1. An apparatus for detecting a radiation source, said apparatus comprising: a visible light camera that detects electromagnetic radiation in a visible range; a high energy radiation imager that detects high energy radiation; and an image analysis device that is configured to execute a program of machine-executable instructions to calibrate high energy radiation imager pixels of said high energy radiation imager to a real-world coordinate of a moving vehicle, wherein said program includes the steps of: determining a visible light camera pixel coordinate of a moving vehicle; determining a real-world coordinate of said moving vehicle based on said visible light camera pixel coordinate; determining a high energy radiation imager pixel position based on said real-world coordinate of said moving vehicle; and determining a scale parameter for said high energy radiation imager based on said real-world coordinate, wherein said scale parameter correlates a change in said high energy radiation imager pixel position to a change in an x-coordinate of said real-world coordinate in a real-world coordinate system having an x-axis that is parallel to an image plane of said high energy radiation imager.