Optical “seeing” through the atmosphere by an interferometric technique*

Abstract

An improved cube-corner shearing interferometer for measuring the MTF of atmospheric propagation paths and for making coherence measurements is described. The laboratory unit used in all the experiments described was operated satisfactorily on board a KC-135 jet aircraft. MTF data over a 13.3-km horizontal path near the ground, and through the atmosphere using star sources, have been compared with the MTF curves estimated by use of the Fried theory and published models for the atmospheric structure constant CN. The MTF has been measured with laser sources between the wing tip and the skin of the KC-135 in flight, and through the boundary layer within 25 cm of the skin in daylight and at night. The main degradation to the seeing was found to be in the boundary layer within 25 cm of the skin outside the aircraft window.