Recent interest in 3-D vectorial sensors requires the development of vectorial propagation methods, rather than scalar wave equation approaches. We derive a vector wave equation from Maxwell's equations for a medium which has an inhomogeneous dielectric permittivity dominated by variation along one dimension. It is well known that the electric field components decouple for homogeneous media. However, 1-D permittivity variations yield an upper triangular system of scalar wave equations with the wave polarization component parallel to the inhomogeneous direction/axis acting as a forcing term for the orthogonal components. The main implication is that waves with polarization oriented parallel to the permittivity gradient will act as a forcing term and excite other polarization components and, thus, induce depolarization. Contemporary studies treat the permittivity as a constant when deriving a wave equation or paraxial approximation, and then re-introduce via inhomogeneous wave speed, variable permittivity, thus missing important terms and physical mechanisms in their resulting equations. Contemporary studies neglect the term in the Maxwell vector wave equation responsible for this effect. Application of the electromagnetic propagation depolarization effect is demonstrated numerically for an air-sea interface evaporation duct with a 500 MHz source.

A method of representing grid-scale heterogeneous development density for urban climate models from probability density functions of subgrid-resolution observed data is proposed. Derived values are evaluated in relation to normalized Shannon entropy to provide guidance in assessing model input data. Urban fraction for dominant-class and mosaic urban contributions is estimated by combining analysis of 30-m-resolution National Land Cover Database 2006 data products for continuous impervious surface area and categorical land cover. The aim of the method is to reduce model error through improvement of urban parameterization and representation of observations employed as input data. The multiscale variation of parameter values is demonstrated for several methods of utilizing input. This approach provides multiscale and spatial guidance for determining where parameterization schemes may be misrepresenting heterogeneity of input data, along with motivation for employing mosaic techniques that are based upon assessment of input data. The proposed method has wider potential for geographic application and complements data products that focus on characterizing central business districts. It utilizes observations to obtain a parameterization of urban fraction that is dependent upon resolution and class-partition scheme, thus providing one means of influencing simulation prediction at various aggregated grid scales.

Forecasts of noise pollution from a highway line segment noise source are obtained from a sound propagation model utilizing effective sound speed profiles derived from a Numerical Weather Prediction (NWP) limited area forecast with 1 km horizontal resolution and near-ground vertical resolution finer than 20 m. Methods for temporal along with horizontal and vertical spatial nesting are demonstrated within the NWP model for maintaining forecast feasibility. It is shown that vertical nesting can improve the prediction of finer structures in near-ground temperature and velocity profiles, such as morning temperature inversions and low level jet-like features. Accurate representation of these features is shown to be important for modeling sound refraction phenomena and for enabling accurate noise assessment. Comparisons are made using the parabolic equation model for predictions with profiles derived from NWP simulations and from field experiment observations during mornings on November 7 and 8, 2006 in Phoenix, Arizona. The challenges faced in simulating accurate meteorological profiles at high resolution for sound propagation applications are highlighted and areas for possible improvement are discussed. (C) 2015 Elsevier Ltd. All rights reserved.

AbstractPhysical mechanisms of incongruency between observations and Weather Research and Forecasting (WRF) Model predictions are examined. Limitations of evaluation are constrained by (i) parameterizations of model physics, (ii) parameterizations of input data, (iii) model resolution, and (iv) flux observation resolution. Observations from a new 22.1-m flux tower situated within a residential neighborhood in Phoenix, Arizona, are utilized to evaluate the ability of the urbanized WRF to resolve finescale surface energy balance (SEB) when using the urban classes derived from the 30-m-resolution National Land Cover Database. Modeled SEB response to a large seasonal variation of net radiation forcing was tested during synoptically quiescent periods of high pressure in winter 2011 and premonsoon summer 2012. Results are presented from simulations employing five nested domains down to 333-m horizontal resolution. A comparative analysis of model cases testing parameterization of physical processes was done usin...

The authors present a generalized terrain PE (GTPE) model for sound propagation in non-uniform terrain following the work of Sack and West (1995). Results for simplified terrain cases illustrate the new model’s capabilities and the effects of terrain in a neutral atmosphere. The model is extended by deriving a reflection scheme to account for two-way propagation. Thus, their model enables the study of backscatter from vertical terrain features and forward propagation of traffic noise in complex terrain. Future developments will extend the reflection scheme to terrain features with arbitrary angles. Future possibilities include coupling the sound model with flow calculation software to determine the flow response to terrain and the sound field response to perturbed flow. Additionally, the authors apply ARW-WRF v3.2’s new option of vertical nesting within the finest nest to a numerical experiment studying highway noise pollution in the Phoenix metropolitan area. This experiment was conducted for comparison on November 7, 2006, in Phoenix by Ovenden et al (2009). Vertical profiles with near-ground resolution finer than 20 m were extracted for input into a sound propagation model to produce forecasts of noise pollution from a highway line segment noise source. Vertical nesting improved the resolution of finer structures in the temperature and velocity profiles. Ovenden et al. (2009) previously demonstrated sensitivity of the resultant sound field within 600 m of the source to input effective sound speed vertical profiles, Ceff (z), in the lowest 300 m of the planetary boundary layer. Hence, resolution of such features is important when forecasting Ceff (z) for use in the highway noise propagation model.

This paper examines the impact of meteorological conditions on the propagation of vehicular noise from urban freeways. A parabolic equation model coupled to an analytical Green's function solution close to the source field is used to compute the refracted sound field up to half a mile from the freeway to predict the noise exposure of residential areas nearby. The model was used in conjunction with meteorological and sound-level measurements taken at two freeway sites over the course of four days in Phoenix, AZ. From the data collected, three test cases of varying levels of atmospheric stratification and wind shear are presented and discussed. The model demonstrates that atmospheric effects are able to raise sound levels by 10-20 dB at significant distances away from the highway, causing violations of acceptable limits imposed by the Federal Highway Administration in residential areas that are normally in compliance.