Vegetation-Limited Ground-to-Air Surveillance

It is possible to estimate the limitations on ground-to-air visibility around a point using digital terrain models in which terrain height is given on a rectangular grid and the vegetation class within defined areas is specified. The screening effect of the vegetation can be estimated better by using the inherent autocorrelation in elevation angle data given as a function of azimuth angle about a fixed point. This type of model is useful when the proposed number of observation sites is too large to warrant surveying them, or the precise actual locations cannot be ascertained in advance of the requirement, as is often the case in simulation studies involving mobile observers. The distribution of elevation angle may be non-normal. A procedure is described here to facilitate the use of autoregressive equations which require normally distributed variables.