Radar Palet e Home Radar Systems Analysis & Diagnosis 1 Radar Systems Where are the radars located? What is the radar coverage? What are some of the characteristics

Analysis & Diagnosis 1Radar Palette Home Radar Systems

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?


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


The distribution of stations after implementation

DND ConventionalNew Doppler

Existing Doppler

Dopplerized/Relocated

U.S. Doppler

DND Doppler

Dopplerized DND

The radar network in 2003.


North American Radar Coverage


Canadian Radar Coverage – Canadian Composite

For the masses….


Nominal Radar Coverage with 256 km range

However, in winter …


Effective Radar Coverage with 2 km echo tops

Large blind swaths across the country

Even here on the 401

♫ I’m dreaming of gap-filling X-band network …


Pacific Network


Prairie Network


Ontario Network


Quebec Network


Atlantic Network


Radar Data in Ontario


NWS Radar Composite

Meteorologists without Borders


Antenna Scan Strategies

• Conventional: – 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

• Doppler:– 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


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


Some basic radar products

CAPPI 1.0 km vs. PRECIP product

range (km)

beam

heigh

t (km

)

2 2

1010

1818

0.0 00.0 0

2.0 02.0 0

25.0 025.0 0

CAPPI 1.0PRECIP

Doppler reflectivity Conventional reflectivity


PRECIP product example

Boundary between doppler & conventional reflectivity scans


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


Weather Radar Bands

• The more common weather radar wavelengths and letter designations are:

BAND (cm) EXAMPLE S 10 NEXRAD,

MCGILL C 5 NRP, EUROPE

X 3 U OF TORONTO, MCGILL


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


PRF and radar range

• 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.

rmax=c/2PRFOr….


Rmax vs PRF

0

100

200

300

400

500

600

700

PRF

R m

ax (

km)


Rmax in selected modes

Mode PRF Rmax (km)

Reflectivity 250 600

Doppler 900 & 1200

125

Clear Air 50 3000

The Clear Air PRF is 50 allowing greater range.


CONVENTIONAL RADAR DISPLAYS•PPI

•CAPPI

•FOUR CAPPI

•MAX R

•ECHO TOP

•SEVERE WEATHER

•CROSS SECTION STYLE:

-DIAMETER CROSS SECTION

-ARBITRARY CROSS SECTION


PPI Elevations and Angles


Radar beam height vs. range

Height of radar beam in normal atmospheric conditions

range (km)

beam

heigh

t (km

)

2 2

1010

1818

0.0 00.0 0

2.0 02.0 0

25.0 025.0 0

1.00 beam

Beam widens with range

Overshoots low tops

Cone of silence


PPI Display - 0.3 Degree Angle


PPI and CAPPI

1.5km CAPPI

4.0 km CAPPI

0.3 Degree PPI

0.3 Degree PPI


CAPPI


Cross-sections - CAPPI - Echo Top


MAXR Data Display


Severe Weather Display

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Radar Palet e Home Radar Systems Analysis & Diagnosis 1 Radar Systems Where are the radars located? What is the radar coverage? What are some of the characteristics