Position determination of a point source through turbulent atmosphere

Abstract

The reliable tracking of fast-flying distant objects such as rockets, artillery and mortars (RAM) or UAVs is necessary for the implementation of threat-warning and counter measurement systems. Accuracies in the sub-μrad range are required for such tracking systems in real time applications, but are limited by atmospheric turbulence. In this paper, we present results from measurement campaigns showing the influence of atmospheric turbulence on the apparent random motion and broadening of a point source by taking video streams of a stationary and moving point source. At our test site we use an LED serving as a point source mounted on a highly accurate linear translation stage which can be accelerated to velocities up to 5 m/s. The motion of this point source is observed from a distance of 130 m by several imaging systems like photo objectives, spotter scopes or telescopes. Each imager is fixed on a rigid mount in order to isolate it from mechanical vibrations and gusts as well to ensure that the apparent random motion of the point source image is only caused by atmospheric turbulence. The centroid of the point source was determined down to sub-pixel accuracy from the streams via post-processing the acquired videos considering the specific signal to noise ratio of the imaging system. The local weather conditions were continuously monitored with a scintillometer to determine the relevant turbulence parameter Cn². Our experimental data of the rms angular position jitter is compared for several values for Cn² with a theoretical model based on Kolmogorov theory taking the turbulence into account.