The spatial and temporal distributions of density structure in the upper stratosphere and lower mesosphere (40 to 80 km altitude) are observed by Rayleigh scatter lidar at USU. We utilize advanced two dimensional Fourier filter techniques to derive estimates of the temporal and spatial (altitude) power spectral densities for the altitude-binned and time-binned structure, and of the 2-D spacetime structure of an entire observing period (e.g., 8 hours). Coherent, wavelike spectra are observed in both altitude and time, and appear to be superimposed upon a background of continuous spectral power which may be characteristic of unsaturated turbulence. We observe upwardly propagating gravity waves having (downward) vertical phase velocities in the approximate range 0.15 to 1 meter/second (0.5 to 4 km/hr.). Wave structures are often not apparent in the raw density fluctuation data, but are brought out clearly by means of a 2-D Parzen filter in Fourier space followed by appropriate reconstruction of the density fluctuations in altitude-time coordinates.