An Optically-Based Technique

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An Optically-Based Technique for Producing Merged Water- Leaving Radiances; Validation and Application for the Mediterranean Basin otivation: Combining the data records of L WN from independent latforms to create a single consistent time series with optimal cove re-requisite: Inter-comparison of sensor-specific products Djavidnia et al., MERSEA report, 2006) rinciple of the Technique & Field Data alidation of Radiometric Products (L WN ) & Merger Validation est with a 3 rd Sensor (MERIS) enefits of Merging & Time Series for the Mediterranean Global Environment Monitoring Unit, E.C. - Joint Research C http://marine.jrc.ec.europa.eu Frédéric Mélin , Giuseppe Zibor

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An Optically-Based Technique for Producing Merged Water-Leaving Radiances; Validation and Application for the Mediterranean Basin. Frédéric Mélin , Giuseppe Zibordi. Global Environment Monitoring Unit, E.C. - Joint Research Centre. - PowerPoint PPT Presentation

Transcript of An Optically-Based Technique

Page 1: An Optically-Based Technique

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

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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

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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)

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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

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SeaPRISM

SeaW

iFS

Validation of SeaWiFS Radiometric Products

Zibordi, Mélin, Berthon, GRL, 2006

SeaWiFS vs. SeaPRISM match-ups

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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

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Merger Validation

SeaPRISM

MER

GED

SeaWiFS only

SeaWiFS + MODIS(N=173)

MODIS only

MERGED vs. SeaPRISM match-ups

Mélin & Zibordi, submitted

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SeaPRISMM

ER

IS

Overestimate of LWN in the blue ≠ SeaWiFS & MODIS

Test with 3rd Sensor: MERIS [1]

Mélin & Zibordi, submitted

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SeaPRISMM

ER

GED

MERIS+MODIS+SeaWiFS

Test with 3rd Sensor: MERIS [2]

NB: Compensation of Overestimate and Underestimate of LWN in the blue

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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

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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]

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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

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Time Series of Differences

Mélin, Zibordi, Djavidnia, submitted

2|SWF-MOD|/(SWF+MOD)

2(SWF-MOD)/(SWF+MOD)

RMSD(SWF-MOD)

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The Merged Series

Mélin, Zibordi, Djavidnia, submitted

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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