An optical radar-lidar-has been operational at the Amundsen-Scott South Pole Station since summer 1987-1988. The observations were specially directed to the detection of aerosol layers and polar stratospheric clouds (PSCs). The lidar utilized a Nd-YAG laser followed by a second harmonic generator, and a 0.5-m diameter Cassegrain receiving telescope. Results obtained during the period May-October 1988 are summarized. Some 10,000 profiles of the lidar echoes, each the result of 1-min averaging, were obtained. Data sets consisting of profiles of the scattering ratio and of the backscattering cross section Ba, based on half-hour averaging, are presented. The data can be related to profiles of the atmospheric temperature T, usually obtained on a daily basis at South Pole. Stratifications appear to have two distinct types of structures: one structure shows only a modest variation with height; the other is characterized by sharp features, with large changes of the cross section with height. The basic results, the relationship between Ba, and T, and their statistical relevance are considered in this paper. The microphysical interpretation, the attribution of these structures to PSC Type I and Type II, respectively involving the condensation of nitric acid trihydrate and of water ice, and the seasonal evolution of the phenomena are treated in a companion paper. ¿ American Geophysical Union 1992