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- Author or Editor: Gene B. Walker x
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Abstract
A vertically looking, multiple-wavelength Doppler radar technique to estimate vertical velocity, drop size distribution and turbulence is presented. The ratio of the Doppler spectra, corresponding to the drop fall velocities at two different wavelengths, is uniquely related to the ratio of the radar scattering cross sections at the appropriate temperature. These ratios are used to estimate drop fall velocities and therefore drop size distributions and vertical wind. Turbulence, which broadens the velocity power spectrum, can be estimated by deconvolution and the drop size distribution subsequently derived.
Abstract
A vertically looking, multiple-wavelength Doppler radar technique to estimate vertical velocity, drop size distribution and turbulence is presented. The ratio of the Doppler spectra, corresponding to the drop fall velocities at two different wavelengths, is uniquely related to the ratio of the radar scattering cross sections at the appropriate temperature. These ratios are used to estimate drop fall velocities and therefore drop size distributions and vertical wind. Turbulence, which broadens the velocity power spectrum, can be estimated by deconvolution and the drop size distribution subsequently derived.
Abstract
The validity of the extension of R-meter theory advanced by W. H. Lob has been tested experimentally by laboratory simulation of both radar signals and typical radar signal processing equipment. The experimental results show the theory to be valid, subject to restrictions on signal-to-noise ratio and crossing-rate-to-sampling-rate ratio, for both linear and logarithmic signal amplification. The restrictions can be attributed to limitations of the experimental technique and to aliasing. It is concluded that Lob's theory should be used to determine Doppler power spectrum variance in lieu of conventional R-meter theory.
Abstract
The validity of the extension of R-meter theory advanced by W. H. Lob has been tested experimentally by laboratory simulation of both radar signals and typical radar signal processing equipment. The experimental results show the theory to be valid, subject to restrictions on signal-to-noise ratio and crossing-rate-to-sampling-rate ratio, for both linear and logarithmic signal amplification. The restrictions can be attributed to limitations of the experimental technique and to aliasing. It is concluded that Lob's theory should be used to determine Doppler power spectrum variance in lieu of conventional R-meter theory.
Abstract
The potential of acoustic radar for indirect probing of meteorological phenomena in the planetary boundary layer is reviewed and the relevant acoustical theory is summarized for sound scattering by regions of temperature fluctuations and reflection by airborne particulate matter. The point is made that the high sensitivity of acoustic radar to temperature and velocity fluctuations in comparison with radar or lidar and its low cost of construction and operation relative to alternative sounding methods make the technique attractive as a remote probe for boundary layer studies. The operation of the University of Oklahoma acoustic radar facility, in essentially continuous operation since August 1971, is described in detail and its capability tabulated. Acoustic radar data are presented in the form of three-dimensional facsimile recordings of time, altitude, and reflected signal strength for seven phenomena of particular interest: thermal plumes, stratus, helicopter wakes, insects in flight, cold frontal passage, unstable Kelvin-Helmholtz waves, and a persistent frontal temperature inversion. The data are discussed in terms of the sources of the particular phenomena and the ambient meteorological conditions. Plans are discussed for expanded investigations at a site adjacent to the 500 m WKY-TV instrumented tower in Oklahoma City.
Abstract
The potential of acoustic radar for indirect probing of meteorological phenomena in the planetary boundary layer is reviewed and the relevant acoustical theory is summarized for sound scattering by regions of temperature fluctuations and reflection by airborne particulate matter. The point is made that the high sensitivity of acoustic radar to temperature and velocity fluctuations in comparison with radar or lidar and its low cost of construction and operation relative to alternative sounding methods make the technique attractive as a remote probe for boundary layer studies. The operation of the University of Oklahoma acoustic radar facility, in essentially continuous operation since August 1971, is described in detail and its capability tabulated. Acoustic radar data are presented in the form of three-dimensional facsimile recordings of time, altitude, and reflected signal strength for seven phenomena of particular interest: thermal plumes, stratus, helicopter wakes, insects in flight, cold frontal passage, unstable Kelvin-Helmholtz waves, and a persistent frontal temperature inversion. The data are discussed in terms of the sources of the particular phenomena and the ambient meteorological conditions. Plans are discussed for expanded investigations at a site adjacent to the 500 m WKY-TV instrumented tower in Oklahoma City.
Abstract
Doppler velocity spectra collected at vertical incidence contain information on vertical air motions and drop-size distributions with high spatial and temporal resolution. In the past, the computational interdependence between vertical air velocities and drop-size distributions has severely limited the accuracy with which they could be estimated. A dual-wavelength technique is applied in which vertical air motion is determined independently of the drop-size distribution. The Rogers reflectivity method and an extended version of the Hauser-Amayenc method are also applied. The latter technique fits Doppler spectra in a nonlinear least-squares sense using two exponential drop-size distribution models. Results of applying each method to Oklahoma squall line data are compared and the strengths and weaknesses of the three techniques are assessed. For the methods tested, there is a trade-off between potential accuracy and potential for successful application. For example, the dual wavelength method is theoretically quite accurate but is extremely sensitive to poor data quality.
Abstract
Doppler velocity spectra collected at vertical incidence contain information on vertical air motions and drop-size distributions with high spatial and temporal resolution. In the past, the computational interdependence between vertical air velocities and drop-size distributions has severely limited the accuracy with which they could be estimated. A dual-wavelength technique is applied in which vertical air motion is determined independently of the drop-size distribution. The Rogers reflectivity method and an extended version of the Hauser-Amayenc method are also applied. The latter technique fits Doppler spectra in a nonlinear least-squares sense using two exponential drop-size distribution models. Results of applying each method to Oklahoma squall line data are compared and the strengths and weaknesses of the three techniques are assessed. For the methods tested, there is a trade-off between potential accuracy and potential for successful application. For example, the dual wavelength method is theoretically quite accurate but is extremely sensitive to poor data quality.
Abstract
In radar meteorology, the average of the weather echo power is used in the computation of reflectivity, liquid water content, rainfall rate, etc. The uncertainty in measuring or estimating average weather echo power is then important in establishing confidence in the above computed values. To help establish a confidence level, we note that there exists a unique relationship between the weather radar echo correlation function and the receiver detected output correlation function. This unique relationship is used here to calculate the variance of the average (mean) weather echo estimates. Another measure of uncertainty related to the variance is the number (or equivalent number) of independent samples. In this work, we show the equivalent number of independent samples for average weather echoes at the output of three common radar receivers: linear, logarithmic and square law. This is shown for correlated samples of receiver output at different times, angles and ranges, Gaussian-shaped Doppler spectra and antenna patterns, a rectangular transmitted pulse, and an infinite bandwidth receiver.
Abstract
In radar meteorology, the average of the weather echo power is used in the computation of reflectivity, liquid water content, rainfall rate, etc. The uncertainty in measuring or estimating average weather echo power is then important in establishing confidence in the above computed values. To help establish a confidence level, we note that there exists a unique relationship between the weather radar echo correlation function and the receiver detected output correlation function. This unique relationship is used here to calculate the variance of the average (mean) weather echo estimates. Another measure of uncertainty related to the variance is the number (or equivalent number) of independent samples. In this work, we show the equivalent number of independent samples for average weather echoes at the output of three common radar receivers: linear, logarithmic and square law. This is shown for correlated samples of receiver output at different times, angles and ranges, Gaussian-shaped Doppler spectra and antenna patterns, a rectangular transmitted pulse, and an infinite bandwidth receiver.
