DYNAMO radar workshop University of Washington, Seattle 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 1

QC-V1 Data Set QC version 1 data set released July 7 Format is CfRadial – Times are given in UTC – Filename contains start and end times of volume: cfrad _ _to_ _ _SPOL_v9373_SUR.nc – Time variable in file is relative to the start time Available for download: – URL: – 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 2

QC-V1 Data Set Web documentation is available at: This contains: – Project information – Data set description – Data quality and calibration reports – Download procedures – Links to format documents 3

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 4

QC-V1 Spol-Ka Data Fields – 41 FIELD NAMEDescriptionFIELD NAMEDescriptionFIELD NAMEDescription DBZ_S Reflectivity S-band DBZ_NAA_S DBZ no atmos atten S-band VEL_S Radial velocity (combined) S-band VEL_ALT_S Velocity alternating mode S-band VEL_HV_S Velocity H and V separately S-band WIDTH_S Spectrum width S-band ZDR_S ZDR S-band LDRH_S LDR H channel S-band LDRV_S LDR V channel S-band RHOHV_S HV Cross-correlation Noise corrected RHOHV_NCC_S HV Cross-correlation Not noise corrected PHIDP_S Differential phase S-band KDP_S Specific differential phase S-band PSOB_S Phase shift on back-scatter (not good in this release) SNRHC_S SNR H co-polar S-band SNRVC_S SNR V co-polar S-band SNRHX_S SNR H cross-polar S-band SNRVX_S SNR V cross-polar S-band DBMHC_S Power H co-polar Not noise corrected DBMVC_S Power V co-polar Not noise corrected DBMHX_S Power H cross-polar Not noise corrected DBMVX_S Power V cross-polar Not noise corrected NCP_S Normalized coherent power S-band PID Particle ID S-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 removed S-band CPA_S Clutter phase alignment S-band CMD_S Clutter mitigation decisiion field CMD_FLAG_S CMD flag – indicates where filter is applied DBZ_K Reflectivity Ka-band DBZ_NAA_K DBZ no atmos atten (Same as DBZ_K) LDRH_K LDR H-channel Ka-band SNRHC_K SNR H co-polar Ka-band SNRVX_K SNR V cross-polar Ka-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: l l 6

DBZ S Attenuation correction: from Doviak and Zrnic, Page 44 Correction depends on elevation angle and range 7

DBZ NAA S Reflectivity with no attenuation correction applied 8

VEL_ALT_S Radial 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. 9

VEL_S Velocity computed from VEL_HV_S and unfolded using VEL_ALT_S. Less noisy than VEL_ALT_S. Folds at 26.7 m/s. 10

VEL_HV_S Velocity computed from H pulses and V pulses and then averaged. Has less noise than alternating mode V. Folds at m/s. 11

Why do we need VEL_HV? VEL_HV is useful for finding the velocity in bird echoes. Consider the following boundary in reflectivity 12

PHIDP in echoes with phase shift on back-scatter Because of phase shift on back-scatter, phidp can be very noisy in bird echoes 13

Noisy VEL in regions with phase shift on backscatter SPOL VEL depends on PHIDP, so VEL will also be noisy in bird echoes 14

VEL_VH is not noisy in phase-shifted echoes Because VEL_VH is not dependent on PHIDP, it will not be noisy in regions of phase-shift on back-scatter 15

WIDTH_S Spectrum width No changes were made to the spectrum width estimator. 16

ZDR_S ZDR – differential reflectivity between H and V No calibration changes were made in post-processing. 17

RHOHV S RHOHV is now corrected for noise. This has important implications for PID. Bright-band regions 18

RHOHV_NCC_S Compare the previous image with this one, which is computed without noise correction (as in the field) Low SNR region leads to low RHOHV values, confusing the PID algorithm 19

PID PID has been improved with tighter membership functions for RHOHV, and other tuning details for tropical convection 20

TEMP_FOR_PID The temperature field used for PID is based on the GAN sounding closest in time to the radar scan. 21

PHIDP_S PHIDP is unchanged from the field. However, KDP has been improved. 22

KDP_S The KDP algorithm was improved with better treatment of noisy regions. Also, it is no longer constrained by DBZ. 23

RATE_KDP The improved KDP field leads to improvement in precip rate derived from KDP. However, it must still be used in conjunction with other precip estimators. 24

RATE_HYBRID The hybrid precip rate has been tuned for better agreement with the disdometer measurements. However, further work on this topic is clearly required. 25

SNRHC_S SNR 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. 26

DBMHC_S DBMfields 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. 27

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. 28

DBZ_NAA_K For 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. 29

CMD – clutter detection CMD 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. 30

CMD_FLAG_S The spectral clutter filter is only applied at the gates shown in yellow. 31

CLUT_S CLUT_S is the ratio, in dB, by which the original signal power is reduced through application of the filter 32

Censoring Censoring is applied to reduce the file sizes and clean up the data. The uncensored DBZ S-band field is shown. 33

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. 34

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. 35

DBM_SDEV In a similar way, the standard deviation of power in range is a good discriminator. 36

NOISE_FLAG Combining the various feature fields using fuzzy logic and applying a threshold yields the noise identification flag 37

Example – uncensored NCP This is the Normalized Coherent Power field (NCP) without the application of any censoring. 38

Example – censored NCP This shows the NCP field after application of censoring at noise-only gates. 39

Noise estimation beam-by-beam Since 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. 40

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_S Signal-to-noise ratio co-polar H channel 43

SNRVC_S Signal-to-noise ratio co-polar V channel 44

SNRHX_S Signal-to-noise ratio cross-polar H channel 45

SNRVX_S Signal-to-noise ratio cross-polar V channel 46

RATE_ZH Precip rate from Z only 47

RATE_Z_ZDR Precip rate from Z and ZDR 48

RATE_KDP_ZDR Precip rate from KDP and ZDR 49

RATE_HYBRID Hybrid precipitation estimator from combination of other estimators 50

SNRHC_K Signal to noise ratio, Ka-band, co-polar H channel 51

SNRVX_K Signal to noise ratio, Ka-band, co-polar V channel 52

DBZ NAA S Attenuation correction: from Doviak and Zrnic, Page 44 Correction depends on elevation angle and range 53

DBZ NAA S Attenuation correction: from Doviak and Zrnic, Page 44 Correction depends on elevation angle and range 54