an optically-based technique for producing merged water-leaving radiances; validation and...

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