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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

Radar Issues

Francis J. Merceret

NASA/YA-D

12 November 2002

issues and instruments
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 equivalent attenuation wsr 88d
Beam Filling – Equivalent Attenuation, WSR-88D

Size

Range

Eff. Attn. as function of feature size (Km) and range (Km)

slide5

Beam Filling – Equivalent Attenuation, WSR-74C

Size

Range

Eff. Attn. as function of feature size (Km) and range (Km)

wet radome attenuation methodology
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)

wet radome attenuation results

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
precipitation attenuation methodology
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
conclusions
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