Radar Basics
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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
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Radar Basics
Analysis & Diagnosis 1
RADAR BEAM
The
beam
of energy
spreads out
with distance,
taking a shape
resembling a cone
just like the light beam
from a coastal lighthouse.
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Radar Basics
First pulse
Second pulse
beam width
beam
axis
h (pulse
length
in
space)
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t (pulse
length
in
time)
Radar Basics
Widening Beam
Beamwidth
(Wb)
at a range (r)
is given by:
200
150
q
Wb = r  sin q
100
For small angles
it can be
approximated as
Wb  r q
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50
r
Radar Basics
EM Wave Propagation
Vacuum :
approximately 3 * 108 m/s
in a homogeneous medium
- straight line
- constant speed
atmosphere not being homogeneous...
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Radar Basics
Atmospheric Interactions
Refraction – beam bending
Absorption – energy absorption
Scattering – beam scattering
Reflection – beam reflection
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Radar Basics
Refraction
refractive index
n=c/u
n: refractive index
c: lightspeed (in vacuum)
u: lightspeed in medium
Refractivity (N)
N = (n-1) 106
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Radar Basics
Radar Propagation
depends mainly on vertical refractivity gradient
assumed straight line propagation
under “normal” conditions:
- constant standard refractive index gradient
- constant radius of the earth
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Radar Basics
Radar Equation
h
K

10
q
P
G

P  1024 ln 2

r
2
2
3
t
r
b
18
b
2
Z
2
Pr : average received power (W)
Pt : peak transmitted power (W)
ke:
G : antenna gain
pulse length in space (m)
qb : horizontal beam width
b : vertical beam width
 : transmitted wavelength (m)
|K|2: target’s refractive index
r : target’s slant range (m)
Z:
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target reflectivity factor
6 -3
Radar
or ZBasics
e (mm m )
Assumptions
•
•
•
•
Radar range Equation
non uniform vertical distribution
Z-R variations
beam filling
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Radar Basics
Simpler Radar Equation
Pr average received power
P
r

C
K
r
2
Z
2
where C is the Radar Constant
K target’s refractive index
Z target reflectivity factor
r target’s slant range
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Radar Basics
Sampling Reflectivity
Dimensions of volume elements being scanned
are determined by the beam widths and pulse length.
Beam width is associated with the equipment:
q
b

70
D
antenna
Pulse length affects the size of
conical section being sensed.
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Radar Basics
ATMOSPHERIC
ATTENUATION
As radiation interacts
with encountered particles
within a swept portion
of the atmosphere,
the associated energy
undergoes several changes
which tends to further reduce
its flux along the pulsating beams.
This is mainly due to:
• absorption
• scattering
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Radar Basics
ATMOSPHERIC
ABSORPTION
For microwaves, main absorbing gases are:
Water vapor :
Oxygen :
• pressure
• temperature (inverse)
• absolute humidity
• pressure (squared)
• temperature
•
weaker variables:
- climate
- season
Corrections to the order of 3 to 4 dB (within 200 km)
can be applied to precipitation measurements.
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Radar Basics
Attenuation
PRF can theoretically determine
a maximum unambiguous range.
In practice, within a network,
the useful range of weather radars
would be less than 200 km.
Quantitative precipitation measurements
near the surface can extend to a distance of 130 km.
Doppler may expand intrinsic limitations
with new developments.
Special requirements for long range detection
of thunderstorm can also be serviced.
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Radar Basics
Hydrometeors
attenuation relates to:
- shape
- size
- composition
- wavelength:
@ 10 cm: rather weak
@ 5 cm: acceptable (higher latitude)
@ 3 cm: significant
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Radar Basics
Water mass
larger water mass
causes more attenuation:
ice has less effect than liquid.
Attenuation increases in:
- more dense precipitation areas
- heavier precipitation
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Radar Basics
Size
Melting precipitation and
larger particles such as
- wet snow
- hail
can distort precipitation estimates.
Cloud particles have little effect;
it can be ignored
(unless more precision required)
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Radar Basics
normal atmospheric conditions
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Radar Basics
abnormal atmospheric conditions
subrefraction
superrefraction
cool, moist air aloft
warm, dry air below
warm dry air aloft
cool, moist air below
ducting
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Radar Basics
RADAR BEAM
The
beam
of energy
spreads out
with distance,
taking a shape
resembling a cone
just like the light beam
from a coastal lighthouse.
Radar Palette Home
Radar Basics
First pulse
Second pulse
beam width
beam
axis
h (pulse
length
in
space)
Radar Palette Home
t (pulse
length
in
time)
Radar Basics
Widening Beam
Beamwidth
(Wb)
at a range (r)
is given by:
Wb = r  sin q
For small angles
it can be
approximated as
Wb  r q
Radar Palette Home
200
150
q
100
50
r
Radar Basics
EM Wave Propagation
Vacuum :
approximately 3 * 108 m/s
in a homogeneous medium
- straight line
- constant speed
atmosphere not being homogeneous...
Radar Palette Home
Radar Basics
Atmospheric Interactions
Refraction – beam bending
Absorption – energy absorption
Scattering – beam scattering
Reflection – beam reflection
Radar Palette Home
Radar Basics
Refraction
refractive index
n=c/u
n: refractive index
c: lightspeed (in vacuum)
u: lightspeed in medium
Refractivity (N)
N = (n-1) 106
Radar Palette Home
Radar Basics
Radar Propagation
depends mainly on vertical refractivity gradient
assumed straight line propagation
under “normal” conditions:
- constant standard refractive index gradient
- constant radius of the earth
Radar Palette Home
Radar Basics
Radar Equation
h
K

10
q
P
G

P  1024 ln 2

r
2
2
3
t
r
b
18
b
2
Z
2
Pr : average received power (W)
Pt : peak transmitted power (W)
ke:
G : antenna gain
pulse length in space (m)
qb : horizontal beam width
b : vertical beam width
 : transmitted wavelength (m)
|K|2: target’s refractive index
r : target’s slant range (m)
Z:
Radar Palette Home
target reflectivity factor
6 -3
Radar
or ZBasics
e (mm m )
Assumptions
•
•
•
•
Radar range Equation
non uniform vertical distribution
Z-R variations
beam filling
Radar Palette Home
Radar Basics
Simpler Radar Equation
Pr average received power
P
r

C
K
r
2
Z
2
where C is the Radar Constant
K target’s refractive index
Z target reflectivity factor
r target’s slant range
Radar Palette Home
Radar Basics
Sampling Reflectivity
Dimensions of volume elements being scanned
are determined by the beam widths and pulse length.
Beam width is associated with the equipment:
q
b

70
D
antenna
Pulse length affects the size of
conical section being sensed.
Radar Palette Home
Radar Basics
ATMOSPHERIC
ATTENUATION
As radiation interacts
with encountered particles
within a swept portion
of the atmosphere,
the associated energy
undergoes several changes
which tends to further reduce
its flux along the pulsating beams.
This is mainly due to:
• absorption
• scattering
Radar Palette Home
Radar Basics
ATMOSPHERIC
ABSORPTION
For microwaves, main absorbing gases are:
Water vapor :
Oxygen :
• pressure
• temperature (inverse)
• absolute humidity
• pressure (squared)
• temperature
•
weaker variables:
- climate
- season
Corrections to the order of 3 to 4 dB (within 200 km)
can be applied to precipitation measurements.
Radar Palette Home
Radar Basics
Attenuation
PRF can theoretically determine
a maximum unambiguous range.
In practice, within a network,
the useful range of weather radars
would be less than 200 km.
Quantitative precipitation measurements
near the surface can extend to a distance of 130 km.
Doppler may expand intrinsic limitations
with new developments.
Special requirements for long range detection
of thunderstorm can also be serviced.
Radar Palette Home
Radar Basics
Hydrometeors
attenuation relates to:
- shape
- size
- composition
- wavelength:
@ 10 cm: rather weak
@ 5 cm: acceptable (higher latitude)
@ 3 cm: significant
Radar Palette Home
Radar Basics
Water mass
larger water mass
causes more attenuation:
ice has less effect than liquid.
Attenuation increases in:
- more dense precipitation areas
- heavier precipitation
Radar Palette Home
Radar Basics
Size
Melting precipitation and
larger particles such as
- wet snow
- hail
can distort precipitation estimates.
Cloud particles have little effect;
it can be ignored
(unless more precision required)
Radar Palette Home
Radar Basics
normal atmospheric conditions
Radar Palette Home
Radar Basics
abnormal atmospheric conditions
subrefraction
superrefraction
cool, moist air aloft
warm, dry air below
warm dry air aloft
cool, moist air below
ducting
Radar Palette Home
Radar Basics
B
Warm Frontal Cross-section along
Leading Branch of the Warm Conveyor
Belt (WCB)
Common location for virga
A
WCB
Increasing CCB
Moistening
Surface
Warm Front
CCB
A
B
Cold air in Cold Conveyor Belt (CCB) deep and dry
Link to Classic
Example
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
WCB typically veers with height (it is after all, a warm 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
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Radar Basics
Analysis & Diagnosis 40
Vertical Deformation Zone Distribution and the CBM
Simplified Summary
C
WCB
The WCB overrides the warm front
The CCB undercuts the warm front
The frontal surface overlies the
mixing layer
Wind shear in the CCB is variable
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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
Radar Basics
Analysis & Diagnosis 41
Range Ring versus Radial Zero Velocity Doppler Lines
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Radar Basics
Analysis & Diagnosis 42
D
A
C
G
B
E
F
Need to
emphasize
The PPI
nature of the
Doppler
scan
- The cone
H
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Radar Basics
Analysis & Diagnosis 43
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Radar Basics
Analysis & Diagnosis 44
D
A
C
G
B
E
F
H
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Radar Basics
Analysis & Diagnosis 45
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Radar Basics
Analysis & Diagnosis 46
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Radar Basics
Analysis & Diagnosis 47
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Radar Basics
Analysis & Diagnosis 48
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
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Radar Basics
Analysis & Diagnosis 49
B
Warm Frontal Cross-section along
Central Branch of the Warm Conveyor
Belt (WCB)
A
Common location for virga
WCB
Increasing CCB
Moistening
Surface
Warm Front
Precipitation
At Surface
CCB
A
B
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
WCB shows little directional shift with height. A greater WCB depth is frontal perpendicular
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.
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Radar Basics
Analysis & Diagnosis 50
Vertical Deformation Zone Distribution and the CBM
Simplified Summary
C
WCB
The WCB overrides the warm front
The CCB undercuts the warm front
The frontal surface overlies the
mixing layer
Wind shear in the CCB is variable
Radar Palette Home
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
Radar Basics
Analysis & Diagnosis 51
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.
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Radar Basics
Analysis & Diagnosis 52
Range Ring versus Radial Zero Velocity Doppler Lines
B
A B
C
A
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
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
The real Doppler data is a combination of these two patterns
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Radar Basics
Analysis & Diagnosis 53
D
A
C
G
B
E
F
Need to
emphasize
The PPI
nature of the
Doppler
scan
- The cone
H
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Radar Basics
Analysis & Diagnosis 54
Active or Anabatic Warm Front
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Radar Basics
Analysis & Diagnosis 55
CCB Doppler Diagnosis
B
B
A
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
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A
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
Radar Basics
Analysis & Diagnosis 56
WCB Doppler Diagnosis
D
A
C
G
B
E
F
H
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Radar Basics
Analysis & Diagnosis 57
WCB Doppler Diagnosis – Diagnosis on the Eagle Wing
C
C
A
D
B
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
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A
B
D
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
Radar Basics
Analysis & Diagnosis 58
WCB Doppler Diagnosis – Diagnosis on the Gull Wing
C
C
D
A
B
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
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A
B
D
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
Radar Basics
Analysis & Diagnosis 59
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
Radar Palette Home
Radar Basics
Analysis & Diagnosis 60
B
Warm Frontal Cross-section along
Trailing Branch of the Warm Conveyor
Belt (WCB)
A
Common location for virga
WCB
Increasing CCB
Moistening
Surface
Warm Front
Precipitation
At Surface
CCB
A
B
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
WCB probably backs slightly with height in spite of the warm air advection. A greater WCB depth is frontal perpendicular
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.
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Radar Basics
Analysis & Diagnosis 61
C
WCB
Vertical Deformation Zone Distribution and the CBM
Summary
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Radar Basics
Analysis & Diagnosis 62
G
D
C
A
B
F
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Radar Basics
Analysis & Diagnosis 63
Behind WCB
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Radar Basics
Analysis & Diagnosis 64
Behind WCB
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Radar Basics
Analysis & Diagnosis 65
Behind WCB
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Radar Basics
Analysis & Diagnosis 66
Behind WCB
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Radar Basics
Analysis & Diagnosis 67
Behind WCB
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Radar Basics
Analysis & Diagnosis 68
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.
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Radar Basics
Analysis & Diagnosis 69