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Optimizing Multiple Scattering Calculations in the CRTM: IR Results

Optimizing Multiple Scattering Calculations in the CRTM: IR Results. Tom Greenwald, Jim Davies and Ralf Bennartz University of Wisconsin. The 12th JCSDA Technical Review Meeting & Science Workshop on Satellite Data Assimilation, May 21-23, 2014. Motivation.

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Optimizing Multiple Scattering Calculations in the CRTM: IR Results

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  1. Optimizing Multiple Scattering Calculations in the CRTM: IR Results Tom Greenwald, Jim Davies and Ralf Bennartz University of Wisconsin The 12th JCSDA Technical Review Meeting & Science Workshop on Satellite Data Assimilation, May 21-23, 2014

  2. Motivation • Multiple scattering calculations dominate CRTM FWD/ADJ calculations in cloud/precipitation-affected radiance data assimilation • Extend our work in optimizing the CRTM in the microwave spectrum to the infrared • “Optimize” means finding the minimum number of RT solver streams (i.e., angular resolution) needed to achieve a desired accuracy The 12th JCSDA Technical Review Meeting & Science Workshop on Satellite Data Assimilation, May 21-23, 2014

  3. Methods • Developed a scattering indicator (SI) to estimate degree of scattering; more scattering usually requires more angular resolution (i.e., streams) • SI is function of optical depth and single-scattering albedo • Tested using high-resolution WRF model simulations of hurricane Katrina and marine stratocumulus • Applied to the HIRS (High Resolution Infrared Radiation Sounder) for longer wavelengths (6-15 µm) • Assumed target solution accuracy of 0.2 K The 12th JCSDA Technical Review Meeting & Science Workshop on Satellite Data Assimilation, May 21-23, 2014

  4. Katrina results Timings relative to current CRTM The 12th JCSDA Technical Review Meeting & Science Workshop on Satellite Data Assimilation, May 21-23, 2014

  5. Katrina results cont. The 12th JCSDA Technical Review Meeting & Science Workshop on Satellite Data Assimilation, May 21-23, 2014

  6. Marine Sc results Timings relative to current CRTM The 12th JCSDA Technical Review Meeting & Science Workshop on Satellite Data Assimilation, May 21-23, 2014

  7. Marine Sc results cont. The 12th JCSDA Technical Review Meeting & Science Workshop on Satellite Data Assimilation, May 21-23, 2014

  8. Summary • A method for accelerating IR cloudy-sky calculations in the CRTM has been developed • Correctly predicts optimum number of streams over 75% of the time for most sounding bands, leading to potential speedup of up to 30x • For window bands this drops to 25-50% of the time but still provides potential speedup of up to 2x as compared to current CRTM • Has tendency to predict too few streams more often than current CRTM The 12th JCSDA Technical Review Meeting & Science Workshop on Satellite Data Assimilation, May 21-23, 2014

  9. Remaining tasks • Investigate ways to improve the method • Integrate it into the CRTM (much easier than before since code infrastructure already in place in V2.2) • Manuscript in preparation The 12th JCSDA Technical Review Meeting & Science Workshop on Satellite Data Assimilation, May 21-23, 2014

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