THE MODIS 2.1-MU-M CHANNEL - CORRELATION WITH VISIBLE REFLECTANCE FORUSE IN REMOTE-SENSING OF AEROSOL

A new technique for remote sensing of aerosol over the land and for at mospheric correction of Earth imagery is developed, It is based on det ection of dark surface targets in the blue and red channels, as in pre vious methods, but uses the 2.1-mu m channel, instead of the 3.75 mu m for their detection, ii 2.1-mu m channel is present on ADEOS OCTS and GLI, and planned on EOS-MODIS and EOSP, and a similar 2.2-mu m channe l is present on Landsat TM. The advantage of the 2.1-mu m channel over the 3.75-mu m channel is that it is not affected by emitted radiation , The 2.1-mu m channel is transparent to most aerosol types (except du st) and therefore can be used to detect dark surface targets, Correlat ion between the surface reflection in the blue (0.49 mu m), red (0.66 mu m), and 2.1 mu m is established using atmospherically corrected Lan dsat TRI and AVIRIS aircraft images collected over the Eastern United States, Maine, and California and spectral data obtained from the grou nd and Light aircraft near San Diego, CA. Results from a variety of su rface covers show that the surface reflectance at 0.49 mu m (rho(0.49) ) and 0.66 mu m (rho(0.66)) can he predicted from that at 2.2 mu m (rh o(2.2)) within Delta rho = +/-0.006 for rho(2.2) less than or equal to 0.10, using rho(0.49) = rho(2.2)/4 and rho(0.66) = rho(2.2)/2. Error in surface reflectance of 0.006 corresponds to an error in remote sens ing of aerosol optical thickness, tau, of Delta tau similar to +/-0.06 . These relationships were validated using spectral data taken close t o the surface over vegetated areas in a different biome, This method e xpands application of dark targets for remote sensing of aerosol to br ighter, nonforested vegetation, The higher reflection of the surface a t 2.2 mu m than that of 3.75 mu m mag even enable remote sensing of du st above surfaces with reflectivity rho(2.2) = 0.15 +/- 0.05. For this reflectivity range the dust radiative effect at 2.2 mu m is small, an d the surface reflectance in the blue and red channels can be retrieve d.