There was a team from a Large Defense Contractor at my local airfield recently with thermal-imaging equipment that seemed to be doing a good job of tracking lig

There was a team from a Large Defense Contractor at my local airfield recently with thermal-imaging equipment that seemed to be doing a good job of tracking light piston-engined aircraft, many of which are tube-and-fabric construction like WW1 machines. They wouldn't say what they were testing but it seemed fairly obvious. The whole engine block glowed hot as did the uppersides exposed to the Sun, let alone the exhaust, at what I guessed to be several kilometres distance. Before we were shooed away :)