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Rain Detection & Attenuation for Remote sensing; & auxiliary sensors. Dr. Sandra Cruz-Pol INEL 5995 DCAS –network weather radars. Total number of drops per unit volume. in units of mm -3. Reflectivity in other books. For Rayleigh approximation . The cross sectional areas of a scatterer.

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rain detection attenuation for remote sensing auxiliary sensors

Rain Detection & Attenuation for Remote sensing;& auxiliary sensors

Dr. Sandra Cruz-Pol

INEL 5995

DCAS –network weather radars

for rayleigh approximation
For Rayleigh approximation
  • The cross sectional areas of a scatterer.

D=2r =diameter of drop

observe scattering in visible em forward scattering vs backscattering
Observe scattering in Visible EM; forward scattering vs. backscattering

Mie scattering by dust particles and aerosols

Rayleigh scattering by water vapor molecules and gases.

volume extinction from clouds
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
raindrops symmetry
Raindrops symmetry

polarimetric radars

volume backscattering from clouds
Volume backscattering from Clouds
  • Many applications require the modeling of the radar return.
  • For a single drop
  • For many drops (cloud)
reflectivity factor z
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.
reflectivity reflectivity factor
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).

precipitation rain
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

rain rate mm hr
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
volume backscattering for rain
Volume Backscattering for Rain
  • For many drops in a volume, if we use Rayleigh approximation
  • Marshall and Palmer developed
  • but need Mie for f>10GHz.
rain retrieval algorithms
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

disdrometer

X-band polarimetric radar simulation -estimator R(KDP) - less sensitive to natural variations in DSD

Disdrometer

2-Dimensional video disdrometer

R-Z relation

also called distrometers
Also called Distrometers
  • http://www.iac.ethz.ch/en/groups/richner/cd/doc/optisch/2d-video-distrometer.jpg

$80K $25K

  • http://www.imk.uni-karlsruhe.de/download/parsivel.jpg
rain gauges
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.
calibrated r z for 3 regions

Rain gauge data

NEXrad data

Calibrated R-Z for 3 regions

R-Z calibration

Leonid Tolstoy, UPRM-CSU Collaborative Ph.D. student

puerto rico testbed ip3
Puerto Rico Testbed IP3
  • Update:1st radar is here http://casa.ece.uprm.edu/index.html
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