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- Author or Editor: Paul L. Smith x
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Comments are made on opportunity recognition, treatment, and evaluation aspects of the implementation and testing of seeding concepts. The main topics include experimental design, experimental units, delivery and dispersion of seeding agents, and statistical evaluation procedures.
Abstract
Comments are made on opportunity recognition, treatment, and evaluation aspects of the implementation and testing of seeding concepts. The main topics include experimental design, experimental units, delivery and dispersion of seeding agents, and statistical evaluation procedures.
Abstract
Gamma functions are widely used in an effort to represent characteristics of observed raindrop size distributions, especially at the small-particle end. However, available instruments do not agree about the character of the small-drop region, and for many purposes that part of the spectrum is unimportant. At the large-drop end, sampling limitations impede reliable measurements. Thus, when moment methods are used to determine parameters for the fitted functions, the experimental uncertainties tend to be greater than the differences in important bulk quantities, such as rainfall rate or radar reflectivity factor, between the resulting gamma distributions and corresponding, simpler exponential distribution functions. It consequently makes little practical difference whether exponential or gamma functions are employed, and the exponential model is appropriate for many purposes.
Abstract
Gamma functions are widely used in an effort to represent characteristics of observed raindrop size distributions, especially at the small-particle end. However, available instruments do not agree about the character of the small-drop region, and for many purposes that part of the spectrum is unimportant. At the large-drop end, sampling limitations impede reliable measurements. Thus, when moment methods are used to determine parameters for the fitted functions, the experimental uncertainties tend to be greater than the differences in important bulk quantities, such as rainfall rate or radar reflectivity factor, between the resulting gamma distributions and corresponding, simpler exponential distribution functions. It consequently makes little practical difference whether exponential or gamma functions are employed, and the exponential model is appropriate for many purposes.
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Sampling Issues in Estimating Radar Variables from Disdrometer DataAbstract
Simulation of sampling from gamma-distributed raindrop populations demonstrates that significant biases and substantial errors can occur in estimates of polarimetric radar variables based on samples of raindrop populations obtained with disdrometers. Biases and RMS errors of 0.5 dB or more in estimates of differential reflectivity Z dr can occur with samples of even a few hundred drops; significant biases and errors also occur in estimates of reflectivity Z H or specific differential phase K dp. The results indicate that very large samples would be required to obtain adequate representation of the population characteristics for many radar applications. They also suggest that greater attention is needed to the sample sizes in the disdrometer data used in developing polarimetric rainfall-rate estimators or hydrometeor classification algorithms.
Abstract
Simulation of sampling from gamma-distributed raindrop populations demonstrates that significant biases and substantial errors can occur in estimates of polarimetric radar variables based on samples of raindrop populations obtained with disdrometers. Biases and RMS errors of 0.5 dB or more in estimates of differential reflectivity Z dr can occur with samples of even a few hundred drops; significant biases and errors also occur in estimates of reflectivity Z H or specific differential phase K dp. The results indicate that very large samples would be required to obtain adequate representation of the population characteristics for many radar applications. They also suggest that greater attention is needed to the sample sizes in the disdrometer data used in developing polarimetric rainfall-rate estimators or hydrometeor classification algorithms.
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The antenna beam pattern for low elevation angles is examined in relation to the radar horizon to assess the impact of base-scan elevation angle on sensitivity to near-horizon weather features, as well as its effect on reflectivity measurements and ground clutter. The results from a simple model neglecting details of surface characteristics and multipath propagation suggest that a base elevation angle of about 0.3 beamwidth above the horizon would yield near-optimum sensitivity with acceptable degradation in reflectivity observations and ground clutter.
Abstract
The antenna beam pattern for low elevation angles is examined in relation to the radar horizon to assess the impact of base-scan elevation angle on sensitivity to near-horizon weather features, as well as its effect on reflectivity measurements and ground clutter. The results from a simple model neglecting details of surface characteristics and multipath propagation suggest that a base elevation angle of about 0.3 beamwidth above the horizon would yield near-optimum sensitivity with acceptable degradation in reflectivity observations and ground clutter.
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This note argues that the proper symbol for the logarithmic unit of radar reflectivity factor is dBz. The basis for this contention lies in both customary engineering practice and the international standard for unit symbols.
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This note argues that the proper symbol for the logarithmic unit of radar reflectivity factor is dBz. The basis for this contention lies in both customary engineering practice and the international standard for unit symbols.
