Rytov parameter estimation by use of differential-tilt measurements

The Rytov parameter is a common name given to the log- amplitude variance predicted by an approximate solution to Maxwell's equations for propagation through media with random index of refraction (Rytov theory). Empirical evidence suggests that the Rytov parameter is a non- observable in many practical experiments where the variance of irradiance saturates, an effect not predicted by the standard theory. Nevertheless, the Rytov parameter is useful as an indicator of integrated turbulence strength for extended propagation and thus a desirable experimental quantity to estimate. In this work, we propose an optical configuration and related analysis techniques that provide a practical method for determining the Rytov parameter when scintillometry-based methods fail. This method employs differential-tilt measurements, resulting in a measurable quantity which is proportional to the Rytov parameter and for which Rytov theory is a good approximation. The differential-tilt technique is also insensitive to gimbal motion and additive noise. We illustrate that this method provides approximately 5% relative error in determining the Rytov parameter and may be used to characterize atmospheric turbulence well beyond the limits of conventional scintillometry.