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Early Results from the MODIS Cloud Algorithms

cloud detection optical, microphysical, and cloud top properties. Early Results from the MODIS Cloud Algorithms. S. Platnick 5,2 , S. A. Ackerman 1 , M. D. King 2 , W. P. Menzel 3,1 , B. A. Baum 4,1 , et al.

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Early Results from the MODIS Cloud Algorithms

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  1. cloud detection optical, microphysical, and cloud top properties Early Results from theMODIS Cloud Algorithms S. Platnick5,2, S. A. Ackerman1, M. D. King2, W. P. Menzel3,1, B. A. Baum4,1, et al. 1 U. Wisconsin/CIMSS, 2 NASA GSFC, 3 NOAA NESDIS, 4 NASA LaRC, 5 UMBC/JCET AGU Fall Meeting San Francisco, CA December 19, 2000

  2. MODIS (MODerate resolution Imaging Spectroradiomter) Outline • MODIS - a quick introduction • MODIS cloud products • Algorithm descriptions and example retrievals • Data status S. Platnick, AGU, 19 Dec. 2000

  3. MODIS instrument highlights • Filter radiometer, 4 detector arrays, 36 spectral bands; 250 m, 500 m, 1 km spatial resolution • Onboard calibration via Solar Diffuser/Stability Monitor, Spectral Radiometric Calibration Assembly instruments • First light on 24 February 2000 (Terra launch 18 Dec 1999) • Science teams organized into atmosphere, land, and ocean discipline groups S. Platnick, AGU, 19 Dec. 2000

  4. MODIS Atmosphere Global 19 April 2000 L1B True color RGB (0.65, 0.56, 0.47 µm bands) example data granule coverage (5 min) S. Platnick, AGU, 19 Dec. 2000

  5. MODIS cloud products, granule level • Pixel level products (Level 2) overview – Cloud mask for determining “clear-sky” – Cloud top properties – Cloud optical, microphysical properties (optical thickness, effective particle size, water path, thermodynamic phase, cirrus reflectance) • Unique aspects – New algorithms from greater spectral coverage – Heritage algorithms at higher spatial resolution – Includes QA (processing and assessment info) S. Platnick, AGU, 19 Dec. 2000

  6. MODIS cloud products, globalcomposites • Gridded time-average products (Level 3) – Daily, 8 day, monthly composites containing all atmosphere products – 1˚ x 1˚ equal angle grid – mean, standard deviation, marginal and joint probability distributions – quick look available on the web details at the MODIS atmosphere web page http://modis-atmos.gsfc.nasa.gov S. Platnick, AGU, 19 Dec. 2000

  7. Cloud mask(S. Ackerman, R. Frey, K. Strabala – U. Wisconsin/CIMSS) • Bottom of the algorithmic “food chain”, input to all MODIS products. • 1 km nadir spatial resolution day & night, (250 m day) • 17 spectral bands (0.55-13.93 µm, incl. 1.38 µm) – 11 spectral tests (function of 5 ecosystems) – temporal consistency test over ocean, desert (nighttime) – spatial variability test over ocean • 48 bits per pixel including individual test results and processing path; generation of clear sky maps • Bits 1,2 give combined test results as: confident clear, probably clear, uncertain, obstructed/cloudy(clear sky conservative) S. Platnick, AGU, 19 Dec. 2000

  8. Cloud mask, cont. • Spectral tests use fuzzy thresholds, examples include – low cloud tests: 3.9 µm - 11 µm BT – high cloud tests: 13.9 µm (CO2), 1.38 µm (H2O), 11-12 µm BT – 1.6 µm snow/ice test – NIR/VIS reflectance test; IR tests (dependent on sfc emissivity, PW, aerosols); et al. Ackerman, S. A. et al. 1998: JGR, 103, 32141-32157. S. Platnick, AGU, 19 Dec. 2000

  9. Cloud mask, validation activities • Mask consistent with radar/lidar cloud boundary measurements at Oklahoma ARM CART site and ER-2 observations during spring 2000 campaign (including correct snow identification). • Improvements being made for sun glint, warm cloud in arid ecosystems, Antarctica, nighttime low cloud over land, nighttime snow/ice surfaces • Regional/global validation is ongoing. Gobal clear sky composite images being used to identify problem regions. S. Platnick, AGU, 19 Dec. 2000

  10. 1.6 µm image 0.86 µm image 11 µm image 3.9 µm image cloud mask Snow test (impacts choice of tests/thresholds) 11 - 12 BT test (primarily for high cloud) VIS test (over non-snow covered areas) 13.9 µm high cloud test (sensitive in cold regions) 3.9 - 11 BT test for low clouds aa MODIS cloud mask example (confident clear is green, probably clear is blue, uncertain is red, cloud is white)

  11. MODIS 5-8 September 2000 Band 31 (11.0 µm) Daytime Clear sky Brightness Temperature

  12. MODIS 5-8 September 2000 Band 1, 4, 3 (R/G/B) Daytime Clear sky Reflectance Composite

  13. Cloud top properties(P. Menzel, R. Frey, K. Strabala, L. Gumley, et al. – NOAA NESDIS, U. Wisc./CIMSS) • Cloud top pressure, temperature, effective emissivity • Retrieved for every 5x5 box of 1 km FOV’s, when at least 5 FOV’s are cloudy, day & night • CO2 Slicing technique (5 bands, 12.0-14.2 µm) – ratio of cloud forcing in 2 nearby bands – retrieve pc; Tc from temperature profile – most accurate for high and mid-level clouds • Previously applied to HIRS (NOAA POES, 20 km). MODIS 1st satellite sensor capable of CO2 slicing at high spatial resolution. S. Platnick, AGU, 19 Dec. 2000

  14. Cloud top properties, validation activities • Activities proceeding via early ER-2 effort (March 2000 with lidar and HIS IR interferometer), and NOAA HIRS intercomparisons • Cloud top pressure compares well with HIRS and aircraft validation,better than 50 mb. Frey, R. A. et al, 1999: JGR , 104, 24547-24555. S. Platnick, AGU, 19 Dec. 2000

  15. CO2 slicing • Technique: - ratio of cloud forcing at two near-by wavelengths - effective emissivity includes cloud fraction in 5x5 box - actual cloud emissivity assumed same for each band - radiance gradient used when clear sky not available • The more absorbing bands are more sensitive to high clouds, weighting functions Frey, R. A. et al, 1999: A comparison of cloud top heights computed from airborne lidar and MAS radiance data. J. Geophys. Res.,104, 24547-24555. S. Platnick, AGU, 19 Dec. 2000

  16. Cloud Mask – MODIS 12 March 2000, 1730 UTC snow ARM CART site MODIS band 31 11 µm Cloud Mask clear=green cloud=white uncertain=red

  17. Cloud Top Pressure – MODIS 12 March 2000, 1730 UTC ARM CART site MODIS band 31 11 µm Cloud top pressure 900-1000mb=purple500-600mb=blue300-400mb=red

  18. Comparison of ER2 lidar (nadir view), HIRS (3 hrs later), RAOB, & MODIS Cloud Properties over ARM CART site, Oklahoma lidar CTP vs. HIRS effective emissivity vs. HIRS

  19. MODIS 5-8 September 2000 Cloud top Pressure Cloud top Temperature Cloud Fraction Cloud Effective Emissivity

  20. IR thermodynamic phase algorithm(B. Baum, S. Ackerman, K. Strabala – NASA LaRC, U.W. CIMSS) ice cloud April 1996 Success • Tri-spectral method, 5 km resolution • NIR, MWIR reflectance technique being developed water cloud Jan 1993 TOGA/ COARE Strabala, Menzel, and Ackerman, 1994, JAM, 2, 212-229. Baum et al, 2000, JGR, 105, 11781-11792. S. Platnick, AGU, 19 Dec. 2000

  21. MODIS cloud thermodynamic phase - IR algorithm VIS IR window cloud phase Ice Mixed Phase Clouds over Southern India 19 April 2000 Water Uncertain

  22. MODIS 5-8 September 2000 IR retrieval - percent liquid water

  23. MODIS 5-8 September 2000 IR retrieval - percent ice water

  24. MODIS IR phase retrieval vs. Cloud Top Temperature frequency of ice phase & Tc < 253 K statistics from 5 Sept day and night, 60ºN-60ºS, water surface only frequency (%)

  25. MODIS IR phase retrieval vs. Cloud Top Temperature frequency of ice phase & 253< Tc< 273 K statistics from 5 Sept day and night, 60ºN-60ºS, water surface only frequency (%)

  26. MODIS IR phase retrieval vs. Cloud Top Temperature frequency of ice phase & Tc> 273 K statistics from 5 Sept day and night, 60ºN-60ºS, water surface only frequency (%)

  27. Cloud optical, microphysical properties(M. D. King, S. Platnick, M. Gray, E. Moody, J. Li, S.-C. Tsay, et al. – NASA GSFC, UMBC) • Optical thickness, particle size (effective radius), water path • 1 km spatial resolution, daytime only, liquid water and ice clouds • Land, ocean, snow/sea ice surfaces • Solar reflectance technique, VIS through MWIR (0.65, 0.86, 1.2, 1.6, 2.1, 3.7 µm) MODIS 1st satellite sensor with all useful SWIR, MWIR bands S. Platnick, AGU, 19 Dec. 2000

  28. Cloud optical, microphysical properties, cont. • Required input: – cloud mask (tuned for cloudy not clear using individual cloud mask tests) – cloud top temperature for 3.7 µm retrieval – cloud top pressure for atmospheric correction (being implemented) – cloud phase (currently derived from individual cloud mask tests, not IR or solar tests) – surface albedo (currently assigned from IGBP ecosystem map & NISE snow/ice data set) • Early validation effort as part of SAFARI 2000 S. Platnick, AGU, 19 Dec. 2000

  29. MODIS SAFARI granule RGB composite 13 September 2000, 0925 UTC Angola Zambia Botswana Namibia Angola South Africa ER-2 ground track marine stratocumulus Etosha Pan Namibia

  30. (>99%) (>95%) (>66%)

  31. Data summary • Atmosphere L2 products processed on P.I. system at GSFC (except cloud mask) • Cloud products archived at GSFC DAAC – series starts at 8/20/00 for L2, 10/31/00 for L3(1d) • Current archived products are “beta” release – early data product, useful for familiarity with data formats/parameters, minimal validation, temporary • Consistent processing time series (instrument bias settings, L1B algorithm) underway • Order through EOS Data Gateway - details athttp://modis.gsfc.nasa.gov/DATA/ S. Platnick, AGU, 19 Dec. 2000

  32. Data summary, cont. • Data file info –“MOD35” cloud mask ~ 48 MB/granule daytime –“MOD06” cloud product ~ 65 MB/granule daytime, 16 MB nighttime, 12 GB/day - L3 atmospheres ~ 400-800 MB/day - L1B ~ 340 MB/granule, 70 GB/day • L2 production system limits – currently running at approximately “1x”, not sufficient for reprocessing needs S. Platnick, AGU, 19 Dec. 2000

  33. L3 optical thickness (liquid water) statistics, 10/2/00, from atmo web page mean maximum minimum standard deviation S. Platnick, AGU, 19 Dec. 2000

  34. Algorithms summary • MODIS provides an unprecedented opportunity for cloud and other atmospheric studies – 36 spectral channels, high spatial resolution • Comprehensive set of cloud algorithms • Archive of pixel level retrievals, global statistics • Product intercomparison for small number of selected day(s) proven useful • Validation activities ongoing (gnd. based, in situ, aircraft, satellite intercomparisons, etc.); detailed plans on atmosphere web site S. Platnick, AGU, 19 Dec. 2000

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