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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