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1/34 2003 IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 Validation of MERIS level-2 geophysical products derived.

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Presentation on theme: "1/34 2003 IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 Validation of MERIS level-2 geophysical products derived."— Presentation transcript:

1 1/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 Validation of MERIS level-2 geophysical products derived above oceanic Case 1 waters : Early results obtained at three contrasted oceanic sites David Antoine, André Morel, Malik Chami, Bernard Gentili, Francis Louis, Joséphine Ras, Alec Scott, Dominique Tailliez Laboratoire d’Océanographie de Villefranche, CNRS-UPMC, BP 8 Quai de la Darse, Villefranche sur mer, FRANCE Chuck R. McClain, Stanford B. Hooker NASA/Goddard Space Flight Center / Code 970.2, Bldg 28, Greenbelt, MD 20771, USA Dennis K. Clark NOAA National Environmental Satellite Data Information Service (NESDIS), Suitland, Maryland, USA Simon Bélanger, Ludovic Bourg, Vincent Fournier-sicre, Jean-françois Desté, Pierre Guevel ACRI-in/Genimar, 260 route du pin Montard, Sophia Antipolis, FRANCE

2 2/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 Results from 3 contrasted oceanic sites The Benguela Upwelling An ESA/NASA/MCM-SA co-funded cruise took place from Oct. 5 to Oct. 17, 2002 (F.R.S. AFRICANA), in the region of the Benguela current. Conditions : from rich waters near the coast (Chl up to 10 mg m -3 ) to moderate concentrations offshore (around 0.5 mg m -3 ) The BOUSSOLE site An ESA/CNES/NASA/CNRS co-funded project, centred on the deployment of a new type of optical mooring (Mediterranean sea), as well as on monthly cruises on the buoy site. Conditions : oligotrophic to mesotrophic (0.05 < Chl < 1 mg m -3 ). The MOBY site A NASA/NOAA co-funded project, centred on the deployment of a new type of optical mooring (Hawaii archipelago), as well as on monthly cruises on the buoy site. Was set up for SeaWiFS/MODIS cal/val operations. Conditions : oligotrophic (0.05 < Chl < 0.2 mg m -3 ).

3 3/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 What are the requirements as for the accuracy of the atmospheric corrections above Case 1 waters ? An uncertainty of 5% max in the blue for an oligotrophic ocean is aimed at This can be expressed as well as a maximum of ±0.002 in terms of reflectance in the blue, and probably no more than ±0.001 in the green. These numbers are close to the MERIS “Noise equivalent reflectance” (Ne  ) These requirements have been defined so as to be able to appropriately discriminate between reflectance levels, and, at the end, to appropriately discriminate between chlorophyll concentration levels (“30 logarithmically equivalent classes of Chl from 0.03 to 30 mg m -3 ”) [Gordon, H. R., 1997, Atmospheric correction of ocean color imagery in the Earth observing system era, Journal of Geophysical Research 102, [Antoine, D. and A. Morel, 1999, A multiple scattering algorithm for atmospheric correction of remotely-sensed ocean colour (MERIS instrument) : principle and implementation for atmospheres carrying various aerosols including absorbing ones, International Journal of Remote Sensing 20,

4 4/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 The cruise in the Benguela current “BENCAL” cruise October F.R.S. AFRICANA Participants from : Laboratoire d’Océanographie de Villefranche, FRANCE Plymouth Marine Laboratory, UK Marine & Coastal Management (MCM-SA), South Africa NASA GSFC, USA University of Miami, RSMAS, USA University of Cape Town, South Africa First validation site : the “BENCAL” cruise

5 5/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 Cruise map Red arrows : matchup stations

6 6/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 MERIS matchups during the “BENCAL” cruise October 2002, Benguela upwelling The cruise last 13 days 9 MERIS overpasses were occurring during the cruise 7 images were made available 3 matchups were possible at the end MER_RR__2PNACR _084033_ X000_00107_03167_0000.bin_benguela MER_RR__2PNACR _080918_ X000_00121_03181_0000.bin_benguela MER_RR__2PNACR _084610_ X000_00150_03210_0000.bin_benguela MER_RR__2PNACR _081455_ X000_00164_03224_0000.bin_benguela MER_RR__2PNACR _085147_ X000_00193_03253_0000.bin_benguela MER_RR__2PNACR _082032_ X000_00207_03267_0000.bin_benguela MER_RR__2PNACR _085733_ X000_00236_03296_0000.bin_benguela

7 7/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 MERIS imagery (chlorophyll) during the BENCAL cruise October 11, 2002

8 8/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 Agreement is satisfactory, especially for the Oct 15, where the chlorophyll concentration was about 5 mg/m3 and the reflectance in the blue particularly low MERIS matchups during the “BENCAL” cruise October 2002, Benguela upwelling MERIS : red in situ : blue

9 9/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 Second validation site : the BOUSSOLE site

10 10/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 The “ BOUSSOLE ” project ( BOUée pour l’acquiSition de Séries Optiques à Long termE ) P.I. : David ANTOINE Laboratoire d’Océanographie de Villefranche « short title » : Building a time series of surface ocean optical properties for satellite ocean color cal/val and (bio)optics research

11 11/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 Funding Agencies / Supports European Space Agency Centre National d’Etudes Spatiales, France National Aeronautics and Space Administration of the USA The SIMBIOS project Centre National de la Recherche Scientifique, France Institut National des Sciences de l’Univers, France Observatoire Océanologique de Villefranche sur mer, France

12 12/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 People involved RESEARCH STAFF (L.O.V., Villefranche sur mer, and collaborators)  David ANTOINE,Chief Scientist  Marcel BABIN,Natural phytoplankton fluorescence  Annick BRICAUD,IOPs  Malik CHAMI,Ocean colour vicarious calibration  Hervé CLAUSTRE,IOPs, Biogeochemical proxies  André MOREL,AOPs  Stanford B HOOKERAOPs, calibrations, optics protocols TECHNICAL STAFF (L.O.V., Villefranche sur mer)  Alec SCOTT,Chief Engineer for the project, monthly cruises, data processing  Bernard GENTILI,Data processing codes  Francis LOUIS,Servicing, electronics, design  Joséphine RAS,HPLC and a p measurements  Dominique TAILLIEZ,CTD + IOPs, monthly cruises  David LUQUET,Diving TECHNICAL STAFF (ACRI-st, Genimar, “Avance Conceptuelle”, and Satlantic Inc.)  Pierre GUEVEL,Buoy design, hydrodynamics calculations  Jean-François DESTE,Engineering work (e.g., reduced scale model), testing, logistics  Philippe BARDEY,Expertise  Alpha CAMARA,Buoy design, structure calculations  Cyril DEMPSEY et al.Satlantic Inc.

13 13/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 Motivations - Science objectives : short-term changes in IOPs and AOPs, relationships between both, role of CDOM, seasonal and inter-annual changes, bidirectionality of the ocean reflectance... - Operational objective : vicarious calibration of ocean colour observations from space, and validation of the level- 2 “geophysical products” (e.g., chlorophyll, radiances). Establishing a time series of inherent and apparent optical properties (IOPs and AOPs), with two parallel objectives :

14 14/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 Short reminder Vicarious calibration of the ocean colour satellite observations : Reconstructing the top-of-atmosphere signal (i.e., the total radiance) through radiative transfer calculations, which are fed with parameters (aerosols in particular) and boundary conditions as they are determined in situ. Validation of the level-2 “geophysical products” as derived from ocean colour satellite observations (e.g., chlorophyll, radiances) : Comparing the same properties as derived from both in situ measurements and the satellite observations (after atmospheric correction has been performed). The uncertainty in both the in situ technique and the satellite algorithms must be (known) specified.

15 15/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 Strategy - A deep sea mooring, collecting data on a “continuous” basis - Monthly cruises for collecting data that are not accessible to the mooring (vertical profiles, water sampling), as well as for servicing the mooring - A coastal AERONET station, providing the necessary information about the aerosol properties, which are a central element of the vicarious calibration process Combination of 3 elements :

16 16/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 Measurement suite - Buoy: Surface irradiance (E s ), downwelling irradiance (E d ), upwelling irradiance (E u ) and upwelling radiance (L u ) at 4 and 9 meters (7 wavelengths), attenuation coefficient, backscattering coefficient, chlorophyll fluorescence. Temp., Pressure, Salinity at 9 meters. - Monthly cruises In-water profiles of E d and E u at 13 wavelengths, above water determination of L w, phytoplankton pigments (HPLC), phytoplankton absorption (filtered water), total absorption, scattering and attenuation coefficients at 9 wavelengths (profiles), backscattering profile and CDOM fluorescence. Aerosol optical thickness. - Coastal AERONET Station (sun photometer) : aerosol optical thickness, sky radiances (aerosol type).

17 17/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 MERIS matchups at the BOUSSOLE site day monthly campaigns on site from July 2001 to April of these cruises were totally cancelled because of meteo hazards or logistic difficulties - The total of workable days at sea is 37 at the end, among which 22 during the MERIS life - Among these 22 days, 10 correspond to MERIS overpasses - Among these 10 MERIS overpasses, only 4 has been used up to now for a matchup (others have strong glint or are not available)

18 18/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 MERIS matchups at the BOUSSOLE site October 5, 2002 MERIS : light blue in situ :yellow and dark blue

19 19/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 November 28, 2002 MERIS matchups at the BOUSSOLE site September 3, 2002 MERIS : yellow in situ :dark blue

20 20/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 The MOBY project is funded/maintained by NASA/GSFC, NOAA, The SeaWiFS, MODIS & SIMBIOS projects. P.I. is Dennis K. Clark © NASA/GSFC Third validation site : the MOBY site MOBY deployment MOBY site

21 21/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 MERIS matchups at the MOBY site A total of 164 MOBY measurement days were available between May 1 st, 2002 and Feb. 27, After clouds and glint have been discarded, about 40 MERIS passes are available for good matchups.

22 22/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 MERIS imagery (chlorophyll) at the MOBY site Sept. 21, 2002 Oct. 10, 2002

23 23/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 MERIS imagery (chlorophyll) at the MOBY site (cont’d) Oct. 20, 2002 Dec. 19, 2002

24 24/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 MERIS imagery (chlorophyll) at the MOBY site (cont’d) May 23, 2002 August 1 st, 2002 Glint area

25 25/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 All points for wavelengths 620, 665, 681 and 708 nm MERIS matchups at the MOBY site

26 26/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 MERIS matchups at the MOBY site 708 nm 665 & 681 nm 620 nm 560 nm 510 nm 490 nm 443 nm 412 nm These light blue bars represent an error of about +/ in terms of reflectance, centred onto the 1:1 line

27 27/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 MERIS matchups at the MOBY site : some individual spectra (1/2)

28 28/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 MERIS matchups at the MOBY site : some individual spectra (2/2)

29 29/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 MERIS Vicarious calibration : status õ The sun photometer (AERONET) provided continuous record from July 2002 to April Will restart in August 2003 Near IR bands (no marine signal) õ Days with stable conditions have been selected Visible bands õ The same exercise is to be performed. Additional difficulty is to get simultaneous in-water radiometry, so as to reconstruct the total TOA reflectance as the sum of the atmospheric signal (same technique than for the near IR bands) and the marine signal multiplied by a diffuse transmittance õ A “Successive Orders of Scattering” code, including polarisation, is being used in order to determine which is the best candidate aerosol model in each of these situations (Shettle&Fenn models as well as simple models defined by a Jünge law for the particle size distribution). The decision is made on the basis of the measurements in the principal plane as well as on the basis of the polarisation rate õ Forward calculations are then performed to compute the TOA signal that MERIS should record.

30 30/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 MERIS Vicarious calibration : (1) retrieving the aerosols properties Sky radiances (measured : dots; computed : dashed line) Polarization rate (measured : dots; computed : dashed line)

31 31/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 MERIS Vicarious calibration : (2) generating the TOA signal and comparing to what MERIS is measuring UPD (%)

32 32/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 Conclusions (1/2) - Validation of the MERIS water-leaving reflectance does not show major problems over oceanic Case 1 waters - A largest data set will be built after the next deployment of the BOUSSOLE buoy will be achieved - Additional punctual efforts (cruises) remain necessary in other parts of the ocean - The vicarious calibration does not show significant problems : to be confirmed as well when more measurements and more MERIS data will be available - Glint correction must be improved as far as possible, because glint is affecting large portions of the MERIS images - Some improvements remain needed, in the red in particular

33 33/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 Conclusions (2/2) - Some artefacts are still appearing here and there : camera limits, high frequency line-to-line noise : should be improved - Level-3 data would be extremely helpful for next steps of the validation (mean values over ocean gyres, comparison with other sensors, global and regional means etc..) - Some specific aspects of the algorithms have not yet been tested, such as the dust aerosol detection ==> should not trust for the moment the flags indicating their presence - Further validation is as well still needed for the aerosol optical thickness, the epsilon ratio and the chlorophyll concentration

34 34/ IEEE International Geoscience and Remote Sensing Symposium, Toulouse, July 21-25, 2003 End of presentation


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