Using numerical weather prediction to forecast optical turbulence

Free Space Optical communication (FSO) is strongly affected by atmospheric effects such as scattering and optical turbulence. To predict availability and performance of terrestrial and ground to space systems, forecasts of these effects are needed. Unfortunately, global measurements of optical loss and scintillation are not available. So, it is not even possible to make predictions based on historical records. However, there have been many measurement campaigns that have produced data that connects optical turbulence parameters, such as C_n², to weather, as well as models that show reasonable agreement with experiment. Similarly, optical scattering loss can be related to rain rate and visibility. Thus, numerical weather prediction (NWP) systems may offer a way to predict FSO system performance globally. The Naval Research Laboratory’s (NRL) Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) represents a state-of-the-art NWP, and includes both Nowcast capability and short-term (up to 72 hours) forecast tools applicable for any given region of the Earth in both the atmosphere and ocean. Recently COAMPS has added forecasts of Cn 2 to its capabilities. In this work we compare COAMPS predictions of optical turbulence, to measurements on NRL’s Chesapeake Bay optical range. We measure scintillation on the range, and then use COAMPS Cn 2 calculations, together with a wave optic simulation code, to compare model and experiment.