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GOES-R AWG Ocean Dynamics Team: Ocean Currents and Offshore Ocean Currents Algorithm June 14, 2011

GOES-R AWG Ocean Dynamics Team: Ocean Currents and Offshore Ocean Currents Algorithm June 14, 2011. Presented By: Eileen Maturi 1 , Igor Appel 2 , Andy Harris 3 1 NOAA/NESDIS/STAR 2 NOAA/NESDIS/STAR/IMSG 3 University of Maryland/CICS.

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GOES-R AWG Ocean Dynamics Team: Ocean Currents and Offshore Ocean Currents Algorithm June 14, 2011

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  1. GOES-R AWG Ocean Dynamics Team: Ocean Currents and Offshore Ocean Currents AlgorithmJune 14, 2011 Presented By: Eileen Maturi1, Igor Appel2, Andy Harris3 1 NOAA/NESDIS/STAR 2 NOAA/NESDIS/STAR/IMSG 3 University of Maryland/CICS GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  2. Outline • Executive Summary (1 slide) • Algorithm Description (2-4 slides) • ADEB and IV&V Response Summary (1-2 slides) • Requirements Specification Evolution (2 slides) • Validation Strategy (3-5 slides) • Validation Results (3-5 slides) • Summary (1-2 slides) GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  3. Executive Summary • The Ocean Dynamic Algorithm (ODA) generates the Option 2 products of Ocean Currents and Ocean Currents: Offshore . • Algorithm Version 4 was delivered in March. ATBD (100%) is on track for a June 30 delivery • A 1-channel IR-only approach has been developed that utilizes improved ABI resolution capabilities over GOES-IM and GOES-NOP. • Validation tools have been developed and applied to 4 weeks of SEVIRI data. • Comparisons with output from the global version of the Navy Coastal Ocean Model (NCOM) indicate 80% spec compliance for all products. GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  4. Algorithm Description GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  5. Algorithm Summary • This Ocean Dynamic Algorithm (ODA) generates the Option 2 products Ocean Currents and Ocean Currents: Offshore • We use an IR-only approach that provides day/night consistency and takes advantage of the ABI’s higher resolution information • We use three images to monitor motion of the ocean features characterized by the maximum gradient in sea surface brightness temperature • SEVIRI 10.8 micron channel is a proxy for ABI channel 14 (11.2 micron) • A cloud mask is applied to identify cloud free areas GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  6. Ocean Currents Mathematical Description: Feature Tracking Sum-of-Squared Differences (SSD) Search Region Matching Scene I1 = Temperature at pixel (x1,y1) of the target scene I2 = Temperature at pixel (x2,y2) of the search scene Original Target Scene • Summation is carried out for all possible target scene positions within the search region • The matching scene corresponds to the scene where the function takes on the smallest value GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  7. EXAMPLE of SUM SQUARED DIFFERENCE RESULTS Example SSD for 5×5 pixel target applied to t0 & 3 hr, Note displacements are ~symmetrical c.f. zero displacement This is a good consistency check GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  8. Ocean Dynamics Algorithm Processing Schematic Read GOES-R IR & SST data Apply Cloud Mask & Land Mask Ocean Currents Algorithm (feature detection, pattern matching – SSD*, vector derivation, QC) *SSD = Sum of Squared Differences Output Ocean Current Vectors GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  9. Qualifiers Theses are made with the following qualifiers • Sensor zenith angle < 67 degrees • Region must be cloud-free in image triplet • Cloud & land masks available • Dependent on navigation accuracy • Errors depend on strength of SST gradient in feature being tracked GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  10. Expected ABI Performance Relative to Other Sensors • Current GOES Imager has approximately 4-km resolution so ABI has a 4x better resolution • Critical, especially for Ocean Currents where image-to-image displacements are small • N.B. MSG-SEVIRI has resolution of 3 km • Navigation accuracy of ABI expected to be much better (750 m) • Again, critical for Ocean Currents because image-to-image registration errors contribute directly to retrieval error GOES-R AWG Annual Meeting, Madison, Wisconsin, June 14-16, 2011

  11. Next Steps to Reach 100% • Refine internal QC metrics based on various parameters (e.g. gradient strength) • Investigate impact of navigation errors on performance using proxy data to ascertain if expected ABI navigation improvement will reduce errors sufficiently to meet 100% specification • Careful co-registration of sample of individual SEVIRI images for triplets which contain notable retrieval errors GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  12. Example ODA Output Example Ocean Current Vectors derived from MSG-SEVIRI image triplet centered at 12Z Vector length indicates derived current strength (1 degree = 1 m.s-1) Shows upwelling off N Africa, combined with complex current pattern in the vicinity of the Canary Islands July 8, 2005 Canary Islands North Africa GOES-R AWG Annual Meeting, Fort Collins, Colorado June 14-16, 2011

  13. Algorithm Changes from 80% to 100% • Added multi-layer cloud analysis that accounts for height of the lower cloud layer. At the 80% version, the lower cloud height was assumed to be 2 km above the surface. • Metadata output added. • Quality flags standardized. GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  14. ADEB and IV&V Response Summary “OK for advance to 100%, with caveat that team pursue further validation with SEVIRI and also explain N-S vs E-W asymmetry” • Validation expanded to use HYCOM 1/12 degree resolution DA Experiment results for surface currents • Also validation using CODAR with vectors derived from GOES-Imager • N-S / E-W variations in geolocation accuracy are suspected and this is being investigated GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  15. Requirements GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  16. Qualifiers Theses are made with the following qualifiers. • Sensor zenith angle < 65 degrees • Cloud optical thickness > 1 • Cloud mask and cloud type available GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  17. Validation Approach GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  18. Validation Strategy: Comparison of MSG-derived current vectors vs. Model • Use ocean current vector components from the global version of the Navy Coastal Ocean Model (NCOM) • Advantage of using model field is that vectors are available “everywhere” • Potential for model-related biases (e.g. displaced currents, errors in forcing fields). However, NCOM does assimilate data (e.g. Altimetry) and is therefore constrained by it • “Global” NCOM is high resolution (at least eddy-resolving) GOES-R AWG Annual Meeting, Madison, Wisconsin, June 7-10, 2010

  19. Validation Results (2) 5x5 window (Meteosat-8 SEVIRI vs NCOM, 2005 days 2-9, 92-99, 183-190, 275-282) Orange = gaussian curve representedby S.D. Green = gaussian represented by R.S.D. Blue = histogram of errors (MSG – NCOM) Median = 0.13 R.S.D. = 0.348 Median = 0.06 R.S.D. = 0.297 Note: green curve matches peak & central distribution GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  20. Validation Results (3) 5x5 window (Meteosat-8 SEVIRI vs NCOM, 2005 days 2-9, 92-99, 183-190, 275-282) Note errors in U-component are more prevalent in certain geographical areas V-component errors display little geographical preference GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  21. DEPENDENCE OF RETRIEVAL QUALITY ON SST GRADIENTS – 5x5 WINDOW =0.5 =0.3 80% 100% GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  22. Validation statistics for 5x5 window excluding weak (<0.5 K) gradients GREEN CELLS=100% YELLOW CELLS=80% RED CELLS=< 80% Meteosat-8 SEVIRI vs NCOM, 2005 days 2-9, 92-99, 183-190, 275-282 GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  23. NEW Validation Strategy: Comparison of MSG-derived current vectors vs. HYCOM Filtered using QI>30 (retains 72%) Days 182 – 189 (“Summer”) Every 30 minutes (previously just 12Z) tests effect of day & night cloud masking Median = 0.02 R.S.D. = 0.258 Median = -0.03 R.S.D. = 0.247 GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  24. Summary • 100% specification requirement is met using a 5x5 target when considering robust statistics (vs. HYCOM data) and “mild” filter on Quality Indicator • Retains 72% for QI>30 (range is 0 – 100) • HYCOM validation has been performed for 30 min intervals throughout day c.f. previous 12Z-only • Increased outliers may be due to variations in cloud mask performance – investigations ongoing • Delivery of Version 5 Algorithm (100%) is on track • Various algorithm aspects (e.g. QC) will be refined in order to meet 100% requirement (e.g. outlier rejection) GOES-R AWG Annual Meeting, Fort Collins, Colorado, June 14-16, 2011

  25. Summary cont’d Working with CIOSS on GOES-R Risk Reduction • Analyze the representativeness of feature-tracked motions to ocean currents in a 1-km resolution regional ocean model and the findings will be reported in the next version of the ATBD • Also explore different variants of feature-tracking and possible transfer functions from motion to surface current • Also explore data assimilation approach GOES-R AWG Annual Meeting, Fort Collins, Colorado June 14-16, 2011

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