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Compatibility between, and Merging of, OC data streams Globcolour first user consultation meeting (Dec. 06, Villefranche-sur-mer) André Morel.

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Presentation on theme: "Compatibility between, and Merging of, OC data streams Globcolour first user consultation meeting (Dec. 06, Villefranche-sur-mer) André Morel."— Presentation transcript:

1 Compatibility between, and Merging of, OC data streams Globcolour first user consultation meeting (Dec. 06, Villefranche-sur-mer) André Morel

2 OVERVIEW Before merging: Coherency of the various algorithms - The various [Chl] algorithms - The Kd(490) algorithms After merging: Other Developments and applications - From near surface [Chl], to the depth of the euphotic layer - From near-surface [Chl], to the Secchi disk depth - From Kd(490) to Kd(PAR), to the thickness of the heated layer - From {Chl] and geometry, to turbidity-related radiance excess

3 Differing Algorithms for [Chl] ° OC4v4 and OC3Mo empirical ° OC4Me semi-analytical (based on a hyperspectral model for Case 1 waters) The same hyperspectral model allows the Derivation of MERIS-type algo. spectrally tuned for the other sensors (other band setting), Such as OC4Me555 -> OC4v4 OC3Me550 -> OC3Mo SeaWiFs MODIS MERIS OC4v4 OC3Mo OC4Me

4 Same Reflectance ratios (Ri/Rj) are Introduced into OC4v4 and its MERIS- type Counterpart (OC4Me555) and OC3Mo and counterpart (OC3Me550) THEN Compare the [Chl] returns Conclusions: - Small discrepancies When [Chl] < 0.03 And [Chl] > 2 mg/m3 - Agreement for 95% of the whole ocean Transfer functions (convertibility) available

5 Curvature (sigmoidal shape) In the relationships between any Ri/Rj and [Chl] Must be present in The relationship between Ri/Rj and Kd(490) Analytically derived relationship (black curve) + NOMAD data This relationship can be used as an algorithm for Kd(490) METHOD 1 (algo OK2-555) Kd(490) Algorithms (Newport NASA Workshop April 2006)

6 METHOD 1 (Semi-analytical Algo OK2-555) Applied to NOMAD data

7 Method 1 (alg 1.1) and Method 2 (algo 2-2) provide exactly the same results (both are semi-analytical and rest on the same hyperspectral bio- optical model) Methods 1.1 and 2-1 slightly diverge (semi-analytical Kd(490) vs empirical retrieval for Chl ) (Kd490 = [Chl]^0.633)

8 Kd(490) and [Chl] empirical relationships (Case 1 waters only) LOV data (old + new) NOMAD best fit NOMAD data LOV best fit (Morel-Maritorena, 2001, slightly revised) Excellent agreement -> METHOD 2

9 METHOD 2 Via (Chl) as Intermediate tool NOMAD N = 1751 METHOD 1 Direct from R490/R555 INTER-COMPARISON

10 SeaWiFS (OC4v4) CHL September 2005 Level-3 (used for following examples)

11 -30% +30% 0 Unbiaised Rel % Diff in Kd(490) = 200 (Kd-Werdell – Kd-0K2) / (Kd-Werdell + Kd-0K2)

12 Application 1 Zeu from near-surface [Chl] Theoretical computations (Morel-Gentili, 2004) Recent (LOV) data SCAPA bank (Stan B.Hooker )

13 Zeu (from 5 to 180 m) <

14 Zsd = Γ / [cv (Zsd→0) + Kd,v (0→Zsd)] Tyler”s Equation (V = visual “scotopic human vision”) cv and Kd,v are computed through Case 1 water model, Kd,v (0→Zsd) = (Zsd)^-1 Ln [Ev(Zsd)/ Ev (0)] and cv (Zsd→0) = (Zsd)^-1 Ln { ∫ Ev(λ,Zsd) d λ / ∫ Ev(λ,Zsd) exp(-c(λ)zsd) d λ } Finally: Zsd = 8.59 – X X2 – 2.35 X3 where X = log10 [Chl] Application 2: Secchi disk depth estimate via (Chl]

15 Zsd Secchi disk depth From near-surface [Chl] MODIS - Chl Summer 2003 vs NODC Zsd All summers ( N= data) (Increment 1m)

16 Secchi disk depth (Zsd : 2-80m)

17 APPLICATION 3: K d (PAR) from Kd(490) Then, 2 / Kd(PAR) = Zhl (95% of heat deposition occur within this layer) Relationship between Kd(PAR) And Kd(490for the upper layer (2/Kd(490) thick) ) Theoretical (model 2004) SCAPA data Theoretical (model 2004)

18 Thickness of the heated layer (Zhl : 2 to 65m) 2 65

19 Upper limit value (flag) : [Lw ( )]N,lim(  s,  v,  ) = Rlim(, Chl,  s) F0( )  (  v,W) / Q(  s,  v, , Chl, ) (lookup Tables available ) Then the relative excess of radiance is quantified through:  [Lw]N / [Lw]N lim = 100 ([Lw]N - [Lw]N lim) / [Lw]N lim Detection of turbid (sediment) zones through an excess of Normalized radiance at λ = 555 nm. Quantification of this excess. (A. Morel and S. Bélanger, RSE, 2006, )

20 Excess of 555-Radiance (= turbidity index) - (July GlobColour merged product) -

21 PRELIMINARY CONCLUSIONS (Dec.06) Only for Case 1 waters (97% of the whole ocean) Various Chl algorithms (NASA-ESA) are not coincident, but compatible, and reversibility is feasible, even after merging (transfer functions for [Chl]) MADE Transfer functions for Normalized water-leaving radiances (nLw) are available (in particular for those differing in the green, 550, 555, and 560 nm) MADE Proposition for a unified Kd algorithm (before or after merging) MADE Possibilities of new, straightforward, products (euphotic layer, Secchi disk depth, heated layer) Easy discrimination/quantification of turbid Case 2 waters

22 This presention is extracted from a paper (submitted on the 12th of Nov. 2006) by André Morel, Yannick Huot, Bernard Gentili P.Jeremy Werdell, Bryan Franz, Stan B. Hooker ____________________________________________________ THANK YOU !


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