Sentinel-3 Synergy Technical Guide - FAQs

Find answers to Frequently Asked Questions (FAQs) on Sentinel-3 Synergy products:

FAQ-SYN-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 consequences, 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)
  • And "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-SYN-002 - I am trying to use the Sentinel-3 synergy product. In each of the reflectance files, two variables are present, e.g. SDR_Oa01 and SDR_Oa01_err. However, for the case of OLCI reflectance error, only out-of range values are present, while for SLSTR-N and -O, the error fields are filled with zeroes.

What does this mean?

These error estimates datasets have been included in the SYN product (or in OLCI and SLSTR L1b products) as a placeholder for further evolutions.

However, no algorithm have been defined yet and there is actually no specific error computation in OLCI L1, or SLSTR L1 processing chains and as a consequence nothing either in the SYN L2 processing chain.

These datasets are filled with dummy values, but unfortunately it is not the same value for OLCI SDR and SLSTR SDR. The dummy value is set to -10,000 for OLCI SDR_ERR and set to 0 for SLSTR_SDR_ERR

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