Toward aerosol optical depth retrievals over land from GOES visible radiances: determining surface reflectance

Abstract

Frequent observations of aerosol over land are desirable for aviation, air pollution and health applications. Thus, a method is proposed here to correct surface effects and retrieve aerosol optical depth using visible reflectance measurements from the Geostationary Operational Environmental Satellite (GOES). The surface contribution is determined from temporal compositing of visible imagery, where darker pixels correspond to less atmospheric attenuation and surface reflectance is deduced from the composite using radiative transfer. The method is applied to GOES‐8 imagery over the eastern US. Retrieved surface reflectance is compared with separate retrievals using a priori ground‐based observations of aerosol optical depth. The results suggest that surface reflectances can be determined to within ±0.04. The composite‐derived surface reflectance is further analysed by retrieving aerosol optical depth and validating retrievals with Aerosol Robotic Network (AERONET) observations. This analysis indicates that the retrieved optical depth is least biased, hence the surface reflectance is most accurate, when the composite time period varies seasonally. Aerosol optical depth retrievals from this validation are within ±0.13 of AERONET observations and have a correlation coefficient of 0.72. While aerosol optical depth retrieval noise at low optical depths may be limiting, the retrieval accuracy is adequate for monitoring large outbreaks of aerosol events.

Acknowledgments

The authors acknowledge numerous people that have made this research possible through the provision of data. Cindy Combs of CIRA was instrumental by providing access to data after a system failure. Andy Heidinger's advice concerning cloud masking was valuable. The AERONET is an invaluable resource for this work, therefore we are grateful to Brent Holben and the AERONET staff, and the principal investigators listed in table 1 for making their AERONET data available for this research as well as the AEROCAN/AERONET network (PIs Norm O'Neill and Alain Royer). Also, thanks to Peter Romanov for providing access to the GOES data. Finally, this work was supported by the NOAA/GIMPAP and the NASA/Global Aerosol Climatology Project (purchase order S‐10189X, Michael Mishchenko, Project Scientist).