dynamo radar workshop university of washington, seattle 22-24 august 2012 mike dixon, bob rilling,...
TRANSCRIPT
DYNAMO radar workshopUniversity of Washington, Seattle
22-24 August 2012
Mike Dixon, Bob Rilling, Scott Ellis,John Hubbert and Scot Loehrer
Earth Observing Laboratory (EOL)
National Center for Atmospheric Research (NCAR)Boulder, Colorado
Status of Spol-Ka Data Sets
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QC-V1 Data Set
• QC version 1 data set released July 7 • Format is CfRadial
– http://www.ral.ucar.edu/projects/titan/docs/radial_formats/CfRadialDoc.pdf• Times are given in UTC
– Filename contains start and end times of volume: cfrad.20111210_063031.993_to_20111210_063528.867_SPOL_v9373_SUR.nc
– Time variable in file is relative to the start time• Available for download:
– URL: http://data.eol.ucar.edu/codiac/dss/id=347.017– Max download per session: 16 GB – Mean data size per observation day: 7 GB
• Available on ~1 TB USB external disks containing: – QC version 1 data set– Radar scan image browser– Web cam images
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QC-V1 Data Set
• Web documentation is available at: http://www.eol.ucar.edu/projects/dynamo/spol/SpolKa_DYNAMO_UsersGuide.toc.html
• This contains:– Project information– Data set description– Data quality and calibration reports– Download procedures– Links to format documents
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Summary of Data Quality and Calibration Procedures
• Tower targets: for checking range accuracy• Solar scans: for pointing, leveling and power calibration• Engineering calibration for S-band and Ka-band• S and Ka systems sensitivity checks• S/Ka comparisons• Self-consistent method for S-band calibration (PHI-cal)• Vertical pointing for Zdr bias determination• LDR sensitivity check• Monitoring using Automated Test Equipment (ATE)• Monitoring of data transfer and recording
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QC-V1 Spol-Ka Data Fields – 41
FIELD NAME Description FIELD NAME Description FIELD NAME Description
DBZ_S ReflectivityS-band
DBZ_NAA_S DBZ no atmos attenS-band
VEL_S Radial velocity (combined)S-band
VEL_ALT_S Velocity alternating modeS-band
VEL_HV_S Velocity H and V separately S-band
WIDTH_S Spectrum widthS-band
ZDR_S ZDR S-band LDRH_S LDR H channelS-band
LDRV_S LDR V channelS-band
RHOHV_S HV Cross-correlationNoise corrected
RHOHV_NCC_S HV Cross-correlationNot noise corrected
PHIDP_S Differential phaseS-band
KDP_S Specific differential phaseS-band
PSOB_S Phase shift on back-scatter(not good in this release)
SNRHC_S SNR H co-polarS-band
SNRVC_S SNR V co-polarS-band
SNRHX_S SNR H cross-polarS-band
SNRVX_S SNR V cross-polarS-band
DBMHC_S Power H co-polarNot noise corrected
DBMVC_S Power V co-polarNot noise corrected
DBMHX_S Power H cross-polarNot noise corrected
DBMVX_S Power V cross-polarNot noise corrected
NCP_S Normalized coherent power S-band
PID Particle IDS-band
TEMP_FOR_PID Temperature profile used for PID
RATE_ZH Precip Rate using Z only RATE_Z_ZDR Precip rate using Z and ZDR
RATE_KDP Precip rate using KDP RATE_KDP_ZDR Precip rate using KDP and ZDR
RATE_HYBRID Hybrid precip rate
CLUT_S Clutter power removedS-band
CPA_S Clutter phase alignmentS-band
CMD_S Clutter mitigation decisiion field
CMD_FLAG_S CMD flag – indicates where filter is applied
DBZ_K ReflectivityKa-band
DBZ_NAA_K DBZ no atmos atten(Same as DBZ_K)
LDRH_K LDR H-channelKa-band
SNRHC_K SNR H co-polarKa-band
SNRVX_K SNR V cross-polarKa-band
DBMHC_K Power H co-polar not noise corrected – Ka band
DBMVX_K Power V cross-polar not noise corrected – Ka band 5
Summary of changes from field data sets
• Noise power for all S-band and Ka-band power quantities has been re-estimated on a beam-by-beam basis. This mostly affects SNR, RHOHV, ZDR in low power regions.
• Advanced techniques for data censoring have been applied.• A merged data set has been created, incorporating S-band, PID, rain rates, and several of the most
useful Ka-band fields.• Multiple S-band velocity fields have been created, reprocessed from the original phase data.• KDP estimation was improved through better unfolding techniques and bug fixes. • PID uses local soundings to develop information on freezing levels. PID has been modified for tropical
conditions.• Some tuning of the precipitation rate algorithms was performed.• The test pulse was eliminated from the final data set.• The S-band atmospheric attenuation was re-estimated using a technique detailed in Doviak and Zrnic.• RHOHV was changed to use noise-correction. The original RHOHV field has been renamed to
RHOHV_NNC_S (for NoNoiseCorrection).• Minor changes were made to the Ka reflectivity for calibration differences between magnetrons.• There were no changes to either the S-band power calibrations or the value of the Zdr-bias used during
the field phase.• These details are listed at:
http://www.eol.ucar.edu/projects/dynamo/spol/SpolKa_DYNAMO_UsersGuide.toc.html
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DBZ SAttenuation correction: from Doviak and Zrnic, Page 44
Correction depends on elevation angle and range
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DBZ NAA SReflectivity with no attenuation correction applied
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VEL_ALT_SRadial velocity computed from alternating pulses. Tends to be noisy in low
SNR regions. This was as used in the field. Folds at 26.7 m/s.
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VEL_SVelocity computed from VEL_HV_S and unfolded using VEL_ALT_S.
Less noisy than VEL_ALT_S. Folds at 26.7 m/s.
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VEL_HV_SVelocity computed from H pulses and V pulses and then averaged.
Has less noise than alternating mode V. Folds at 13.35 m/s.
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Why do we need VEL_HV?
VEL_HV is useful for finding the velocity in bird echoes.Consider the following boundary in reflectivity
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PHIDP in echoes with phase shift on back-scatter
Because of phase shift on back-scatter, phidp canbe very noisy in bird echoes
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Noisy VEL in regions with phase shift on backscatter
SPOL VEL depends on PHIDP, so VEL will alsobe noisy in bird echoes
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VEL_VH is not noisy in phase-shifted echoes
Because VEL_VH is not dependent on PHIDP, it will notbe noisy in regions of phase-shift on back-scatter
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WIDTH_SSpectrum width
No changes were made to the spectrum width estimator.
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ZDR_SZDR – differential reflectivity between H and V
No calibration changes were made in post-processing.
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RHOHV SRHOHV is now corrected for noise.
This has important implications for PID.
Bright-bandregions
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RHOHV_NCC_SCompare the previous image with this one, which is computed without noise correction (as in the field)
Low SNR regionleads to low RHOHV values, confusing the PID algorithm
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PIDPID has been improved with tighter membership functions
for RHOHV, and other tuning details for tropical convection
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TEMP_FOR_PID
The temperature field used for PID is based on the GAN sounding closest in time to the radar scan.
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PHIDP_SPHIDP is unchanged from the field.However, KDP has been improved.
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KDP_SThe KDP algorithm was improved with better treatment of
noisy regions. Also, it is no longer constrained by DBZ.
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RATE_KDPThe improved KDP field leads to improvement in precip rate
derived from KDP. However, it must still be used in conjunction with other precip estimators.
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RATE_HYBRIDThe hybrid precip rate has been tuned for better agreement with the disdometer measurements. However, further work
on this topic is clearly required.
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SNRHC_SSNR fields are available for H co-polar (HC), V co-polar (VC),H cross-polar (HX) and V cross-polar (VX). HC is shown here.
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DBMHC_SDBMfields are available for H co-polar (HC), V co-polar (VC),H cross-polar (HX) and V cross-polar (VX). HC is shown here.
DBM powers are NOT noise-corrected.
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Ka-Band - DBZ_K
The K-band radar operated with a 75-m native gate spacing.For the merged qc-v1 data set, the K-band fields are averaged
onto a 150m spacing to match the S-band data set.
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DBZ_NAA_KFor the Ka-band, the DBZ field is not corrected for atmospheric attenuation.
Therefore DBZ_K and DBZ_NAA_K are identical.DBZ_NAA_K is included for consistency.
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CMD – clutter detectionCMD is a fuzzy logic-based algorithm for clutter detection.A threshold of 0.5 is applied to the CMD field to determine
where to filter.
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CMD_FLAG_SThe spectral clutter filter is only applied at the gates
shown in yellow.
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CLUT_SCLUT_S is the ratio, in dB, by which the original signal
power is reduced through application of the filter
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CensoringCensoring is applied to reduce the file sizes and clean up the data.
The uncensored DBZ S-band field is shown.
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VEL is a good indicator of noise
The velocity field is basically random in noise regions.We can use this feature to detect noise-only gates.
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PHASE_CHANGE_ERROR
The phase change error field is a measure of phase change compared to a smooth velocity trend in range. It is a good
feature field for detecting noise.
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DBM_SDEVIn a similar way, the standard deviation of power in range is
a good discriminator.
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NOISE_FLAGCombining the various feature fields using fuzzy logic and
applying a threshold yields the noise identification flag
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Example – uncensored NCPThis is the Normalized Coherent Power field (NCP) without
the application of any censoring.
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Example – censored NCPThis shows the NCP field after application of censoring at
noise-only gates.
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Noise estimation beam-by-beamSince we know the gates with only noise, we can then
estimate the noise on a beam-by-beam basis.This shows the estimated noise bias at 0.5 degrees.
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Thank you
NCAR is supported by the National Science Foundation. 41
Other fields included in case questions arise
NCAR is supported by the National Science Foundation. 42
SNRHC_SSignal-to-noise ratio co-polar H channel
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SNRVC_SSignal-to-noise ratio co-polar V channel
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SNRHX_SSignal-to-noise ratio cross-polar H channel
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SNRVX_SSignal-to-noise ratio cross-polar V channel
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RATE_ZHPrecip rate from Z only
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RATE_Z_ZDRPrecip rate from Z and ZDR
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RATE_KDP_ZDRPrecip rate from KDP and ZDR
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RATE_HYBRIDHybrid precipitation estimator from combination of
other estimators
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SNRHC_KSignal to noise ratio, Ka-band, co-polar H channel
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SNRVX_KSignal to noise ratio, Ka-band, co-polar V channel
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DBZ NAA SAttenuation correction: from Doviak and Zrnic, Page 44
Correction depends on elevation angle and range
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DBZ NAA SAttenuation correction: from Doviak and Zrnic, Page 44
Correction depends on elevation angle and range
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