Weather Radar

1
Weather Radar

• Meteorological Operational
• Internship Program
• Fall 2004

2
Weather Radar A Brief History

• had its roots in radio... things got in the way
• late 1930s .. rapid development of radar
  technology .. to detect aircraft
• first recorded precip. measurements in Feb 1941
• post WWII .. research on wx radar starts up in
  USA and Canada
• early 1950s .. first Doppler measurements

3
Weather Radar in Canada

• Radar research started in 1950s at McGill
  University
• Wx Service research radar Woodbridge ON (just NW
  of Toronto) 1965
• McGill University radar 1968
• EC conventional radars installed in scattered
  locations across Canada in the 1970s and early
  1980s
• data viewed as real-time, monochromatic, radar
  beam view

4
Weather Radar in Canada

• EC radars converted to digital data processing
  and product generation in early 1980s
• Carvel AB radar installed 1982
• Woodbridge radar dopplerized 1984
• Edmonton tornado 1987 gt Carvel dopplerized 1990

5
Weather Radar in Canada

• By 1997 16 radars across country, including only
  2 doppler
• 1998 National Radar Project (NRP) is devised.
  The software component is called the Unified
  Radar Processing project (URP).

6
Brief Notes on the NRP

• goals
• standardize hardware and software infrastructure
• network of 32 units by 2004
• funding
• 39 million funding approved for 1998-2003
  so 2M per new unit and 500K per upgrade
• Private Wx Radar suppliers quoted 10 M per unit
  .. therefore a savings of about 250 M due to
  some bright and enthusiastic engineers and
  technicians

7
Radar Network
Goose Bay
Holyrood
a
Marble Mt
a
Spirit River
a
Prince George
a
Jimmy Lake
a
a
Port Hardy
Marion Bridge
Val dIrene
a
a
Lac Castor
a
a
a
Carvel
Radisson
a
a
a
a
Landrienee
a
a
Strathmore
Gore
a
a
a
Foxwarren
a
a
Dryden
Chipman
a
a
a
Mt Sicker
Mt Silverstar
Villeroy
Lasseter Lake
a
Schuler
a
a
Aldergrove
Bethune
a
Woodlands
McGill
a
Britt
Montreal River Harbour
Franktown
a
a
King City
Exeter

Done
a
8
Weather Radar a remote sensing tool

• remote sensing tool (unlike an upper air balloon)
• active vs. passive .. radar bursts out
  radiation and then listens for returns .. vs.
  satellite that records existing natural
  radiation
• has the ability to penetrate weather systems
  (see through the storm)
• high (meso) resolution in 3dt of lower atmos.
  vs. satellite which has meso resolution in 2dt
  of layered atmosphere

9
Radar Systems FundamentalsModule 1.4a

• 1. The basic principle of R-A-D-A-R
• 2. Basic radar system operation
• 3. Radar beam dimensions
• 4. PPI vs. CAPPI

RA
D
A
R
dio
etection
nd
anging
10
1. The Basic Principle of RADAR
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1.1 Detection of Targets(1 of 2)

• RAdio Detection And Ranging
• Pulsed microwave energy
• Radar antenna concentrates and transmits energy
• Weather targets intercept and reflect energy back
  to antenna
• Trip time determines range, antenna position
  determines azimuth and elevation

12
1.1 Detection of Targets(2 of 2)
13
1.2 Radar Targets

• Rain, Snow, Hail, Drizzle (met targets)
• Hills, Buildings, Vehicles, Birds, Insects
• Strong gradients in T, Td

14
2. Basic Radar System Operation
15
2.1 The Pulsed Radar System(1 of 2)

• Pulsed energy
• allows use of same antenna for both transmission
  and reception (speak mode, then listen mode)
• simplifies ranging (range, azimuth) of targets
  because position can be established by pointing
  single antenna
• minimal power requirement because peak power is
  only emitted during the pulsed energy burst

16
2.1 The Pulsed Radar System(2 of 2)
17
2.2 The Main Components(1 of 2)
18
2.2 The Main Components(2 of 2)

• Transmitter
• AC-gtDC power supply, magnetron .. out to wave
  guide
• Antenna System (horn, dish, tower, duplexer)
• focusing energy, outgoing and incoming, duplex
  switch
• Receiver
• amplifies received signal and converts to video
  signal
• Processor
• processes analog video signal, controls antenna
• Displays
• Plan Position Indicator (PPI) video display

19
2.3 System Operation

• Synchronizer signal Modulator and Processor
• sends out DC burst to magnetron, starts processor
  time base
• Outgoing energy
• along wave guides, through duplexer, to horn,
  focused by antenna .. then listens
• Incoming (reflected energy)
• target scattering .. antenna focuses, through
  guides, then duplexer, then receiver (u-wave to
  video signal)
• Processor
• converts video signal to digital signal ..
  integrates in space/time .. and creates basic PPI
  product

20
2.4 Wavelength and Frequency(1 of 3)
21
2.4 Wavelength and Frequency(2 of 3)
TSRA
RA/SN
SN
dilemma
22
2.4 Wavelength and Frequency(3 of 3)
resolution
1 / attenuation (ability to penetrate)
sensitivity
x
s
c
23
3. Radar Beam Dimensions
24
3.1 Pulse Length(1 of 4)

• Energy burst duration
• 2.0 us in Conventional Mode
• 2x10-6 s 3x108 m/s 6x102 m 600 m
• 0.5 us in Doppler Mode, giving a 150 m length
• 0.5x10-6 s 3x108 m/s 1.5x102 m 150 m

dilemma
25
3.1 Pulse Length(2 of 4)
dilemma

• high PRF .. short listening period .. good
  sampling of target
• but shorter radar range for unambiguous target
  placement
• low PRF .. good radar range but poor sampling

26
3.1 Pulse Length(3 of 4)

• A pulse travelling to a target at range Rmax and
  back will cover a distance 2Rmax
• Time between pulses is pulse interval PI
• The pulse will make it back to the radar before
  the next pulse is emitted if

27
3.1 Pulse Length(4 of 4)Unambiguous Maximum
Range
Conventional Radar PRF 250 hz Doppler Radar PRF
1000 hz
28
3.2 Beam Width(1 of 2)
Beam Width defined as 2x the off-axis angle where
transmitted power falls to half of maximum (main
lobe)
29
3.2 Beam Width(2 of 2)
example of a real beam
relative power (dB)
off-axis angle (degrees)
30
3.3 Beam Volume(1 of 2)

• beam widens as it travels away from radar

beam height (km)
range (km)
31
3.3 Beam Volume(2 of 2)

• likelihood of intercepting a target increases
  with range
• .. but strength of returned echo (per unit
  volume) may be less since beam is not usually
  filled with targets

32
4. PPI. vs. CAPPI.
33
4.1 PPI Plan Position Indicator
34
4.2 CAPPI Constant Altitude PPI
example CAPPI 15,000 ft beamwidth 1 deg
35
Radar Systems The Canadian NRPModule 1.4b

• Overview of Network
• For more information on current status..
• wwwib.tor.ec.gc.ca/projects/nrp/index_java_e.html

36
Radar Network
Goose Bay
Holyrood
a
Marble Mt
a
Spirit River
a
Prince George
a
Jimmy Lake
a
a
Port Hardy
Marion Bridge
Val dIrene
a
a
Lac Castor
a
a
a
Carvel
Radisson
a
a
a
a
Landrienee
a
a
Strathmore
Gore
a
a
a
Foxwarren
a
a
Dryden
Chipman
a
a
a
Mt Sicker
Mt Silverstar
Villeroy
Lasseter Lake
a
Schuler
a
a
Aldergrove
Bethune
a
Woodlands
McGill
a
Britt
Montreal River Harbour
Franktown
a
a
King City
Exeter

Done
a
37
Conventional Radar InterpretationModule 2.4a

• A. Basic Principles
• B. Reflectivity of Hydrometeors
• C. Relation between Reflectivity and Precip. Rate
• D. Attenuation
• E. Anomalous Propagation
• F. Distortion

38
A. Basic System

• topic covered in Module 1.4a
• echoes result of e/m back scattering from
  collection of water/ice particles
• 100x103 W out .. 1x10-13 W returned

39
B. Radar Reflectivity of Hydrometeors(1 of 5)
40
B. Radar Reflectivity of Hydrometeors(2 of 5)
The Probert-Jones Radar Range Equation
41
B. Radar Reflectivity of Hydrometeors(3 of 5)

• the reflectivity factor .. (from RogersYau)

Ddiameter of target N(D)distribution 10logZrefl
ectivity factor in dbZ
42
B. Radar Reflectivity of Hydrometeors(4 of 5)
Some assumptions..

• Z is uniform in target volume
• Rayleigh scattering
• Target volume filled with targets
• Targets all the same type
• Effect of side lobes neglected
• Main Radar Beam Gaussian

Z can be measured to 1-2 dbZ
43
Radar Reflectivity of Hydrometeors(5 of 5)
cross section
target size
44
Reflectivity (Z) vs. Precip. Rate (R)(1 of 4)

• empirical relationship .. of form
• Z a Rb
• Marshall-Palmer (stratiform rain) Z 200R1.6
• U.S. Nexrad Z 300R1.4 US cvctv Z
  55R1.6
• Srivastava , for snow Z 200R2.1 (for Tlt-5C)
• Xin-Reuter TRW study (Edmonton)
• Z63.6R1.15 for dbZ lt 30, Z0.58R2.89 for dbZ gt
  30

45
Reflectivity (Z) vs. Precip. Rate (R)(3 of 4)

• Factors which can affect R
• hardware calibration
• incomplete beam filling, distortion (covered
  later)
• increasing height of CAPPI surface with range
• imperfect Z-R relationship
• presence of hail or mixed precipitation
• attenuation of radar signal going through precip.
• evaporation or growth of precip. below radar scan
• wind drift giving poor correlation between
  precip. aloft vs. on ground
• anomalous propagation causing false echoes

46
Reflectivity (Z) vs. Precip. Rate (R)(4 of 4)
common example of beam underfilling with targets

• impact is to report weaker echoes as range
  increases
• common in synoptic snow situations

47
D. Attenuation(1 of 3)

• met targets ( other) absorb part of the e/m
  energy that impacts on them
• this leaves a weakened beam to continue on to
  detect other targets
• attenuation is proportional to wavelength
  (stronger for short wavelengths)
• attenuation is proportional to target strength
  (dbZ)

48
D. Attenuation(2 of 3)
example beam passing through 3 identical
targets reports a weaker dbZ on the second hit,
and an even weaker dbZ on the last target
49
D. Attenuation(3 of 3)
10 db/km
attenuation
60 dbZ
reflectivity
50
Attenuation Example

• Warm Frontal Supercell
• Attenuation NE Quad

51
Attenuation Example

• north end of derecho?

52
Attenuation Example radome wetting

• When radome is wet, significant outgoing and
  returning signal can be lost momentarily
• Can occur during heavy rain or with ice buildup
• May only show up in some scan azimuths if only
  one side of the dome is wet (depending on the
  wind)

53
RadomeWetting
54
E. Anomalous Propagation(1 of 8)

• microwave behaves like light .. refraction
  effects due to variation of medium density
• results in the beam bending in response to
  various temperature and moisture profiles
• ducting of beam causing certain ground returns or
  targets well beyond the normal range
• Doppler can filter AP (see this later)

55
E. Anomalous Propagation(2 of 8)

• In typical conditions (standard atmosphere)
  .. beam will refract with a 4/3 earth model

56
E. Anomalous Propagation(3 of 8)
57
E. Anomalous Propagation(8 of 8)

• dont despair ..
• super-refraction (type A) is probably the only
  one you will see on a common basis
• AP usually easy to detect .. particularly when
  the images are animating
• Vertical cross-sections of AP have distinct
  signal
• echoes decrease uniformly sharply with height
• Doppler can remove AP .. leaving behind a very
  clean image. (this will be covered later)

58
Spirit River, AB/BC
Anomalous Propagation Example

• Persistent Ground clutter Beam blockage
• N Clear Hills
• S Rockies

59
Standard Conventional NRP Productsan overview

• CAPPI
• ECHOTOP
• MAXR
• PA RFA
• SVRWX
• VIL VIZ
• CROSS SECTION

60
The CAPPI (1)
where
what
rates
intensity
info
scale
when
61
The CAPPI (2)

• Represents quasi-surface of radar echoes
• Cappi concept developed at McGill U .. 1956
• most popular product .. easy to interpret
• typically 1.5 km for rain, 1.0 km for snow
• surface for 1.5 km CAPPI starts to lift beyond
  120 km .. (the lowest scan angle is above 1.5km)
• Typically displays dbZ and precipitation rate
• 40 km range rings, out to 256 km

62
where
what
heights
The ECHOTOP (1)
info
scale
when
63
The ECHOTOP (2)

• Represents maximum detectable top over the area
• used to quickly identify most sig. cells and
  their height
• reports the highest minimum detectable signal ..
  typically interpreted as cloud top
• used in general forecasting (say GFA) to report
  cloud tops .. usually convective ..
• typical lower threshold set to 2.0 km .. anything
  lower than that ignored completely
• beam filling problems abound ..
• black hole within about 40 km of radar (no high
  scans)

64
The ECHOTOP(3)Banding Effect
65
where
what
rates
The MAXR (1)
intensity
info
scale
when
66
The MAXR (2)

• Represents max intensity in the vertical column
  .. regardless of height at which it was detected
• Frequently reveals development aloft that may be
  a pre-cursor to most significant weather
• Typically have a lower level 2.0 km cut off to
  avoid ground targets

67
where
what
units
The PA RFA (1)
accum
info
scale
when
68
The PA RFA (2)

• Represents Precipitation Accumulation or RainFall
  Accumulation over the specified period
• Shows tracks of precipitationa loop of RFA can
  show whos in line for the approaching precip
• Must be careful with quantitative interpretation
  of dataremember multitude of errors that can
  occur

69
where
what
heights
The SVRWX (1)
info
scale
when
70
The SVRWX (2)

• Represents maximum detected height of strong
  (gt40dbz) targets in a vertical column
• Good to flag potential severe storms
• Height thresholds are
• 5.5-8.5 km dark blue .. nasty TSRA
• 8.5-10.5 km light blue .. intense TSRA
• 10.5-12.0 km yellow .. likely large hail TSRA
• 12.0 km pink .. wish I was home TSRA (large
  hail etc)

71
where
what
units
The VIL VIZ (1)
mass/area
info
scale
when
72
The VIL VIZ (2)

• Represents Vertically Integrated Liquid or
  Vertically Integrated Z (reflectivity)
• High VIL values related to very heavy pcpn and
  greater chance of hail
• Could give rise to strong downdraft if it were to
  collapse gt WDRAFT product

73
The X-SECTION (1)
74
The X-Section (2)

• Represents vertical cross-section of reflectivity
  cut through the radar volume scan between two
  user-defined points
• A user-defined product generated on-the-fly

75
NRP Conventional Products

• the sky is the limit
• URP system is open-ended .. allows for regional
  development and customization of any number of
  products
• composites are an example of a regional product

76
URP2 Interactive Viewer
Select the product you want
77
URP2 Interactive Viewer
tool bar
78
URP2 Interactive Viewer Demo

• Lets check it out
• Run IV to connect to live URP2 servers