Backscattering from the Upper Atmosphere (75–160 km) detected by Optical Radar

Abstract

AN optical radar system has recently been used to detect and study backscattering from the upper atmosphere (75–160 km). Although a much more detailed investigation is in progress, our preliminary results seem to indicate rough agreement with those of Fiocco and Smullin¹. These authors suggested micrometeorites as a source of the echoes. When observations were made for brief time intervals (0.5 h or less), peaks were sometimes observed in the return-signal profiles. It should be noted, however, that when averaged over a period of several hours the return signal tends to become relatively smooth. It would seem, therefore, that the altitudes of the scattering layers, if they exist, fluctuate rapidlv with time. The total scattering cross-section at 6943 Å observed by us is of the same order of magnitude as that reported by Fiocco and Colombo² (N̄σ ≈ 10⁻¹² cm⁻¹).