Absolute atmospheric correction relies on Radiative transfer models (RTMs). RTMs can be used for computing radiances for a wide variety of atmospheric and surface conditions. They require full descriptions of the atmospheric components at fixed altitudes throughout the atmosphere. RTMs are relatively easy to use when the complexity of the atmospheric input is simplified by using one standard atmosphere as input.
Because of the rapid dynamics of the atmosphere in terms of the temporal and spatial variation of its constituents, researchers have found the need to define some often-observed “common profiles” that correspond to average atmospheric conditions for different parts of the Earth. Compilation of these “fixed atmospheres” has been based on actual radio soundings carried out at different research sites, resulting in what are called “standard atmospheres”, e.g. mid-latitude summer, mid-latitude winter, tropical, desert, arctic, US standard, and so on. Researchers use these well-defined standards to characterize typical on-site atmospherics. RTMs have these standards built into the system, allowing the influence of different constituents to be compared under strict simulations.
For instance, the influence of water vapour in the thermal, or of aerosols and air molecules in the visible, part of the spectrum can be accurately predicted for different atmospheres, allowing sensitivity analyses for evaluating the importance of these constituents in attenuation processes at different wavelengths.