An Optically-Based Technique for Producing Merged Water-Leaving Radiances; Validation
and Application for the Mediterranean Basin
Motivation: Combining the data records of LWN from independent platforms to create a single consistent time series with optimal coverage
Pre-requisite: Inter-comparison of sensor-specific products(Djavidnia et al., MERSEA report, 2006)
Principle of the Technique & Field Data
Validation of Radiometric Products (LWN) & Merger Validation
Test with a 3rd Sensor (MERIS)
Benefits of Merging & Time Series for the Mediterranean
Global Environment Monitoring Unit, E.C. - Joint Research Centre
http://marine.jrc.ec.europa.eu
Frédéric Mélin , Giuseppe Zibordi
LWN,1(λi1)LWN,2(λi2)…
MERGER
LWN,m(λ)
bio-optical modelparameters selectiona*ph , S, η
arbitrarywavelength
Chlabbp(550)ads+dt(440)
1. modelinversion
2. forward mode
Schematic of the merger: A two-step procedure
Principle of the Technique [1]
- combination of all available spectral information- selection of output wavelengths- the merged product is a primary radiometric quantity
Mélin & Zibordi, submittedIOCCG Report #6, Chap.4
Bio-optical model: (inversion by non-linear LM inversion technique)
Back-scattering:
Absorption:
parameters of the model
variables of the model
Principle of the Technique [2]
Mélin & Zibordi, submitted
Sensitivity Analysis: Dependence of the merged outputs on the bio-optical parameter set: < 4%(tested for various combinations of η, S, a*ph)
CE-318 (sea-viewing)CE-318 (sky-viewing)
Optical Field Measurements:Acqua Alta Oceanographic Tower
AAOT
Above-Water RadiometryAERONET-OC(May 2002)
SeaPRISM Lwn at 412, 440, 500, 555, 675 nm
AERONET (Jul. 1996 - now)
AERONET-OCZibordi et al., EOS, 2006
Mélin et al., IEEE, 2003Zibordi et al., IJRS, 2004Mélin & Zibordi, GRL, 2005Mélin et al., JGR, 2006Mélin et al., RSE, accepted
Operational validation of OC radiometric products[SeaWiFS, MODIS-T, -A, MERIS, GLI]
Zibordi et al., IEEE, 2004, 2006Zibordi et al., GRL 2006, EOS 2006, ECSS 2006
SeaPRISM
SeaW
iFS
Validation of SeaWiFS Radiometric Products
Zibordi, Mélin, Berthon, GRL, 2006
SeaWiFS vs. SeaPRISM match-ups
Validation of MODIS Radiometric Products
MO
DIS
-A
Zibordi, Mélin, Berthon, GRL, 2006
173 of these SeaWiFS and MODIS match-ups are on the same day, and can be the basis for validating the merged product
significant match-up dataset for both sensors
MODIS vs. SeaPRISM match-ups
SeaPRISM
Merger Validation
SeaPRISM
MER
GED
SeaWiFS only
SeaWiFS + MODIS(N=173)
MODIS only
MERGED vs. SeaPRISM match-ups
Mélin & Zibordi, submitted
SeaPRISMM
ER
IS
Overestimate of LWN in the blue ≠ SeaWiFS & MODIS
Test with 3rd Sensor: MERIS [1]
Mélin & Zibordi, submitted
SeaPRISMM
ER
GED
MERIS+MODIS+SeaWiFS
Test with 3rd Sensor: MERIS [2]
NB: Compensation of Overestimate and Underestimate of LWN in the blue
Benefits of Merging [1]
Time Series at AAOT site
SeaWiFS only (110)
SeaWiFS + MODIS (213)
MODIS only (150)
N=473 over ~ 4 years
SeaWiFS (363)
MODIS (323)
Mélin & Zibordi, submitted
MODIS - 412 nm
SeaWiFS - 412 nm
MODIS - 551 nm
SeaWiFS - 555 nm
MERGED - 412 nm MERGED - 555 nm
Daily spatial coverage - 19th Jul. 2003
Benefits of Merging [2]
Benefits of Merging [3]
SeaWiFS
MODIS
Merged
36%
Daily coverage over the Mediterranean Sea for 2003 (2-km gridded products)
22%
42%
Mélin, Zibordi, Djavidnia, submitted
Nb. Days – 2003
Time Series of Differences
Mélin, Zibordi, Djavidnia, submitted
2|SWF-MOD|/(SWF+MOD)
2(SWF-MOD)/(SWF+MOD)
RMSD(SWF-MOD)
The Merged Series
Mélin, Zibordi, Djavidnia, submitted
CONCLUSIONS
Presentation and validation of a merging technique for the production of a LWN multi-sensor record
Performance at least as good as for the sensor-specific products
Merges in a consistent way the various sensor-specific LWN spectra,taking full advantage of the available spectral bands
Allows the subsequent applications of any bio-optical algorithm
Application on the Mediterranean Sea with time seriesof differences and merged products
Still a lot to learn from the inter-comparison of the sensor-specific products