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Radar Calibration Radar Snowfall Estimation Automated Precipitation Detection, Amount and Typing. Paul Joe, Brian Sheppard, Nick Kouwen Isztar Zawadzki, Norman Donaldson. Outline. General Comments Wx Radar/Precip Measurements Radar Calibration Workshop Automated Snowfall Amounts/Typing.

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radar calibration radar snowfall estimation automated precipitation detection amount and typing

Radar CalibrationRadar Snowfall Estimation Automated Precipitation Detection, Amount and Typing

Paul Joe, Brian Sheppard, Nick Kouwen

Isztar Zawadzki, Norman Donaldson

outline
Outline
  • General Comments Wx Radar/Precip Measurements
  • Radar Calibration Workshop
  • Automated Snowfall Amounts/Typing
conclusions
Conclusions
  • Radar for QPE not there yet
  • Can work well in certain situations
  • Long range and large areas problems are being solved
  • But not demonstrated to the hydrology community
general comments
General Comments
  • Since 1948/52
    • Z related to Drop Size Distributions
    • Z = nD6 ; R~D4.5
    • Z = 200 R 1.6
    • “valid for rain and snow”
    • many more since then (+/- 3 dB)
  • Z related to R in ‘ideal situation’
    • short range
  • Z related to snow water equivalent
  • DSD is only one of the factors
    • long range
    • Joss and Waldvogel 1990
snow rainfall estimation factors
Snow/Rainfall Estimation Factors
  • Space-time sampling
  • Ground Clutter/Anomalous Propagation
  • Vertical Profile Correction/Bright Band
  • Calibration
  • Attenuation
  • Partial Beamfilling
  • DSD Z-R/Rain Classification and type
    • convective vs stratiform
    • wet bulb technique (rain vs snow)
    • Drop Size Distribution
    • Z-R convective, Z-R stratiform, Z-A
  • Wind drift problem for snow (application dependent)
snowfall
Snowfall
  • 3 seasons of very good comparisions
  • well calibrated radar
  • well sited gauge
  • consistent snow type
  • low wind speed
  • better than rain results
  • effective climatological ZS relationships
  • low snow gradients
low level scanning
Low Level Scanning

0o

GC removal

network processing qa
Network Processing (QA)

Using two radars goes along way toward filling gaps

radar calibration workshop summary
Radar Calibration Workshop Summary
  • Complex system - Stable electronic calibration but consistent?
  • Rainfall as a “success criteria”
  • Expansive definition of calibration
    • various criteria of success
    • calibration, performance measurements, validation, adjustment
  • Inter-radar/network comparisons
    • cross-radar comparisons including TRMM (GPM)
  • Validation
    • problematic standards
    • trend to use basins
  • Successful absolute external target “calibrations”
  • Prevalent use of the Sun
calibration and validation andy white nexrad roc
Calibration and Validation(Andy White Nexrad ROC)
  • Calibration is the process of quantitatively defining system responses to known, controlled signal inputs.
  • Validation is the process of assessing by independent means the quality of the data products derived from system inputs.
  • Validation is a natural adjunct to calibration.
  • Calibration - validation inseparable

Mean Reflectivity Error of -1.47 dB, σ = 1.34 dB before solar cal

slide15
Calibration with a DSD gage (POSS) Using the Z-R relationship for each day or by event(Zawadzki, MRO; Sheppard and Joe, MSC)

By Event and ZR coefficients

34% to 7.5% error reduction

range correction with raingauges approach to resolve a heterogeneous network daniel michelson smhi
Range Correction with Raingauges ApproachTo Resolve a Heterogeneous Network(Daniel Michelson, SMHI)

Range Correction

See also USBR studies

calibration measurements
Calibration Measurements
  • Transmitter:
    • Frequency, PRF, Average RF power
  • Antenna:
    • Gain, Beamwidths
  • Receiver:
    • Output vs. RF input, IF filter loss, [Range]

Uncertainty Analysis

inter radar comparisons
Inter-radar Comparisons

TRMM & WSR88D(Meneghini, NASA)

TRMM PR Stability ~0.5 dB;

Consistent device

Compare with WSR88D

Inter-radar Comparisons(Asko Huuskonen FMI)

needs
Needs
  • Consistency of calibration
  • Redundant measurements
  • Error estimates
  • Use small basins to integrate the measurements (USWRP QPE workshop) - overcome scale and time sampling

(Uijlenhoet, Princeton)

high temporal snow rate measurements

High Temporal Snow Rate Measurements

Experiment to assess our ability to provide 1 minute information on precipitation type and amount.

slide21

Vaisala FD12P

Biral VPF730

Fwd Scattering, capacitance

Fwd & Back Scattering, pulse

detection of terminal velocity

POSS

WiVis

Microwave

CW

Doppler

Fischer-Porter

Manual Obs

IR scintillation, spectral analysis

of fluctuations, fwd scattering

slide23

POSS and Snowfall

1 minute data

window matching vs minutely matching
Window Matching vs Minutely Matching
  • Minutely matching - too many ways for mismatch
  • Develop “window matching” to try to mimic how an observation is made
  • “sensor observation time window” is defined
    • to match the uncertainty in manual observation period
  • “percentage of window” is defined
    • predominant type is determined
    • to match the persistence criteria
  • “observation window” determined by an “observer report”
    • one event = one observation
    • no report = no event = no comparison (even if sensor reports)
slide26

How are we doing with the various steps?

(Zawadzki)

Removing non meteorological data:

Filtering at signal processing

Morphology of reflectivity and Doppler

Polarization diversity

VPR correction for beam height and shadows:

Morphology of reflectivity

Adjustments with gages (N N, Optimization)

Probability Matching

Correction for attenuation:

Networks of radars?

Polarization diversity?

Z-R relations:

Polarization diversity?

Morphology of reflectivity?

Validation: not enough

summary
Summary
  • Progress on many fronts
    • user success criteria
    • network consistency needed
    • radar adjustments
    • calibration
    • automated high temporal measurements
  • Much more to do
    • complete correction system needed
    • need to demonstrate
  • Need a standard for high temporal rate measurements
    • necessary but not sufficient demonstration