Indian MST Radar Location

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Indian MST Radar Location
Bay of Bangal
Arabian Sea
Indian Ocean
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VIEW
Indian MST radar
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Equatorial Atmosphere Radar, Indonesia (0.21 S,
100 E)
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Principles of radar

• Main components
• Transmitter, antenna and receiver
• Tx Generates a pulses of energy at a repeated
  frequency
• Pulses intercepts the objects of different
  refractive index characteristics - back
  scattering radiation
• Rangect/2
• Unambiguous range R(max) c/2fr , fr ?denotes
  PRF radar pulse repetition frequency
• Typical specification for a cloud physics
  (weather radar)
• Peak Power ? kW
• Radio frequency ?GHz
• PRF ? 200 2000 per sec
• Pulse duration 0.1- 5 micro sec

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Electromagnetic pulse transmission

• Pulse length and inter pulse period (IPP)

Pulse length
IPP
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Different Beam formation depends on antenna array
size and wavelength. This is defined as radiated
intensity as a function of angular distance from
the beam axis OR this is an angular separation
between points where the transmitted intensity
has fallen to half its maximum value
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Diameter of the circle traced by the beams
N
E
W
S
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Typical specification for a VHF radar for
convection experiment

• It operates at 53 MHz
• Pulse width 1 µs
• IPP 250 µs
• NCI 512
• FFT 256
• No of beams Zx, Zy E,W, Zx, Zy, N,S (10 degree
  off zenith)

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Radar Equation

• The radar range equation expresses the
  relationship between the returned power and
  characteristics of the radar and the target.
  Lets consider first a target of negligible
  spatial extent, called a point target.
• Let Pt ?the radar transmits a peak power
• If this were radiated isotropically, a small
  area? At at range r would intercept an amount of
  power given by
• The antenna is used to focus the energy in a
  narrow beam, increasing the power relative to the
  isotropic-radiated value. If centered on the beam
  axis, the small area At intercepts an amount of
  power given
• where G is a dimensionless number called the
  antenna axial gain.

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• Now if this area were to scatter the incident
  radiation isotropically, the power returned to an
  antenna with aperture area Ae would be
• Further because the gain and the antenna aperture
  are approximately related by a relation
• But At is replaced by sigma called scattering
  cross section as the entire At is not
  contributing to the back scatter.
• The form of radar equation for a single target of
  cross section sigma

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Weather radar

• Raindrops, snowflakes, and cloud droplets are
  examples of an important class of radar targets
  known as distributed targets. Such targets are
  characterized by the presence of many effective
  scattering elements that are simultaneously
  illuminated by a transmitted pulse. The volume
  containing those particles that are
  simultaneously illuminated is called the
  resolution volume of the radar, and is determined
  by beam width and pulse length.
• For distributed targets whose scattering
  elements move relative to each other, the power
  returned from a given range is observed to
  fluctuate in time. Such fluctuations occur in
  weather radar signals because the raindrops or
  snowflakes move relative to one another owing to
  different fall speeds and wind variations across
  the resolution volume.
• 
  Contd/

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• It turns out, however, that a suitably long time
  average (in practice about .01 s) of the received
  power from a given rage is given by
• where Ss is the sum of the backscatter
  cross-sections of all the particles within the
  resolution volume. This contributing volume is
  given approximately by where hct is the pulse
  length and ? is the beamwidth. We can combine
  these two equations
• where ? denotes the radar reflectivity per unit
  volume.

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Example of rain and wind echo taken by MST radar
Rain Echo
Doppler shift (Hz)