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ESA UNCLASSIFIED - For Official Use F. Steinmetz & D. Ramon | HYGEOS | 17/05/2019 | Slide 2

Evaluation of OLCI Ocean Colour products from Sentinel-3A and Sentinel-3B processed by Polymer

François Steinmetz, Didier Ramon


• Iterative coupled ocean-atmosphere atmospheric correction

François Steinmetz, Pierre-Yves Deschamps, and Didier Ramon, "Atmospheric correction in presence of sun glint: application to MERIS," Opt.

Express 19, 9783-9800 (2011)

François Steinmetz and Didier Ramon, “Sentinel-2 MSI and Sentinel-3 OLCI consistent ocean colour products using POLYMER”, Proc. SPIE 10778,

Remote Sensing of the Open and Coastal Ocean and Inland Waters, 107780E (30 October 2018).

• Uses a polynomial-like model for the atmospheric + sun glint signal

• Analytic model for water reflectance based on (Park and Ruddick, 2005)

2 parameters, chlorophyll concentration and backscattering coefficient

• Full spectrum iterative optimization using Nelder-Mead simplex algorithm

• Sensor-generic: applied consistently to S-3 OLCI (A and B), S-2 MSI (A and B), MERIS, MODIS-Aqua, SeaWiFS, VIIRS,

HICO, Landsat-8

• Used in OC-CCI (selected after Round-Robin selection), in Copernicus Global Land Service water quality and by

many other users

The Polymer Atmospheric correction


Daily spatial coverage with S3A + S3B

S3A [chl], 2019-03-17S3B [chl], 2019-03-17S3A+S3B [chl], 2019-03-17

• Water colour is retrieved in the sun glint without significant degradation of quality

• Very good daily spatial coverage with S3A and S3B

• Good inter-orbit consistency


• Use multiple daily observations of the polar regions (close to solstices) to assess how atmospheric correction is affected by increasingly high zenith angles

• Each ocean point can be observed several times per day due to overlapping orbits

• Time difference is less than 12 hours• Analysis is performed in terms of air mass, m*=1/cos(sza)

+1/cos(vza)• Products are reprojected in a common grid• The difference between each reflectance value, and the

reference (the daily observation at the lowest air mass), is plotted as a function of the air mass and accumulated for 10 days

• Applied to the Arctic (close to June solstice: July 2018 for OLCI and June 2010 for MERIS) and Antarctic (close to December solstice, December 2018)

Consistency analysis at high latitudes: method

Example of overlapping orbits in the Arctic region. About 8 hours separate these two observations.


Consistency analysis at high latitudes

Polymer S3BPolymer S3A S3A standardMERIS 4th

reprocessing

Results at 412 nm

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S3B standard

Air mass anomaly:Difference between per-pixel reflectance and corresponding reference obtained at the lowest daily air mass, as a function of the air mass.



Polymer S3BPolymer S3A S3A standardMERIS 4th

reprocessing

Results at 560 nm

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S3B standard

Air mass anomaly:Difference between per-pixel reflectance and corresponding reference obtained at the lowest daily air mass, as a function of the air mass.


• Self-consistency verification method, using only 10 days of observations close to solstices in polar regions

• Consistent results between Arctic and Antarctic analysis (with fewer points for the Antarctic because of the land coverage)

• Significant anomaly for standard OLCI products (IPF)

Both S3A and S3B Not for MERIS products

• Weak air mass dependency for Polymer, with better self-consistency


Overview of the « air mass dependencies »at all bands (slopes between reflectance difference and air mass) :


Validation of Polymer (using vicarious calibration gains) and OLCI standard (reduced resolution) over Aeronet-OC sites:Galata_Platform, Gloria, Gustav_Dalen_Tower, Helsinki_Lighthouse, MVCO, Socheongcho, Thornton_C-power,USC_SEAPRISM, USC_SEAPRISM_2, Venise, WaveCIS_Site_CSI_6 (using Aeronet-OC Level 1.5).Validation is easened by:• fast coda/codarep access• efficient query and download tools

(python module: sentinelsat)• small RR productsTime difference: 6 hours, using central matchup in RR• OLCI Polymer v4.11 flags: CLOUD (Polymer), INVALID, NEGATIVE_BB, OUT_OF_BOUNDS, EXCEPTION, THICK_AEROSOLS, HIGH_AIR_MASS• OLCI standard product flags: INVALID, LAND, CLOUD, CLOUD_AMBIGUOUS, CLOUD_MARGIN, SNOW_ICE, SUSPECT, HISOLZEN, SATURATED,

HIGHGLINT, WHITECAPS, AC_FAIL, OC4ME_FAIL, ANNOT_TAU06, RWNEG_02..08, ANNOT_ABSO_D, ANNOT_DROUT, ANNOT_MIXR1

Validation using Aeronet-OC in-situ data

Venise timeseries of Rw560 from early 2019


Validation results at 412 nm

Polymer OLCI-A

Polymer OLCI-B

Standard OLCI-A

• Large difference in the number of valid matchups

• Good quality regression with Polymer, even with sun glint contamination but with some positive bias in the blue bands

• Consistent Polymer results between OLCI-A and B



Polymer OLCI-A

Polymer OLCI-B

Standard OLCI-A





Some independent references demonstrating the good performance of Polymer

• Müller, D et al (2015) The Ocean Colour Climate Change Initiative: II. A methodology for assessing atmospheric correction processors based on in-situ measurements, Remote Sensing of Environment, http://dx.doi.org/10.1016/j.rse.2013.11.026

• Qin, P., Simis, S. G. H. & Tilstone, G. H., 2017. Radiometric validation of atmospheric correction for MERIS in the Baltic Sea based on continuous observations from ships and AERONET-OC. Remote Sensing of Environment, Volume 200, pp. 263-280. https://doi.org/10.1016/j.rse.2017.08.024

• Liu, Y. et al., 2018. Underway spectrophotometry in the Fram Strait (European Arctic Ocean): a highly resolved chlorophyll a data source for complementing satellite ocean color. Optics Express, 3, Volume 26, p. A219. https://doi.org/10.1364/OE.26.00A678

• Minwei Zhang et al, Comparison of two atmospheric correction approaches applied to MODIS measurements over North American waters, Remote Sensing of Environment, Volume 216, 2018, Pages 442-455, ISSN 0034-4257, https://doi.org/10.1016/j.rse.2018.07.012

• C. Jamet et al, Evaluation of Atmospheric Correction Algorithms over contrasted coastal waters for MSI on Sentinel-2, Ocean Optics conference 2018

• M. Costa, Sentinel-3a performance: radiometry and retrieval of biogeophysical properties of coastal waters in British Columbia, Canada, S3VT meeting 2019

• K. Alikas, Performance of Sentinel-3 OLCI products over optically complex inland and coastal waters, S3VT meeting 2019• G. Tilstone, Radiometric validation of Sentinel3A products in the Atlantic Ocean, Baltic Sea and Western English Channel, S3VT

meeting 2019• D. Odermatt, Development of a DIAS water quality processing chain and validation for Swiss lakes, S3VT meeting 2019

References

http://dx.doi.org/10.1016/j.rse.2013.11.026

https://doi.org/10.1016/j.rse.2017.08.024

https://doi.org/10.1364/OE.26.00A678

https://doi.org/10.1016/j.rse.2018.07.012


• The Polymer software is available aspython+cython source code

www.hygeos.com/polymer

• Good validation results, high number of matchups(robustness to sun glint, aerosols, thin clouds,adjacency effects)

• OLCI Polymer SVC will be updated• Air mass issue with standard OLCI products• Great data availability for Sentinel-3

as well as Sentinel-2

Conclusions and code availability

Thanks to S3-MPC, ESA, EUMETSAT, Copernicus, and AERONET-OC PIs

Register for free to Hygeos forum

http://www.hygeos.com/polymer

esa unclassified - for official use · olci standard (reduced resolution) over aeronet-oc sites:...

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