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James R. Jordan and Richard J. Lataitis

Abstract

Clear-air Doppler wind profilers perform poorly in dry, calm conditions when reflectivities are low. One solution to this problem is to use acoustic waves, generated by a collocated acoustic source, as the scattering target instead of clear-air turbulence. The idea for such an acoustically enhanced profiler was proposed more than 10 years ago. In a recent Antarctic experimental campaign, a vertically pointing acoustic source was used to extend the coverage of a standard four-beam 915-MHz wind profiler. Preliminary testing of the system revealed large biases in the retrieved wind profiles. A simple theory and a limited dataset suggest that the observed biases are consistent with a nonuniform acoustic illumination of the radar beams caused by the different acoustic and radar beam pointing angles. Our results suggest that this bias can be eliminated by aligning the acoustic and radar beams.

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Daniel E. Wolfe and R. J. Lataitis
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A. B. White, R. J. Lataitis, and R. S. Lawrence

Abstract

It is well known that the width of a clear-air Doppler radar spectrum can be used to estimate the small-scale variability of the wind. To do this accurately requires that all contributions to the spectral width be accounted for. Recently, an approximate formula for correcting Doppler spectral widths for spatial and temporal filtering effects was proposed. The formula assumes independent additive contributions to the spectral width from the inherent volume averaging of the radar-sampling volume and the finite measurement interval. In the present paper the approximate formula is compared to an exact triple-integral formulation in which the spatial and temporal effects are shown to be coupled in a nonlinear fashion. The required integrations are evaluated numerically and are carried out over the full range of scales in wavenumber space, in contrast to earlier work, where truncated forms of isotropic, inertial-subrange spectral forms were used to obtain a simple, closed-form expression. Comparisons show that the approximate formula provides a good approximation to the integral solution over small to moderate length scales, but that it diverges from the integral solution at larger scales. Asymptotic limits to the exact integral formulation for large and small scales are presented. Finally, a double-integral solution that can be rapidly evaluated by any one of a number of commercial mathematics packages has been developed and shown to agree within 2% of the exact solution over all scales.

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James R. Jordan, Richard J. Lataitis, and David A. Carter

Abstract

New algorithms for removing ground and intermittent clutter contamination from wind profiler data are presented. The techniques use wavelet transforms to “filter” the contribution of clutter to the wind profiler signals. Examples of typical clutter contamination using simulated and actual signals are presented. The corresponding Doppler spectra before and after wavelet filtering are compared. The authors find that wavelet filtering can reduce the clutter-to-clear-air signal power by as much as 40 dB, even when the clutter and clear-air peaks cannot be resolved in the Doppler spectrum. The enhancement in clear-air signal detectability in the presence of clutter is due to the more efficient separation of clutter and clear-air energy in the wavelet domain.

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Ting-I. Wang, R. Lataitis, R. S. Lawrence, and G. R. Ochs

Abstract

Prototype Laser Weather Identifier (LWI) systems designed to detect fog, rain and snow were tested for several months at Stapleton International Airport in Denver, and at the AFGL Weather Test Facility at Otis Air Force Base, Massachusetts. We present a detailed analysis of the performance of these systems, compared with human weather observations and tipping-bucket raingages, and suggest modifications for future operational instruments.

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