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## New Fluorescence Algorithms for the MERIS Sensor

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**New Fluorescence Algorithms for the MERIS Sensor**Yannick Huot and Marcel Babin Laboratoire d’Océanographie de Villefranche Antoine Mangin and Odile Fanton d'Andon ACRI-ST 28 September 2005 Research funded by: A fellowship from the NaturalSciencesandEngineeringResearchCouncil (NSERC)**Phytoplankton fluorescence**Fluorescence volume flux Quantum yield of fluorescence Chlorophyll concentration Chlorophyll specific absorption Reabsorption parameter Scalar Irradiance • Just outside the cells:**Two products of interest**The Biomass Index of physiological status May be useful in regions where the chlorophyll concentration cannot be obtained with standard ocean colour algorithms Processes studies in case 1 waters Today we are developing algorithms for these two products applicable to case 1 waters**Measurement optics**Subsurface upwelling radiance due to fluorescence Attenuation of downwelling and upwelling light Terms from previous page Geometrical factor**The two products**Fixed quantum yield Measured chlorophyll concentration**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**WARNING:For today’s presentationsome approximations are**made that would not be necessary in standard algorithms.**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:**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**Going from w to Lu**First step to Lw(0+) Atmospheric transmission (td) has to be approximated when one doesn’t have access to the processing chain intermediate products (probably a small error) Second step to Lu(0-) • Problem: MERIS algorithm returns w: to calculate a quantum yield we need Lu(0-):**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)**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**Kd490: A “MERIS” algorithm**NOMAD 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/**Checking the Kd(490) algorithm**Best fit polynomial Morel and Maritorena 2001 -The two algorithms are consistent, with some bias at high chl -Waters examined do not depart strongly from case 1 relationships**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**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:**Noise in the 681nm band**Scene from the Benguela upwelling region measured on July 14, 2003, Second reprocessing.**Chlorophyll algorithm**Best fit 1:1 line**Comparison with MODIS: f**MODIS MERIS -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?**Are we measuring something real?**No clear reason for this trend Consistent with non-photochemical quenching**Are we measuring something real?**Answer: Perhaps, but what?**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.**Future prospects: first glimpse**Today’s algorithm Fluorescence bands only FLH It’s potential will depend on our ability to reduce the noise observed in the 681 nm channel**Thanks to**• David Antoine • Norman Fomferra • André Morel