The MODIS 2.1-μm channel-correlation with visible reflectance for use in remote sensing of aerosol

A new technique for remote sensing of aerosol over the land and for atmospheric correction of Earth imagery is developed. It is based on detection of dark surface targets in the blue and red channels, as in previous methods, but uses the 2.1 /spl mu/m channel, instead of the 3.75 /spl mu/m for their detection. A 2.1-/spl mu/m channel is present on ADEOS OCTS and GLI and planned on EOS-MODIS and EOSP, and a similar 2.2-/spl mu/m channel is present on Landsat TM. The advantage of the 2.1-/spl mu/m channel over the 3.75-/spl mu/m channel is that it is not affected by emitted radiation. The 2.1-/spl mu/m channel is transparent to most aerosol types (except dust) and therefore can be used to detect dark surface targets. Correlation between the surface reflection in the blue (0.49 /spl mu/m), red (0.66 /spl mu/m), and 2.1 /spl mu/m is established using atmospherically corrected Landsat TM and AVIRIS aircraft images collected over the Eastern United States, Maine, and California and spectral data obtained from the ground and light aircraft near San Diego, CA. Results from a variety of surface covers show that the surface reflectance at 0.49 /spl mu/m (/spl rho//sub 0.49/) and 0.66 /spl mu/m (/spl rho//sub 0.66/) can be predicted from that at 2.2 /spl mu/m (/spl rho//sub 2.2/) within /spl Delta//spl rho/=/spl plusmn/0.06 for /spl rho//sub 2.2//spl les/0.10, using /spl rho//sub 0.49/=/spl rho//sub 2.2//4 and /spl rho//sub 0.66/=/spl rho//sub 2.2//2. Error in surface reflectance of 0.006 corresponds to an error in remote sensing of aerosol optical thickness, /spl tau/, of /spl Delta//spl tau//spl sim//spl plusmn/0.06. These relationships were validated using spectral data taken close to the surface over vegetated areas in a different biome. This method expends application of dark targets for remote sensing of aerosol to brighter, nonforested vegetation. The higher reflection of the surface at 2.2 /spl mu/m than that of 3.75 /spl mu/m may even enable remote sensing of dust above surfaces with reflectivity /spl rho//sub 2.2/=0.15/spl plusmn/0.05. For this reflectivity range the dust radiative effect at 2.2 /spl mu/m is small, and the surface reflectance in the blue and red channels can be retrieved.