Investigation of optical turbulence from an unmanned aerial system
Van Eijk, A.M.J.
Gladysz, S. (editor)
Stein, K.U. (editor)
Wave propagation of electro-optical systems, lasers or imaging depends on the state of the atmosphere their beams are passing through. Fluctuations in the refractive index of air are responsible for signal attenuation and image degradation. This atmospheric effect is called optical turbulence and its strength is quantified by the structure function parameter of the refractive index Cn 2. In the atmospheric surface layer it is highly variable. Usually Cn 2 decreases with height. In non-uniform terrain, big horizontal variations can arise. We developed a mobile airborne system for monitoring Cn 2 to investigate the three-dimensional character of optical turbulence. Therefore the dodecacopter system HORUS ) was chosen as mobile platform. An ultrasonic anemometer was mounted on a boom for high-resolution measurements of temperature and wind speed. Analyzing the time series of temperature, Cn 2 values were derived from time averages of several minutes. The measurements took place in the surface layer over land in the vicinity of an 80 m high tower, equipped with ultrasonic anemometers at four discrete heights. Comparison measurements were performed. The minimum length of the boom outside the turbulent influence of the rotors was investigated. The comparison of the Cn 2 values shows a good agreement. A second, smaller quadrocopter system in combination with a new very small and light-weight ultrasonic anemometer was also tested for turbulence measurements. The system is introduced and the applicability shown. Results from first field trials are presented and discussed. © 2018 SPIE.
To reference this document use:
Proceedings of SPIE - The International Society for Optical Engineering, 10787
The Society of Photo-Optical Instrumentation Engineers