Operational atmospheric correction of Landsat TM data

The recent algorithms developed for biophysical variables assessment requir e accurate surface reflectance measurements. This article describes algorit hms used for atmospheric correction of Landsat Thematic Mapper (TM) data. A tmospheric corrections include Rayleigh scattering gaseous absorption, and aerosol scattering in three visible channels (480 nm, 560 nm, and 660 nm), and the near-infrared channel (830 nm). Atmospheric constituents such as wa ter vapor and ozone are extracted from climatology data sets, while aerosol optical depths (AODs) are derived from the TM scene itself by adopting the dark target approach. The dark target pixels are identified, and their ref lectances in the visible channels are estimated using TBI Channel 7 (2.1 mu m). Atmospheric transmittance and aerosol optical depth are derived for 16 grid points equally distributed over the scene, then interpolated to match the TM spatial resolution. This technique considerably reduces the computi ng time without decreasing the accuracy. These algorithms were tested using 11 TM scenes over a wide variety of sites, including forest, crop, ann sem iarid areas. The AOD in the blue, green, and red channels retrieved using t he dark target technique was validated using sunphotometer measurements. Th e absolute error associated with AOD assessment was less than 0.15. A stati stical analysis teas also conducted to evaluate the atmospheric correction method. Based on data from the FIFE (First ISLSCP Field Experiment) experim ent, the absolute error between ground measurements and TM reflectance was less than 0.015 in the visible channels, and less than 0.08 in the near-inf rared channel. (C) Elsevier Science Inc., 1999.