Hello everyone,
In my masters thesis I am using Sentinel-2 Lvl 1C data for small field time series monitoring and therefore the geometric accuracy is of high importance. I am not sure if I understand the state of geometric refinement correctly and would appreciate if someone here could clarify my questions.
This S2 processing page says that “The geometric refinement of the Copernicus Sentinel-2 imagery relies on the GRI and is part of the Sentinel-2 geometric calibration process, applied worldwide since August 2021. It has highly improved the absolute geolocation and the multi-temporal co-registration of Sentinel-2 products. Indeed, thanks to the geometric refinement using the GRI, all the products inherit the same absolute geolocation performance.” and “Copernicus Sentinel-2 data systematically distributed by the ESA Ground Segment are geometrically refined over the Euro-Africa region since the 30th of March, 2021, and worldwide since the 23rd of August, 2021. Since then, both the Sentinel-2 data absolute geolocation and relative (multi-temporal) performance have significantly improved.”
At first I interpreted this to mean that only data produced since 23 August 2021 will be geometrically refined worldwide, and not earlier data. Or does it mean that ALL S2 products have been geometrically refined since that date
At the top of the above linked page it says:
"Collection-1 Processing Baseline
The Copernicus Sentinel-2 Collection-1 is currently being generated using the Sentinel-2 historical archive to ensure consistent time series from Sentinel-2A and Sentinel-2B, with uniform processing baselines and enhanced calibration. This process particularly focuses on improving the geometric performance of the products and their radiometry. All historical data, from the launch of Sentinel-2A in 2015 up until December 13th, 2023 (when the latest processing baseline for Collection-1 reprocessing was released in operation), is scheduled for reprocessing."
and then
"The improvements introduced in processing baselines up to baseline 04.00 (in operations since 25 January 2022) have been generalised to the historical archive:
- Geometric refining using the high-quality Copernicus Digital Elevation Model (introduced in Processing Baseline PB 03.00)"
I would interpret this to mean that the entire historical archive has now been geometrically refined. But then I looked at the Data Quality Report which says on p.7 “The geometric refinement relies on the Sentinel-2 Global Reference Image (see section 4.2.2). Introduced in operation since 30 March 2021 (PB 03.00) over the Euro-Africa region and then in August worldwide (except Antarctica, some isolated islands and some high latitude areas), it has improved the multitemporal co-registration and the relative geolocation accuracy of the Sentinel-2 products (see section 4.2 for more details).
Since the deployment of PB 05.09 in December 2023, the orthorectification is performed with the Copernicus Digital Elevation Model (DEM) at 30 m spatial resolution. This improves the local geolocation for all products in mountainous areas. This applies also to unrefined products, although the improvement is more effective for refined products.”
When I then check the properties of an image from e.g. 03.01.2016 in GEE, it has PROCESSING_BASELINE: 02.01 in the metadata. So I guess this would mean that this data is not geometrically refined, as it is below 3.0?
I hope my point is clear and would appreciate any help if anyone can clarify this. Thanks and have a nice weekend!