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Thresholds of Detection for Falling Snow from Satellite-Borne Active and Passive Sensors

Thresholds of Detection for Falling Snow from Satellite-Borne Active and Passive Sensors. IGARSS 2011 Vancouver, Canada. Gail Skofronick Jackson Benjamin Johnson Joe Munchak NASA Goddard Space Flight Center, Greenbelt, Maryland Gail.S.Jackson@nasa.gov. Presentation Outline.

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Thresholds of Detection for Falling Snow from Satellite-Borne Active and Passive Sensors

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  1. Thresholds of Detection for Falling Snow from Satellite-Borne Active and Passive Sensors IGARSS 2011 Vancouver, Canada Gail Skofronick Jackson Benjamin Johnson Joe Munchak NASA Goddard Space Flight Center, Greenbelt, Maryland Gail.S.Jackson@nasa.gov

  2. Presentation Outline • Contributions to Brightness Temperatures • Falling Snow Detection Thresholds • Analysis framework • Active thresholds based on instrument sensitivity • Passive thresholds • Comparison between active and passive • Future improvements • Snow Field Campaign (Jan – Feb 2012) • Summary

  3. Percentages from Surface, Snow, & Water Vapor Macro and microphysical cloud characteristics affect TB signal Blizzard ~10km tops (0.5 to 1.0 IWP) Lake Effect 2-3km tops (0.5 to 1.0 IWP) (a) (a) Synoptic 5-7km tops (0.5 to 1.0 IWP) Blizzard ~10km tops (9 to 10 IWP) (b) (b) These use dendrite snowflakes “Surface and Atmospheric Contributions to Microwave Brightness Temperatures for Falling Snow   Events,” by Gail Skofronick-Jackson and Benjamin Johnson, JGR-Atmos, published Jan 2011.

  4. Falling Snow Detection Thresholds • What are the thresholds of detection in terms of IWP or IWC of falling snow? • Analysis Approach: • Use WRF models of Lake Effect and Synoptic snow • Vertical profiles: IWC, temperature, water vapor profiles • Surface: temperature, land classification, snow depth • Joint active and passive computations of Z and TB • Use Liu’s 2004 DDA tables for abs, scat, asymmetry, & backscatter • 11 non-spherical snowflake shapes • Adjust N0 to integrate Liu’s min-max DDA sizes to ensure WRF IWC is preserved

  5. WRF Simulations (1) Surface Emissivity Part 1 Lake Effect Case Synoptic Snow Case Snow Depth Vegetation Type Surface Temperature Urbancropland deciduousevergreen/mixedwater IWP (Jan 20 0400UTC) IWP (Jan 22 0600UTC) Courtesy of W.-K. Tao & team

  6. Radar Calculations Ku-Band (18dBZ) Ka-Band (12dBZ) W-Band (-26dBZ) These use 3-bullet rosette snowflakes Thresholds of Detection for Falling Snow from Satellite-borne Active and Passive Sensors by G. Skofronick-Jackson, et al., IEEE TGRS, submit 9/11

  7. Reflectivities Depend on Particle Shape Ka-Band Ku-Band W-Band

  8. Reflectivities Depend on Particle Shape Ka-Band Ku-Band Ka W-Band

  9. Z-Thresholds Depend on Particle Shape Average IWC Detectedat Surface Assumed minimum instrument Z: Ku: 18 dBZ Ka: 12 dBZ W: -15 dBZ ±One std dev of variability over 11 shapes is plotted

  10. Radiometer Threshold Procedure Y-Axis: TBhydr – TBclearair (with perfect surface, etc knowledge) X-Axis: IWP (max of 6 kg/m2) 3-Bullet Rosette Shape: Red Line = Land surfaces, Blue line = Water Surfaces 10V 37V 89V 166V 183±3V 183±7V These use 3-bullet rosette snowflakes

  11. Radiometer Thresholds Depend on Shape 166H 166V 89V 166V 166V 22 Jan 183±7V 183±3V

  12. Radiometer Thresholds Depend on Snow Vertical Structure and Surface Type

  13. Radiometer Thresholds Depend on Snow Vertical Structure and Surface Type

  14. Active Versus Passive Snow Detection Active Avg. Surface IWC Detected: Ku Ka W Units 0.08 0.07 0.004 g m-3 Simple falling snow conversion (melted snow rate) 1.01 0.93 0.027 mm hr-1 Passive over land Avg. Columnar IWP Detected: 89 166 183±3 183±7 Units Land V-Pol Lake Effect 0.43 0.16 1.85 0.37 kg m-2 Land V-Pol Synoptic 0.53 0.26 1.10 0.63 kg m-2 Simple IWC conversion (correct assumption????) Lake Effect (3 km clouds) 0.14 0.05 0.62 0.12 g m-3 Synoptic (6 km clouds) 0.09 0.04 0.18 0.11g m-3 Simple falling snow conversion (melted snow rate) Lake Effect (3 km clouds) 1.97 0.61 11.19 1.65 mm hr-1 Synoptic (6 km clouds) 1.11 0.47 2.64 1.36 mm hr-1 • Thresholds for passive could be improved with additional information Thresholds of Detection for Falling Snow from Satellite-borne Active and Passive Sensors by G. Skofronick-Jackson, et al., IEEE TGRS, submit 9/11

  15. RGB Composite AMSU-B Emissivity Map Three Color Emissivity Map by Joe Munchak 89 GHz (red),150 GHz (green),183 GHz (blue) Darker colors indicate lower emissivities (more reflective) Missing data (black).

  16. GCPEx Snowfall Campaign (Near Toronto, Canada Jan.-Feb. 2012) • GV Science • Radiometer/DPR Snowfall measurement sensitivities to snow type, rate, surface and tropospheric characteristics • Physics of snowfall in the column and relation to extinction characteristics • Model databases for forward modeling and retrieval development. Ht. PSD: 2DVD, Parsivel, POSS,SVI Radar: Ka/Ku,X,W(2),MRR SWER: Pluvio, Hot Plate SWE/Depth L-Band + g-sensor e: (Land/Snow) 10-89 GHz Radiometer Aircraft: DC-8, Citation 7-8 km 0.4-0.8 km x x Georgian Bay DFIR Clusters CARE D3R King City C-band Dual-pol O (10 km) O (60 km) • Approach: • DFIR instrument clusters (account for measurement uncertainty, mitigate wind, complimentary physics) centered around X/W/Ka-KU/MRR radars and a ground-staring radiometer at CARE site. • Clusters located under C-band/D3R multi-freq/dual-pol radar umbrella; D3R V-point with W and X-bands or cover clusters in scanning/RHI/spectral sampling modes. • Overfly in-situ aircraft in coordination with DC-8 (APR-2 and CoSMIR radiometer); • Pre and post land surface radiative measurements by Ka-Ku and radiometers.

  17. Today’s Messages • Falling snow retrievals are complex • Challenges being addressed: • non-spherical particles • surface emissivity • (2) Thresholds of Detection • Theoretical thresholds of detection are promising • Differences between active and passive detection thresholds • Thresholds for passive could be improved with additional constraints • (3) What matters? IWP, cloud thickness, surface underneath, snow particle shapes and PSD limits, and more • (4) The GCPEx Field Campaign in 2012 will provide data to help address challenges and finalize algorithms.

  18. Questions? Questions? IEEE Geoscience and Remote Sensing Society Administrative Committee (AdCom) Member Voting is open All GRSS members can vote for new AdCom members Please vote this week at the GRSS booth or online by Sept. 16, 2011

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