Profiling atmospheric turbulence using a non-cooperative target and a camera bank and validating with sonic anemometers

Abstract

Knowledge of turbulence distribution along a path can be useful for effective compensation in a highly anisoplanatic situation. In an earlier work, a method to profile turbulence using time-lapse imagery of a distant building from two spatially separated cameras was demonstrated. By using multiple cameras instead of just a pair, the profiling resolution as well as the fraction of the path that can be reasonably profiled can be improved. This idea is demonstrated by using 5 spatially separated cameras capturing images of a distant target with features on it. Extended features on the target are tracked and by measuring the variances of the difference in wavefront tilts sensed between cameras due to all pairs of target features, turbulence information along the imaging path can be extracted. The mathematical framework is discussed and the profiling results are compared against point measurements from a 3D sonic anemometer placed onboard an unmanned aerial system which is driven along the imaging path. The method is relatively low cost and does not require sophisticated instrumentation. Turbulence can be sensed remotely from a single site without deployment of sources or sensors at the target location. Additionally, the method is phase-based, and hence has an advantage over irradiance-based techniques which suffer from saturation issues at long ranges. By imaging elevated targets in the future, turbulence changes with altitude can be investigated as well.

Attempting to understand the vertical distribution of turbulence in the surface layer from multi-camera time-lapse imagery

“…The multi-camera approach was first tested in summer of 2021 over a 1.9 km slant path using 10 LED sources as imaging targets and then in summer of 2022 with a noncooperative target. 12,13 The results were promising. Wind pushing against the camera cables caused some undesirable camera motion in these experiments.…”