Abstract: A remote sensor for detecting a nuclear source, comprises: a Field-of-View (FOV) structure having an aperture therethrough of area A and a Field-of-View (FOV) angle, the FOV angle centered on a source, and subtending a solid angle &OHgr; to the nuclear source; a plurality of optical filters for filtering photons outside a selected Ultraviolet (UV) band and for transmitting in-band photons according to a selected Transfer Function defining an out-of-band rejection ratio and an in-band transmittance ratio for the selected UV band, the Transfer Function supporting a sensor sensitivity S at the selected UV band for the Field-of-View (FOV) structure to support a Signal-to-Noise ratio of greater than one (1) to detect a nuclear source of nuclear material having a brightness of at least about IR, the selected UV band being selected such that naturally occurring in-band photons are at a brightness of about less than 104 R during daylight and are not naturally occurring at night up to about 20 km Earth altitude, and t