Laser beam behavior on a long high path

Observations of the atmospheric effects on a laser beam over a unique path are discussed. The path is 80 km long and 1.3 km above the surface. Correlations are discussed between temperature lapse rate at the path level and the spreading and deflection of the beam. Beam deflection and beam spread are found to be generally consistent with results obtained by others over lower and shorter paths. Diurnal movements of the beam are not nearly as noticeable, and on one occasion a remarkable degree of collimation occurred that lasted for several hours.