The aggregate behavior of branch points: branch point density as a characteristic of an atmospheric turbulence simulator

Abstract

The Atmospheric Turbulence Simulator used in testing in the Atmospheric Simulation and Adaptive-optic Laboratory Test-bed at Air Force Research Laboratory, Directed Energy Directorate's Starfire Optical Range is configured based on three characteristics; Fried's parameter, r₀, the Rytov number, σ²_χ , and the Greenwood Frequency, f_G. All three may be estimated from open loop data as a means of verifying the simulated turbulence conditions for a given test configuration. However, unlike r₀ and f_G, the Rytov number isn't directly calculated. Instead the scintillation index is estimated from intensity measurements. At low Rytov values, (< 0.3 - 0.4), this measurement can approximate the Rytov number, however beyond a Rytov of 0.4 this parameter becomes saturated. Branch Points begin to appear after the Rytov value exceeds 0.1. In this work the behavior of the branch point density is examined to determine its viability as another parameter for calibration our turbulence simulator.