Pathfinder MODIS VIIRS Evolution of a CDR

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Pathfinder gt MODIS -gt VIIRS Evolution of a CDR

• Robert Evans, Peter Minnett, Guillermo Podesta
• Kay Kilpatrick (retired), Sue Walsh,
• Vicki Halliwell, Liz Williams
• OCRT May 4-6, 2009

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Standard SST Retrieval Equation(Pathfinder,
MODIS and VIIRS)

• SST a bT4 c(T4-T5)Tsurface
  d(sec(q)-1)(T4-T5)
• where q is the zenith angle of the instrument
• T4 and T5 are the brightness temperatures from
  AVHRR channels 4 and 5, or channels 31 and 32 for
  MODIS
• Two set of monthly coefficients are determined
  for
• T4 - T5 lt 0.7 (temperate to polar)
• T4 - T5 gt 0.7 (equatorial to temperate)
• Quality Levels
• Pathfinder defines eight quality level (0-7)
  where 7 indicates the highest confidence of an
  accurate retrieval, (0-3 for MODIS)
• Current Challenges
• Mid-high latitude seasonal anomalies,
• Dust aerosols and high water vapor

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V5 Path HadSST2(night)5.1 for N7
PathfinderHADSST2 residuals for 1982 through
2007, now includes NOAA-7
N7
N11
N9
N9
N14
N16
N18
Operational AVHRR HadSST2 (night)
V5 Path HadSST2(day)
Operational AVHRR HadSST2 (day)
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Next Generation SST Improvements

• Minimize High Latitude Seasonal Oscillation
• Approach
• Estimate Coefficients using 20o zonal bands
• centered at the Equator, 2.5o transition
  between bands
• - Coefficients estimated monthly and repeat for
  each year for a given sensor (volcano
  periods to be handled separately)
• - Reference SST Reynolds ¼o, daily
• Uses AMSR, Pathfinder and In situ
  observations
• retains SST in high gradient regions
• New algorithms are first developed and tested for
  MODIS (improved sensor characterization and more
  stable operating environment)
• Latband algorithms will be transitioned to AVHRR
  as part of our SDS program

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Application of LATBAND to MODIS AQUA 11 µm SST
MODIS algorithm produces a skin temperature
product
Latband implementation removes seasonal residual
oscillations
Note high latitude seasonal oscillations
Median of SST residuals (VALIDATION set) by
quarter (2002-2008). Each line corresponds to a
latitude band. Upper panel corresponds to
latitude-specific SST residuals lower panel is
current SST (CSST).
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Application of LATBAND to MODIS AQUA 11 µm SST
Latband S.D. order 0.4
Current algorithm S.D. order 0.5
Standard Deviation of SST residuals (VALIDATION
set) by quarter (2002-2008). Each line
corresponds to a latitude band. Upper panel
corresponds to latitude-specific SST lower panel
is current MODIS SST retrieval-buoy (CSST).
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Next Generation MODIS VIIRS SST algorithm

• Reference SST field is the V2 daily, 0.25o
  Reynolds OI analysis that incorporates AMSR,
  Pathfinder and In Situ observations.
• Use of this higher spatial and temporal
  resolution field enables retention of Pathfinder
  and MODIS retrievals in high gradient regions.
• For MODIS and VIIRS, a 3band algorithm permits
  more accurate retrievals in regions of high water
  vapor and dust aerosols.
• The 3band algorithm significantly minimizes the
  presence of cold fringes around clouds.
• For MODIS (VIIRS TBD) the use of the 3-4 µm bands
  extends the available retrievals in the presence
  of high water vapor and dust aerosols relative to
  the coverage provided by the 11-12 µm bands.

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MODIS AQUA 2 and 3 band (8.6, 11, 12µ) Night -
Latband SST- Quality 1
2 Band 02 Jul 06
Difference Field Reynolds V2- MODIS Yellow,
Red MODIS Cold
3 Band, 02 Jul 06
Use of Q0 data removes cold retrievals
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MODIS AQUA SST4 2 3 band (Night) (3.75, 3.95,
4.05 µm)Quality 1 (Reynolds V2 MODIS)
Latband 2 band
Difference Field Reynolds V2- MODIS Yellow, Re
d MODIS Cold
Latband 3 band
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Next generation MODIS SST algorithm results
02 JUL 06 Nighttime 4 um SST Using Latband
3band algo
4um SST cloudy areas filled with Reynolds V2
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Histograms of MODIS AQUA SST residuals Latband
algorithm has reduced cold residuals
Histograms comparing Latband retrievals for 2 and
3-band nighttime SST, MODIS AQUA night 02 Jul
06Reynolds V2 (2 or 3) band Q0 residuals
3 band algorithm reduces cold retrievals
Residuals calculated as Satellite - Buoy
Top panel shows distribution of latitude SST
residuals, bottom panel shows old SST (CSST). The
vertical lines correspond to, from left to right,
percentiles 0.05, 0.25, 0.50, 0.75, and 0.95.
From MODIS satellite-in situ match-up database.
Dashed curve is 2-band algorithm (cold
tail) Solid curve is 3-band algorithm (more
symmetric) 2-band algorithm has increased number
of colder retrievals
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AQUA MODIS Summary statistics for SST and
SST4Referenced to Buoys
Current Algorithm StdDev SST .45-0.50 SST4
0.38 0.40 Data Set Min Q1 Median Mean Q3 Max
StdDev N Latitude SST Training -2.509 -0.
399 -0.164 -0.178 0.056 2.114 0.387 75011 Validati
on -2.285 -0.403 -0.170 -0.181 0.055 2.348 0.389 4
0391 Dust SST Training -2.454 -0.432 -
0.186 -0.182 0.041 1.646 0.362 75011 Validation -2
.688 -0.403 -0.181 -0.180 0.044 1.742 0.363 40391
Latitude SST4 Training -2.218 -0.356 -0.1
77 -0.208 -0.017 2.237 0.346 81906 Validation -2.1
23 -0.358 -0.177 -0.208 -0.018 2.176 0.346 44104
Dust SST4 Training -2.577 -0.330 -0.19
8 -0.211 -0.072 0.903 0.240 81906 Validation -2.51
6 -0.329 -0.198 -0.211 -0.071 0.927 0.242 44104
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V6 MODIS Pathfinder Status

• SEADAS code base is being used to support MODIS
  and is being modified to support AVHRR
  Pathfinder, will facilitate distribution to
  interested users
• MODIS Latband code recently delivered to GSFC for
  incorporation into SEADAS
• For AVHRR
• L2GEN Pathfinder (SEADAS) has been delivered to
  Ken Casey, will need to be integrated into
  current GSFC L2GEN version. Tested on N16, 17,
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• Add GHRSST format output files including
  hypercube
• Latband for NOAA sensors will be integrated when
  NOAA SDS funding becomes available

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Conclusions

• New algorithm approaches (Latband) has resulted
  in a significant reduction of uncertainty in IR
  satellite SST retrievals
• S.D. reduced from 0.5 to lt0.4 for 11µm band
  retrievals,
• 0.4 to lt 0.35 for 4µm band retrievals
• Future implementation of 3 band algorithm for
  MODIS and VIIRS suggests that cold fringes around
  clouds and aerosols can be detected and
  correction in these conditions is significantly
  improved, S.D. 0.36 _at_11um, 0.24_at_4um.
• Latband and 3 band algorithm approaches will be
  implemented for VIIRS.
• AVHRR, MODIS and VIIRS satellite observations
  will be available through community accessible
  SEADAS programs.
• Pathfinder processing is being transferred to
  NODC to ensure continued availability of the
  multi-decade Pathfinder SST time series.

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