Second-generation operational algorithm: Retrieval of aerosol properties over land from inversion of Moderate Resolution Imaging Spectroradiometer spectral reflectance

Since first light in early 2000, operational global quantitative retrievals of aerosol properties over land have been made from Moderate Resolution Imaging Spectroradiometer (MODIS) observed spectral reflectance. These products have been continuously evaluated and validated, and opportunities for improvements have been noted. We have replaced the surface reflectance assumptions, the set of aerosol model optical properties, and the aerosol lookup table (LUT). This second-generation operational algorithm performs a simultaneous inversion of two visible (0.47 and 0.66 mu m) and one shortwave-IR (2.12 mu m) channel, making use of the coarse aerosol information content contained in the 2.12 mu m channel. Inversion of the three channels yields three nearly independent parameters, the aerosol optical depth (tau) at 0.55 mu m, the nondust or fine weighting (eta), and the surface reflectance at 2.12 mu m. Retrievals of small-magnitude negative tau values (down to -0.05) are considered valid, thus balancing the statistics of tau in near zero tau conditions. Preliminary validation of this algorithm shows much improved retrievals of tau, where the MODIS/Aerosol Robotic Network tau (at 0.55 mu m) regression has an equation of: y = 1.01x + 0.03, R = 0.90. Global mean tau for the test bed is reduced from similar to 0.28 to similar to 0.21.