1. On polarimetric characteristics of mesoscale cellular convection in the marine atmospheric boundary layer Haiyan Li, William Perrie, Lanli Guo ， Biao Zhang 2011 IEEE International Geoscience and Remote Sensing Symposium 24-29 July Vacouver, Canada

2. Outline  Motivation  Dataset  WRF  Polarimetric Characters of Convection  Polarimetric Characters of open ocean surface  Summary

3. Motivation ‘Blister’ like provided inFig 7 in Babin et al.(2003)

4.  Linked the imaging pattern with convective process Gerling 1986; Alpers and Brummer 1994; Beal et al. 1994; Nilsson and Tildesley 1995; Sikora et al. 1995…  Estimated the parameter: depth of a convective MABl (Sikora et al. 1997) Obukhov lengths and drag coefficinets (Sikora et al. 2001)  Study dynamic and structure Babin et al. 2003; Young et al. (2005,2007) ; Fisher (2007) ;Sikora et at (2009) Motivation (continuous) Before above work, firstly,we should distinguish convective process SAR images from open ocean surface SAR images.

5.  RS-2 PolSAR (HH+HV+VH+VV)  Modis  NARR (North American Regional Reanalysis) data  QuikSCAT L3 data  SSM/I Dataset

6. RS-2 Quad-Pol UTC 05:05:35 on Feb. 2, 2009, RADARSAT-2 Data and Products© MacDonald, Dettwiler and Associates Ltd. (2008- 2009) - All Rights Reserved. A BC

7. MODIS data  at 22:10:00 UTC on 1 Feb. and 7 hours before SAR; ‘  ’ represents SAR image. The MODIS image suggests that convection did occur from the morphology and that the SAR image area appears to be a transition zone between open and closed convection.

8.  Air pressure field from NARR data Dataset ( continuous)

9.  SST vertical profile Dataset (continuous) The atmosphere is instability on 2 February 2009 at (49.67 o N 170 o W), Air-Sea difference : -4 o C

10.  Wind field from QuikScat L3 Dataset (continuous) UTC 06:22:45, 77 minutes after the SAR image

11.  Rain rate from F15 SSM/I Dataset (continuous) on 2 February 2009, 29 minutes after the SAR imaging time

12. Dataset summary  provide an overview of the meteorological conditions ；  no precipitation

13.  Cyclone trajectory in space WRF Results 

14. WRF Results （ continuous ）  horizontal distribution of vertical velocity field at 1000hPa A B C

15. WRF Results （ continuous ）  Vertical profile of the vertical velocity along 170.01 o W along 49.65 o N

16. WRF Results （ continuous ）  accumulated precipitation from UTC 18:00 on 1 February to UTC 05:05 on 2 February 2009

17. WRF Summary  verify that the SAR imaging area was influenced by cyclonic processes. After the passage of the vigorous cyclone, a high pressure ridge gradually developed and dominated this area;  upward and downward air motions at the bottom of atmosphere ；  exclude rain effects.

18. Polarimetric Characters of convection  Variations of backscatter intensity cross section A B C

19. Polarimetric Characters of convection (continuous)  Area AArea BArea C ϕ hhvv 20°43°70° H0.570.600.68 α38°40°51° A0.340.320.37 Range Meaning ϕ hhvv 0-180°Odd, even bounce H0-1randomness α0-90°type A0-1roughness

20. MCC Polarimetric Characters summary  mesoscale cellular convection(MCC) is with higher modulation depths of HH and VV polarizations, the co- polarization phase difference, average alpha angle, and entropy. However, the contrast in anisotropy is not as obvious as that of the other three parameters.

21. What is the difference in the polarimetric characteristics between MCC and open ocean surface? To compare the polarimetric characteristics of MCC with those of the ocean surface, 641 open ocean surface quad-polarization RS-2 SAR images collocated with 52 NDBC buoys were analyzed.

22. Polarimetric charateristics of open ocean The distributions do not show any obvious regular pattern and the actual variations are small, resulting from variations in these four parameters. The range is limited between 0 o to 6 o. Area A Area B AreaC ϕ hhvv 20° 43° 70°

23. Polarimetric charateristics of open ocean H clearly tends to increase with increasing incidence angles, for each of the three sea state parameters. There are a few exceptional cases, however. When wind speeds are larger than 2 m/s, the largest H value is less than 0.55; the maximum value for H is ~ 0.68. Area A Area B AreaC H 0.57 0.60 0.68

24. Polarimetric charateristics of open ocean  increases with increasing incidence angles, for each of the three sea state parameters. There are a few exceptions to this trend, however. Except for the maximum in , when wind speed is about 2 m/s, the variation in  is from 3 o to 25 o, and taking its standard deviation into account, the variation of  is from 2 o to 27 o, which is smaller than that of MCC. Area A Area B AreaC α 38° 40° 51°

25. Polarimetric charateristics of open ocean A generally tends to decrease with increasing incidence angles. Area A Area B AreaC A 0.34 0.32 0.37

26. MCC typical areas A, B and C tend to show higher co-polarization phase difference, H and , compared to typical polarimetric characteristics of the ocean surface. Comparison Summary

27. Conclusions  The collated data and WRF model results verified that the signals in SAR images are MCC;  The polarimetric characteristics of MCC are different with those of open ocean surface;  Polarimetric parameters show good potential to identify atmospheric convection phenomena from open ocean surface SAR images.

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