A variety of radiative transfer models exist, both for the calculation of radiative fluxes and the simulation of radiances measured by satellite sensors. However, those used for the calculation of radiative fluxes are generally components of climate models (cf., Ellingson et al., 1991) and are not well documented or easy to use. For this reason they will not be discussed further in this paper. Radiative transfer models that are well documented, reliable, and available to the scientific community include LOWTRAN (Kneizys et al., 1988), MODTRAN (Snell et al., 1995), and 6S (Vermote et al., 1994). While other general-purpose models exist, these three have been widely used in remote sensing applications. They are all medium or high spectral resolution band models and incorporate thorough treatments of gas absorption. However, the cloud models in LOWTRAN/MODTRAN are not very easy to modify, and the two-stream approximation for multiple scattering can result in significant errors under certain conditions. The 6S model does not include clouds but is very flexible for clear sky satellite simulations. None of these models computes fluxes directly, and the user interfaces are somewhat crude. Some of the major similarities and differences between these models are listed in the table below.