A simple parabolic model for the optics of the atmospheric surface layer

A simple yet accurate model is developed for optical ray tracing in the surface layer of a refracting atmosphere. The model consists of a small number of concentric spherical layers or shells, the surface of each being isothermal. If the temperature is taken to vary linearly between the surfaces, then the curvature of nearly-horizontal rays is approximately constant within each layer. Replacement of circular by parabolic arcs produces simple quadratic expressions for the rays. The procedure is easily implemented on a minicomputer, and a compact version fits into a programmable pocket calculator. This is particularly convenient for checking field observations. An example is given, as well as a discussion on error sensitivity due to simplifying assumptions.