We develop methods for detecting and localizing a moving biochemical source in a semi-infinite medium (e.g., in air above the ground) using sensor array measurements. Potential applications include security, environmental monitoring, pollution control, and explosives detection. We derive models for the source substance concentration diffusion under different boundaries and environment conditions. A maximum likelihood estimation algorithm to localize the moving source is presented and its

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... ance is analyzed by the Cramér-Rao bound. We derive two detectors (generalized likelihood ratio test as well as a mean-difference detector) and determine their performances in terms of the probabilities of false alarm and detection. Numerical examples illustrate the source diffusion model and the performances of the proposed methods.