x band radar observation of precipitation...v. chandrasekar and daniel feldman click to edit master...
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X band Radar Observation of precipitation
V. Chandrasekar and Daniel Feldman
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Radar measuring rainfall concept
Radar
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Dual-polarization radar measurementsPolarimetric Radar-based Precipitation Estimation
ScatteringMatrix
Reflectivity:
ππβ =ππ4
ππ5 πΎπΎπ€π€ 2 οΏ½ππβ(π·π·)ππ(π·π·)πππ·π·
πππ£π£ =ππ4
ππ5 πΎπΎπ€π€ 2 οΏ½πππ£π£(π·π·)ππ(π·π·)πππ·π·
Differential reflectivity:
ππππππ ππππ = 10 log10ππβπππ£π£
ππ: radar wavelength
ππβ,π£π£: radar cross section at H/V polarization
πΎπΎπ€π€ 2 = (ππππ β 1)/(ππππ + 2) 2: dielectric factor of water (ππππ is the complex relative dielectric constant of water)
π·π·: particle equivalent diameter
ππ(π·π·): number of drops per unit volume with size from π·π· to π·π· + πππ·π·
(Bringi and Chandrasekar, 2001)
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Dual-polarization radar measurements
ππβ,π£π£: complex forward scattering amplitudes atH/V polarization
Specific differential propagation phase:
πΎπΎππππ = 180ππππReβ« ππβ π·π· β πππ£π£ π·π· ππ(π·π·)πππ·π·
Polarimetric Radar-based Precipitation Estimation
Rainfall rate:π π = 0.6ππ Γ 10β3 β« π£π£(π·π·)π·π·3ππ(π·π·)πππ·π·π£π£ π·π· = 9.65 β 10.3ππβ0.6π·π·
π£π£ π·π· : raindrop terminal velocity
(Bringi and Chandrasekar, 2001)
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Polarimetric Radar-based Precipitation EstimationX-band radar rainfall algorithm (Bringi and Chandrasekar, 2001)
π π (πΎπΎππππ) = πππΎπΎππππππIn applications, πΎπΎππππ is estimated as οΏ½πΎπΎππππ = π·π·ππππ ππ2 βπ·π·ππππ(ππ1)
2(ππ2βππ1),
where differential phase π·π·ππππ is obtained from radar measured differential phase ππππππ.
o π π (πΎπΎππππ) is immune to radar systemcalibration, attenuation, and partial beamblockage.
o πΎπΎππππ in rain is proportional to the product ofrainwater content and the mass-weightedmean diameter.
o πΎπΎππππ is more sensitive at X-band compared toS-band, and it can be directly applied in lightrain circumstance.
ππ =ππ6
Γ 10β3ππ οΏ½π·π·min
π·π·max
π·π·3ππ π·π· πππ·π·
π·π·m =β«π·π·min
π·π·max π·π·4ππ π·π· πππ·π·
β«π·π·min
π·π·max π·π·3ππ π·π· πππ·π·
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Validation of high-resolution rainfall products
15-min rainfall and rainfall accumulations at sample gauge locations during 2015 Thanksgiving event
The DFW X band Urban Radar Network
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Snow processes
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Precipitation processes
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Scatterplot of Z vs. S derived from disdrometertogether with S-Z power-law fitting.
The reflectivity factor at Ku band can be calculated using the equation:
ππβ =ππ4
ππ5 πΎπΎπ€π€ 2 οΏ½ππβ(π·π·)ππ(π·π·)πππ·π·
The liquid water equivalent snowfall rate is calculated using the equation:
ππ = 6ππ β 10β4 οΏ½πππ π π·π·3π£π£ π·π· ππ π·π· πππ·π·
A power-law equation can be used to obtain a relationship between Z and S
ππ = ππππππ
Snowfall rate estimation
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β’ Density of snow plays a major role in estimating snowfall rate
β’ There are many size-density relationships not easy to use for the snow rate
β’ The terminal velocity and diameter measured by disdrometercan be used to indirectly get an idea of the density of snow from which snowfall rate is estimated from particle velocity measurements.
Snowfall estimation
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Time
scale
Algorith
m
MD NSE (%) CORR
30-min S-Z 0.0338 11.86 0.9164
Comparison of snow accumulation
Statistics:
Snowfall estimation using S-Z algorithm from Ku band radar and gauge at YPO site for 30 min accumulation.
(c)
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X band observations of vertical cross sections
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Snow event on 28 Feb 2018Ku Band data, Azimuth: 51.36Β°
Ka band
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Summary
β’ X band radar deployment to measure rainfall and snowfall.
β’ Rainfall measurement well established still must be validated locally at a high altitude environment.
β’ Precipitation processes and snow measurements
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Thank You
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