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Operational Weather Radar Featuring: WSR-88D Doppler Radar

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Radar Featuring: WSR-88D Doppler Radar Transmission Power 750,000 W Gain 35,481 Beam Width – PowerPoint PPT presentation

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Title: Operational Weather Radar Featuring: WSR-88D Doppler Radar


1
Operational Weather Radar Featuring WSR-88D
Doppler Radar
Transmission Power 750,000 W Gain 35,481 Beam
Width lt2º _at_ 125 nmi Pulse Length - 0.47 or 1.35
km Transmission Time 1.57 of 4.5 µs
2
DOWs measure record high wind speeds of 301 /-
20 mph (135 /- 10 m/s) in 03 May 1999 Oklahoma
City tornado. 
3
Abstract
  • Sensors
  • WSR88 standard weather service radar
  • 158 Operational Sites Across the Country
  • Common Radar Bands K,Ku, C,X, Ka
  • ?1-10cm, 1-10x size of particles (rain ice) of
    interest
  • Makes use of Rayleigh Scattering
  • Phased Array Radar
  • Algorithms
  • Radar Equation
  • Attenuation

4
Brief Weather Radar History
  • 1950 RADAR discovered
  • RADAR RAdio Detection And Ranging
  • In early use, WWII military operators picked up
    on what they thought was noise
  • Really environmental returns, only noise if you
    want to see airplanes
  • 1950-1980 Continued development of reflectivity
    radar
  • 1980-2000 Invention and implementation of
    Doppler radar
  • As of 1988 the US started using 10 cm wavelength
    radars (WSR-88D) as their standard radar device
    for radar networks
  • 2000-present Dual Polarization Radar and Phased
    Array Radar

5
source http//www.cocorahs.org/media/docs/radar_b
asics.pdf
6
source http//www.cocorahs.org/media/docs/radar_b
asics.pdf
7
Introduction
  • Key concepts
  • Doppler effect
  • Rayleigh scattering
  • Sensing the return
  • Reflectivity, dbz
  • Vertical cross section
  • Range Height Indication Scan
  • Constant Azimuth
  • Improvement with WSR-88D
  • Volume Scanning
  • Vary azimuth along with elevation
  • Optimally interpolate 3d volume or reflectance

8
Radar, Doppler and Raleigh
  • Radar Equation
  • Whn transmiter and reciever are in the same
    place, signal decreases in power to the fourth
    power
  • Doppler Equation
  • Where F observed frequency, F emitted
    frequency, v velocity in medium, vs velocity
    of source
  • Raleigh Scattering
  • EM radiation returned from a field with average
    particle size smaller than the wavelength of the
    radiation

9
Reflectivity off a target
  • Power of the return signal - reflectivity (z)?
  • z has the units mm6/m3 -
  • density of water droplets which would return the
    reflectivity
  • emissivity is implicit
  • To cover a large range it is often described in
    decibels
  • Intensity of the return echo helps determine the
    precipitation rate
  • significant precipitation
    usually is above 15 dBz
  • Reported reflectivity is an average of
    at least 25 pulses from a given azimuth
    and elevation

10
Applications
  • Nowcast/ short term forecast
  • useful for extreme weather
  • Easily deployed in remote locations
  • Lee Rotors
  • Precipitation Estimation
  • Links to related topics
  • RUCOOL Codar Maps
  • Radar Altimetry
  • Police Radar
  • Small Aircraft Detection
  • Benefits from radial
    movement of parts

11
Radar Bands and Uses
  • 2-4 S GHz, 7.5-15cm. Sirius and XM radio. Long
    range weather, marine weather, ATC
  • 4-8 Ghz - C band satellite transponders,
    satellite TV, raw satellite communications,
    weather.
  • 18-27 Ghz - K - police, small drizzle/fog
    research ?
  • 27-40 Ghz Ka police
  • 8-12 Ghz - X airport radar very long range,
    missile guidance

12
Making a Signal
  • The listen time (millisecond) is 1000x the
    pulse duration
  • This allows the radar an opportunity to be able
    to receive the signal again without interference
    from previous signals
  • Must wait until signal has reached maximum range
    and returned.
  • Knowing exact pulse travel time allows for
    calculation of the horizontal distance to the
    target
  • Intensity of the return, or backscatter -gt target
    size
  • Radial Target Motion -gt Doppler shift

13
What happens to the returned signal?
  • Must orient the returns (power at certain
    frequencies) into an accurate measure of
    precipitation
  • Measurements over a spherical volume are sliced
    up into horizontally and vertically to produce
    2,3 and 4d visualizations
  • Account for ambient background noise

14
Source http//cimms.ou.edu/rvamb/Documents/Report
_7.pdf
15
Algorithms
  • VIL
  • Vertically Integrated Liquid
  • HAIL
  • Estimates presence and size of
    hailstones
  • Potential Wind Gusts
  • Uses VIL, cloud top height
  • Estimates the winds under the cloud (ie
    downdraft)?
  • Doppler measurement readily reveals wind shear
    storm relative velocity
  • Mesocyclone Detection Algorithm
  • Tornado Detection Algorithm
  • Wind Shear Detection (low level)?

16
Products
  • Base reflectivity
  • how much precipitation is falling
  • precipitation type
  • assess a storm's structure and dimension
  • Composite Reflectivity
  • Scans from all elevations, imaging precipitation
    intensity and storm structure
  • Base Velocity
  • radial wind field, speed of fronts/strong wind
  • range of 140 mi
  • Storm relative motion
  • Track a circulation (show up well in doppler
    return) over time to determine storm motion.
  • Removing the storm relative motion from base
    radials gives an estimate of the flow with
    respect to the storm.

17
Complications
  • Migrating Birds
  • Insects
  • Aircraft, solid buildings,
  • large aerosols
  • for air traffic controller rain
  • for meteorologist airplanes.
  • Identification of snow, and snow type,
  • modification of observed matter before hitting
    the ground (fallstreaks)?
  • big enough sample of precip for identification?
  • In precip estimates Z-R relationship

18
Phased Array Radar
Proven NAVY technology
  • Multiple beams with variable dwell times scan
    continuously
  • perform full volume scan every 20-30s
  • track cooperative aircraft
  • track non-cooperative aircraft
  • perform medium dwell scan on heavy cumuliform
    convection
  • perform long dwell scan on area of suspected
    tornadic development.
  • Expected that tornado warning could in to to 45
    min

19
In Closing
  • Take precipitation rates with caution
  • Highly accurate under most conditions
  • Misleading in cases of extreme precipitation
  • The ultimate in nowcast and high resolution
    spatial time series for precipitation.
  • Extremely useful in adaptive forecasting of
    extreme weather events
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