Radiation source localization systems and related techniques are provided to improve the operation of handheld or unmanned mobile sensor or survey platforms. A radiation source localization system includes a logic device configured to communicate with a communications module and a directional radiation detector, where the communications module is configured to establish a wireless communication link with a base station associated with the directional radiation detector and/or a mobile sensor platform, and the directional radiation detector includes a sensor assembly configured to provide directional radiation sensor data as the directional radiation detector is maneuvered within a survey area.