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Radar Calibration

Radar Calibration. August 16, 2011 Eric Loew Earth Observing Laboratory (EOL) NCAR, Boulder, Colorado. 1. The Radar Equation. Where: P r is the received power at the antenna P t is the peak transmitted power at the antenna G is the antenna gain

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Radar Calibration

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  1. Radar Calibration August 16, 2011 Eric Loew Earth Observing Laboratory (EOL) NCAR, Boulder, Colorado 1

  2. The Radar Equation Where: Pr is the received power at the antenna Pt is the peak transmitted power at the antenna G is the antenna gain Θ is the horizontal antenna beamwidth Φ is the vertical antenna beamwidth τ is the transmit pulsewidth λ is the wavelength η is the reflecitivity r is the range l is the atmospheric loss due to water vapor and oxygen absorption lr is the receiver mismatch loss or finite bandwidth loss 2

  3. ReflectivityFactor Where: |Kw|2 is the dielectric factor of water; 0.93 at S-Band Z is the reflectivity factor

  4. Radar Reflectivity

  5. S-Pol Transmit Power Measurement • Pt(W) = 10^{[Pavg(dbm) + coupling_factor(dB) + 10log10(duty cycle) - 10log10(W/1000mw)]/10} • e.g. Pt = 10^[(19 + 37 + 33 – 30)/10] = 10^5.9 = 749,328.2 W

  6. S-Pol Receiver Calibration

  7. Noise Source • Allows us to determine net gains/losses and also receiver NF • Characterized by ENR (excess noise ratio) • ENR expressed in dB • Calibrated regularly by manufacturer • ENR varies with frequency and value used is linearly interpolated from manufacturer’s data

  8. Noise Source Equations • ENR = 10log10[(TSON – T0)/T0], where T0 = 290K • Y = NON/NOFF = TON/TOFF • Y = (TsON + TDUT)/(TsOFF + TDUT) • TDUT = (TsON - YTsOFF)/(Y – 1) • Loss = 10log10[Tdish/TATE]

  9. S-Pol Solar Calibration for Antenna Gain Measurement • The Sun is a non-polarized source of electromagnetic radiation whose flux density at S-band is measured and logged daily at several sites worldwide • G(dB) = D(dB) – Antenna loss(dB) • D(dB) = 10log10(4πAη/λ2) • η = Tsun/Tintercepted flux • Tsun is determined using Y factor as per noise source, where Y = Tsun/Tbluesky

  10. Tintercepted flux = SACpolCatmCexs/k , where S = solar_flux_density (W/m2/Hz) A = antenna area Cpol = polarization_correction (0.5) Catm = atmospheric_atten_correction (0.997) Cexs = extended_source_correction (.857) k = Boltzman’s constant (1.38e-23 kgm2/s2K)

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