Remote Measurement of the Atmospheric Isoplanatic Angle and Determination of Refractive Turbulence Profiles by Direct Inversion of the Scintillation Amplitude Covariance Function with Tikhonov Regularization

摘要

It is difficult to propagate a diffraction-limited laser beam through the atmosphere, since the atmosphere contains random index of refraction fluctuations. Two parameters that characterize the atmosphere for optical propagation are the atmospheric isoplanatic angle, theta sub 0, and the refractive turbulence structure parameter, (C sub n, sup 2) squared. This thesis deals with improved methods for measuring theta sub 0 and (C sub n, sup 2) squared profiles using optical techniques. By apodizing the receiver telescope aperture, one can improve the weighting function for isoplanatic angle measurement substantially over previous systems. The weighting function is not found significantly affected by inner scale changes with altitude and that the error in isoplanatic angle measurement from strong low altitude turbulence (z < 1 km) with this weighting function is small. Data collected with the improved isoplanometer shows temporal trends in the isoplanatic angle on the order of 90 seconds that have not been observed before. Direct inversion of the amplitude covariance function (including aperture averaging effects) to yield refractive turbulence profiles is known to be ill-posed. I suppress this condition using Tikhonov regularization and reproduce refractive turbulence profiles from actual (C sub n, sup 2) squared data with some success. Keywords: Isoplanatic angle; Refractive turbulence profiles; Stellar scintillation; Apodization; Tikhonov regularization; Thesis.