  For security, environmental, and regulatory purposes it is useful to
continuously monitor wide areas for unexpected changes in radioactivity. We
report on a temporal anomaly detection algorithm which uses mobile detectors to
build a spatial map of background spectra, allowing sensitive detection of any
anomalies through many days or months of monitoring. We adapt
previously-developed anomaly detection methods, which compare spectral shape
rather than count rate, to function with limited background data, allowing
sensitive detection of small changes in spectral shape from day to day. To
demonstrate this technique we collected daily observations over the period of
six weeks on a 0.33 square mile research campus and performed source injection
simulations.
