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D. W. Beran and F. F. Hall Jr.

The application of ground-based remote-sensing systems for monitoring those meteorological parameters of importance in urban air pollution is discussed. Typical system considerations include an analysis of site characteristics and sensor location. Examples of how remote-sensing systems might be applied to air pollution meteorology are given.

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A. J . Bedard Jr., W. H. Hooke, and D. W. Beran

Wind shear has long been recognized as one of the major aviation hazards in the airport environment. A principal source of dangerous wind shear is the thunderstorm gust front, a cold air outflow from the thunderstorm downdraft. The gust front is particularly hazardous not only because of the large surface wind shears associated with it, but also because of its highly localized character. Often the downdraft or downburst region producing such fronts is of the order of a few kilometers or less in dimension.

As a result, vertically profiling wind shear detection techniques such as the hybrid acoustic–microwave radar system described in the companion paper by Hardesty et al 1977 do not provide adequate total protection. In this paper we describe an array of pressure sensors installed at Dulles International Airport in Washington, D.C., to detect and monitor gust fronts that could endanger aircraft operations. The pressure sensors (designed to respond only to sudden pressure increase) are so inexpensive that they can be used in dense networks of large spatial extent to monitor in detail the gust front progress as it approaches the airport. Some 125 sensors have been installed at Dulles. Indeed, a major cost of the installation is the cost of the phone lines required to return the information to a central data-processing location.

The system has been operating unattended for extended periods of time, registering the frontal passages that have also been detected by the acoustic–microwave radar system as they pass overhead. Results are presented showing the complementary nature of the two monitoring methods.

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R. J. Wyckoff, D. W. Beran, and F. F. Hall Jr.

Abstract

Temperature profiles measured with a radiosonde are compared with returns from an acoustic echo sounder throughout the height range 50–700 m. In general, the sounder records indicate the temperature inversion to be somewhat lower than do the radiosonde records. Reasons for this apparent discrepancy and the advantage of the sounder, in being able to monitor continuously the inversion structure and undulations produced by wind shear, are discussed. It was proved feasible to operate the acoustic sounder in a noisy commercial district with little detrimental effect on the ability to detect atmospheric temperature structure. It is concluded from this preliminary investigation that the combination of the radiosonde and the acoustic echo sounder provides a much more valuable tool for monitoring structure in the stable planetary boundary layer than either device used alone.

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A. G. Kjelaas, D. W. Beran, W. H. Hooke, and B. R. Bean

Abstract

Three acoustic sounders, with antennas having vertically-pointed beams located at the vertices of a triangle about 300 m on a side, have been used successfully to calculate horizontal phase velocities of gravity waves in the lowest 1000 m of the atmosphere. The wave parameters obtained were compared with those obtained by an array of micrographs. The results from the two independent techniques agreed well in all cases where the waves were detected by both methods. However, the acoustic-sounder array was also able to detect gravity waves propagating in an inversion overlying the convective boundary layer that were undetected by the microbarograph array because of wave attenuation in the convective region.

Wave-associated vertical-velocity fluctuations inside the undulating structure were measured using Doppler techniques to an accuracy of about ±0.1 m sec−1. Vertical-velocity fluctuations of about ±0.5 m sec−1 were measured inside one wave with displacement amplitude of 120 m and wavelength of 5.5 km. From wave-associated vertical-velocity fluctuations, displacement amplitude and wave period, we could calculate the wind speed component along the wave propagation direction. This calculated wind speed component agreed reasonably well with the value derived independently from radiosonde measurements.

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D. W. Beran, W. H. Hooke, C. G. Little, and F. Coons

The current state of aviation weather forecasting and its effect on weather-related aircraft accidents are reviewed. The authors predict that new approaches will be necessary if the technological gap is to be narrowed between weather forecasting and aircraft design and utilization. The importance of mesoscale modeling and new remote sensing devices is discussed. (Increased emphasis in these areas is to some extent a response to aviation needs and also to the need for improved synoptic-scale modeling.) Statistical and deterministic models that can assist in the prediction of the evolution of area weather are currently under development, but major obstacles, such as the difficulty in parameterizing the planetary boundary layer, suggest that useful models are at least 10 years away. Furthermore, it is predicted that, although weather modification and aircraft design will undoubtedly play important roles, the most immediate improvements will come from departures from traditional approaches to forecasting.

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R. M. Hardesty, P. A. Mandics, D. W. Beran, and R. G. Strauch

Wind shear has been recognized as a major aviation hazard in the airport environment. A dual, acoustic Doppler–microwave Doppler radar system has been installed at Dulles International Airport near Washington, D.C., to measure the vertical profile of wind from the surface to 510 m in 30 m height increments. The acoustic system gathers data under clear-air conditions, and the microwave radar takes over automatically when precipitation is present. System performance is being assessed by comparing its output with National Weather Service radiosondes and with balloon-borne anemometers and by intercomparing the acoustic- and microwave-measured winds under light precipitation conditions. The dual-sensor system has been operating for several months, registering the passage of fronts, some with potentially hazardous wind shears.

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