As some of you might be aware, ESA will be updating the Sentinel-2 processing baseline in January 2022. One breaking change is the definition of digital numbers (DN) in the source files. Negative reflectance values will be possible and DNs before and after the change will no longer be comparable.
For most users, this change will hardly be noticeable. Data in REFLECTANCE units (which is the default - you get this unless you specifically ask otherwise in the evalscript) will stay the same. Sentinel Hub takes care of this. The only difference is the already mentioned possibility of negative reflectance values.
Users explicitly requesting data in DN units will, by default, get data exactly as before. While we realize that in this case you are not getting the actual digital numbers from the files themselves, this is done to prevent breaking changes; it represents a harmonized DN value. To facilitate getting the actual DN values as opposed to the default harmonized ones, we are adding a “dnFormat” parameter to Sentinel-2 requests. This parameter will be available once ESA updates the processing baseline (January 2022).
dnFormat: [harmonized (default), raw]
- harmonized: DN is returned to behave exactly as before, so processing baseline < 04.00. Negative values are clamped to zero. DN = reflectance * 10000.
- raw: You get exactly the values of the digital numbers of the source data. The “true” DN you could say.