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7 November 2018 at 10:25 #1291blovedayModerator
Current status of S3A:
OLCI-A and SLSTR-A are both in full nominal status. Despite two camera outages over the summer, OLCI-A continues to perform within mission parameters.
The current OLCI-A Level-2 product baseline is PB2.29. This implements the current system vicarious calibration (SVC) gains, mitigating the radiometric bias that is present in the Level-1B data (2-3% excess brightness). Temporal stability of the instrument remains good and L2 reflectances mostly meet mission requirements on an averaged global scale.
Pigment retrievals are good for mesotrophic and eutrophic waters, but there is an underestimate of chlorophyll concentration in oligotrophic waters for the CHL_OC4ME product. The CHL_NN product underestimates chlorophyll when compared to CHL_OC4ME (please see new product development section for information on future plans to mitigating this issue).
The list of recommended flags to use at Level-2 can be found in the latest product notices at https://www.eumetsat.int/website/home/Data/Sentinel3Services/OceanColour/index.html. Users should be aware of the application of the ANNOT_DROUT flag. This should be applied in global validations of OLCI measurements. However, in regional cases that consider coastal and/or optically complex waters, using the ANNOT_DROUT flag may result in substantial loss of potential match-up data, and users should exercise their own discretion in applying it.
Regional ‘speckling’ of OLCI-A products in some coastal regions is currently under-investigation. Planned updates to the current bright-pixel correction are expected to partially alleviate this issue.
Current status of S3B:
Sentinel-3B manoeuvre and data release timeline:
- 28/06/2018: OLCI-B Level-1B data released to S3VT
- 12/07/2018: OLCI-B Level-2 data released to S3VT
- 27/07/2018: Sentinel-3B lunar calibration manoeuvre
- 17/10/2018: In Orbit Commission Review successfully completed.
- 16/10/2018: Sentinel 3B in drift phase to the nominal orbit.
- 23/11/2018: Sentinel 3B drift manoeuvre complete, nominal position at 140 deg ahead of S-3A
- 28/11/2018: EUMETSAT takeover of the operational control
- end-11/2018: OLCI-B Level-1B public release
- early-2019: OLCI-B Level-2 public release
Public data releases will include data from the release point onwards. It will not include all archive data.
OLCI-B L1-B validation activities:
There have been two novelties to the Sentinel-3B mission thus far:
- Tandem phase. The goal is to understand relative bias better and to inter-compare S3A and S3B products while keeping geographical variability to a minimum.
- Lunar calibration. The goal of this is to allow a better assessment of the effects of stray light on the instrument, and to assess feasibility of moon calibration procedure to see if that can be turned into a nominal procedure in the future. It is also of interest for SRAL and SLSTR, which can utilise deep sky measurements as a calibration point.
In Orbit Commission Review (IOCR):
This was passed successfully on 17 October. It included full platform and instrument characterisation, calibrations of all payload instruments (including preliminary validations of L1-B products), full verification of the space and operations segments and indicated the start of ramp-up towards the nominal operations. Signal to noise is fully compliant, and dark offsets remain stable, although frequent dark calibrations are required to reduce periodic noise.
Radiometrically, desert calibrations show that OLCI-B 1-2% uncertainty remains closer to MERIS than OLCI-A is. Band Oa21 shows quite a high bias within about 4% (but still better than OLCI-A), possibly due to stray-light issues, which may be alleviated through lunar calibration. Spectrally, OLCI-B is compliant showing only small trends in the early mission, comparable to MERIS. Spectral calibration is within mission specifications, apart from a spectral mis-registration in camera 4 which is currently under investigation.
As with OLCI-A, planned yaw manoeuvres will be used to better characterise the inflight bidirectional reflectance distribution function (BRDF) of the solar diffuser, with is expected to lead to major improvements in the BRDF model and L1/L2 temporal stability.
S3 MPC is currently working on a new geometric calibration, which will be applied to the product baseline for the public data release.
OLCI-B L2 validation activities:
OLCI-B is still in the ramp up phase, with calibrations (particularly geometric calibrations) still ongoing. The currently OLCI-B product baseline (PB v1.05) fully matches the OLCI-A operational product baseline (PB v.2.29), but OLCI-B has no System Vicarious Calibration (SVC) applied, with all gains set to 1.0. Recommended flags for OLCI-B L2 data are the same as those that are recommended for OLCI-A. The implementation of the ANNOT_DROUT flag for OLCI-B is consistent with the notes given at the top of this document for OLCI-A.
Radiometrically, OLCI-B continues to perform better than OLCI-A, and nearer to MERIS. However, SVC is still needed to correct L2 reflectances in all bands. SVC gains will be ready before public release.
New product developments:
The following OLCI Level-2 product changes are in preparation:
- the implementation of an improved bright pixel correction (see notes at top of document)
- the implementation of a new Chlorophyll Index switch for oligotrophic waters
- the introduction of the new altNN for Complex Water Products
- introduction of SVC gains specific to Complex Water Products
- the introduction of an additional cloud risk for complex water products
- smile correction for band Oa10 (681 nm)
For more information on S3VT activities across all Sentinel-3B sensors, keep an eye on the EUMETSAT news stream. For any non-S3VT members who are interested in joining the validation team, you can this via application to the rolling S3VT call, here:
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