William S. Smith

Coupled influences of topography and wind on wildland fire behaviour

Ten simulations were performed with the HIGRAD/FIRETEC wildfire behaviour model in order to explore its utility in studying wildfire behaviour in inhomogeneous topography. The goal of these simulations is to explore the potential extent of the coupling between the fire, atmosphere, and topography. The ten simulations described in this paper include five different topographies, each run with two different ambient wind speeds of 6 and 12 m s–1. The five topologies explored are: an idealised hill (which serves as the base centerline for the other topographies), two variations of the hill with lateral gradients downwind from the ignition line (one sloping up from the ‘hill’ at the centerline to form an upward sloping canyon parallel to the ambient wind, and the other sloping down from the centerline to form a ridge parallel to the ambient flow), one with a second hill upwind of the ignition line such that the fire is ignited in the bottom of a canyon that runs perpendicular to the ambient wind, and finally a flat terrain. The four non-trivial topographies have the same profile along the centerline downwind of the ignition line to help assess the impacts of topographic gradients that are perpendicular to the ambient wind. It is hoped that analysis of these simulations will help reveal where point-functional models are sufficient, where topographically modified wind fields are needed, and where fully coupled fire and transport models are necessary to properly describe wildfire behaviour.

A Hierarchy of Explicit Low-Dispersion FDTD Methods for Electrically Large Problems

A framework for the construction of a hierarchy of explicit low-dispersion, low anisotropy FDTD algorithms is developed herein. The framework allows for the separation of dispersive and anisotropic effects due to a given explicit FDTD model construction using an extended stencil on a Yee-type staggered grid. Isotropic low-dispersion (2,4) and (4,4) FDTD algorithms are constructed by eliminating second- and fourth-order errors due to dispersion and anisotropy. The dispersive and anisotropic performance of these algorithms is compared to previously published schemes that fit within this hierarchical structure. The algorithms are examined for propagation of a wave pulse in an electrically large domain.

Large-angle light scattering at large size parameters

The generalized eikonal amplitude for light scattering at large size parameters by a dielectric sphere is modified to account more rigorously for the phase-change difference caused by the presence of the medium. The resulting amplitude is shown to work well for scattering at large angles. It accurately predicts the positions of maxima and minima for scattering angles up to 60 degrees for perpendicularly polarized light.

USING STATE-OF-THE-ART HYDRODYNAMIC MODELS TO GENERATE SYNTHETIC DATA CUBES FOR IMAGING SPECTRAL SENSING APPLICATIONS

An airborne IR hyperspectral imaging sensor based on the Fourier transform spectrometer technique has been used for studying atmospheric gaseous plumes under the auspice of U.S. Department of Energy. Model generated synthetic data of spectral intensity associated withe the plume and the surface background is useful in terms of performing trade studies as well as testing new algorithms. To cope with the highly turbulent and transient atmospheric boundary layer where plume emissions and evolution are embedded, we have used a high-resolution (at the scale of 1 m) time-dependent Napier-Stoke atmospheric hydrodynamic code, HIGRAD, to replace the Gaussian/multi-fractal approach in the original package of the Los Alamos End-to-End Modeling of Imaging Spectral Sensing Applications (EMISSA). The output from HIGRAD is then used for calculations of radiance reaching the sensor through the Fast Atmospheric Signature Code (FASCODE) with a spectral resolution of 1 cm-1 or less. The modeled plume structure in concentrations and associated plume images in radiance bear great resemblance to the contrast model for its capability in quantifying the column densities of chemical species. The synthetic data produced through our approach proves to be effective in evaluation our understanding of the thermal infrared imaging process.

Development of coronary prevention strategies by health authorities in the United Kingdom.

The United Kingdom has one of the highest coronary heart disease mortality rates in the world. However, over the last decade there has been a growing impetus in coronary prevention. In 1988 the Faculty of Community Medicine carried out a survey of all health authorities in the UK to assess the progress and problems with coronary prevention. This survey received a 92 per cent response rate and shows some interesting findings. The picture at present reveals a growing momentum in the last couple of years with half the health authorities at present claiming to have a programme. The main hindrances reported are lack of funding rather than lack of interest. The development and difficulties with nutrition and smoking policies, and with blood pressure screening are also described. The regional pattern of development of these programmes and policies is complex. Many authorities favour a general health promotion approach rather than a negative, disease oriented one; this conflict in approach requires further debate.