Characterizing and comparison of uncertainty in the AVHRR

Pathfinder SST field, Versions 5 & 6

Robert EvansGuilllermo Podesta’

RSMASNov 8, 2010

with special thanks to R. Reynolds forthe provision of reference fields

Description of Satellite Data

LATBANDLatitude

increments

•Pathfinder Version 6 (PF6) based on LATBAND formulation – 6 zonal bands 20 degrees wide centered on the Equator•2.5 degree wide transition band, linearly interpolated•Coefficients estimated monthly, e.g. all January sat-in situ observations grouped, for available years of a given sensor•Matchup criteria – within 2km and ±30 minutes for buoy-satellite observation•Skin temperature product•SST retrievals validated againstradiometer matchups (MAERI)

Description of Satellite Data-2•Test data set, NOAA-18 for years [2005-2010]•NOAA-18 chosen due to processing speed of GAC data , approximately 30 minutes/year of global GAC observations and good availability of buoy observations and reference fields•All available satellite pixels processed and compared to reference field•Subsequent processing averages all best quality pixels within a ¼ degree box•Time of observation, Difference from reference field (DT) included

Pathfinder Version 6 Quality Hypercube

Quality variables and partitions

Provides per pixel Bias andStandard Deviation

Comparison Products• Processed ~5.4 years of NOAA-18, 2005-2010•¼ degree daily Pathfinder – Reference field (DT)•Comparison with each of 5 reference fields

•Three types of comparison•Reference to buoys using buoys not included in coefficient estimation•Daily DT fields, to show regions of difference•Latitude, Time plots based on best quality zonal average of each DT field, to show persistent zonal differences and temporal trends

Buoy Comparison of Pathfinder Versions 5 & 6

SST Reference File – 5 versions

• Richard Reynolds provided 3 versions of the ¼ degree, daily V2 OI• OI + AVHRR (from NAVO, day + night satellite data)• OI + AVHRR + AMSR (day + night satellite data)• OI + AVHRR + AMSR (night only satellite data, minimize

possible impact of residual diurnal warming)• 3 Day AMSR composite (day + night), daily, ¼ degree field (RSS)• AATSR (night only), based on 0.1 degree night only, 3 channel,

dual view product (processing version: May, 2010)• R . Reynolds processed AATSR daily fields into monthly, ¼

degree maps to fill gaps due to combination of narrow swath and cloudy observing conditions

Product Validation July 19, 2009 N18 night

Version 6 LATBANDSST

DT FieldV6 SST – 3day AMSR composite,Yellow-green shows agreement within0.2KDark blue near Equator shows dustaerosol affected coldretrievalsSignificant 11, 12 μmSST challenge

Comparison of 1 day vs Ref Fields

3day AMSR reference

OISST (NAVO AVHRR)

reference

Monthly AATSR referenceNight only, dual view, 3 channel

July 19, 2009 N18 night

Note differences:Mediterranean Sea, High north latitude

2009200 N18 Night with and without new Quality test

Pathfinder V6without qualitytree

Pathfinder V6with qualitytree, minimizesaerosol pixels

Color step = 0.2K, “zero” at blue-green transition

PF6 minimizes seasonal low and mid-latitude anomalies compared to PF5 (2006-2009)

Bias stable across time series• Ref: OI+(NAVO)AVHRR+AMSR Night only-sat, N18

• PF5

• Grey ±0.1K

• PF6

6 Year Night Pathfinder V6-Reference Comparisons3day AMSR

Little difference at high lat, minimal zonal and

temporal oscillation

OISST: NAVO AVHRRHigh north lat summer,

mid lat zonal oscillation (N)

OISST: NAVO AVHRR+ AMSR

Similar comparison for all OI versions

Middle grey band ± 0.1K

AATSR : Monthly AverageNight – Dual view, 3 channel

High lat not available in summerPronounced seasonal zonal oscillation

(N+S)N equatorial aerosol more pronounced

Conclusions

•Comparison with 3day AMSR fields shows smallest residuals, OI and AATSR show larger seasonal, zonal oscillation•Comparison with July night field shows differences between reference fields (High Lat, western N Pacific, Mediterranean Sea)•Ensemble average of reference fields possibly the preferred approach•Improved quality test reduced cloud and aerosol impact•However, dust aerosol impact remains an issue

Conclusions-2

•Pathfinder V6 stable for 5.4 years of N-18, no long term trends observed•Pathfinder Version 6 reduced but did not eliminate seasonal anomalies except for AMSR comparison•PF6 includes Quality Hypercube, time of observation and DT fields, consistent with MODIS and VIIRS implementation•AVHRR, MODIS and VIIRS all now supported in SeaDAS L2gen

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