Analysis & Diagnosis 1Radar Palette Home Radar Basics

Radar Basics

• How does radar work?• What are the characteristics of all radar systems?• What are the characteristics of Canadian radars?• Introduction to the basic radar systems.

– Conventional– Doppler– Dual Polarized

Radar Palette Home Radar Basics

The The beam beam

of energy of energy spreads out spreads out

with distance, with distance, taking a shape taking a shape

resembling a cone resembling a cone just like the light beam just like the light beam

from a coastal lighthouse.from a coastal lighthouse.

RADAR BEAMRADAR BEAM RADAR BEAMRADAR BEAM

Radar Palette Home Radar Basics

beam

wid

th

beamaxis

First pulse

(pulse(pulselengthlength

in in time)time)

Second pulse

hh (pulse(pulselengthlengthin in space)space)

Radar Palette Home Radar Basics

Widening BeamWidening Beam Widening BeamWidening Beam

Beamwidth Beamwidth (W(Wbb))

at a range (r) at a range (r) is given by:is given by:

Wb = r sin

For small angles For small angles it can be it can be

approximated asapproximated as

Wb r

200

150

100

50

r

Radar Palette Home Radar Basics

Vacuum :Vacuum :

approximately 3 * 10approximately 3 * 1088 m/s m/s

in a homogeneous mediumin a homogeneous medium

- straight line - straight line - constant speed- constant speed

EM Wave Propagation EM Wave Propagation EM Wave Propagation EM Wave Propagation

atmosphere not being homogeneous...atmosphere not being homogeneous...

Radar Palette Home Radar Basics

Refraction – beam bendingRefraction – beam bending

Absorption – energy absorptionAbsorption – energy absorption

Scattering – beam scatteringScattering – beam scattering

Reflection – beam reflectionReflection – beam reflection

Atmospheric Interactions Atmospheric Interactions Atmospheric Interactions Atmospheric Interactions

Radar Palette Home Radar Basics

refractive indexrefractive index

n = c / un = c / u

n: refractive indexn: refractive indexc: lightspeed (in vacuum)c: lightspeed (in vacuum)u: lightspeed in mediumu: lightspeed in medium

Refractivity (N)Refractivity (N)

N = (n-1) 10N = (n-1) 1066

Refraction Refraction Refraction Refraction

Radar Palette Home Radar Basics

depends mainly on vertical refractivity gradientdepends mainly on vertical refractivity gradient

assumed straight line propagationassumed straight line propagation

under “normal” conditions:under “normal” conditions:

- - constant standardconstant standard refractive index gradient refractive index gradient

- - constantconstant radius of the earth radius of the earth

Radar Propagation Radar Propagation Radar Propagation Radar Propagation

Radar Palette Home Radar Basics

Radar Equation Radar Equation Radar Equation Radar Equation

r

t b bPP G K

r

h Z

3 2

2

2 18

21024 2

10 ln

Pr : average received power (W) Pt : peak transmitted power (W)

ke: pulse length in space (m) G : antenna gain

b : horizontal beam width b : vertical beam width

: transmitted wavelength (m) |K|2: target’s refractive index

r : target’s slant range (m) Z : target reflectivity factor or Ze (mm6m-3)

Radar Palette Home Radar Basics

• Radar range Equation• non uniform vertical distribution• Z-R variations• beam filling

Assumptions Assumptions Assumptions Assumptions

Radar Palette Home Radar Basics

Simpler Radar Equation Simpler Radar Equation Simpler Radar Equation Simpler Radar Equation

rPKr

C Z

2

2

where C is the Radar Constantwhere C is the Radar ConstantK target’s refractive indexZ target reflectivity factor

r target’s slant range

Pr average received power

Radar Palette Home Radar Basics

Sampling Reflectivity Sampling Reflectivity

Dimensions of volume elements being scannedDimensions of volume elements being scannedare determined by the beam widths and pulse length.are determined by the beam widths and pulse length.

Beam width is associated with the equipment:Beam width is associated with the equipment:

Pulse length affects the size ofPulse length affects the size ofconical section being sensed.conical section being sensed.

bantennaD

70

Radar Palette Home Radar Basics

ATMOSPHERICATMOSPHERIC

ATTENUATIONATTENUATION

ATMOSPHERICATMOSPHERIC

ATTENUATIONATTENUATION

This is mainly due to:This is mainly due to:

• absorptionabsorption• scatteringscattering

As radiation interacts As radiation interacts with encountered particles with encountered particles

within a swept portion within a swept portion of the atmosphere,of the atmosphere,

the associated energy the associated energy undergoes several changes undergoes several changes

which tends to further reduce which tends to further reduce its flux along the pulsating beams.its flux along the pulsating beams.

Radar Palette Home Radar Basics

ATMOSPHERICATMOSPHERIC

ABSORPTIONABSORPTION

ATMOSPHERICATMOSPHERIC

ABSORPTIONABSORPTION

Water vapor :Water vapor :

For microwaves, main absorbing gases are:For microwaves, main absorbing gases are:

• pressurepressure• temperature (inverse)temperature (inverse)• absolute humidityabsolute humidity

Oxygen :Oxygen :

• pressure (squared)pressure (squared)• temperature temperature •

weaker variables:weaker variables:- climate - climate - season- season

Corrections to the order of 3 to 4 dB (within 200 km) Corrections to the order of 3 to 4 dB (within 200 km) can be applied to precipitation measurements.can be applied to precipitation measurements.

Radar Palette Home Radar Basics

Attenuation Attenuation

PRF can theoretically determine PRF can theoretically determine a maximum unambiguous range.a maximum unambiguous range.

In practice, within a network,In practice, within a network,the useful range of weather radars the useful range of weather radars

would be less than 200 km.would be less than 200 km.

Special requirements for long range detectionSpecial requirements for long range detectionof thunderstorm can also be serviced.of thunderstorm can also be serviced.

Quantitative precipitation measurementsQuantitative precipitation measurementsnear the surface can extend to a distance of 130 km.near the surface can extend to a distance of 130 km.

Doppler may expand intrinsic limitationsDoppler may expand intrinsic limitationswith new developments.with new developments.

Radar Palette Home Radar Basics

Hydrometeors Hydrometeors Hydrometeors Hydrometeors

attenuation relates to:attenuation relates to:- shape - shape

- size- size- composition- composition- wavelength:- wavelength:

@ 10 cm: rather weak 10 cm: rather weak @ 5 cm: acceptable (higher latitude)5 cm: acceptable (higher latitude)

@ 3 cm: significant 3 cm: significant

Radar Palette Home Radar Basics

Water mass Water mass Water mass Water mass

larger water mass larger water mass causes more attenuation:causes more attenuation:

ice has less effect than liquid.ice has less effect than liquid.Attenuation increases in:Attenuation increases in:

- more dense precipitation areas- more dense precipitation areas- heavier precipitation- heavier precipitation

Radar Palette Home Radar Basics

Size Size Size Size

Melting precipitation and Melting precipitation and larger particles such aslarger particles such as

- wet snow- wet snow- hail- hail

can distort precipitation estimates.can distort precipitation estimates.

Cloud particles have little effect;Cloud particles have little effect;it can be ignoredit can be ignored

(unless more precision required)(unless more precision required)

Radar Palette Home Radar Basics

Normal propagation

straight li

ne propagation

4/3 OF EARTH’SRADIUS

normal atmospheric conditionsnormal atmospheric conditions

Radar Palette Home Radar Basics

abnormal atmospheric conditions

subrefraction

superrefraction

ducting

warm dry air aloft cool, moist air below

cool, moist air aloft warm, dry air below

Radar Palette Home Radar Basics

The The beam beam

of energy of energy spreads out spreads out

with distance, with distance, taking a shape taking a shape

resembling a cone resembling a cone just like the light beam just like the light beam

from a coastal lighthouse.from a coastal lighthouse.

RADAR BEAMRADAR BEAM RADAR BEAMRADAR BEAM

Radar Palette Home Radar Basics

beam

wid

th

beamaxis

First pulse

(pulse(pulselengthlength

in in time)time)

Second pulse

hh (pulse(pulselengthlengthin in space)space)

Radar Palette Home Radar Basics

Widening BeamWidening Beam Widening BeamWidening Beam

Beamwidth Beamwidth (W(Wbb))

at a range (r) at a range (r) is given by:is given by:

Wb = r sin

For small angles For small angles it can be it can be

approximated asapproximated as

Wb r

200

150

100

50

r

Radar Palette Home Radar Basics

Vacuum :Vacuum :

approximately 3 * 10approximately 3 * 1088 m/s m/s

in a homogeneous mediumin a homogeneous medium

- straight line - straight line - constant speed- constant speed

EM Wave Propagation EM Wave Propagation EM Wave Propagation EM Wave Propagation

atmosphere not being homogeneous...atmosphere not being homogeneous...

Radar Palette Home Radar Basics

Refraction – beam bendingRefraction – beam bending

Absorption – energy absorptionAbsorption – energy absorption

Scattering – beam scatteringScattering – beam scattering

Reflection – beam reflectionReflection – beam reflection

Atmospheric Interactions Atmospheric Interactions Atmospheric Interactions Atmospheric Interactions

Radar Palette Home Radar Basics

refractive indexrefractive index

n = c / un = c / u

n: refractive indexn: refractive indexc: lightspeed (in vacuum)c: lightspeed (in vacuum)u: lightspeed in mediumu: lightspeed in medium

Refractivity (N)Refractivity (N)

N = (n-1) 10N = (n-1) 1066

Refraction Refraction Refraction Refraction

Radar Palette Home Radar Basics

depends mainly on vertical refractivity gradientdepends mainly on vertical refractivity gradient

assumed straight line propagationassumed straight line propagation

under “normal” conditions:under “normal” conditions:

- - constant standardconstant standard refractive index gradient refractive index gradient

- - constantconstant radius of the earth radius of the earth

Radar Propagation Radar Propagation Radar Propagation Radar Propagation

Radar Palette Home Radar Basics

Radar Equation Radar Equation Radar Equation Radar Equation

r

t b bPP G K

r

h Z

3 2

2

2 18

21024 2

10 ln

Pr : average received power (W) Pt : peak transmitted power (W)

ke: pulse length in space (m) G : antenna gain

b : horizontal beam width b : vertical beam width

: transmitted wavelength (m) |K|2: target’s refractive index

r : target’s slant range (m) Z : target reflectivity factor or Ze (mm6m-3)

Radar Palette Home Radar Basics

• Radar range Equation• non uniform vertical distribution• Z-R variations• beam filling

Assumptions Assumptions Assumptions Assumptions

Radar Palette Home Radar Basics

Simpler Radar Equation Simpler Radar Equation Simpler Radar Equation Simpler Radar Equation

rPKr

C Z

2

2

where C is the Radar Constantwhere C is the Radar ConstantK target’s refractive indexZ target reflectivity factor

r target’s slant range

Pr average received power

Radar Palette Home Radar Basics

Sampling Reflectivity Sampling Reflectivity

Dimensions of volume elements being scannedDimensions of volume elements being scannedare determined by the beam widths and pulse length.are determined by the beam widths and pulse length.

Beam width is associated with the equipment:Beam width is associated with the equipment:

Pulse length affects the size ofPulse length affects the size ofconical section being sensed.conical section being sensed.

bantennaD

70

Radar Palette Home Radar Basics

ATMOSPHERICATMOSPHERIC

ATTENUATIONATTENUATION

ATMOSPHERICATMOSPHERIC

ATTENUATIONATTENUATION

This is mainly due to:This is mainly due to:

• absorptionabsorption• scatteringscattering

As radiation interacts As radiation interacts with encountered particles with encountered particles

within a swept portion within a swept portion of the atmosphere,of the atmosphere,

the associated energy the associated energy undergoes several changes undergoes several changes

which tends to further reduce which tends to further reduce its flux along the pulsating beams.its flux along the pulsating beams.

Radar Palette Home Radar Basics

ATMOSPHERICATMOSPHERIC

ABSORPTIONABSORPTION

ATMOSPHERICATMOSPHERIC

ABSORPTIONABSORPTION

Water vapor :Water vapor :

For microwaves, main absorbing gases are:For microwaves, main absorbing gases are:

• pressurepressure• temperature (inverse)temperature (inverse)• absolute humidityabsolute humidity

Oxygen :Oxygen :

• pressure (squared)pressure (squared)• temperature temperature •

weaker variables:weaker variables:- climate - climate - season- season

Corrections to the order of 3 to 4 dB (within 200 km) Corrections to the order of 3 to 4 dB (within 200 km) can be applied to precipitation measurements.can be applied to precipitation measurements.

Radar Palette Home Radar Basics

Attenuation Attenuation

PRF can theoretically determine PRF can theoretically determine a maximum unambiguous range.a maximum unambiguous range.

In practice, within a network,In practice, within a network,the useful range of weather radars the useful range of weather radars

would be less than 200 km.would be less than 200 km.

Special requirements for long range detectionSpecial requirements for long range detectionof thunderstorm can also be serviced.of thunderstorm can also be serviced.

Quantitative precipitation measurementsQuantitative precipitation measurementsnear the surface can extend to a distance of 130 km.near the surface can extend to a distance of 130 km.

Doppler may expand intrinsic limitationsDoppler may expand intrinsic limitationswith new developments.with new developments.

Radar Palette Home Radar Basics

Hydrometeors Hydrometeors Hydrometeors Hydrometeors

attenuation relates to:attenuation relates to:- shape - shape

- size- size- composition- composition- wavelength:- wavelength:

@ 10 cm: rather weak 10 cm: rather weak @ 5 cm: acceptable (higher latitude)5 cm: acceptable (higher latitude)

@ 3 cm: significant 3 cm: significant

Radar Palette Home Radar Basics

Water mass Water mass Water mass Water mass

larger water mass larger water mass causes more attenuation:causes more attenuation:

ice has less effect than liquid.ice has less effect than liquid.Attenuation increases in:Attenuation increases in:

- more dense precipitation areas- more dense precipitation areas- heavier precipitation- heavier precipitation

Radar Palette Home Radar Basics

Size Size Size Size

Melting precipitation and Melting precipitation and larger particles such aslarger particles such as

- wet snow- wet snow- hail- hail

can distort precipitation estimates.can distort precipitation estimates.

Cloud particles have little effect;Cloud particles have little effect;it can be ignoredit can be ignored

(unless more precision required)(unless more precision required)

Radar Palette Home Radar Basics

Normal propagation

straight li

ne propagation

4/3 OF EARTH’SRADIUS

normal atmospheric conditionsnormal atmospheric conditions

Radar Palette Home Radar Basics

abnormal atmospheric conditions

subrefraction

superrefraction

ducting

warm dry air aloft cool, moist air below

cool, moist air aloft warm, dry air below

Analysis & Diagnosis 40Radar Palette Home Radar Basics

WCB

CCB

Warm Frontal Cross-section along Leading Branch of the Warm Conveyor

Belt (WCB)

Cold air in Cold Conveyor Belt (CCB) deep and dry

Moist portion of Warm Conveyor Belt (WCB) is high and veered from frontal perpendicular – katabatic tendency

Dry lower levels of WCB originate from ahead of the system and backed from frontal perpendicular

Mixing Zone

SurfaceWarm Front

Frontal slope is more shallow than the typical 1:200

Precipitation extends equidistant into the unmodified CCB

Precipitation extends further into the moistened, modified CCB

Increasing CCB Moistening

WCB oriented for

maximum frontal lift

WCB oriented for

less frontal lift

Virga Precipitation

Lower

Hydrometeor

Density

Common location for virga A

B

A B

WCB typically veers with height (it is after all, a warm front)

Link to ClassicExample

Analysis & Diagnosis 41Radar Palette Home Radar Basics

Vertical Deformation Zone Distribution and the CBMSimplified Summary

C

C

WC

B

DCB

CCB

DCB

C

The WCB overrides the warm frontThe CCB undercuts the warm frontThe frontal surface overlies the mixing layerWind shear in the CCB is variable

Looking along the flow:•In WCB to the right of the Col expect veering winds with height – Katabatic warm front•In WCB approach to the right of the Col expect maximum divergence – the eagle pattern with ascent and increasing pcpn•In WCB to the left of the Col expect backing winds with height – Anabatic warm front

Analysis & Diagnosis 42Radar Palette Home Radar Basics

Range Ring versus Radial Zero Velocity Doppler Lines

Analysis & Diagnosis 43Radar Palette Home Radar Basics

BCAD

E

F

G

H

Need to emphasizeThe PPI nature of theDoppler scan- The cone

Analysis & Diagnosis 44Radar Palette Home Radar Basics

Analysis & Diagnosis 45Radar Palette Home Radar Basics

BCAD

E

F

G

H

Analysis & Diagnosis 46Radar Palette Home Radar Basics

Analysis & Diagnosis 47Radar Palette Home Radar Basics

Analysis & Diagnosis 48Radar Palette Home Radar Basics

Analysis & Diagnosis 49Radar Palette Home Radar Basics

Under WCB

• Virga only likely on the leading edge of the WCB• The CCB is becoming increasingly moist• Frontal overrunning and isentropic lift is

increasing thus increasing the intensity of the precipitation process.

• Warm front becoming more likely Anabatic

Click for the Conceptual Model and Explanation

Analysis & Diagnosis 50Radar Palette Home Radar Basics

WCB

CCB

Warm Frontal Cross-section along Central Branch of the Warm Conveyor

Belt (WCB)

Cold air in Cold Conveyor Belt (CCB) more shallow and moist

Moist portion of Warm Conveyor Belt (WCB) is thicker, higher and perpendicular to front

Lower levels of WCB have the same origin as the upper level of the WCB - frontal perpendicular

Mixing Zone

SurfaceWarm Front

Frontal slope is near the typical 1:200

Precipitation extends further into the moistened, modified CCB. Horizontal rain area begins to expand as CCB moistens.

Increasing CCB Moistening

WCB oriented for

maximum frontal lift

Virga Precipitation

Lower

Hydrometeor

Density

Common location for virga A

B

A B

WCB shows little directional shift with height. A greater WCB depth is frontal perpendicular

PrecipitationAt Surface

Analysis & Diagnosis 51Radar Palette Home Radar Basics

Vertical Deformation Zone Distribution and the CBMSimplified Summary

C

C

WC

B

DCB

CCB

DCB

C

The WCB overrides the warm frontThe CCB undercuts the warm frontThe frontal surface overlies the mixing layerWind shear in the CCB is variable

Looking along the flow:•In WCB to the right of the Col expect veering winds with height – Katabatic warm front•In WCB approach to the right of the Col expect maximum divergence – the eagle pattern with ascent and increasing pcpn•In WCB to the left of the Col expect backing winds with height – Anabatic warm front

Analysis & Diagnosis 52Radar Palette Home Radar Basics

Diagnosis of the Conveyor Belts

• Wind direction and speed diagnosis should be completed independently in each conveyor belt

• Given the nature of isentropic flow, this is a prudent mode of diagnosis. Isentropic flows stay relatively separate and maintain their distinctive properties.

• The Doppler characteristics depicted in the CCB are separate from those in the WCB. When added, instructive patterns are revealed.

Analysis & Diagnosis 53Radar Palette Home Radar Basics

Range Ring versus Radial Zero Velocity Doppler Lines

A

B

C

Range Ring Zero Lines

•A is the radar site•A zero Doppler Velocity line that follows a range ring like BC depicts velocity vectors that are•All at the same elevation•Depictions of horizontal wind differences•Range Ring Zero Lines thus depict spatial wind difference

A B C

Radial Zero Lines

•A is the radar site•A zero Doppler Velocity line that follows a radial from the radar like BC depicts velocity vectors that are•At every increasing heights•Depictions of vertical wind differences•Radial Zero Lines thus depict vertical wind difference

The real Doppler data is a combination of these two patterns

Analysis & Diagnosis 54Radar Palette Home Radar Basics

BCAD

E

F

G

H

Need to emphasizeThe PPI nature of theDoppler scan- The cone

Analysis & Diagnosis 55Radar Palette Home Radar Basics

Active or Anabatic Warm Front

Analysis & Diagnosis 56Radar Palette Home Radar Basics

CCB Doppler Diagnosis

A

B

C

The Beaked Eagle

•A is the radar site•AB is backing with height indicative of cold advection where really there should be veering with the Ekman Spiral•BC is veering with height indicative of warm advection•B is the front with the mixing layer hidden in the cold advection•This is a strong cold advection•The warm front will be slow moving or stationary

A

B

C

The Headless Eagle

•A is the radar site•ABC is all veering with height indicative of warm advection. Layer AB is apt to be partially the result of the Ekman Spiral•BC is veering with height indicative of warm advection•Where is the front and the mixing layer?•The cold advection is not apparent and the warm front will advance

Analysis & Diagnosis 57Radar Palette Home Radar Basics

BCAD

E

F

G

H

WCB Doppler Diagnosis

Analysis & Diagnosis 58Radar Palette Home Radar Basics

WCB Doppler Diagnosis – Diagnosis on the Eagle Wing

A

The Right Eagle Wing

•A is the radar site•BC is backing with height indicative of cold advection. •CD is veering with height indicative of warm advection•Larger angles subtended by the arcs BC and CD by the radar site A, are associated with strong thermal advections•A broad wind in the eagle is associated with strong advections

B

C

D B

C

DA

The Left Eagle Wing

•A is the radar site•BC is veering with height indicative of warm advection. •CD is backing with height indicative of cold advection•Larger angles subtended by the arcs BC and CD by the radar site A, are associated with strong thermal advections•A broad wind in the eagle is associated with strong advections

Analysis & Diagnosis 59Radar Palette Home Radar Basics

WCB Doppler Diagnosis – Diagnosis on the Gull Wing

A

The Right Eagle Wing

•A is the radar site•BC is backing with height indicative of cold advection. •CD is veering with height indicative of warm advection•Larger angles subtended by the arcs BC and CD by the radar site A, are associated with strong thermal advections•A broad wind in the eagle is associated with strong advections

B

CD B

C

DA

The Left Eagle Wing

•A is the radar site•BC is veering with height indicative of warm advection. •CD is backing with height indicative of cold advection•Larger angles subtended by the arcs BC and CD by the radar site A, are associated with strong thermal advections•A broad wind in the eagle is associated with strong advections

Analysis & Diagnosis 60Radar Palette Home Radar Basics

Behind WCB

• Virga much less likely• The CCB has become moist• Frontal overrunning and isentropic lift is

maximized thus maximizing the intensity of the precipitation process.

• Warm front is likely Anabatic

Click for the Conceptual Model and Explanation

Analysis & Diagnosis 61Radar Palette Home Radar Basics

WCB

CCB

Warm Frontal Cross-section along Trailing Branch of the Warm Conveyor

Belt (WCB)

Cold air in Cold Conveyor Belt (CCB) even more shallow and more moist

Moist portion of Warm Conveyor Belt (WCB) is thicker, higher and backed from frontal perpendicular – anabatic tendency

Lower levels of WCB have the same origin as the upper level of the WCB

Mixing Zone

SurfaceWarm Front

Frontal slope likely steeper than the typical 1:200

Precipitation extends further into the moistened, modified CCB. Horizontal rain area expands rapidly as CCB moistened.

Increasing CCB Moistening

WCB oriented for

maximum frontal lift

Virga Precipitation

Lower

Hydrometeor

Density

Common location for virga A

B

A B

WCB probably backs slightly with height in spite of the warm air advection. A greater WCB depth is frontal perpendicular

PrecipitationAt Surface

Analysis & Diagnosis 62Radar Palette Home Radar Basics

Vertical Deformation Zone Distribution and the CBMSummary

C

C

C

C

C

WC

B

DCB

CCB

DCB

C

Analysis & Diagnosis 63Radar Palette Home Radar Basics

ABC

D

F

G

Analysis & Diagnosis 64Radar Palette Home Radar Basics

Behind WCB

Analysis & Diagnosis 65Radar Palette Home Radar Basics

Behind WCB

Analysis & Diagnosis 66Radar Palette Home Radar Basics

Behind WCB

Analysis & Diagnosis 67Radar Palette Home Radar Basics

Behind WCB

Analysis & Diagnosis 68Radar Palette Home Radar Basics

Behind WCB

Analysis & Diagnosis 69Radar Palette Home Radar Basics

This must be and remain as Slide 31.

• The links to the three sections of the airflows that comprise each of the conveyor belts are located at Slide 1,11 and 21.

• Slide 11 is always the central, col limited circulation.

• This leaves 10 PowerPoint slides for the development of the training material which should be more than adequate.