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

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)

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

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.

Radar Sampling Problem-Horizontal x y a ISSAOS, L’Aquila, Italy, 31Aug 2004

Radar Sampling Problem -Vertical z b x a ISSAOS, L’Aquila, Italy, 31Aug 2004

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

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

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

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

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

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 Raw Obs Anomalous Radial Removed Clutter Removal

Sea Clutter

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.

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

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

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

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

Multiple Folded Data Mean Wind Raw Obs Shear Check

KTLX 10 May 2010 6.47 Scan Raw Obs Mean Wind Shear Check Quad Fit

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?