new fluorescence algorithms for the meris sensor
DESCRIPTION
New Fluorescence Algorithms for the MERIS Sensor. Yannick Huot and Marcel Babin Laboratoire d’Oc éanographie de Villefranche Antoine Mangin and Odile Fanton d'Andon ACRI-ST 28 September 2005. Research funded by: - PowerPoint PPT PresentationTRANSCRIPT
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New Fluorescence Algorithms for the
MERIS SensorYannick Huot and Marcel Babin
Laboratoire d’Océanographie de Villefranche
Antoine Mangin and Odile Fanton d'AndonACRI-ST
28 September 2005
Research funded by: A fellowship from the Natural Sciences and Engineering Research Council (NSERC)
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What is fluorescence andwhy would one care?
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Phytoplankton fluorescence• Just outside the cells:
F =ϕ f chl aϕ* Qa
* Eo
Fluorescence volume flux
Quantum yieldof fluorescence
Chlorophyllconcentration
Chlorophyll specificabsorption
Reabsorption parameter
Scalar Irradiance
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Two products of interest
F =ϕ f chl aϕ* Qa
* Eo
The Biomass
Index of physiological status
Today we are developing algorithms for these two products applicable to case 1 waters
May be useful in regions where the chlorophyll concentration cannot be obtained with standard ocean colour algorithms
Processes studies in case 1 waters
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Measurement optics
Luf 0−( ) =
14π
chl a∗__
ϕ f Qa* E
o
PAR 0−( )1
af + KPURsurf
Terms from previous page
Subsurface upwelling radiance due to fluorescence
Geometrical factor
Attenuation of downwelling and upwelling light
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Adapting recently published MODIS algorithms to MERIS
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The two products
chl =Luf 0−( ) 4π af + KPUR
surf⎡⎣ ⎤⎦
a∗__
ϕ f Qa* E
o
PAR 0−( )
ϕ f =Luf 0
−( ) 4π a f + KPURsurf⎡⎣ ⎤⎦
chl a∗__
Qa* E
o
PAR 0−( )
Fixed quantum yield
Measured chlorophyll concentration
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• Satellite algorithms:– : MERIS PAR– Chl: MERIS case 1, blue to green ratio algorithm
– Luf(0-): Transform from w to Lu and baseline method
– Kd(490): “Improved” blue to green ratio algorithm
• Case 1 waters relationships functions of Kd(490)
– versus measured Kd(490);• Bricaud et al. 1998 statistics, vs. chl
• Morel et al. 2001, Kd(490) vs. chl
Concept of the algorithm
Luf 0−( ) =
14π
chl a∗__
ϕ f Qa* E
o
PAR 0−( )1
af + KPURsurf
Eo
PAR 0−( )
a∗__
a∗__, Qa
* , KPURsurf
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WARNING:For today’s presentation
some approximations are made that would not be necessary in standard
algorithms.
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Scalar irradiance• MERIS product gives Ed(0-,PAR)
– For fluorescence we want • We assumed: 1) Upwelling irradiance negligible
2) d(0-) = 0.75 for the whole scene
We thus use:
Eo
PAR 0−( )
Eo
PAR 0−( ) =
1d
Ed 0−,PAR( )
=1.33 Ed 0−,PAR( )
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• Satellite algorithms:– : MERIS PAR– Chl: MERIS case 1, blue to green ratio algorithm
– Luf(0-): Transform from w to Lu and baseline method
– Kd(490): “Improved” blue to green ratio algorithm
• Case 1 waters relationships functions of Kd(490)
– versus measured Kd(490);• Bricaud et al. 1998 statistics, vs. chl
• Morel et al. 2001, Kd(490) vs. chl
Concept of the algorithm
Luf 0−( ) =
14π
chl a∗__
ϕ f Qa* E
o
PAR 0−( )1
af + KPURsurf
Eo
PAR 0−( )
a∗__, Qa
* , KPURsurf
a∗__
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Going from w to Lu
• Problem: MERIS algorithm returns w :
w' =π Lw 0
+( )
Ed 0+
( )
Atmospheric transmission (td) has to be approximated when one doesn’t have access to the processing chain intermediate products (probably a small error)
to calculate a quantum yield we need Lu(0-):
Lw 0+
( ) =w'π
Ed 0+( )
=w'π
Fo ε cosθsun td τ a,τ r ,θsun( )
First step to Lw(0+)
Lu (0−) =tw−a Lw nw
2
Second step to Lu(0-)
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The baseline method• MERIS bands dedicated to the natural
fluorescence measurements are:– 665, 681, and 709 nm (bands 7, 8, 9)
This approximation is good in case 1 waters (Huot et al. 2005) but great care must be taken in case 2 waters (see next talk by Babin and Huot)
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Concept of the algorithm• Satellite algorithms:
– : MERIS PAR– Chl: MERIS case 1, blue to green ratio algorithm
– Luf(0-): Transform from w to Lu and baseline method
– Kd(490): “Improved” blue to green ratio algorithm
• Case 1 waters relationships functions of Kd(490)
– versus measured Kd(490);• Bricaud et al. 1998 statistics, vs. chl
• Morel et al. 2001, Kd(490) vs. chl
Luf 0−( ) =
14π
chl a∗__
ϕ f Qa* E
o
PAR 0−( )1
af + KPURsurf
Eo
PAR 0−( )
a∗__, Qa
* , KPURsurf
a∗__
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Kd490: A “MERIS” algorithmNOMAD dataset: see Werdell, P.J. and S.W. Bailey, 2005: An improved bio-optical data set for ocean color algorithm development and satellite data product validation. Remote Sensing of Environment , 98(1), 122-140. Thank you to all contributors…
See also: http://oceancolor.gsfc.nasa.gov/REPROCESSING/Aqua/R1.1/
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Checking the Kd(490) algorithm
Morel and Maritorena 2001
Best fit polynomial
-The two algorithms are consistent, with some bias at high chl-Waters examined do not depart strongly from case 1 relationships
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Concept of the algorithm• Satellite algorithms:
– : MERIS PAR– Chl: MERIS case 1, blue to green ratio algorithm
– Luf(0-): Transform from w to Lu and baseline method
– Kd(490): “Improved” blue to green ratio algorithm
• Case 1 waters relationships functions of Kd(490)
– versus measured Kd(490);• Bricaud et al. 1998 statistics, vs. chl
• Morel et al. 2001, Kd(490) vs. chl
Luf 0−
( ) =14π
chl a∗__
φf Qa* E
o
PAR 0−( )
1af +KPUR
surf
Eo
PAR 0−( )
a∗__, Qa
* , KPURsurf
a∗__
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Case 1 water relationships
Bricaud, A., H. Claustre, J. Ras, and K. Oubelkheir. 2004. Journal of Geophysical Research 109: C11010,doi:11010.11029/12004JC002419.
Morel, A., and S. Maritorena. 2001. Journal of Geophysical Research 106: 7163-7180.
A little algebra:
A little more algebra:
Some calculus and a numerical model:
a∗ = f Kd(490)( )
Qa* = f Kd(490)( )
KPURsurf = f Kd(490)( )
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Let’s apply it on an image now…
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Noise in the 681nm band
Scene from the Benguela upwelling region measured on July 14, 2003, Second reprocessing.
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Measured by MERIS
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Chlorophyll algorithm
Best fit 1:1 line
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Chlorophyll algorithm map
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Quantum yield algorithm
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Quantum yield algorithm
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Comparison with MODIS: ϕf
MERIS MODIS
-Very noisy-Hard to use presently-However, much of the noise is not random and it may be possible to correct for it
- Quantum yield too high?
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Are we measuring something real?
No clear reason for this trend
Consistent with non-photochemical quenching
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Are we measuring something real?
Answer: Perhaps, but what?
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Conclusion• We proposed two algorithms for MERIS fluorescence bands– One for chlorophyll– One for the quantum yield
• MERIS band at 681 nm is more noisy than the 665 and 709 bands
• Algorithms need to be fully validated but preliminary results are encouraging
Future prospects• We hope to implement the algorithms with intermediate products of the processing chain to avoid the limitations of the level two products.
• We are testing iterative fluorescence algorithms using only the fluorescence bands for the retrieval of chlorophyll.
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Future prospects: first glimpse
FLH Today’s algorithm
Fluorescence bands only
It’s potential will depend on our ability to reduce the noise observed
in the 681 nm channel
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Thanks to
• David Antoine
• Norman Fomferra
• André Morel