<title>Evaluation of tilt for a high-altitude horizontal path</title>

Abstract

A high priority Air Force interest is to understand the tilt (or jitter) induced by atmospheric turbulence on a laser beam propagated over a high altitude long horizontal path. This will aide in the design of the pointing and tracking systems such as used for communication systems and laser beam propagation. The Phillips Laboratory has undertaken a technology program to simulate, measure, and evaluate the implications of this high altitude tilt. This paper includes 3 related efforts; a simulation that predicts high altitude tilt using present knowledge of the atmosphere, a flight measurements program that is gathering data at high altitude, and a simulation effort to understand the implications on a pointing and tracking system of this high altitude tilt. The simulation is a ray trace code that has been developed at the Phillips Laboratory over the past 15 years and has been anchored using available data. Until recently this simulation had not include high altitude horizontal propagation data. However, the Phillips Laboratory has recently completed a high altitude measurement of scintillation and a temperature probe measurement effort to measure the atmospheric structure. This information has been included in the simulations. A controls simulation is used to evaluate the requirements for bandwidths and controls design and utilizes the disturbance data produced by the atmospheric simulation.