Rain Detection

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Rain Detection Attenuation for Remote sensing
auxiliary sensors

• Dr. Sandra Cruz-Pol
• INEL 5995
• DCAS network weather radars

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Total number of drops per unit volume
in units of mm-3
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Reflectivity in other books
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For Rayleigh approximation

• The cross sectional areas of a scatterer.

D2r diameter of drop
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Observe scattering in Visible EM forward
scattering vs. backscattering
Mie scattering by dust particles and aerosols
Rayleigh scattering by water vapor molecules and
gases.
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Mie forward scattering nos impide ver bien a
menos que haya alto contraste.
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Volume extinction from clouds

• Total attenuation is due to gases,cloud, and rain
• cloud volume extinction is (eq.5.98)
• Liquid Water Content LWC or mv )
• water density 106 g/m3

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Raindrops symmetry
polarimetric radars
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Volume backscattering from Clouds

• Many applications require the modeling of the
  radar return.
• For a single drop
• For many drops (cloud)

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Reflectivity Factor, Z

• Is defined as
• so that
• and sometimes expressed in dBZ to cover a wider
  dynamic range of weather conditions.
• Z is also used for rain and ice measurements.

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Reflectivity in other books
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Reflectivity Reflectivity Factor
h
Z (in dB)
Reflectivity, h cm-1
dBZ for 1g/m3
Reflectivity and reflectivity factor produced by
1g/m3 liquid water Divided into drops of same
diameter. (from Lhermitte, 2002).
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Precipitation (Rain)

• Volume extinction
• where Rr is rain rate in mm/hr
• dB/km and b define an algorithm and can
  depend on polarization since large drops are not
  spherical but oblong.

dB/km
Mie coefficients
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Rain Rate mm/hr

• If know the rain drop size distribution, each
  drop has a liquid water mass of
• total mass per unit area and time
• rainfall rate is depth of water per unit time
• a useful formula

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W-band UMass CPRS radar
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Volume Backscattering for Rain

• For many drops in a volume, if we use Rayleigh
  approximation
• Marshall and Palmer developed
• but need Mie for f10GHz.

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Rain retrieval Algorithms

• Several types of algorithms used to retrieve
  rainfall rate with polarimetric radars mainly
• R(Zh),
• R(Zh, Zdr)
• R(Kdp)
• R(Kdp, Zdr)
• where
• R is rain rate,
• Zh is the horizontal co-polar radar reflectivity
  factor,
• Zdr is the differential reflectivity
• Kdp is the differential specific phase shift
  a.k.a. differential propagation phase, defined as

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Disdrometer
2-Dimensional video disdrometer R-Z relation
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Also called Distrometers

• http//www.iac.ethz.ch/en/groups/richner/cd/doc/op
  tisch/2d-video-distrometer.jpg
• 80K 25K
• http//www.imk.uni-karlsruhe.de/download/parsivel.
  jpg

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Rain Gauges

• Tipping bucket - 0.2 mm (0.007 in) falls the
  lever tips and an electrical signal is sent to
  the recorder
• Weighing rain gauge-storage bin atop a pen
  recording the changes of weight on a rotating
  drum . More expensive than Tipping buckets.
• Optical -These have a row of collection funnels.
  In an enclosed space below each is a laser diode
  and a phototransistor detector. When enough water
  is collected to make a single drop, it drips from
  the bottom, falling into the laser beam path. The
  sensor is set at right angles to the laser so
  that enough light is scattered to be detected as
  a sudden flash of light. The flashes from these
  photodetectors are then read and transmitted or
  recorded.

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Calibrated R-Z for 3 regions
R-Z calibration
Leonid Tolstoy, UPRM-CSU Collaborative Ph.D.
student
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Puerto Rico Testbed IP3

• Update1st radar is here http//casa.ece.uprm.edu/
  index.html