The performance of certain free space optical applications such as laser communication, LIDAR, target designation and astronomical observations may be improved by using beams of different wavelengths for the auxiliary actions of pointing/tracking or turbulence correction. Thus, wavelength dispersion in the atmosphere is a topic of concern for such applications. The chromatic effects of refraction in the atmosphere are generally well-understood and are a function of temperature, pressure, humidity and altitude, as well as the refractive index gradients. In applications such as astronomical observations, chromatic effects are typically predicted based on standard atmospheric models. However, for long horizontal or near-horizontal paths near the Earth’s surface, significant refractive index gradients can be encountered that are associated with features such as inverse temperature layers and ducts. In this study, we explore the wavelength dependence of optical propagation through these temporary and reoccurring refractive index profiles. A ray tracing approach is implemented and the chromatic divergence of the rays through an inverse temperature layer is studied and compared with the behavior expected for the standard atmosphere.
|