ADVANCED RADAR APPLICATIONS IN METEOROLGY

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ADVANCED RADAR APPLICATIONS IN METEOROLGY

• Nurgül Ertem
• 110000531

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Radar in Meteorology

• Radar stands for Radio Detection and Ranging. It
  refers to the use of radio waves to detect
  objects and determine the distance (range) to the
  object.
• Radars, however, will be our focus here. They
  have particularly become important in meteorology
  because of the following reasons.
• (i) They can see through fog, cloud, rain and
  other types of atmospheric conditions which light
  cannot pass through.
• (ii) They can observe many places in the sky
  almost simultaneously.
• (iii) They can run continuously, often without
  operators being present (computer controlled).
• (iv) They can operate during both day and night.
• (v) The data from them can be easily stored to
  computer and then subjected to many types of
  sophisticated analysis.
• (vi) Modern solid-state radars often need little
  maintenance, or replacement of parts, so the
  largest expense is often the setup costs.
• (vii) Radars are not restricted to ground-level
  studies, and can often observe several kilometres
  upward into the atmosphere

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Signal Processing and Product Generation

• The processing of radar data generally involve
  two distinct steps. The first step, called signal
  processing, is the extraction of raw radar
  parameters like echo strength (reflectivity) or
  Doppler velocity from the radar signals coming
  out of the receiver. The second step, called data
  processing or product generation, is the further
  processing of raw radar parameters in order to
  obtain information that is useful for
  meteorological or hydrological purposes. In
  general, these two steps are done by different
  computers, signal processing being done at the
  radar site, while product generation can be done
  everywhere the data are sent to.

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Simple Radar System
antenna
transmitter 106 W
display
T/R switch
receiver 10-14 W
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Radar System

• Transmitter--produces high power pulses at
  desired frequency. Pulses may be 1 microsecond
  in duration.
• Receiver--detects, amplifies and converts
  (digitizes) received voltages from each
  pulse as a function of range
• Antenna--radiates transmitted power in narrow
  beam for maximum gain
• --receives backscattered signal
  from targets
• T/R switch--switches antenna between transmitter
  and receiver at high rate, typically once every
  millisecond
• Receivers are designed to detect very weak
  signals, on the order of 10-13 to 10-14 watts.
  Transmitted power is typically 106 watts, peak
  power.

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Radar Systems

• More advanced radars provide either frequency
  agility or polarization agility.
• Frequency agility--transmit and receive multiple
  frequencies (near in frequency to each other) to
  increase sampling rate
• Polarization agility--alternatively transmit
  either horizontal or vertical polarization to
  provide wealth of information on particle phase,
  shape and orientation

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• Sending and Receiving Signals
• detecting a target

• The radar creates an electromagnetic energy pulse
  which is focused by an antenna and transmitted
  through the atmosphere. Objects in the path of
  this electromagnetic pulse, called targets,
  scatter the electromagnetic energy. Some of that
  energy is scattered back toward the radar.
• The receiving antenna (which is normally also the
  transmitting antenna) gathers this back-scattered
  radiation and feeds it to a device called a
  receiver.

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RADAR

• Radar weather information are used to determine
  current atmospheric conditions, but
  meteorologists must integrate data from many
  sources to get a complete and accurate picture of
  atmospheric conditions. Meteorologists feed
  current data into computer models to help them
  predict weather conditions (forecast) and make
  critical decisions
• Radar could be used to answer the following
  questions about the line of precipitation. What
  is the intensity of the precipitation (in this
  case snow)? What direction and at what speed are
  the snow bands moving? Will the snow bands become
  stronger or weaker?

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COLORED RADAR

• The location of the colored radar echoes indicate
  where precipitation is falling and the various
  colors indicate the intensity of the
  precipitation through the color code in the lower
  left corner of the image.
• The example radar image above shows several
  strong thunderstorms moving through Illinois and
  Indiana on April 20, 1996. Regions of light and
  dark blue indicate regions of lighter
  precipitation while areas of red and pink
  indicate strong, to occasionally severe
  thunderstorms. Normally, it is difficult to
  distinguish precipitation type on the basis of
  the radar reflectivity alone. Snow and light
  drizzle both produce radar reflectivity with
  about the same value. Melting snow and moderate
  rain also have similar values. Very high
  reflectivities (the grays on the scale on the
  image above) are always associated with hail.

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Radar in meteorology

• Weather radars play a vital role in short term
  weather forecasting and for meteorological
  research. They are being used routinely in
  meteorology to monitor storms and follow their
  evolution, as well as observe winds and detect
  regions where severe weather might
• develop. Specialists in radar meteorology, with
  backgrounds in meteorology, engineering, and
  computer science, work to improve the use of
  radar as a meteorological instrument.
• For example, our large S-band Doppler radar is
  used for weather surveillance around the Montreal
  area. Part of the Canadian radar network, it is
  used by the local weather office to monitor
  weather in real-time. Its data are used in a
  variety of applications, from severe weather
  detection to sewer flow forecasting.

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• How Does Radar Work?

Return back
single antenna
target
send
short pulses of energy
The antenna rotates about a vertical axis,
scanning the horizon in all directions
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Radar - How Radar Works

• Radar works by transmitting a pulse of
  electromagnetic energy.
• Objects (raindrops, ice, snow, birds, insects,
  terrain, and buildings) reflect that energy. Part
  of the reflected energy is received back at the
  radar. Once the radar receives the reflected
  signal, computer programs and meteorologists
  interpret the signal to determine where it is
  precipitating.

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Radar Observatory

• Marshall Radar Observatory itself where the main
  radar facility is located. It consists of a
  dual-wavelength, dual-polarization, Doppler
  scanning radar system. With its 9 m antenna
  sitting on top of a tower, it is one of the most
  sophisticated weather radar in the world. The
  first element of the system is a
  dual-polarization, Doppler, long wavelength
  (S-band) radar which measures the intensity, the
  velocity, and the shape of weather targets (rain,
  snow, hail, etc.) up to a range of 250 km. It is
  complemented by a shorter wavelength (X-band)
  radar and two additional receivers located
  elsewhere which help us obtain a more complete
  picture of the weather. This radar is used 24
  hours a day to monitor the storms around
  Montreal. After the radar signals have been
  processed and interpreted, the data are sent to
  the weather office and the downtown campus where
  they are made available on the web in real-time.
• Two other radars are located in Ste-Anne de
  Bellevue. One is a small dual-polarization radar
  called X-Polito, while the other is a vertically
  pointing radar (VPR). X-Polito is a prototype
  low-cost radar developed to measure rainfall over
  short distances. The VPR is a research radar used
  primarily to study the formation of precipitation.

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Interpreting Doppler Radar Velocities

• To understand Doppler radial velocity patterns,
  one first has to consider the geometry of a radar
  scan. Normally the radar beam is pointed at an
  elevation angle greater than zero so that the
  beam, as it moves away from the radar, moves
  higher and higher above the surface of the earth.
  Because of this geometry, radar returns
  originating from targets near the radar represent
  the low-level wind field, while returns from
  distant targets represent the wind field at
  higher levels.

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Interpreting Doppler Radar Velocities speed
shear wind patterns

• On a radar PPI display, the distance away from
  the radar at the center of the display represents
  both a change in horizontal distance and a change
  in vertical distance. To determine the wind field
  at a particular elevation above the radar, one
  must examine the radial velocities on a ring at a
  fixed distance from the radar. The exact
  elevation represented by a particular ring
  depends upon the elevation angle of the radar
  beam.

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DOPPLER

• Doppler velocity patterns (right) correspond to
  vertical wind profiles (left), where the wind
  barbs indicate wind speed and direction from the
  ground up to 24,000 feet. Negative Doppler
  velocities (blue-green) are toward the radar and
  positive (yellow-red) are away. The radar
  location is at the center of the display
• For this first example, wind direction is
  constant with height, but wind speed increases
  from 20 knots at the ground to 40 knots at 24,000
  feet. Note on the radial velocity field that the
  maximum inbound velocity is to the west and
  maximum outbound to the east while to the north
  and south the radar measures zero radial
  velocity. This is because the winds are
  perpendicular to the radar beam when viewed to
  the north or south.

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dual-polarization

• In general, weather radars send and receive
  microwaves at one polarization, usually
  horizontal. By transmitting and/or receiving
  radar waves at more than one polarization,
  additional information can be obtained on the
  nature of the targets
• The most common dual-polarization scheme is the
  transmission and reception of horizontally and
  vertically polarized waves.

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WSR-88D Radar Imagery detecting precipitation

• The word radar is an acronym from "Radio
  Detection and Ranging". Radar images are useful
  for locating precipitation. As a Magnetic
  Resonance Imaging (MRI) scan examines the inside
  of a human body, a radar examines the inside of a
  cloud. A radar sends a pulse of energy into the
  atmosphere and if any precipitation is
  intercepted by the energy, part of the energy is
  scattered back to the radar. These returned
  signals, called "radar echoes", are assembled to
  produce radar images.

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Radar Instrumentation

• King City C-band doppler scanning radar

• Portable C-Band Doppler Scanning Radar

• Portable X-Band Doppler Scanning Radar

• Portable 915 MHz Wind Profiler

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Radar Instrumentation

• Portable/airborne Ka-Band 35 GHz Cloud Radar

• Joss-Waldvogel Disdrometer

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RADAR IMAGES

• REFLECTIVITY / REFLECTIVITE

• The radar only makes measurements if sufficient
  scattering targets (eg rain, snow, etc) are
  present, although the tops of mountains are also
  frequently picked up (they can often be
  recognized by their zero velocity on the radial
  velocity image)

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Reflectivity CAPPIIN CONVECTION
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Interpretation of the radar reflectivity scale

Type and intensity Type and intensity Reflectivity
Drizzle or clear air targets (bugs, etc.) Drizzle or clear air targets (bugs, etc.) 0 dBZ
Very light rain or snow A few raindrops or snowflakes 10 dBZ
Light rain or snow Typical of spring/fall 1-2 mm/hr 25 dBZ
Moderate precipitation Strong for spring/fall 5 mm/hr 35 dBZ
Heavy rain Summer showers 20 mm/hr 45 dBZ
Very heavy rain or hail Peak of thunderstorms 100 mm/hr 55 dBZ
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Reflectivity CAPPI

• The reflectivity CAPPI (Constant Altitude Plan
  Position Indicator - radar lingo for a horizontal
  section at constant altitude - ) is the most
  often used product for displaying precipitation
  intensity around the McGill radar. It shows the
  intensity of all the echoes received by the
  radar, those we want (like precipitation) as well
  those we don't (like ground targets)
• align"justify"In this case, a large area of
  precipitation is approaching from the North West.
  It is made of light stratiform precipitation (in
  green) with several embedded showers and
  thundershowers (in warmer colors). Some of these
  thundershowers actually spawned tornadoes

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Surface refractivity

• In this example, the refractivity field measured
  by radar (bottom) is contrasted with simultaneous
  weather observations over a range of 45 km. Two
  air masses can be identified, a drier one to the
  north (10C dew point temperature) and a wetter
  one to the south (14C dew point temperature).
  The refractivity computed using surface
  observations (shown in brackets in the upper
  window) match well the refractivity measured by
  radar. While the presence of a gradient in
  moisture could have been inferred from surface
  observations alone, the radar measured
  refractivity allow the precise determination of
  the position of the boundary between the two air
  masses (shown with heavy dashes).

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McGill S-band radar

• This radar is used for weather surveillance,
  providing data in real-time to various users
  including the local weather office, as well as
  for meteorological research and the development
  of automated algorithms of weather detection and
  identification.

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National Weather Service Doppler Radars
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Radar Images

• PPI, antenin belirli bir yükseklik açisinda
  (vertical elevation) sabit tutulmasiyla elde
  edilen bir üründür. Yatayda (azimut) 0-360
  tarama yaparak elektromanyetik dalga gönderilir.
  Bu görüntüde, radarin tespit ettigi ekolarin
  reflektivite degerlerine göre radarin kaplama
  alani içerisinde yer alan hedeflerin gerçek
  koordinatlari ve varsa yagisli bölgeler
  belirlenir. Görüntünün saginda bulunan renk
  skalasi dBZ cinsinden reflektivite degerlerini
  gösterir

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Yagisin Cinsi dBZ YagisMiktari mm/saat
           Dolu ile birlikte Yogun ve Siddetli Gürültülü Saganak Yagis 55gt gt100
           Siddetli Gök Gürültülü Saganak Yagis 50-54 51 ile 100
           Mutedil veya Siddetli Yagmur veya Karla Karisik Yagmur 45-49 26 ile 50
           Mutedil Yagmur veya  Karla Karisik Yagmur 40-44 13 ile 25
           Hafif Yagmur , Mutedil veya Kuvvetli Kar 30-39 3 ile 12
           Çok Hafif Yagmur veya Hafif Kar 15-29 0.1 ile 2.9
           Çisenti veya açik hava hedefleri (böcek,toz vb.) lt15 0 ile Iz
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• KIZILÖTESI

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GÖRÜNÜR
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Renklendirilmis
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CONCLUSION
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THANKS