1. IGARSS July 2011 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. IGARSS July 2011 2 Presentation Outline (1)Contributions to Brightness Temperatures (2)Falling Snow Detection Thresholds Analysis framework Active thresholds based on instrument sensitivity Passive thresholds Comparison between active and passive Future improvements (3)Snow Field Campaign (Jan – Feb 2012) (4)Summary

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

4. IGARSS July 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. IGARSS July 2011 5 (1) Surface Emissivity Part 1 Urban crop land deciduous evergreen/mixed water Surface Temperature Vegetation Type Snow Depth WRF Simulations Courtesy of W.-K. Tao & team IWP (Jan 20 0400UTC) IWP (Jan 22 0600UTC) Lake Effect CaseSynoptic Snow Case

6. IGARSS July 2011 6 Radar Calculations W-Band (-26dBZ) Ka-Band (12dBZ)Ku-Band (18dBZ) Thresholds of Detection for Falling Snow from Satellite-borne Active and Passive Sensors by G. Skofronick-Jackson, et al., IEEE TGRS, submit 9/11 These use 3-bullet rosette snowflakes

7. IGARSS July 2011 7 Reflectivities Depend on Particle Shape W-Band Ka-Band Ku-Band

8. IGARSS July 2011 8 Reflectivities Depend on Particle Shape W-Band Ka-Band Ku-Band Ka

9. IGARSS July 2011 9 Z-Thresholds Depend on Particle Shape Average IWC Detected at Surface Assumed minimum instrument Z: Ku: 18 dBZ Ka: 12 dBZ W: -15 dBZ ±One std dev of variability over 11 shapes is plotted Snowflake Shape (#)Ku-BandKa-BandW-Band Long Hex Col. (0)0.0370.0200.0020 Short Hex Col. (1)0.0370.0200.0019 Block Hexag. Col. (2)0.0390.0200.0020 Thick Hex Plate (3)0.0350.0190.0019 Thin Hex Plate (4)0.0330.0180.0022 3-Bullet Rosette (5)0.0620.0380.0018 4-Bullet Rosette (6)0.0650.0520.0026 5-Bullet Rosette (7)0.0620.0470.0022 Six Bullet Rosette (8)0.0630.1010.0023 Sector Snowflake (9)0.0770.0490.0018 Dendrite Snow (10)0.0790.1450.0032

10. IGARSS July 2011 10 Radiometer Threshold Procedure Y-Axis: TBhydr – TBclearair (with perfect surface, etc knowledge) X-Axis: IWP (max of 6 kg/m 2 ) 3-Bullet Rosette Shape: Red Line = Land surfaces, Blue line = Water Surfaces 10V 183±3V 166V 89V37V 183±7V These use 3-bullet rosette snowflakes

11. IGARSS July 2011 11 Radiometer Thresholds Depend on Shape 89V 166V 166H 183±3V 183±7V 166V 22 Jan

12. IGARSS July 2011 12 Radiometer Thresholds Depend on Snow Vertical Structure and Surface Type Channel (GHz) Total Threshold Cutoff (rounded up) (in K) From 0.05 error in emissivity From 10 o C error in surface T From 10% change in Tprofile From 10% change in RHprof 1025141000 1925141000 2325141000 37251310 00 8925139 00 16620118 11 183±3512 11 183±7 15 56 01

13. IGARSS July 2011 13 Radiometer Thresholds Depend on Snow Vertical Structure and Surface Type Channel (GHz) Total Threshold Cutoff Average Detected IWP Lake Effect over Land Detected IWP Lake Effect over Lakes V-pol Detected IWP Lake Effect over Lakes H-pol Detected IWP Synoptic over Land Detected IWP Synoptic over Lakes V-pol Detected IWP Synoptic over Lakes H-pol 1025 1925 23253.2na 37251.22.0 1.1 89250.40.5 1.50.50.60.8 166200.2 0.3 183±351.8 na1.1 na 183±7 15 0.4 na0.6 na

14. IGARSS July 2011 14 Active Versus Passive Snow Detection Thresholds of Detection for Falling Snow from Satellite-borne Active and Passive Sensors by G. Skofronick-Jackson, et al., IEEE TGRS, submit 9/11 Active Avg. Surface IWC Detected: Ku Ka W Units 0.080.070.004g m -3 Simple falling snow conversion (melted snow rate) 1.010.930.027mm hr -1 Passive over land Avg. Columnar IWP Detected: 89 166 183±3 183±7Units Land V-Pol Lake Effect0.430.161.850.37kg m -2 Land V-Pol Synoptic0.530.261.100.63kg m -2 Simple IWC conversion (correct assumption????) Lake Effect (3 km clouds)0.140.050.620.12g m -3 Synoptic (6 km clouds)0.090.040.180.11g m -3 Simple falling snow conversion (melted snow rate) Lake Effect (3 km clouds)1.970.6111.191.65mm hr -1 Synoptic (6 km clouds)1.110.472.641.36mm hr -1 Thresholds for passive could be improved with additional information

15. IGARSS July 2011 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. 16 IWSSM March 2011 GCPEx Snowfall Campaign (Near Toronto, Canada Jan.-Feb. 2012) GV Science 1.Radiometer/DPR Snowfall measurement sensitivities to snow type, rate, surface and tropospheric characteristics 2.Physics of snowfall in the column and relation to extinction characteristics 3.Model databases for forward modeling and retrieval development. 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. O (60 km) O (10 km) 7-8 km 0.4-0.8 km Ht. King City C-band Dual-pol DFIR Clusters x Georgian Bay CARE D3R PSD: 2DVD, Parsivel, POSS,SVI Radar: Ka/Ku,X,W(2),MRR SWER: Pluvio, Hot Plate SWE/Depth L-Band +  -sensor  (Land/Snow) 10-89 GHz Radiometer Aircraft: DC-8, Citation x

17. IGARSS July 2011 17 Today’s Messages (1)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. IGARSS July 2011 18 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