achieving global ocean color climate data records aslo aquatic sciences meeting 17 february 2011 –...
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Achieving Global Ocean Color Climate Data Records
ASLO Aquatic Sciences Meeting
17 February 2011 – San Juan, Puerto Rico
Bryan A. Franzand the
NASA Ocean Biology Processing Group
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A climate data record is a time series of measurements of sufficient length, consistency, and continuity to determine climate variability and change.
U.S. National Research Council, 2004
What is a Climate Data Record?
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1980 200019901985 201020051995
Length & continuity achieved via multiple missions
SeaWiFS (NASA)CZCS (NASA)
MODIS-Terra (NASA)
MERIS (ESA)
MODIS-Aqua (NASA)
OCM2 (ISRO)
IOCCG 2010
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How do we achieve consistency?
• Focus on instrument calibration – establishing temporal stability within each mission
• Apply common algorithms– ensuring consistency of processing across missions
• Apply common vicarious calibration approach– ensuring spectral and absolute consistency of water-leaving radiance
retrievals under idealized conditions
• Perform detailed trend analyses (hypothesis testing)– assessing temporal stability & and mission-to-mission consistency
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Trophic Subsets
Deep-Water (Depth > 1000m) Oligotrophic (Chlorophyll < 0.1)
Mesotrophic (0.1 < Chlorophyll < 1) Eutrophic (1 < Chlorophyll < 10)
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How do we achieve consistency?
• Concentrate on instrument calibration – establishing temporal stability within each mission
• Apply common algorithms– ensuring consistency of processing across missions
• Apply common vicarious calibration approach– ensuring spectral and absolute consistency of water-leaving radiance
retrievals under idealized conditions
• Perform detailed trend analyses (hypothesis testing)– assessing temporal stability & and mission-to-mission consistency
• Reprocess multi-mission timeseries– incorporating new instrument knowledge and algorithm advancements
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Latest NASA Reprocessing
Highlights:• incorporated sensor calibration updates**• regenerated all sensor-specific tables and coefficients• improved aerosol models based on AERONET• updated chlorophyll a and Kd algorithms based on NOMAD v2
Status:• MODISA completed April 2010 (update in progress)• SeaWiFS completed September 2010• OCTS completed September 2010• MODIST completed January 2011• CZCS in progress
Scope: MODISA, MODIST, SeaWiFS, OCTS, CZCS
http://oceancolor.gsfc.nasa.gov/WIKI/OCReproc.html
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SeaWiFS & MODISA Rrs in good agreementDeep-Water
solid line = SeaWiFS R2010.0dashed = MODISA R2009.1
Rrs
(st
r-1)
412
443
488 & 490
510531547 & 555
667 & 670
within 5%at all times
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Mean spectral differences agree with expectations
SeaWiFS MODISA
oligotrophicmesotrophiceutrophic488
490
547 & 555
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Variability in SeaWiFS & MODIS/Aqua Rrs timeseries are similar in all trophic subsets
Rrs (443) Rrs (55X)
deep wateroligotrophicmesotrophiceutrophic
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MODISA Rrs showing late-mission drift
412
443
488-490
510
531
Deep-Water
solid line = SeaWiFS R2010.0dashed = MODISA R2009.1
Rrs
(st
r-1)
MODISA to be reprocessedfrom at least 2009 onward
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MODIST & MERIS vs SeaWiFS Rrs
ESA 3rd reprocessing of MERIS underway. First calibration update since 2006.
ESA OC-CCI plan to reprocess MERIS with NASA common algorithms.
Formal arrangments for NASA-ESA data exchange in progress.
MODIST & SeaWiFS MERIS & SeaWiFS
OCL-off
cal model extrapolation
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The Multi-Mission Data Record
SeaWiFS SeaWiFS
MODIS/Aqua MODIS/Aqua
Fall 2002 Fall 2008
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The Multi-Mission Data Record
SeaWiFS SeaWiFS
MODIS/Terra MODIS/Terra
Fall 2002 Fall 2008
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Global Chlorophyll Timeseries
Oligotrophic Subset
Mesotrophic Subset
SeaWiFS
SeaWiFS
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Global Chlorophyll Timeseries
Oligotrophic Subset
Mesotrophic Subset
SeaWiFS MODISA
SeaWiFS MODISA
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Global Chlorophyll Timeseries
Oligotrophic Subset
Mesotrophic Subset
SeaWiFS MODISA MODIST
SeaWiFS MODISA MODIST
before reprocessing
before reprocessing
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Global Chlorophyll Timeseries
Oligotrophic Subset
Mesotrophic Subset
SeaWiFS MODISA MODIST MERIS
SeaWiFS MODISA MODIST MERIS
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Comparison of variability in Chlorophyll Timeseries
SeaWiFS to MODISA SeaWiFS to MODIST
SeaWiFS to MERIS
deep wateroligotrophicmesotrophiceutrophic
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Global Chlorophyll Anomaly Timeseries
Oligotrophic Subset
Mesotrophic Subset
SeaWiFS MODISA
SeaWiFS MODISA
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Global Chlorophyll Anomaly Timeseries
Oligotrophic Subset
Mesotrophic Subset
SeaWiFS MODISA MODIST
SeaWiFS MODISA MODIST
5%, ± 0.003 mg m-3
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Global Chlorophyll Anomaly Timeseries
Oligotrophic Subset
Mesotrophic Subset
SeaWiFS MODISA MODIST MERIS
SeaWiFS MODISA MODIST MERIS
5%, ± 0.003 mg m-3
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Summary
• SeaWiFS is the first decadal-scale climate data record for ocean chlorophyll and, by proxy, phytoplankton biomass.
• MODIS/Aqua open-ocean timeseries in very good agreement– monthly reflectances agree to with 2% on average, 5% at all times
– chlorophyll variability is well correlated (90-95%) and equivalent in scale
– revised calibration model / reprocessing needed to fix late mission trends
• MODIS/Terra in much better agreement with SeaWiFS & MODISA after reprocessing, but after extensive cross-calibration to SeaWiFS– not an independent climate data record
• Instrument degradation is the primary challenge to development of ocean color climate data records. – use additional caution when interpretting data from recent years
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New Missions
NPP/VIIRSOct 2011 launch
Oceansat-2/OCM-2Sep 2009 launch
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OCM-2 Monthly Chlorophyll
limited on-board recording capacity and bi-annual tilt restrict sampling
ISRO data distribution: http://218.248.0.134:8080/OCMWebSCAT/html/controller.jspNASA test products: http://oceancolor.gsfc.nasa.gov/cgi/l3
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1980 200019901985 201020051995
Length & continuity achieved via multiple missions
SeaWiFS (NASA)CZCS (NASA)
MODIS-Terra (NASA)
MERIS (ESA)
MODIS-Aqua (NASA)
OCM2 (ISRO)
IOCCG 2010
VIIRS (USA)
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Different Instruments Designs
SeaWiFS
• 8 spectral bands (412-865nm)
• sufficient signal-to-noise• lunar calibration capability• tilt to minimize glint• very low polarization sensitivity• rotating telescope
• out-of-band response• straylight issues• subsampled global coverage
MODIS/Aqua
• 36 spectral bands (412-2130nm)
• increased signal-to-noise• reduced out-of-band response• global 1km coverage
• significant polarization sensitivity
• greater sunglint losses (no tilt)• multiple detectors (striping)• rotating, exposed scan mirror
(greater optical degradation)
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Outline
Development of an ocean color CDR
Assessment of data quality
Future directions