As of 23 February 2021, the processing of Copernicus Sentinel-1 L1 and L2 products, tagged as NRT-3h and Fast24h, have been aligned.
Before 23 February, a different processing was performed for the two products.
Each product tagged NRT-3h was processed independently for the whole data take, contrary to products tagged Fast24h which were processed with the complete data take (in particular the calibration and noise information), ensuring the radiometric and geometric continuity between adjacent slices.
This different processing flow resulted in a different radiometric quality between NRT3h and Fast24h products. For this reason, NRT-3h products were processed subsequently in Fast24h and made available to all users on the Open Data Access Hub.
In addition, NRT-3h products were generated using the orbit information embedded in the satellite telemetry while Fast24h products where generated using Precise Orbit Determination (POD) information (POD-RESORB).
After 23 February, the same processing is performed for Sentinel-1 L1/2 products tagged NRT-3h or Fast24h. The annotated timeliness depends on the geographical area covered by the product and it is not anymore an indication of a different product quality. Data is processed only once and made available to all users on the Open Data Access Hub.
Data tagged NRT-3h and Fast24h is processed equally, with the complete data take (in particular the calibration and noise information), ensuring the radiometric and geometric continuity between adjacent slices.
In addition, NRT-3h and Fast24h products are processed using Precise Orbit Determination (POD) information, using typically POD-PREORB information for products tagged NRT-3h and POD-RESORB information for products tagged Fast24h.
POD-PREORB orbits have an accuracy typically below 10 cms RMS similar to POD-RESORB.