Atmospheric turbulence characterization of a low-altitude long horizontal path

Abstract

The limitations placed on optical imaging through the earth's atmosphere are well understood. A large portion of the body of work on this subject deals with vertical optical paths. The transition to the study of horizontal propagation of light is currently being made. Various methods exist that quantify the disturbances introduced on optical signals by turbulent air. Small perturbations of the wave front phase can be measured using a Hartmann Wave Front Sensor (H-WFS). For long optical paths through turbulence spatial and temporal variations in intensity called scintillation arise. Using scintillation statistics and theoretical expressions for structure functions of H-WFS slope values, turbulence strength is studied. Data sets taken from two mountains in Hawaii during an optical communications experiment are studied for comparison with slope structure function and scintillation statistics theory. This experiment was performed at an altitude of 10,000 feet over a horizontal path length of 150 km. Results indicate that very strong scintillation exists under these conditions, and that very little faith can be placed in the H-WFS phase-dependent results. Scintillation may provide a more dependable method for optical characterization of these conditions.

A numerical simulation method for laser radiation propagating through large-scale atmospheric inhomogeneities

“…Many long-path experiments [13][14][15][16][17][18][19][20] point to significant deviations of the results from this model.…”