While we understand that there are various atmospheric radiative transfer model out there (see here), Planet uses the 6S model due to a number of reasons:
- It is easily integrated to Planet platform
- It is one of the more widely used radiative transfer codes
- It is used as part of the atmospheric correction of Landsat-8 imagery, so out-of-the-box is tuned towards satellite applications
- Because of its wide use, there are many scientific papers out there validating its accuracy and suitability for Planet surface reflectance product
- It is freely available and unencumbered by licensing issues
- A source code is available and easily compiled, opening the possibility of customizations if needed
- A Python library exists (Py6S) which makes generating configuration files for 6S and reading the output files easier.