Second Simulation of the Satellite Signal in the Solar Spectrum (known, understandably, as 6S) is a Radiative Transfer Model which is widely used within remote sensing. It simulates the effect of the atmosphere on light passing through it, and can basically answer two questions:
- What intensity of light would be received at a satellite or airborne sensor under a specific set of atmospheric and ground reflectance conditions?
- What would the ground reflectance have been, given the measurement of light intensity at a sensor and the atmospheric conditions? (that is, the reverse of the previous question)
Although these questions may seem relatively simple, they're actually quite complicated to answer. They're also very important. Radiative Transfer Models like 6S are often used to atmospherically correct
satellite images (the standard atmospheric corrections for data from the MODIS and Landsat satellites are based upon 6S), and they also have a key role to play in research (for example, assessing the sensitivity of a method to atmospheric contamination.).
6S was originally developed by a team led by Eric Vermote, and is fully described in Vermote et al. (1997) and the original manuals.
As described on the Features page, Py6S is simply a wrapper around the original 6S code. I did not write any of the original 6S code and cannot answer detailed questions about the way that 6S itself works.