term Observations of Column Aerosol Optical Properties: Intercomparison of Aerosol Optical Depth

Abstract

Comparisons of aerosol optical depths (AODs) determined from several types of Sun photometers operating side by side as part of four different networks (GAW PFR, AERONET, SKYNET, and NOAA/ESRL aerosol monitoring programs) were made at 6 different environmental stations to evaluate the different types of current state-of-the-art instruments under different aerosol loading conditions. A comparison between AERONET CIMEL and GAW PFR at a high altitude calibration site, Mauna Loa, shows an excellent agreement with 0.001 bias for 500 nm AOD. AODs obtained from direct Sun-pointing instruments are within 0.01 bias, though these results are similar to or slightly larger than those given in previous short-term intensive studies. These results suggest that well-maintained networks of direct Sun-pointing instruments developed by different companies/institutions can provide quality-assured AOD data across the globe to the aerosol-climate research community. The poorer agreement between a hemispherical field-of-view (FOV) MFRSR and the finite FOV Sun-pointing instrument is found to be due to uncertainty in the angular characterization of the MFRSR optics.

Acknowledgments

This research was supported by the Korean Meteorological Administration R&D programs under grant CATER 2006-4104, and BK 21 program of SEES/SNU. We thank the AERONET principal investigators and Korea Global Atmosphere Watch Observatory (KGAWO) for providing the data.

Notes

¹ Abbreviations: Mauna Loa—MLO, Boulder—BOU, Trinidad Head—THD, Bermuda—BRM, Gosan—GOS, Anmyon—ANM.

¹The Sun photometer x was chosen as the reference instrument. Bias difference (BD), root mean square difference (RMSD), and standard deviation of the difference (SDD) are, 1/N∑₁ ^N (y _i − x _i ), √1/N∑₁ ^N (y _i − x _i )², and √∑₁ ^N [(y _i − x _i ) − BD]²/N − 1, respectively. The percent difference is calculated as [(y-x)/x * 100%].