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Radar Issues

Radar Issues. Francis J. Merceret NASA/YA-D 12 November 2002. Beam Filling Scan Strategy Attenuation Wet Radome Intervening Precipitation. Issues and Instruments. WSR-88D (NEXRAD) 10 cm Doppler NWS/MLB. WSR-74C 5 cm PAFB. Beam Filling – Radar Characteristics.

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Radar Issues

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  1. Radar Issues Francis J. Merceret NASA/YA-D 12 November 2002

  2. Beam Filling Scan Strategy Attenuation Wet Radome Intervening Precipitation Issues and Instruments • WSR-88D (NEXRAD) • 10 cm • Doppler • NWS/MLB • WSR-74C • 5 cm • PAFB

  3. Beam Filling – Radar Characteristics

  4. Beam Filling – Equivalent Attenuation, WSR-88D Size Range Eff. Attn. as function of feature size (Km) and range (Km)

  5. Beam Filling – Equivalent Attenuation, WSR-74C Size Range Eff. Attn. as function of feature size (Km) and range (Km)

  6. Scan Strategy – WSR-88D

  7. Scan Strategy – WSR-74C (old)

  8. Scan Strategy – WSR-74C (new)

  9. Wet Radome Attenuation - Methodology • Literature search (print and electronic) • Compile into single database • Fit empirical formula: L=C*R*tanh2(F/10) R = rainfall rate (mm/hr) F = frequency (GHz) C = 0.165 (standard), 0.0575 (hydrophobic) L = two-way loss (dB)

  10. Rain Rate (mm/Hr) S-Band Hydrophobic S-Band Standard C-Band Hydrophobic C-Band Standard 1 0.01 0.03 0.03 0.10 2 0.02 0.06 0.07 0.19 5 0.05 0.14 0.17 0.48 10 0.1 0.28 0.33 0.95 20 0.2 0.56 0.66 1.9 50 0.49 1.4 1.66 4.8 100 0.98 2.8 3.32 9.5 200 1.95 5.6 6.63 19 Wet Radome Attenuation - Results

  11. Wet Radome Attenuation – Example: 24 June 2001 WSR-88D WSR-74C

  12. Precipitation Attenuation - Methodology • Literature search for relationships among R(mm/hr), Z(mm6/m3) and M(g/m3) • Stratiform rain, convective rain, snow, and Marshall-Palmer precipitation types • Select worst case relationship and worst case type (worst case = highest predicted attenuation for given measured Z) • Empirical Model: A(dB/Km)=a*10^(b*dBZ) where a and b are wavelength-dependent constants

  13. Precipitation Attenuation - Results

  14. Conclusions • Beam filling is rarely a concern • Each radar has scan pattern gaps that might be significant in a particular location, but use of both radars together can mitigate this • Wet radome attenuation is a major problem for the WSR-74C, but not for the WSR-88D • Precipitation attenuation can be a major problem for quantitative measurements

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