Aerosol Optical Depth Analysis with NOAA GOES and POES in the Western Atlantic

Abstract : An aerosol optical depth retrieval algorithm in the visible wavelengths for the NOAA POES AVHRR and GOES-8 visible imager is presented for the cloud free, marine atmosphere. The algorithm combines linearized single-scatter theory with an estimate of surface reflectance. Phase functions are parameterized using an aerosol size distribution model and the ratio of radiance values measured in channels 1 and 2 of the AVHRR. Retrieved satellite aerosol optical depth (AOD) is compared to three land-based sun photometer stations located on islands in the western Atlantic during July and September, 2001. GOES-8 channel 1 (visible wavelength) radiance values were initially calibrated using techniques developed by Rao and Zhang (1999). Additional corrections to the channel 1 GOES-8 radiances were made by applying a linear offset factor obtained during the experimental time period through comparison with AVHRR radiances. The results for the GOES-derived AOD compare favorably to the Aerosol Robotic NETwork (AERONET) AOD values. For both NOAA and GOES data, the comparison dataset has a correlation coefficient of 0.67 with a standard error of 0.7. During dusty conditions with corresponding higher AOD levels greater than or equal to 0.25, the general trend was for the satellite-derived AOD values to underestimate AERONET AOD values. Within these conditions, the scattering phase function pattern deviated from the expected pattern, especially between the scattering angles of 140 degrees to 180 degrees. Overall, the more accurate calculations of AOD occurred over scatter angles between 140 degrees to 150 degrees and 170 degrees to 180 degrees.