Transcript Radar Palette

Radar Systems
• Where are the radars located?
• What is the radar coverage?
• What are some of the characteristics that
differentiate between radar systems?
• Radar Scan strategies?
• Radar products?
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Analysis & Diagnosis 1
Radar History – in Brief
• Radar Radio Detection And Ranging
• In 1887, a physicist named Heinrich Hertz began
experimenting with radio waves in his laboratory in
Germany.
• Sir Robert Alexander Watson-Watt (1892--1973)
Watson-Watt was the Scottish physicist who developed
the radar locating of aircraft in England.
• Radar was patented (British patent) in April, 1935.
• Doppler RADAR is named after Christian Andreas
Doppler, an Austrian physicist who first described in
1842, how the observed frequency of light and sound
waves was affected by the relative motion of the source
and the detector. This phenomenon became known as
the Doppler effect.
• Weather radar. started in 1943 as a Canadian Army
project in Ottawa
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Analysis & Diagnosis 2
The distribution of stations after implementation
Existing Doppler
DND Doppler
Dopplerized/Relocated
Dopplerized DND
New Doppler
DND Conventional
U.S. Doppler
The radar network in 2003.
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Analysis & Diagnosis 3
North American Radar Coverage
The distribution of stations after implementation
Existing Doppler
DND Doppler
Dopplerized/Relocated
Dopplerized DND
New Doppler
DND Conventional
U.S. Doppler
The radar network in 2003.
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Analysis & Diagnosis 4
Canadian Radar Coverage – Canadian Composite
For the masses….
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Analysis & Diagnosis 5
Nominal Radar Coverage with 256 km range
However, in winter …
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Analysis & Diagnosis 6
Effective Radar Coverage with 2 km echo tops
Large blind swaths across the country
♫ I’m dreaming of gap-filling
X-band network …
Even here on the 401
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Analysis & Diagnosis 7
Pacific Network
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Analysis & Diagnosis 8
Prairie Network
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Analysis & Diagnosis 9
Ontario Network
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Analysis & Diagnosis 10
Quebec Network
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Analysis & Diagnosis 11
Atlantic Network
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Analysis & Diagnosis 12
Radar Data in Ontario
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Analysis & Diagnosis 13
NWS Radar Composite
Meteorologists without Borders
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Antenna Scan Strategies
• Conventional:
–
–
–
–
• Doppler:
24 PPI scans
top down
6 RPM
24.6 to 0.3 degrees (0.1 in
winter)
– 5 minutes to complete
– 10 seconds per elevation
angle, 6 per minute
– 3 scan angles
– bottom up ?
– much slower (0.85 RPM)
since more sample points
are collected for the
Doppler processing
– fills much of remaining 5
minutes
10 minute cycle
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Analysis & Diagnosis 15
Some basic radar products
CAPPI vs. PRECIP
• CAPPI 1.0
– Uses conventional reflectivity scans
– 1 km AGL out to 100 km, then rides up the lowest PPI angle (~0.1° winter &
0.3 ° summer) out to 256 km
– Precipitation is relatively high above ground and can grow considerably
between 1 km AGL and the surface
• PRECIP
– Uses long range doppler reflectivity scan within 125 km of radar, including
ground clutter removal
– Uses lowest PPI conventional reflectivity scan beyond 125 km of radar
– Doppler reflectivity not quite as sensitive to weak echoes
– Best product for seeing precipitation close to ground
– Therefore, Precipitation Accums (PA) from PRECIP product should be better
than from CAPPI, as long as ground doesn’t absorb too much beam power
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Analysis & Diagnosis 16
Some basic radar products
CAPPI 1.0 km vs. PRECIP product
CAPPI 1.0
10
25.0 0
PRECIP
2.0 0
beam height (km)
18
2
0.0 0
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range (km)
Analysis & Diagnosis 17
Radar Systems
PRECIP product example
Boundary between
doppler &
conventional
reflectivity scans
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Analysis & Diagnosis 18
Gain vs Beamwidth
• The smaller the beamwidth, better the gain
• Improved gain means higher signal strength for
distant objects or small targets
– e.g. light precipitation may be detected at greater
distances
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Analysis & Diagnosis 19
Weather Radar Bands
• The more common weather radar wavelengths
and letter designations are:
BAND (cm)
S
10
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C
5
X
3
EXAMPLE
NEXRAD,
MCGILL
NRP, EUROPE
U OF TORONTO,
MCGILL
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Analysis & Diagnosis 20
Pulse Repetition Frequency (PRF)
• The pulse repetition frequency (PRF) is the
number of pulses emitted by the radar per
second (pps)
• A pulse travelling to a target at range rmax and
back will cover a distance 2rmax
• The pulse will make it back to the radar before
the next pulse is emitted if:
2rmax=c/PRF
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Analysis & Diagnosis 21
PRF and radar range
Or….
rmax=c/2PRF
• Thus, the higher the PRF, the lower the effective
range (ignoring second-trip echos from objects
located beyond rmax)
• The lower the PRF, the higher the range.
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Rmax vs PRF
700
R max (km)
600
500
400
300
200
100
11
50
10
50
95
0
85
0
75
0
65
0
55
0
45
0
35
0
25
0
0
PRF
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Analysis & Diagnosis 23
Rmax in selected modes
Mode
PRF
Rmax (km)
Reflectivity
Doppler
250
900 &
1200
50
600
125
Clear Air
3000
The Clear Air PRF is 50 allowing greater range.
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Analysis & Diagnosis 24
CONVENTIONAL RADAR DISPLAYS
•PPI
•CAPPI
•FOUR CAPPI
•MAX R
•ECHO TOP
•SEVERE WEATHER
•CROSS SECTION STYLE:
-DIAMETER CROSS SECTION
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-ARBITRARY CROSS
SECTION
Radar
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Analysis & Diagnosis 25
PPI Elevations and Angles
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Radar beam height vs. range
Height of radar beam in normal atmospheric
conditions
18
25.0 0
10
2.0 0
0.0 0
2
beam height (km)
Cone of
silence
Beam widens
with range
range (km)
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Overshoots low tops
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Analysis & Diagnosis 27
PPI Display - 0.3 Degree Angle
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PPI and CAPPI
4.0 km CAPPI
0.3 Degree PPI
1.5km CAPPI
0.3 Degree PPI
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CAPPI
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Cross-sections - CAPPI - Echo Top
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Analysis & Diagnosis 31
MAXR Data Display
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Analysis & Diagnosis 32
Severe Weather Display
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