1. CAPS Radar QC and Remapping
Keith Brewster
Radar Assimilation Workshop National Weather Center
18-Oct-2011

2. Radar I/O & Remapping Capabilities
Remapping Drivers
88D2ARPS
NEXRAD WSR-88D Level-II
China 98D WSR-98D Level-II
TDWR
Solo DORADE I/O
NIDS2ARPS
NEXRAD Level-III
NCRAD2ARPS
CASA NetCDF
WDSS-II Tilt NetCDF (KOUN, Taiwan data)
OU-PRIME NetCDF
FORAY NetCDF (field project data)

3. Radar I/O & Remapping Capabilities
Accessory Script:
Scan2a (Perl)
Creates pseudo-volume lists using meta-data in NetCDF files for use in NCRAD2ARPS
Plotting Routines
radarpltncar & radarpltpost
Polar Coordinate data
pltradcol
Radar Column data
ARPSplot
2D (by tilt) and 3D remapped data

4. 2D and 3D gridded single-variable files
Output
Radar Column Data
2D and 3D gridded single-variable files
Grid-tilt: remapped to Cartesian on tilt surface.

5. Radar Sampling Problem-Horizontalx y a
ISSAOS, L’Aquila, Italy, 31Aug 2004

6. Radar Sampling Problem -Verticalz b x a
ISSAOS, L’Aquila, Italy, 31Aug 2004

7. CAPS Radar Remapping Local least-squares interpolation/smoothing
Quadratic 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

8. ISSAOS, L’Aquila, Italy, 31Aug 2004
Remapping to Dx = 2 km
ISSAOS, L’Aquila, Italy, 31Aug 2004

9. Remapped Radar Field x-z Cross-section
ISSAOS, L’Aquila, Italy, 31Aug 2004

10. AP/Clutter Detection Despeckle (remove isolated point targets)
Calculate 3 terms in small regions around each gate
DdBZ between 0.5° and 1st tilt above 1.1° DdBZ < -12 dBZ assoc with AP
DdBZ < -20 dBZ assoc with ground targets such as wind turbines
Texture.. Spin Change. A lot of changes in sign of gate-to-gate reflectivity gradients associated with AP.
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
Based on statisical studies led by Kessinger at NCAR

11. Reflectivity Quality Control Flowchart
Read Tilt
Anomalous Radial Removal
Despeckle & Median Filter (opt)
Assemble Volume
Ground Clutter Removal
For All Elev < 1.0
Despeckle
Continue to Remapping

12. Sunrise/Sunset Radials

13. 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.

14. KDDC Sunset & Clutter
Raw
Obs
Anomalous Radial
Removed
Clutter Removal

15. Sea Clutter

16. CAPS Real-time Velocity QC & Dealiasing
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.

17. Velocity Dealiasing Steps
Find mean wind profile in area within 90 km of radar.
From model background or sounding
Process by tilt:
Remove mean wind from each radial velocity
Start on a radial perpendicular to the mean wind
For each radial
Check for horizontal continuity
Unfold where vt=vm+nVn improves continuity
Flag any outliers that can’t be resolved
After entire tilt processed
Recheck flagged gates vs. least-squares quadratic fit of neighboring gates

18. Radial Velocity Quality Control Flowchart
Read Tilt
Spectrum Width Filter
All Tilts
Despeckle & Median Filter (opt)
Assemble Volume
Ground Clutter Removal
For All Elev < 1.0
Despeckle
Continue to Unfolding

19. Radial Velocity Quality Control Flowchart
Model Data or Sounding
…Continued
Calculate Mean
Wind Profile
Compare to mean wind
Mean Wind Profile
Create perturbation Vr Field
Gate-to-Gate Shear Check
Quadratic Check at
Gates Marked Uncertain
Continue to Remapping

20. Gate-to-Gate Shear Check
Begin
Mean Wind Profile
Find Radial Perpendicular to Mean WInd
Shear Comparison Template
Forward Pass
Repeat
Reverse Pass
Continue to Remapping
Step Direction

21. Multiple Folded Data
Mean Wind
Raw Obs
Shear
Check

22. KTLX 10 May Scan
Raw Obs
Mean Wind
Shear
Check
Quad Fit

23. Ongoing Work Increasing Flexibility New NAMELIST control file
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
Can we use vortex recognition/fitting techniques to improve QC and analysis near strong vortices?