Pathfinder –> MODIS -> VIIRS Evolution of a CDR Robert Evans, Peter Minnett, Guillermo Podesta Kay Kilpatrick (retired), Sue Walsh, Vicki Halliwell, Liz Williams GHRSST-X – June 1-5, 2009

Standard SST Retrieval Equation (Pathfinder, MODIS and VIIRS) SST = a + b*T4 + c*(T4-T5)*T surface + 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 <= 0.7 (temperate to polar) T4 - T5 > 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

V5 Path – HadSST2 (night) 5.1 for N7 Operational AVHRR – HadSST2 (night) V5 Path – HadSST2 (day) Operational AVHRR – HadSST2 (day) +N7 +N9 +N11 +N9+N14 +N16+N18 Pathfinder–HADSST2 residuals for 1982 through 2007, provided by Casey and Brandon, NODC

Next Generation SST Improvements Minimize High Latitude Seasonal Oscillation Approach: – Estimate Coefficients using 20 o zonal bands centered at the Equator, ± 2.5 o transition between bands - Coefficients estimated monthly and repeat for each year for a given sensor (volcano periods to be handled separately) - Reference SST – Reynolds ¼ o, daily Uses AMSR, Pathfinder and In situ observations retains satelite 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

Application of LATBAND to MODIS AQUA Median of SST residuals (VALIDATION set) by quarter ( ). Each line corresponds to a latitude band. Upper panel corresponds to latitude-specific SST residuals; lower panel is current SST (CSST). MODIS algorithm produces a ‘skin temperature’ product Note high latitude seasonal oscillations Latband implementation removes seasonal residual oscillations

Application of LATBAND to MODIS AQUA Standard Deviation of SST residuals (VALIDATION set) by quarter ( ). Each line corresponds to a latitude band. Upper panel corresponds to latitude-specific SST; lower panel is current MODIS SST retrieval-buoy (CSST). Latband S.D. order 0.4 Current algorithm S.D. order 0.5

Next Generation MODIS + VIIRS SST algorithm Reference SST field is the V2 daily, 0.25 o 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 μ m bands extends the available retrievals in the presence of high water vapor and dust aerosols relative to the coverage provided by the μ m bands.

MODIS AQUA SST4 2 & 3 band (Night) – (3.75, 3.95, 4.05 μm) GHRSST Quality 4 (Reynolds V2 – MODIS) Latband 2 band Latband 3 band Difference Field Reynolds V2- MODIS Yellow, Red MODIS Cold

MODIS AQUA 2 and 3 band (8.6, 11, 12μ) Night - Latband SST- GHRSST Quality 4 2 Band 02 Jul 06 3 Band, 02 Jul 06 Difference Field Reynolds V2- MODIS Yellow, Red MODIS Cold Use of Q0 data removes cold retrievals

Histograms of MODIS AQUA SST residuals Latband algorithm has reduced cold residuals 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 From MODIS satellite-in situ match-up database. Residuals calculated as Satellite - Buoy Histograms comparing Latband retrievals for 2 and 3-band nighttime SST, MODIS AQUA night 02 Jul 06 Reynolds V2 – (2 or 3) band Q0 residuals 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 3 band algorithm reduces cold retrievals 3 band algorithm reduces cold retrievals

MODIS AQUA compared to Reynolds V2 Black – Quality 5, Red – Quality 4 July 2, 2006,East Coast US, Gulf Mex, Caribbean Two bandThree Band Quality 4 includes data approaching cloud fronts, higher water vapor regions and dust aerosols. Use of 3 band provides improved retrievals.

AQUA MODIS Summary statistics for SST and SST4 Full Swath, all StdDev assigned to MODIS, buoy ref Current Algorithm StdDevSST 0.45 – 0.5SST4 0.4 Data SetMinQ1MedianMeanQ3MaxStdDevN 2 band Latitude SST Training Validation band Dust SST Training Validation Latitude SST4 Training Validation Dust SST4 Training Validation Nighttime only – Δ distance < 11kmΔ time < 30 minutes

After grouping MDB records by quality level the dataset is partitioned into a multi-dimensional array with the following 7 dimensions: -time by season (4) -latitude bands (5 steps in 20 degree from 60S to 60N) -surface temperature (8 increments in 5 degree steps) -satellite zenith angle (4 increments) -brightness temperature difference as a proxy for water vapor (4 intervals for 4µ and 3 intervals for 11-12µ SST) -retrieved satellite SST quality level (2 intervals ql=0 and 1) -day/night selection (2 intervals). Can consider interpolation for red dimension

AQUA LATBAND Distribution of RMS as a function of Satellite Zenith Angle and SST The diagram shows SST as a function of (a) buoy SST (x-axis) and (b) satellite zenith angle. The density of occurrence of residuals in the bivariate space is indicated by the colors in each bin (hexagon); the color scale is shown on the right. The overlaid contours indicate the RMS of SST residuals inside each bin. This graphic is intended to help build a “data hypercube”. 0.5 RMS 0.4 RMS <0.4 RMS RMS < 0.4 for 0<T<27C and 0<SatZ<40 RMS < 0.5 for 27<T<30C and 40<SatZ<60

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 <0.4 for 11μm 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. 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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Boxplot of latitude-SST residuals (validation SET), by quarter (Latband AQUA MODIS). Central box contains 50% of residuals, outer bars represent 95% of residuals. Most residuals are within ± 1.5K. Each zonal band consistent with time with same monthly coefficient set applied for each year. Time, by quarter from July 2002 to April, 2008 AQUA SST residuals (SST- buoy)

NOAA-7 added to Pathfinder Time Series RSMAS work supported by Chet Ropelewski, NOAA CPC Challenges – Few buoy in-situ observations exist during this period – El Chichon eruption – volcanic aerosols Approach – Collaboration with R. Reynolds to provide access to ship observations corrected to buoy reference – Iterative approach to compute N7 SST fields (Miami) and OI reference fields (Reynolds, NCDC) using V2 OI ( daily, 1/4° resolution)

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 AVHRR support – Add GHRSST format output files including hypercube – L2GEN Pathfinder (SEADAS) has been delivered to Ken Casey, will need to be integrated into current GSFC L2GEN version. Tested on N16, 17, 18 – Latband for NOAA sensors will be integrated when NOAA SDS funding becomes available

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