esa unclassified - for official use · olci standard (reduced resolution) over aeronet-oc sites:...
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ESA UNCLASSIFIED - For Official Use
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
ESA UNCLASSIFIED - For Official Use F. Steinmetz & D. Ramon | HYGEOS | 17/05/2019 | Slide 3
• 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
ESA UNCLASSIFIED - For Official Use F. Steinmetz & D. Ramon | HYGEOS | 17/05/2019 | Slide 4
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
ESA UNCLASSIFIED - For Official Use F. Steinmetz & D. Ramon | HYGEOS | 17/05/2019 | Slide 5
• 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.
ESA UNCLASSIFIED - For Official Use F. Steinmetz & D. Ramon | HYGEOS | 17/05/2019 | Slide 6
Consistency analysis at high latitudes
Polymer S3BPolymer S3A S3A standardMERIS 4th
reprocessing
Results at 412 nm
Arc
tic
(Ju
ne s
ols
tice
)A
nta
rcti
c(D
ece
mb
er
sols
tice
)
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.
ESA UNCLASSIFIED - For Official Use F. Steinmetz & D. Ramon | HYGEOS | 17/05/2019 | Slide 7
Consistency analysis at high latitudes
Polymer S3BPolymer S3A S3A standardMERIS 4th
reprocessing
Results at 560 nm
Arc
tic
(Ju
ne s
ols
tice
)A
nta
rcti
c(D
ece
mb
er
sols
tice
)
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.
ESA UNCLASSIFIED - For Official Use F. Steinmetz & D. Ramon | HYGEOS | 17/05/2019 | Slide 8
• 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
Consistency analysis at high latitudes
Overview of the « air mass dependencies »at all bands (slopes between reflectance difference and air mass) :
ESA UNCLASSIFIED - For Official Use F. Steinmetz & D. Ramon | HYGEOS | 17/05/2019 | Slide 9
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
ESA UNCLASSIFIED - For Official Use F. Steinmetz & D. Ramon | HYGEOS | 17/05/2019 | Slide 10
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
ESA UNCLASSIFIED - For Official Use F. Steinmetz & D. Ramon | HYGEOS | 17/05/2019 | Slide 11
Validation results at 443 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
ESA UNCLASSIFIED - For Official Use F. Steinmetz & D. Ramon | HYGEOS | 17/05/2019 | Slide 12
Validation results at 490 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
ESA UNCLASSIFIED - For Official Use F. Steinmetz & D. Ramon | HYGEOS | 17/05/2019 | Slide 13
Validation results at 560 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
ESA UNCLASSIFIED - For Official Use F. Steinmetz & D. Ramon | HYGEOS | 17/05/2019 | Slide 14
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
ESA UNCLASSIFIED - For Official Use F. Steinmetz & D. Ramon | HYGEOS | 17/05/2019 | Slide 15
• 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
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