| Historically, "visibility" has been defined as "the greatest distance at which an observer can just see a black object viewed against the horizon sky" (Malm et al., 1981). Dramatic visibility reduction in the Paso del Norte Airshed (PdNA) region occurs frequently in winter, particularly during inversions and severe sandstorms. The Texas Commission on Environmental Quality (TCEQ) initiated monitoring of visibility in PdNA over a decade ago with video and 35mm transparency film. Variability in recording performance of video and batch-to-batch variation in film made quantitative assessment of visibility by image analysis challenging. Recently, a digital camera network was installed by TCEQ in the PdNA and has provided 15-minute images to an archive operated by the University of Texas at El Paso. It was found that the image quality is reproducible and useful for quantitative analysis of visibility conditions in PdNA and developed a novel methodology for quantifying visual deterioration of a scenic vista. (Abstract shortened by UMI.)... |
