in that region and the parameters of this equation can be calibrated either using
radar–raingauge measurements or disdrometer (instruments that measure DSDs)
observations.
Operational weather radars can be classified into Single-Polarization (SP) and
Dual-Polarization (DP) weather radars. DP radars are sensitive to size, shape,
orientation and thermodynamic phase of the precipitation particles [8]. Operational
DP radars alternately or simultaneously transmit vertically and horizontally polarized electromagnetic waves and receive polarized backscattered signals, whereas SP
radars transmit and receive electromagnetic waves using single polarization only
(either horizontal or vertical). SP radars can measure the reflectivity (Z) only and if
the radar has Doppler capability, they also measure the radial velocities of precipitation particles. DP radars can measure additional variables such as the horizontal
and vertical reflectivities (Z h and Z v ), the differential reflectivity (Z dr ), the linear
depolarization ratio (LDR), the correlation coefficient (ρ hv ) and the differential phase
(Φ dp ). These additional measurements from DP radars have shown to provide
significant improvements in terms of data quality and rainfall estimation compared
with SP radars.
2 Sources of Uncertainty in the Estimation of Precipitation
with Radar
Although recent advances in weather radar technology has helped to improve our
understanding of the microphysics of precipitation as well as better rainfall estimates, there are still many challenges to improve the estimation of precipitation at
ground level [9–19]. Rainfall estimation using weather radars can be subject to
different sources of errors such as radar calibration, variations of the DSD, radar
signal attenuation, echoes due to non-meteorological origin, variation of the vertical
profile of reflectivity, radar beam blocking, etc. The following sections describe
some of the work carried out to mitigate some of these errors.
2.1 Radar Calibration
Accurate precipitation estimates using weather radar rely on stable hardware components (e.g. transmitter and receiver) with an accurate calibration. Inaccurate
determination of the radar constant C (hereafter referred as radar calibration bias)
can cause a significant error source to the radar precipitation estimations [15]. This
error can cause significant differences in radar rainfall and therefore C must be
carefully monitored. By using up-to-date hardware, radar calibration bias can be
limited to within 2 dB or 36% error in precipitation rate [13]. Many techniques have
been developed to monitor and adjust the radar calibration bias. For instance,
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N. Nanding and M. A. Rico-Ramirez
radar–raingauge measurements or disdrometer (instruments that measure DSDs)
observations.
Operational weather radars can be classified into Single-Polarization (SP) and
Dual-Polarization (DP) weather radars. DP radars are sensitive to size, shape,
orientation and thermodynamic phase of the precipitation particles [8]. Operational
DP radars alternately or simultaneously transmit vertically and horizontally polarized electromagnetic waves and receive polarized backscattered signals, whereas SP
radars transmit and receive electromagnetic waves using single polarization only
(either horizontal or vertical). SP radars can measure the reflectivity (Z) only and if
the radar has Doppler capability, they also measure the radial velocities of precipitation particles. DP radars can measure additional variables such as the horizontal
and vertical reflectivities (Z h and Z v ), the differential reflectivity (Z dr ), the linear
depolarization ratio (LDR), the correlation coefficient (ρ hv ) and the differential phase
(Φ dp ). These additional measurements from DP radars have shown to provide
significant improvements in terms of data quality and rainfall estimation compared
with SP radars.
2 Sources of Uncertainty in the Estimation of Precipitation
with Radar
Although recent advances in weather radar technology has helped to improve our
understanding of the microphysics of precipitation as well as better rainfall estimates, there are still many challenges to improve the estimation of precipitation at
ground level [9–19]. Rainfall estimation using weather radars can be subject to
different sources of errors such as radar calibration, variations of the DSD, radar
signal attenuation, echoes due to non-meteorological origin, variation of the vertical
profile of reflectivity, radar beam blocking, etc. The following sections describe
some of the work carried out to mitigate some of these errors.
2.1 Radar Calibration
Accurate precipitation estimates using weather radar rely on stable hardware components (e.g. transmitter and receiver) with an accurate calibration. Inaccurate
determination of the radar constant C (hereafter referred as radar calibration bias)
can cause a significant error source to the radar precipitation estimations [15]. This
error can cause significant differences in radar rainfall and therefore C must be
carefully monitored. By using up-to-date hardware, radar calibration bias can be
limited to within 2 dB or 36% error in precipitation rate [13]. Many techniques have
been developed to monitor and adjust the radar calibration bias. For instance,
238
N. Nanding and M. A. Rico-Ramirez