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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
Outline
Motivation
Dataset
WRF
Polarimetric Characters of Convection
Polarimetric Characters of open ocean surface
Summary
Motivation
‘Blister’ like provided inFig 7 in Babin et al.(2003)
Linked the imaging pattern with convective processGerling 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.
RS-2 PolSAR (HH+HV+VH+VV)
Modis
NARR (North American Regional Reanalysis)
data
QuikSCAT L3 data
SSM/I
Dataset
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.
AB C
MODIS data
at 22:10:00 UTC on 1 Feb. and 7 hours before SAR; ‘’ represents SAR image.
The MODIS imagesuggests that convectiondid occur from the morphology and that the SAR image area appears to be a transition zone between open and closed convection.
Air pressure field
from NARR data
Dataset (continuous)
SST vertical profile
Dataset (continuous)
The atmosphere is instability
on 2 February 2009 at (49.67oN 170oW),
Air-Sea difference : -4oC
Wind field from QuikScat L3
Dataset (continuous)
UTC 06:22:45, 77 minutes after the SAR image
Rain rate from F15 SSM/I
Dataset (continuous)
on 2 February 2009, 29 minutes after the SAR imaging time
Dataset summary
provide an overview of the meteorological conditions;
no precipitation
Cyclone trajectory in space
WRF Results
WRF Results ( continuous)
horizontal distribution of vertical velocity
field at 1000hPa
A
BC
WRF Results ( continuous)
Vertical profile of the vertical velocity
along 170.01oW
along 49.65oN
WRF Results ( continuous)
accumulated precipitation
from UTC 18:00 on 1 February to UTC 05:05 on 2 February 2009
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.
Polarimetric Characters of convection
Variations of backscatter intensity cross section
AB
C
Polarimetric Characters of convection (continuous)
Area A Area B Area C
ϕhhvv 20° 43° 70°
H 0.57 0.60 0.68
α 38° 40° 51°
A 0.34 0.32 0.37
Range Meaning
ϕhhvv 0-180° Odd, even bounce
H 0-1 randomness
α 0-90° type
A 0-1 roughness
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.
• 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.
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 0o to 6 o.
Area A Area B AreaC
ϕhhvv 20° 43° 70°
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
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 3o to 25o, and taking its standard deviation into account, the variation of is from 2o to 27o , which is smaller than that of MCC.
Area A Area B AreaC
α 38° 40° 51°
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
• 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
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.