COMPARISON OF ON-LINE AND OFF-LINE FRIED PARAMETER ESTIMATION METHODS

We address the problem of high-accuracy estimation of the Fried parameter r0 by comparing two approaches based on estimation of statistical properties of intensity-based wavefront measurements with parameter-fitting to the theoretically predicted values. In the first approach, the phase of the aberration-degraded field is restored from the measurements to obtain the statistical estimate for the structure function. Due to the iterative nature of the most phase retrieval methods, this approach requires significant computational time and thus cannot provide results in real time. In the second approach, the structure function of the sub-aperture wavefront slopes is directly calculated and related to the turbulence parameters in real time. We describe the equations used to obtain the estimate of the Fried parameter by both methods and check their accuracy with numerical simulations.