SECOND SIMULATION OF THE SATELLITE SIGNAL IN THE SOLAR SPECTRUM, 6S -AN OVERVIEW

Remote sensing from satellite or airborne platforms of land or sea sur faces in the visible and near infrared is strongly affected by the pre sence of the atmosphere along the path from Sun to Target (surface) to Sensor, This paper presents 6S (Second Simulation of the Satellite Si gnal in the Solar Spectrum), a computer code which can accurately simu late the above problems, The 6S code is an improved version of 5S (Sim ulation of the Satellite Signal in the Solar Spectrum), developed by t he Laboratoire d'Optique Atmospherique ten years ago, The new version now permits calculations of near-nadir (down-looking) aircraft observa tions, accounting for target elevation, non lambertian surface conditi ons, and new absorbing species (CH4, N2O, CO), The computational accur acy for Rayleigh and aerosol scattering effects has been improved by t he use of state-of-the-art approximations and implementation of the su ccessive order of scattering (SOS) algorithm, The step size (resolutio n) used for spectral integration has been improved to 2.5 nm, The goal of this paper is not to provide a complete description of the methods used as that information is detailed in the 6S manual, but rather to illustrate the impact of the improvements between 5S and 6S by examini ng some typical remote sensing situations, Nevertheless, the 6S code h as still limitations, It cannot handle spherical atmosphere and as a r esult, it cannot be used for limb observations, In addition, the decou pling we are using for absorption and scattering effects does not allo w to use the code in presence of strong absorption bands.