Characterizing and comparison of uncertainty in the AVHRR Pathfinder SST field, Versions 5 & 6 Robert Evans Guilllermo Podesta’ RSMAS Nov 8, 2010 with special thanks to R. Reynolds for the provision of reference fields

Description of Satellite Data LATBAND Latitude 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 against radiometer matchups (MAERI)

Description of Satellite Data-2 Test data set, NOAA-18 for years [ ] 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 and Standard Deviation

Comparison Products Processed ~5.4 years of NOAA-18, 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 LATBAND SST DT Field V6 SST – 3day AMSR composite, Yellow-green shows agreement within 0.2K Dark blue near Equator shows dust aerosol affected cold retrievals Significant 11, 12 μm SST challenge

Comparison of 1 day vs Ref Fields 3day AMSR reference OISST (NAVO AVHRR) reference Monthly AATSR reference Night only, dual view, 3 channel July 19, 2009 N18 night Note differences: Mediterranean Sea, High north latitude

N18 Night with and without new Quality test Pathfinder V6 without quality tree Pathfinder V6 with quality tree, minimizes aerosol pixels Color step = 0.2K, “zero” at blue-green transition

PF6 minimizes seasonal low and mid-latitude anomalies compared to PF5 ( ) 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 Comparisons 3day AMSR Little difference at high lat, minimal zonal and temporal oscillation OISST: NAVO AVHRR High 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 Average Night – Dual view, 3 channel High lat not available in summer Pronounced 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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