Post on 23-Dec-2015
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.