1. Operational Weather Radar Featuring: WSR-88D Doppler Radar
Transmission Power – 750,000 W
Gain – 35,481
Beam Width 125 nmi
Pulse Length 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 Algorithms WSR88 – standard weather service radar
158 Operational Sites Across the Country
Common Radar Bands: K,Ku, C,X, Ka
λ=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
: Continued development of reflectivity radar
: 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_basics.pdf

6. source: http://www.cocorahs.org/media/docs/radar_basics.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 mm^6/m^3 -
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, cm. 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 -> target size
Radial Target Motion -> 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 HAIL Potential Wind Gusts
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 Composite Reflectivity Base Velocity
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