Estimation of the refraction index structure parameter Cn2 via image analysis of a point source

Kurzfassung

In order to quantitatively determine the strength of atmospheric turbulence mostly scintillometers are used to evaluate the refraction index structure parameter Cn2 by probing a medium using a laser beam. The effect of the same atmospheric turbulence can also be seen when imaging an arbitrary object along the same line of sight. Within the regime of a Kolmogorov spectrum, e.g. weak fluctuations of the turbulence, simple expressions are valid to estimate the refraction index structure parameter Cn2 for plane and spherical waves. Here we propose a method to determine an estimate for the refraction index structure parameter Cn2 when imaging an arbitrary scenario in weak turbulence. As long as an object in this scenario appears like for example a point source, it can be used to estimate the strength of the turbulence. At our test site we verify this method by imaging light of a far distant LED onto a standard CCD camera. Regarding the determination of the beam jitter and power fluctuation we analyze each frame by fitting a 2D-Gaussian distribution onto the column density and calculating the first and second order moments. From both methods we derive a value for refraction index structure parameter Cn2 and compare our results with an already operating scintillometer at our test site. In general this method allows monitoring multiple point sources at the same time in order to measure a spatial profile of the refraction index structure parameter Cn2. Furthermore the estimation of the strength of the optical turbulence allows assessing the performance of an optical system for example developed for tracking objects over long distances.