Anomalous Propagation / 'Radar Angels' & Sensor Spoofing.
documentedgovernment_studyAtomic Energy Commission / ERDA (DOE progenitors)
Temperature inversions, ducting, mylar balloons and camera artifacts produce spurious 'solid' targets on radar/sensors.
Radar angels from atmospheric temperature inversions create solid-looking returns, a recognized cause of radar-only Oak Ridge contacts. Mick West has documented mylar balloons spoofing modern fighter radar and various camera/optical artifacts in military UAP video. The Oak Ridge foil-RAWIN hoax is a concrete instance. West still treats unidentified objects in restricted airspace as a genuine security problem.