Edwards, Clinton LeeThis paper models the effects of the leaves of mature broadleaf trees on air-to-ground free-space optical (FSO) communication systems operating through the leaf canopy. Ecological radiation transfer models are considered and the concept of Leaf Area Index (LAI) is reviewed and related to a probabilistic model. Leaf transmittance is experimentally measured for different leaf types and determined to be very close to zero. A probabilistic canopy model of foliage is developed as obscuring leaves are randomly distributed throughout the treetops. The expected fractional unobscured area statistic is derived as well as the variance around the expected value. Monte Carlo simulation results confirm the probabilistic model's statistical conclusions. Multi-site passive optical measurements are taken in a mature broadleaf forest environment with increasing leaf obscuration then fitted to the model. The model's implications to FSO system links are considered and simulated. Conclusions are discussed as well as further research.en-USThesisEngineering, Electronics and Electrical