Optimizing visibility analysis for visual impact assessment

Abstract

Visibility analysis is a standard procedure used within visual impact assessment (VIA) studies to determine visibility significance. VIA is defined as the procedure to identify the visual effects that a specific development might have on the receiving environment. These visual effects are usually identified through visibility analysis using visibility simulations. Visibility simulations are, however, often limited by the complexity of components included in these approaches, which can all lead to errors and inaccurate descriptions of the possible visual effects. Terrain complexity, interpolation algorithm, resolution, digital elevation model and land cover are all components that can affect these simulations in some manner. With different visibility analysis approaches available and various variables affecting its accuracy, this study aims to identify an optimal visibility analysis approach for use in VIA. Typical visibility analysis approaches were identified from a sample of VIA reports, with viewshed analysis, cumulative viewshed analysis and line-of-sight (LOS) analysis identified as the approaches most often used in VIA. The different approaches were tested and evaluated in three study areas with different levels of terrain complexity and using different types of digital elevation models at various resolutions. Visibility analysis approaches based on digital surface models (DSM’s) showed a significant improvement in accuracy when compared to those based on digital terrain models (DTM’s). The combination of construct sight-lines and LOS proved to be the best overall visibility analysis approach across all terrain complexities and elevation models. The typical approach applied in the majority of the sampled VIA reports was found to be the least accurate.