The objective of this research effort is to investigate the use of a high power-aperture Rayleigh lidar to measure neutral density and temperature in the upper atmosphere, into the lower thermosphere (>100km). The scientific interest with this system is to obtain measurements of atmospheric tides, planetary and gravity wave amplitudes and phase in the lower thermosphere. Measurement of waves into the lower thermosphere is accomplished using Rayleigh lidar methods with high power-aperture (PA) products using new technology lasers and large collecting apertures, resulting in PA of 50–700Wm2. This paper describes the simulation of high PA Rayleigh lidar systems and estimates their capability to measure gravity waves and tides in the mesosphere and lower thermosphere. Both traditional backscatter and bistatic (imaging) methods are simulated. Simulations show that substantive measurements can be achieved for characterizing gravity waves at altitudes >90km and atmospheric tides at altitudes >100km for this lidar system. Measurements of density and temperature to 10% precision are possible up to 120km.