Characterization of Laboratory Generated Turbulence by Optical Phase Measurements
Abstract
The resolution achieved by an optical imaging system in the presence of the random effects of the atmosphere is severely degraded from the theoretical diffraction limit. Techniques exist for recovering near diffraction limited performance of an imaging system in the presence of atmospheric turbulence. As opposed to laboratory testing, testing image enhancement techniques in the Earth's atmosphere imposes many limitations. Unfavorable weather conditions could result in the loss of time and money invested in conducting the experiments. With a properly characterized turbulence generator, with statistics that match those of the atmosphere, experimental testing of image enhancement techniques can be conducted in a controlled laboratory environment. A turbulence chamber has been designed and built for laboratory testing of current and future adaptive optics and image enhancement techniques. The turbulence is produced within a chamber consisting of two small fans and a heating element. A unique method of characterizing the statistics of the turbulence has been developed. The wavefront phase perturbations are measured using a shearing interferometer. The statistical properties of the turbulence are then characterized by estimating the phase structure function from the wavefront phase measurements. The phase structure function is a measure of the correlation of the phase between two points in a plane perpendicular to the direction of propagation. It has been found that the estimate of the phase structure function depends only on the magnitude of the separation between the spatially separated points, and follows the Kolmogorov r(5/3) power law.... Atmospheric Optics, Adaptive Optics, Atmospheric Turbulence, Laboratory Generated Turbulence, Shearing Interferometer, Phase Structure Function.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 23, 1993
- Accession Number
- ADA262596
Entities
People
- Eric P. Magee
Organizations
- Air Force Institute of Technology