Measuring optical turbulence with the PARSAX radar
A.K. Verhoek (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Alexander Yarovoy – Mentor (Microwave Sensing, Signals & Systems)
R. Saathof – Mentor (TU Delft - Aerospace Engineering)
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Abstract
The use of lasers for satellite communication has recently become a growing field. However, a major challenge in their use is the distortion caused by the atmosphere. The distortion that this study focuses on is optical turbulence. The strength of optical turbulence is related to fluctuations in the refractive index of air and is generally described by Cn². There is a growing body of literature that aims to measure this Cn². One of the methods uses radar, and works by receiving backscattered echoes from turbulent eddies under clear-sky conditions, also known as Bragg scattering. This thesis investigates whether this method, that has so far only been applied to pulsed Doppler weather radars, can also be used with an S-band Frequency-Modulated Continuous-Wave (FMCW) radar.
In this work numerical radar data were used to filter out noise and isolate Bragg scattering. When only clear-sky days in June were included, the results from the 12 selected days showed an average correlation of 0.48 when compared with scintillometer validation data. This is higher than the correlation coefficient of 0.34 found using the pulse-Doppler radar method. However the results also showed a large systematic error, which was found to be related to calibration issues of the used radar. Because this error remained relatively stable over time, a correction factor could potentially be applied to compensate for it. Overall, the results indicate that it is possible to measure optical turbulence using vertical reflectivity measurements from a FMCW radar, although further research and improvements are needed before the method can be used operationally.