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The overall goal of the program was to conduct experimental measurements and develop theoretical models to improve our understanding of electromagnetic wave interaction with terrain at millimeter wavelengths. The work was divided into five tasks. Tasks 1 involved the construction of calibrated scatterometer systems at 35, 94, and 140 GHz. In designing, constructing, and testing these systems, a great deal was learnt about system- design trade-offs and system stability requirements, and new calibration techniques were developed. The scatterometer systems were then used in support of the remaining tasks. The objective of Task 2 was to evaluate the effects of signal fading on the radar backscatter from terrain. Based on experiments conducted from asphalt and snow-covered surfaces, it was determined that the Rayleigh fading model is applicable at millimeter wavelengths, and a model was developed to show how frequency averaging can be used to reduce signal fading fluctuations. Task 3 involved the development of a model that relates the transmission loss of dry snow to crystal size in the 18-90 GHz region. In Task 4, we examined the character of bistatic scattering from surfaces of various surface roughness and from two types of trees. The bistatic data for trees proved instrumental in the development of a radar model for scattering from tree foliage at millimeter wavelengths, which was one component of Task 5. The other component of Task 5 involved the development of a model for snow. (aw)