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
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?
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
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
Trophic Subsets
Deep-Water (Depth > 1000m) Oligotrophic (Chlorophyll < 0.1)
Mesotrophic (0.1 < Chlorophyll < 1) Eutrophic (1 < Chlorophyll < 10)
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
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
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
Mean spectral differences agree with expectations
SeaWiFS MODISA
oligotrophicmesotrophiceutrophic488
490
547 & 555
Variability in SeaWiFS & MODIS/Aqua Rrs timeseries are similar in all trophic subsets
Rrs (443) Rrs (55X)
deep wateroligotrophicmesotrophiceutrophic
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
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
The Multi-Mission Data Record
SeaWiFS SeaWiFS
MODIS/Aqua MODIS/Aqua
Fall 2002 Fall 2008
The Multi-Mission Data Record
SeaWiFS SeaWiFS
MODIS/Terra MODIS/Terra
Fall 2002 Fall 2008
Global Chlorophyll Timeseries
Oligotrophic Subset
Mesotrophic Subset
SeaWiFS
SeaWiFS
Global Chlorophyll Timeseries
Oligotrophic Subset
Mesotrophic Subset
SeaWiFS MODISA
SeaWiFS MODISA
Global Chlorophyll Timeseries
Oligotrophic Subset
Mesotrophic Subset
SeaWiFS MODISA MODIST
SeaWiFS MODISA MODIST
before reprocessing
before reprocessing
Global Chlorophyll Timeseries
Oligotrophic Subset
Mesotrophic Subset
SeaWiFS MODISA MODIST MERIS
SeaWiFS MODISA MODIST MERIS
Comparison of variability in Chlorophyll Timeseries
SeaWiFS to MODISA SeaWiFS to MODIST
SeaWiFS to MERIS
deep wateroligotrophicmesotrophiceutrophic
Global Chlorophyll Anomaly Timeseries
Oligotrophic Subset
Mesotrophic Subset
SeaWiFS MODISA
SeaWiFS MODISA
Global Chlorophyll Anomaly Timeseries
Oligotrophic Subset
Mesotrophic Subset
SeaWiFS MODISA MODIST
SeaWiFS MODISA MODIST
5%, ± 0.003 mg m-3
Global Chlorophyll Anomaly Timeseries
Oligotrophic Subset
Mesotrophic Subset
SeaWiFS MODISA MODIST MERIS
SeaWiFS MODISA MODIST MERIS
5%, ± 0.003 mg m-3
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
New Missions
NPP/VIIRSOct 2011 launch
Oceansat-2/OCM-2Sep 2009 launch
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
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)
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)
Outline
Development of an ocean color CDR
Assessment of data quality
Future directions