CAPS Radar QC and Remapping

Keith BrewsterRadar Assimilation Workshop

National Weather Center18-Oct-2011

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

Radar Sampling Problem-Horizontal

a

b

x

y

Radar Sampling Problem -Vertical

a

bx

z

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

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Remapping to Dx = 2 km

Remapped Radar Field x-z Cross-section

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

Sunrise/Sunset Radials

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.

KDDC Sunset & Clutter

RawObs

AnomalousRadialRemoved

Clutter Removal

Sea Clutter

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

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

Multiple Folded Data

ShearCheck

Raw Obs

Mean Wind

KTLX 10 May 2010 6.5° Scan

Raw Obs

Mean Wind

ShearCheck

Quad Fit

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