keith brewster radar assimilation workshop national weather center 18-oct-2011
TRANSCRIPT
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CAPS Radar QC and Remapping
Keith BrewsterRadar Assimilation Workshop
National Weather Center18-Oct-2011
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Remapping Drivers 88D2ARPS
◦ NEXRAD WSR-88D Level-II◦ China 98D WSR-98D Level-II◦ TDWR◦ Output to Solo DORADE
NIDS2ARPS◦ NEXRAD Level-III
NCRAD2ARPS◦ CASA NetCDF◦ WDSS-II Tilt NetCDF (KOUN, Taiwan data)◦ OU-PRIME NetCDF◦ FORAY NetCDF (field project data)
Radar I/O & Remapping Capabilities
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Radar Sampling Problem-Horizontal
a
b
x
y
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Radar Sampling Problem -Vertical
a
bx
z
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Local least-squares interpolation/smoothingQuadratic in horizontal Linear in vertical
Smooths dense data Superobbing consistent with model grid Interpolates accurately in
data-sparse regions Can be applied in 2D on ray surface. Ray paths: 4/3-earth ray path or estimate of bulk
refractive index gradient with height Full range of map projections & vertical grid stretching
supported
CAPS Radar Remapping
gfzexydycybxaxV 22
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Remapping to Dx = 2 km
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Remapped Radar Field x-z Cross-section
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Despeckle (remove isolated point targets) Calculate 3 terms in small regions
around each gatea) DdBZ between 0.5° and 1st tilt above 1.1°
DdBZ < -12 dBZ assoc with APb) DdBZ < -20 dBZ assoc with ground targets such as
wind turbines c) Texture.. Spin Change. A lot of changes in sign of
gate-to-gate reflectivity gradients associated with AP. d) Mean Radial Velocity
Small magnitude of mean radial velocity associated with AP
Weak check: Fails 2 or more of 3 checks Strong check: Fails 1 or more checks
AP/Clutter Detection
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Sunrise/Sunset Radials
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Sunrise/Sunset Radials
Point source interference, such as sun, produces characteristic signature.
• High percentage of radial is non-missing.• Reflectivity factor increasing linearly with range.• Small variance from linearity.
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KDDC Sunset & Clutter
RawObs
AnomalousRadialRemoved
Clutter Removal
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Sea Clutter
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Three Pronged Approach◦ Background Comparison
Most useful for removing shear with height due to mean wind profile
Background from model or VAD◦ Two-dimensional continuity
Applied in multiple directions◦ Final Quadratic fit for uncertain points.
CAPS Real-time Velocity QC & Dealiasing
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Gate-to-Gate Shear Check
Find Radial Perpendicular to
Mean WInd
Reverse Pass
Begin
Forward Pass
Mean Wind
Profile
Continue to Remapping
Step Direction
Shear Comparison
Template
Repeat
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Multiple Folded Data
ShearCheck
Raw Obs
Mean Wind
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KTLX 10 May 2010 6.5° Scan
Raw Obs
Mean Wind
ShearCheck
Quad Fit
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Increasing Flexibility New NAMELIST control file added Correction factors for mobile radars Moving tunable parameters to NAMELIST
Dual-Pol for WSR-88D Some experience with CASA Additional algorithms for clutter and non-precip
echo identification & removal
Radial-by-radial ray tracing.
Can we use vortex recognition/fitting techniques to improve QC and analysis near strong vortices?
Ongoing Work