A Technique for Estimating the Strength of Turbulence and Inner Scale along an Optical Propagation Path
Agency / Branch:
DOD / USAF
Knowledge of key parameters of optical turbulence is essential for prediction of optical performance in both imaging and transmitting applications. Optimal techniques for compensation of turbulence effects are only as good as the knowledge of the turbulence environment. The basic required parameters are r0, the Fried coherence length, and fG, the Greenwood frequency. These are specifications of the mean spatial and temporal statistics of the turbulence. Generally, these parameters plus the Kolmogorov spectrum are utilized for analysis and simulation of optical propagation through turbulence. It is recognized that the Hill spectrum, including inner scale, L0, is a more realistic model of index variations. This model includes a turbulence enhancement in a spectral subrange prior to the inner scale roll-off. Knowledge of this enhancement and the subsequent roll-off is important for predicting the statistics of both phase and scintillation effects and has a direct impact on adaptive optics design and performance. A technique, and sensor design, is proposed that is capable of estimating r0, fG, and L0 as well as scintillation statistics. The technique has been demonstrated in analysis and simulation. A prototype sensor will be built and the technique will be demonstrated in a range of turbulence environments.
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