DART (Discrete Anisotropic Radiative Transfer) simulates the 3D radiative transfer (R.T.) in the Earth-Atmosphere system. Earth scenes are natural and urban landscapes with topography. DART works in the optical domain, from the ultra-violet up to the thermal infrared domain. Its products are spectral remote sensing images, spectra and 3D radiative budget. A major goal of the DART model is to provide accurate simulations with reasonable computation time. This implies an R.T. accurate modeling in the Earth scene and the atmosphere, with an accurate ldquoEarth scene - Atmosphererdquo coupling. Recently, the atmosphere R.T. was greatly improved in terms of accuracy and flexibility. Its algorithm relies on a specific atmosphere grid with the use of atmosphere transfer functions for decreasing computation time. Its accuracy is improved. Compared to ModTran, the mean relative error decreased from 6.5% to 1.3%.