FAQ-SLSTR-001 - Are snow/ice pixels in S3A_SY_2_SYN products processed to surface reflectance? I've seen some examples in the expert user hub and it appears that ice/snow pixels (e.g. the Greenland Ice Sheet) are simply masked out rather than processed. If snow/ice is not included in S3A_SY_2_SYN, where/how might we be able to retrieve surface reflectance values for these areas, for instance equivalent to the MODIS MOD09GA product?
During SLSTR L1 processing, pixels are tested regarding snow detection and this information, included in SLSTR L1b product, are transferred to SYN Level 2 products. As a consequence, you can find in the SY_2_SYN product several dedicated flags:
- "SLN_snow" and "SLO_snow" raised when a pixel has been flagged as "affected by snow" during SLSTR L1 processing (SLN corresponds to the nadir view of SLSTR and SLO to the oblique view)<
- "SYN_snow_risk" which gathers both information
Pixels flagged as "affected by snow" by the SLSTR L1 processing are not descoped from SYNERGY processing. However, a lot of these pixels can be flagged as "bright pixels" by the OLCI L1 processing. This information is also transferred to SYN processing and taken into account to descope these bright pixels from SYN processing.
FAQ-SLSTR-002 - In the 'LST_ancillary_ds.nc' (Level 2 product of SLSTR), was the NDVI data calculated through surface reflectance of TOA reflectance? There does not appear to be a further description of it in the user guide and other documents.
The NDVI is not a primary product, just an anciliary product. It is calculated from top of Atmosphere reflectances.