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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. Outline. Radar Equation for Meteorology Raindrops Volume scattering Mie scattering Rayleigh approximation Radar reflectivity & reflectivity

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Rain Detection & Attenuation for Remote sensing; & auxiliary sensors

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  1. Rain Detection & Attenuation for Remote sensing;& auxiliary sensors Dr. Sandra Cruz-Pol INEL 5995 DCAS –network weather radars

  2. Outline • Radar Equation for Meteorology • Raindrops • Volume scattering • Mie scattering • Rayleigh approximation • Radar reflectivity & reflectivity • Dielectric factor, K • Ancillary Sensors • Rain gauges • disdrometers

  3. Radar equation for Meteorology • For weather applications • for a volume

  4. Radar Equation • For power distribution in the main lobe assumed to be Gaussian function.

  5. Rain drops

  6. Clouds Types in our Atmosphere

  7. Sizes for hydrometeors cloud drops & rain drops

  8. EM interaction with Single drop • Absorption • Cross-Section, Qa =Pa /Si • Efficiency, xa=Qa /pr2 • Scattered • Cross-section , Qs =Ps /Si • Efficiency,xs=Qs /pr2 • Total power removed by sphere from the incident EM wave, xe = xs+ xa • Backscatter,Ss(p) = Sisb/4pR2 • Efficiency,xb=sb /pr2 Si

  9. Mie Scattering (necessary if d/l1), • Mie theory : A complete mathematical-physical theory of the scattering of electromagnetic radiation by spherical particles, developed by G. Mie in 1908. • In contrast to Rayleigh scattering, the Mie theory embraces all possible ratios of diameter to wavelength. The Mie theory is very important in meteorological optics, where diameter-to-wavelength ratios of the order of unity and larger are characteristic of many problems regarding haze and cloud scattering. • When d/l 1 neither Rayleigh or Geometric Optics Theory applies. Need to use Mie. • Scattering of radar energy by raindrops constitutes another significant application of the Mie theory.

  10. Mie Solution • Mie solution where am & bm are the Mie coefficients

  11. Mie coefficients

  12. Backscattering from metal sphere • Rayleigh Region defined as • For conducting sphere (|n|= ) Where,

  13. Single Particle Cross-sections vs.c for Rayleigh region • Scattering cross section • Absorption cross section In the Rayleigh region (nc<<1) =>Qa is larger, so much more of the signal is absorbed than scattered. Therefore For small drops, almost no scattering, i.e. no bouncing from drop since it’s so small.

  14.  >> particle size Scattering from Hydrometeors Rayleigh Scattering Mie Scattering • comparable to particle size --when rain or ice crystals are present. 95GHz (3mm) 33GHz (9mm)

  15. Volume Scattering • Two assumptions: • particles randomly distributed in volume-- incoherent scattering theory. • Concentration is small-- ignore shadowing. • Volume Scattering coefficient is the total scattering cross section per unit volume. [Np/m]

  16. Total number of drops per unit volume in units of mm-3

  17. Volume backscattering • It’s also expressed as • or in dB/km units, Using... [Np/m] [s,e,b stand for scattering, extinction and backscattering.] [dB/km]

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