You really have me interested now ... I worked with IR at Wright Pat when I was in grad school. The EO group had active millimeter wave systems they were conducting experiments on ... I thought I remember one of the folks telling me there were no natural sources of millimeter wave radiation ... and all work was active ...
Of course, that was in the early 1980s ...
I will surely waste a few hours tonight on the internet reading some stuff.
Thanks for the info ...
Refer again to the blackbody curve ... there's not much out there in the mm wavelength realm, perhaps undetectable by 1980s technology. I guess what's "news" is that it isn't 1980 anymore, and that mm wave detection technology (along with most other electronic technologies) has improved significantly since then. IR has improved significantly since then as well.
In any case, the temperature and reflectivity of the objects in the buildings/cars scene varies ... Dark areas are probably shiny and reflecting the sky. Bright areas are warmer and emitting according to their temperature. In the man with the guns scene, he's emitting based on his skin temperature. The outside surface of the guns is cooler than his skin, so is emitting much less. Transmissivity of his clothes is more or less constant throughout the scene ... so the cold (dark) guns stand out against the bright (hot) body.