Optical-turbulence characterization of a littoral test environment using a Shack-Hartmann wavefront sensor

Abstract

Beam propagation systems are often used in a wide range of atmospheric environments. Therefore, it is important to be able to characterize those environments in order to appropriately assess performance and inform design decisions. In this paper, a variety of methods for measuring atmospheric coherence length, r0, were analyzed including a Shack–Hartmann-based differential image motion monitor (DIMM), gradient-tilt variance, slope discrepancy variance, and phase variance methods, as well as using the modulation transfer function (MTF). These methods were tested on varying turbulence strength environments with known atmospheric coherence lengths, first using a single modified von Kármán phase screen, then using full wave-optics simulations with 20 phase screens. The Shack–Hartmann based approaches were shown to greatly increase in error for d/r0> 1 due to discrepancies between gradient tilt and the centroid tilt measured from the SHWFS’ image-plane irradiance patterns. An atmospheric data collection system was built and experimental results were taken for a beam propagating 2.4 km through a littoral environment over a 24 hour period.

Comparison of branch-point detection approaches using a Shack–Hartmann wavefront sensor

“…The PRTR is a littoral test environment and has been previously characterized using various optical-turbulence measurements. 50,51 For the experiments conducted here, a λ ¼ 532 nm LED beacon was situated approximately Z ¼ 2.4 km away from the receive aperture as shown in Fig. 3(b).…”