Compatibility between, and Merging of,

OC data streams

Globcolour first user consultation meeting(Dec. 06, Villefranche-sur-mer)

André Morel

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

Differing Algorithms for [Chl]

° OC4v4 and OC3Mo empirical

° OC4Me semi-analytical (based on a hyperspectral model for Case 1 waters)

The same hyperspectralmodel allows theDerivation of MERIS-type algo. spectrally tunedfor the other sensors (other band setting),

Such as OC4Me555 -> OC4v4OC3Me550 -> OC3Mo

SeaWiFs

MODIS

MERIS

OC4v4

OC3Mo

OC4Me

Same Reflectance ratios (Ri/Rj) areIntroduced into OC4v4 and its MERIS-type Counterpart (OC4Me555) andOC3Mo and counterpart (OC3Me550)

THEN

Compare the [Chl] returns

Conclusions:- Small discrepancies When [Chl] < 0.03And [Chl] > 2 mg/m3- Agreement for 95% of the whole ocean Transfer functions (convertibility) available

Curvature (sigmoidal shape)In the relationships between any Ri/Rj and [Chl]

Must be present in

The relationship betweenRi/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)

METHOD 1 (Semi-analytical Algo OK2-555)

Applied to NOMAD data

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 = 0.0166 + 0.0835[Chl]^0.633)

Kd(490) and [Chl] empirical relationships (Case 1 waters only)

LOV data (old + new)NOMAD best fit

NOMAD dataLOV best fit(Morel-Maritorena, 2001, slightly revised)

Excellent agreement-> METHOD 2

METHOD 2Via (Chl) asIntermediatetool

NOMADN = 1751

METHOD 1Direct from R490/R555

INTER-COMPARISON

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

-30% +30%

0

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

Application 1 Zeu from near-surface [Chl]

Theoretical computations(Morel-Gentili, 2004)

Recent (LOV) data

SCAPA bank (Stan B.Hooker)

Zeu (from 5 to 180 m)

<5 18090

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 – 12.55 X + 8.17 X2 – 2.35 X3 where X = log10 [Chl]

Application 2: Secchi disk depth estimate via (Chl]

ZsdSecchi disk depthFrom near-surface [Chl]

MODIS - Chl Summer 2003 vsNODC Zsd1900-1990All summers

( N= 66009 data)

(Increment 1m)

Secchi disk depth (Zsd : 2-80m)

APPLICATION 3:Kd (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)

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

2 65

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, 237-249)

Excess of 555-Radiance (= turbidity index)

- (July 2002 - GlobColour merged product) -

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

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 !