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Based on the Parabolic equation method, a model for sound propagation over uneven terrain, with mixed ground impedance and range-dependent meteorological conditions, has been developed to improve prediction of the impact of aviation noise on communities. Intended to enhance the noise prediction capabilities for the Federal Aviation Administration’s Aviation Environmental Design Tool in support of the Next Generation Air Transportation System (NextGen), the model uses a hybrid parabolic equation-fast field program approach for computing aviation noise contours. These methods ensure that the low-frequency content, a factor in community impact, is propagated accurately. The model can accommodate a broadband, moving sound source, traveling along a user-specified path, over three-dimensional terrain. A test case, designed to represent simple but realistic propagation conditions, is described, and results for a source traveling along a simple flight path are presented and discussed.

Accurate prediction of sound levels around airports and below flight paths can help faithfully represent the impact of aviation noise on communities. However, for large scale assessments, as are often performed by the U.S. Federal Aviation Administrationis environmental models, the accuracy of a model must be weighed against its efficiency. The hybrid propagation model (HPM) is capable of predicting propagation through complex environments. It is a composite of three methods-the generalized terrain parabolic equation (GTPE), fast field program (FFP), and straight ray models-each utilized in a different region of elevation angles from the source. If propagation conditions do not warrant use of the full model, one of the component models with faster runtime can be chosen as a surrogate. Analyses of cases using different source heights and including uneven terrain, refractive atmosphere, and ground type transitions, indicate when a detailed propagation model is needed, or when a simpler model is sufficient.

New technology and changing student work habits challenge academic libraries to accommodate different types of study by designing different rooms for distinct purposes. This requires not only a variety of technologies, room setups, and seating, but also acoustic conditions that stimulate efficient and comfortable productivity—whether with computers, textbooks, or interactive study groups. Acoustic recordings were taken in 13 different ‘‘favorite’’ rooms, with diverse characteristics and personalities, within the two main libraries at Cornell University. The acoustic measurements were compared with observations of student activity within these spaces to determine relationships between acoustic measurements and student behavior. Factor analysis revealed three types of student-activity categories: quiet concentration, relaxing and socializing, and computer use. The analysis also revealed three categories of room type: quiet study rooms, rooms with computer use, and cafés. These categories of activities and room types correlate with acoustic measurements, pointing to the existence of distinct niches within the library system. Examining the acoustic conditions conducive to certain activities may help future designers of academic libraries to optimize the acoustics of study spaces for different purposes.

The parabolic equation (PE) method is accurate for prediction of low-frequency noise in the situation that the starting field does not emit significant energy at large elevation angles. The typical PE sound source is assumed to be omnidirectional and represented with a Gaussian starting field, defined at all heights of the grid. A method of representing a source with arbitrary directivity has been developed for the unique form of the PE starting field. By extending the defined vertical wave number spectrum of the arbitrary far-field directional function of the source to include evanescent wave numbers, the approach uses array theory and Fourier transform techniques to define the starting field. The approach recognizes the elevation angle limitation of the PE method and adheres to the accepted wavelength-dependent vertical grid point spacing, satisfying the fundamental requirements of the PE method. Results for horizontal and vertical dipole sources in the free field and above a ground surface are presented and compared with analytical solutions within the valid PE elevation angle range. [This research was funded by the Federal Aviation Administration (FAA) Western-Pacific Region through U.S. Department of Transportation Volpe National Transportation Systems Center.]