Dan Satterfield, Chief Meteorologist WHNT-TV, Huntsville James-Paul Dice Meteorologist WHNT-TV Walt...
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Transcript of Dan Satterfield, Chief Meteorologist WHNT-TV, Huntsville James-Paul Dice Meteorologist WHNT-TV Walt...
Dan Satterfield, Chief Meteorologist WHNT-TV, Huntsville
James-Paul Dice Meteorologist WHNT-TVWalt Peterson Senior Atmospheric Scientist UAH
We Really Do Have The Most Advanced TV Radar!
AMS San Antonio 2007
ARMOR: Advanced Radar for Meteorological and Operational Research.
• Location : Huntsville Intl. Airport• Altitude (antenna MSL): 194 m• Transmit frequency: 5625 MHz (C Band)• Peak Power: 350 kW• Pulse width: 0.8 s • Maximum PRF: 1000 s-1
• Antenna Diameter 3.7 m (12 ft CF Parabolic)• Antenna Beam width: 1.0o
• First side-lobe: -23 to -24 dB• Maximum rotation rate: 6 rpm• Transmit polarization: Simultaneous H and V, or H• Receive polarization: SIGMET dual-channel; H and V• Signal Process: SIGMET RVP/8• Variables: Z, V, W, ZDR, DP, KDP, hv, LDR
Partners: UAH, NASA, NSSTC, WHNT-TV
Deployed in Huntsville by the NWS in 1977 as a local warning radar (WSR-74C) then refurbished and upgraded to Doppler in 1991.
Radar donated to UAH in 2002 and upgraded to dual-polarimetry using the SIGMET Antenna Mounted Receiver 11/04. Renamed: ARMOR.
9/23/04 WSR-74C disassembly 10/29-11/05 ARMOR Reassembly
The Science behind ARMOR
Many of these slide courtesy of
Dr. Walt Peterson
Senior Atmospheric Scientist
University of Alabama Huntsville
ConventionalRadar (NEXRAD)
PolarimetricRadar (ARMOR)
POLARIMETRIC RADAR?
Courtesy NSSL
The Basics:
By looking at the difference between Hor. Polarized Z and
Vert. polarized Z we can determine size and shape of
hydrometeors
Is it really that simple??
Don’t I wish it were!
But…
Unfortunately, it isn’t!
Remember when you learned storm relative velocity..VIL…ETC?
Remember when you learned storm relative velocity..VIL…ETC?
Well get ready for some new terms like
Differential ReflectivityLinear Depolarization Ratio
Polarimetric Variables1. Reflectivity factor Z at horizontal polarization
- Measure of size and concentration of scatters
(dominated by SIZE)
2. Differential reflectivity ZDR
- Measure of median drop diameter→ SIZE/SHAPE
- Useful for rain / hail / snow discrimination→ SIZE/SHAPE/PHASE
3. Differential phase ΦDP (Specific Differential Phase- KDP)
- Efficient for accurate rainfall estimation→ NUMBER/SHAPE
- Immune to radar miscalibration, attenuation, and partial beam blockage
4. Cross-correlation coefficient ρhv
- Indicator of mixed precipitation → SHAPE/PHASE
- Efficient for identifying nonmeteorological scatterers
Research:
NCAR, CSU, NASA, UND, DLR, BMRC, NOAA-ETL
ARMOR
Operational:
NEXRAD, TV
vs
Small ZDR Large ZDR
• More accurate rainfall estimation (10-20% max accumulation error as opposed to 200-300%).
• Why? Because we collect information on drop size/shape/concentration and are able to mitigate hail contamination. (Kdp most useful!)
• Identification of precipitation types and discrimination between
meteorological and non-meteorological scatterers
• Improvement in radar data quality: Calibration is more consistent using using polarimetric variables
Advantages of Dual-Polarization Radar
vs
Small ZDR Large ZDRSmall drops Large drops
vs
Hail Rain
vs
Insects Rain
Mitigates the multiple Z-R issues! Estimating rainfall by assuming a standard drop size works, but rather poorly!
• Spherical shape and tumbling of hail results in low ZDR’s (a ZDR “hole”).
• Large drop recirculation on edge of echo vault at x=25 km, z=2-3 km.
• Drop column clearly extends into sub-freezing portion of cloud- the hail process
ZDR in Range-Height mode …………..(ARMOR has this scanning capability and this mode provides an early look into the development of intense storms)
ZH
ZH
ZDR
ZDR
0 15 30 45 60
0 15 30 45 60
-1 0 1 2 3 4 5
-1 0 1 2 3 4 5
ZH
ZH
ZDR
ZDR
ZH
ZH
ZDR
ZDR
0 15 30 45 60
0 15 30 45 60
-1 0 1 2 3 4 5
-1 0 1 2 3 4 5
“ZDR Column” in developing convection
“ZDR Hole” in Hail
61+ dBZ in cells: Hail or Rain?ARMOR: 1541 UTC 12/09/04
ZDR
>3.5 dB ZDR: Big rain drops or melting hail
Squall Line on ARMOR from IRIS display
Squall Line on ARMOR from IRIS display (velocity)
The Television Side- Explaining all this to our viewers!
ARMOR Operates Like No Other TV Radar
• The radar alternates between a traditional Doppler mode and a multi-elevation polarimetric scan. This flexibility means more data into our office.
• Traditional radar measurements (reflectivity and Traditional radar measurements (reflectivity and velocity) are available at all times.velocity) are available at all times.
• Radar alternates its operation between a live .5Radar alternates its operation between a live .5oo surveillance scan and a 3 elevation volumetric scan at surveillance scan and a 3 elevation volumetric scan at .7.7oo,1.3,1.3oo, and 2.0, and 2.0o. o. Other volume scans and sector Other volume scans and sector scans are easily tasked to the radar.scans are easily tasked to the radar.
• Following each volume scan, a hydrometeor Following each volume scan, a hydrometeor identification algorithm produces a product.identification algorithm produces a product.
ARMOR in WHNT WX OfficeARMOR in WHNT WX Office
Sigmet IRIS Workstation
FasTrac VIPIR
ARMOR and KHTX Side-by-Side Comparison December 10, 2004
December 10, 2004 Hail Event
61 dBZ with VIL ~30 kg/m2
-1.8 -0.9 0.1 1.0 1.9 2.9 3.6 -15 - 5 5 15 25 35 45
dBZ ZDR
ARMOR: 12/10/04 17:55:06 EL=1.3o
Rain
55+ dBZ
Hail
55+ dBZ
Rain
2 to 3.5 dB
Hail
-1 to 0.5 dB
Hail
-1.5 to 0.5 dB
Rain/Hail
-0.5 to 2 dB Rain/Hail
40-55 dBZ
Hail
50-55 dBZ
Ground-truth Report of Dime-Size Hail
Owens Crossroads, Alabama.
The Good
• We have the only one in TV (For a few more hours!!)
The Good
• We have the only one in TV (For a few more hours!!)
• Hydro Meteor ID Really Works! (Limited evaluations so far.)
The Good
• We have the only one in TV (For a few more hours!!)
• Hydro Meteor ID Really Works!
• RVP8 Processor is Big Improvement
The Good• We have the only one in TV (For a few more hours!!)• Hydro Meteor ID Really Works!
• RVP8 Processor is Big Improvement
• Future Products Look Very Promising (3d Hydro ID in real time?)
The Bad
•How do you explain it to viewers?(I am open to suggestions!)
•Difficult to interpret in real time. (Algorithims are the key)
•Not a turn key system..Graphics are made for science not TV.
Advantages of Dual Polarization
• Improved Hail Detection (fewer false alarms)
• Hydrometeor Identification works well! (an improved algorithm now available.)
• Possible Tornado Debris Detection to Improve Warnings (close to radar)
• Greatly Improved Rainfall estimates.
Summary
Internet Sites with info on Dual Polarization
Radar
http://www.nssl.noaa.gov/briefings/vol5_no3/polarimetric.html
On NSSL Web Site-by Alexander Ryzhkov
Excellent site by Kevin Scharfenberg at
http://cimms.ou.edu/~kscharf/pol/
Armor is on the Web! (Including Hydro. ID)
http://www.nsstc.uah.edu/ARMOR/webimage/