Improved Global Ocean Color using POLYMER Algorithm

Transcription

1 Improved Global Ocean Color using POLYMER Algorithm François Steinmetz 1 Didier Ramon 1 Pierre-Yves Deschamps 1 Jacques Stum 2 1 Hygeos 2 CLS June 29, 2010 ESA Living Planet Symposium, Bergen, Norway

2 c 2010 Improved Global Ocean Color using POLYMER Algorithm 2 / 25 Introduction Original algorithm for atmospheric scattering and sun glint correction Uses a polynomial atmospheric model (in wavelength), and applied to MERIS F. Steinmetz PhD., 2008 Initial target: retrieve MERIS Ocean Colour data over the sun glint increase useful spatial coverage

3 c 2010 Improved Global Ocean Color using POLYMER Algorithm 3 / 25 Algorithm description The whole spectrum (412 to 865 nm) is used to discriminate the sea water reflectance from the atmosphere and sun glint signal: First corrections: correct the TOA signal from gaseous absorption and rayleigh scattering ρ corr (λ) = ρ TOA (λ)/t oz (λ) ρ mol (λ) Spectral matching of ρ corr (λ) T (λ)c 0 + c 1 λ 1 + c 2 λ 4 + t(λ)ρ + w (λ, chl, b }{{} bs ) }{{} Atmosphere + Sun Glint Ocean Water Model Reflectance Model Simultaneous iterative optimization of these two models (Nelder-Mead simplex method) water reflectance model: based on (Morel and Maritorena, 2001), using variable backscattering of suspended matter b bs, extended to the NIR by the similarity spectrum from (Ruddick et al, 2006) 5 parameters retrieved: c 0, c 1, c 2, chl, b bs Retrieval of water reflectances

4 Example of level 2 product Bay of Biscay June 21, 2005 Sun glint reflectance 10% c 2010 Improved Global Ocean Color using POLYMER Algorithm 4 / 25

5 Example of level 2 product MEGS (standard algorithm) POLYMER chl-a ρ+ w (560) c 2010 Improved Global Ocean Color using POLYMER Algorithm 5 / 25

6 Product analysis and validation c 2010 Improved Global Ocean Color using POLYMER Algorithm 6 / 25

7 Comparison of 2 scenes taken one day apart With sun glint RGB composite ρ+ w (490) May 14, 2007 c 2010 Without sun glint RGB composite ρ+ w (490) May 15, 2007 Improved Global Ocean Color using POLYMER Algorithm 7 / 25

8 c 2010 Improved Global Ocean Color using POLYMER Algorithm 8 / 25 Validation with SIMBADA measurements (1/4) Comparison between reflectances derived in situ from SIMBADA (Deschamps et al., 2004), and MERIS estimations from standard algorithm (MEGS) and POLYMER Data from MERMAID database Comparison of chlorophyll concentrations estimated by the same bio-optical algorithm (OC4Me, Morel and Antoine)

9 c 2010 Improved Global Ocean Color using POLYMER Algorithm 9 / 25 Validation with SIMBADA measurements (2/4) Set 1: without HIGH_GLINT and without PCD_1_13 Set 2: with HIGH_GLINT or PCD_1_13 (PCD_1_13: invalid processing by standard algorithm) Algo. Set RMSE Slope MEGS POLYMER POLYMER No glint Medium glint High glint Better accuracy of chl retrieved by POLYMER

10 c 2010 Improved Global Ocean Color using POLYMER Algorithm 10 / 25 Validation with SIMBADA measurements (3/4) Set 1: without HIGH_GLINT and without PCD_1_13 Set 2: with HIGH_GLINT or PCD_1_13 (PCD_1_13: invalid processing by standard algorithm) + No glint Medium glint High glint

11 c 2010 Improved Global Ocean Color using POLYMER Algorithm 11 / 25 Validation with SIMBADA measurements (4/4) Comparable accuracy of MEGS, POLYMER outside glitter and POLYMER inside glitter Bias increasing in the blue Weak residual dependency with the sun glint brightness More points in set 2 than in set 1

12 Operational NRT application by CLS c 2010 Improved Global Ocean Color using POLYMER Algorithm 12 / 25

13 c 2010 Improved Global Ocean Color using POLYMER Algorithm 13 / 25 The context of Ocean Color use at CLS CLS, subsidiary from CNES and IFREMER, operates a NRT oceanographic data service for scientific, institutional or private users (e.g., offshore fishing industry, offshore oil and gas industry). POLYMER operationally used since late 2008 to produce MERIS Level 2 from ESA Level 1 NRT products. 10-day global chlorophyll maps are then built in NRT merging MODIS and MERIS Polymer Level 2 products

14 c 2010 Improved Global Ocean Color using POLYMER Algorithm 14 / 25 Daily composite of chl, standard product 8% ocean coverage

15 c 2010 Improved Global Ocean Color using POLYMER Algorithm 15 / 25 Daily composite of chl, POLYMER product 20% ocean coverage

16 c 2010 Improved Global Ocean Color using POLYMER Algorithm 16 / 25 MODIS and POLYMER 10-day composites MEGS POLYMER MODIS 49% coverage 69% coverage 71% coverage Comparable coverage by MODIS and MERIS/POLYMER

17 c 2010 Improved Global Ocean Color using POLYMER Algorithm 17 / 25 Qualitative comparison of 10-day composites MODIS + MERIS Polymer MODIS + standard MERIS L3

18 Qualitative comparison of level 2 products (1/5) c 2010 Improved Global Ocean Color using POLYMER Algorithm 18 / 25

19 Qualitative comparison of level 2 products (2/5) c 2010 Improved Global Ocean Color using POLYMER Algorithm 19 / 25

20 Qualitative comparison of level 2 products (3/5) c 2010 Improved Global Ocean Color using POLYMER Algorithm 20 / 25

21 Qualitative comparison of level 2 products (4/5) c 2010 Improved Global Ocean Color using POLYMER Algorithm 21 / 25

22 Qualitative comparison of level 2 products (5/5) c 2010 Improved Global Ocean Color using POLYMER Algorithm 22 / 25

23 c 2010 Improved Global Ocean Color using POLYMER Algorithm 23 / 25 Application to the Beaufort and Chukchi Seas Improving Existing Satellite Color Observations of the Chukchi and Beaufort Seas for Biogeochemical Modeling (in collaboration with R. Frouin) MERIS/MEGS ρ + w (560) MERIS/POLYMER ρ + w (560) Better retrieval in the vicinity of ice (ice environment effect)

24 c 2010 Improved Global Ocean Color using POLYMER Algorithm 24 / 25 Robustness to the environment effect Norwegian coast, MERIS RR, July 04, 2003 (image already discussed by C. Brockmann at MERIS (A)ATSR workshop, 2005) RGB Browse ρ + w (443) from MEGS ρ + w (443) from POLYMER

25 c 2010 Improved Global Ocean Color using POLYMER Algorithm 25 / 25 Conclusion Algorithm successfully applied to MERIS Robust to sun glint, aerosols, thin clouds and environment effect Validation against in-situ measurements: comparable accuracies of the (flagged) standard algorithm, POLYMER outside sun glint and POLYMER inside sun glint Used for almost 2 years in NRT by CLS Work in progress Application to case 2 waters Application to GOCI, MODIS, SeaWiFS