It is possible to get a good estimation of bottom-of-the-atmosphere reflectance as opposed to top-of-the-atmosphere reflectance (which is the default) by enabling the atmospheric correction filter. This filter is a runtime-optimised version of ESA's provided Sen2Cor processor (Sen2Cor is applied at product-scale level and then statistically distributed to tiles).
To enable, either set the Atmospheric correction to 'Full' within the Style Parameters in the Configuration Utility, or add the ATMFILTER parameter to your request URL with the value ATMCOR. Example:
There are two atmospheric correction filters available, both of which use precomputed data:
- DOS1 being simpler and somewhat less accurate as well as available only for RGB bands.
- ATMCOR is the one based on Sen2cor and is available for all bands, with the exception of band 10, but might not be available for all tiles. In this case the system will use DOS1 calculation instead for those tiles.
These filters can be used with any Sentinel imagery product, however if a filter will only affect bands for which it has data. This should not be a problem with ATMCOR but makes NDVI only partially corrected with DOS1, for example, since it will adjust the R band but not the NIR band.