Reflectivity. The metal housing is reflecting the cooler temperatures behind the thermal camera and including it in the imaging.
Relatable similar occurance: I was working on an offshore oil platform once using a thermal gun to try to identify a leaking valve and found out pretty quickly that the polished steel gasket between the valve and pipe would reflect the temperature of open sky. I thought I found a leak when the gun registered a chilly 32F but was actually at like 100F on contact.
0sted t1_j5pd9q2 wrote
Reply to Why does hot air cool? by AspGuy25
Reflectivity. The metal housing is reflecting the cooler temperatures behind the thermal camera and including it in the imaging.
Relatable similar occurance: I was working on an offshore oil platform once using a thermal gun to try to identify a leaking valve and found out pretty quickly that the polished steel gasket between the valve and pipe would reflect the temperature of open sky. I thought I found a leak when the gun registered a chilly 32F but was actually at like 100F on contact.