Transcript Document 7712899

Surveillance Weather Radar
2000 AD
Weather Radar TechnologyMerits in Chronological Order
WSR-07PD
WSR-88D
WSR-57
Technology Developments
• Digital receivers
– Easy to achieve sampling rate higher than reciprocal
of pulse (oversampling)
• Versatile circuits for transmitter control
– Easy to phase code, to interleave PRTs (staggered
and other), to compress pulse
• Signal processing on general purpose
computers (PCs)
– Easy to program algorithms and analyze Doppler
spectra
Capability of the NSSL’s R&D
weather surveillance radar
• Doppler and Dual Polarization
• Phase coding of transmitted pulses
• Transmission of arbitrary non uniform pulse
sequence including staggered PRT
• Oversampling
– by a factor of 5 in Dual Polarization Mode
– By a factor of 10 in Single Polarization Mode
• Arbitrary scanning strategy (including RHI)
• Recording of time series data
Oversampling
• To increase speed of volume coverage
• To decrease errors in estimates of
reflectivity, velocity, spectrum width, and
polarimetric variables
Z, Standard Processing, Aug 04
Z, from Decorrelated Samples
Mitigation of range velocity
ambiguities
• Phase coding at lower elevations
• Staggered PRT at higher elevations
• Demonstration of clutter filtering for both
schemes
• Integration into volume coverage patterns
• Inclusion of oversampling
• Adaptive automatic choice of PRTs based
on obscurations in immediately preceding
scans
Phase Coding
10/08/02 15:11 GMT
EL = 0.5 deg
Reflectivity
Long PRT
Phase Coding
Doppler Velocity
Phase coding, medium PRT
10/08/02 15:11 GMT
EL = 0.5 deg
va = 23.7 m s-1, ra = 175 km
Doppler Velocity
Processing as on WSR-88D
va = 23.7 m s-1, ra = 175 km
Staggered PRT
04/06/03 4:42 GMT
EL = 2.5 deg
Reflectivity
Staggered PRT
Staggered PRT
KTLX Doppler Velocity
VCP 11 – Batch Mode
04/06/03 4:42 GMT
EL = 2.5 deg
KOUN Doppler Velocity
Staggered PRT (184 km/276 km)
148 km
184 km
va = 25.4 m s-1
va = 45.2 m s-1
Dual Polarization at NSSL
• 1983: Upgrade of Cimarron radar to dual polarization; switching between
horizontal and vertical polarization
• 1984: Collection of first (anywhere) dual polarization time series data
• 1985 to 1989: Definition of the complete set of polarimetric variables.
Development of schemes to obtain these variables together with spectral
moments
• 1992: First (anywhere) collection of polarimetric variables at all range
locations
• 1992 to present: Development of schemes to classify hydrometeor type.
Improvement of rainfall estimation. Design of a system functionally
compatible with the WSR-88D; simultaneous transmission and reception
of horizontally and vertically polarized waves
• 2002: Upgrade of KOUN radar to dual polarization
• 2002-2003: Joint POLarization Experiment (JPOLE)
Fields of polarimetric variables
Dual Polarization - Benefits
• Vastly superior data quality: calibration, mitigation
of attenuation and beam blockage effects
• Discrimination between insects, birds, ground
echoes, and precipitation
• Superior measurement of rainfall
• Detection of hail
• Classification of precipitation – rain vs freezing rain
vs snow
• Determination of hail size
• Measurement of snowfall
• Icing detection
Stratiform Rain vs Snow
Imminent Goals
• Combining techniques to mitigate range
and velocity ambiguities with optimum
(pseudo whitening) procedure to increase
speed of volume coverage and decrease
errors of estimates
• Incorporating the above combined
technique into dual polarization radar
• Developing adaptive scanning strategy for
agile beam phased array radar
Three Challenges
• Direct estimation of wind transverse to the
radar beam
• Determination of the alias interval of
Doppler velocity from a single pulse
• Estimation of the forward propagation
coefficient using returns from
hydrometeors or biological scatterers
Major Endeavor
• Explaining bulk hydrometeor properties that cause
distinct polarimetric signatures in convective storms
Major Endeavor
• Assimilation of radar data into local NWP
(short term ~ 3 h, fine resolution ~ 1 km)
model
– coupled to distributed hydrological model for
use over small watersheds (~ 1000s km2)
– capable of predicting tornadoes, strong winds,
hail, and other hazards
END
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