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Optimizing Multiple Scattering Calculations in the CRTM: Update

Optimizing Multiple Scattering Calculations in the CRTM: Update. Tom Greenwald, Ralf Bennartz and Jim Davies University of Wisconsin. JCSDA 11th Workshop on Satellite Data Assimilation, June 5-7, 2013. Motivation.

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Optimizing Multiple Scattering Calculations in the CRTM: Update

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  1. Optimizing Multiple Scattering Calculations in the CRTM: Update Tom Greenwald, Ralf Bennartz and Jim Davies University of Wisconsin JCSDA 11th Workshop on Satellite Data Assimilation, June 5-7, 2013

  2. Motivation • Optimize the CRTM for all-sky microwave and IR radiance data assimilation • “Optimize” means finding the minimum number of RT solver streams (i.e., angular resolution) needed to achieve a desired accuracy JCSDA 11th Workshop on Satellite Data Assimilation, June 5-7, 2013

  3. Methods • Developed a scattering indicator (SI) to estimate degree of scattering; more scattering usually requires more streams • Our SI is based on successive order of scattering (Stephens 1994): Number of times a photon is scattered n = [ ln(D) + ln(1-weff) ] / ln(hweff) h= 1 – e-t/cos(q) weff = S kiwi / S Ki K = Weighting function JCSDA 11th Workshop on Satellite Data Assimilation, June 5-7, 2013

  4. Methods Cont’d • Apply thresholds to the SI to automatically increase the numbers of streams (aka “selection rules”) • CRTM calculations made over a wide range of MW frequencies for 0 (emission only), 2, 4, 6, 8, 16 streams (16-stream solution used as a reference to quantify error) • Source of cloud/prec profiles: WRF model simulations • Hurricane Katrina (1.5 km) • California marine stratocumulus (2 km) • Different thresholds were determined for different target accuracies (0.1, 0.5, 1, 2 K) JCSDA 11th Workshop on Satellite Data Assimilation, June 5-7, 2013

  5. Application of the SI • Target accuracy of 0.5 K • Includes 24 channels (GMI+SSMIS) • No. pts > 16 million Global selection rules for all target accuracies 17% 1% 6% 76% 2/4 4/6 0/2 JCSDA 11th Workshop on Satellite Data Assimilation, June 5-7, 2013

  6. Results – Marine Sc CRTM v2.1.2 CRTM v2.2 (alpha) 2.0 K 1.0 K 0.5 K 0.1 K 10 GHz 10 GHz 183 GHz 183 GHz JCSDA 11th Workshop on Satellite Data Assimilation, June 5-7, 2013

  7. Results – Hurricane Katrina CRTM v2.1.2 CRTM v2.2 (alpha) 2.0 K 1.0 K 0.5 K 0.1 K 10 GHz 10 GHz 183 GHz 183 GHz JCSDA 11th Workshop on Satellite Data Assimilation, June 5-7, 2013

  8. Accomplishments • Developed a simple, robust method of automatically selecting the optimum number of streams in the CRTM • Generally, optimum values achieved 75-95% of the time (depends on target accuracy) • Suboptimal (50-75%) for highest frequency channels • Made significant modifications to CRTM code: • Split CloudScatter and AerosolScatter routines into nStreams dependent/independent procedures and reorganized main modules (FWD/TL/AD/K-Matrix) • Added new SI and nStreams calculator (MW sensors only) • Undergoing final testing in V2.2 (with help from Dave Groff) JCSDA 11th Workshop on Satellite Data Assimilation, June 5-7, 2013

  9. Plans • Project received a no-cost extension to May 2014 • Extend method to IR sensors for clouds and aerosols (IR calculations are currently very inefficient) • Publish paper JCSDA 11th Workshop on Satellite Data Assimilation, June 5-7, 2013

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