This project is to validate and refine the use of incoherent scatter radar (ISR) to measure atmospheric properties of the mesosphere (65-90 km), a key region for energy and momentum transfer between the lower and upper atmosphere. Based on existing data from both the Arecibo Observatory and the AMISR array located in Alaska, as well as new data acquired during the course of this work, this project will improve interpretation of radar backscatter from the collision-dominated mesospheric plasma, a long-standing problem owing to the presence of heavy ions, negative ions, and layer structuring. Specifically, this project is to compare theoretical scattering models with experimental data from the two sites and to compare chemistry models with the derived parameters. Analysis of the resulting mesospheric parameters will be conducted to investigate open questions on mesospheric chemistry and dynamics, particularly regarding the role of minor constituents, as well as climatological dependencies.