hi hi
It is true that planets are a good place to hide things, but at high altitudes where the temperature starts to increase it is because the air is so very thin. The absorption of infrared wavelengths by water vapor does complicate things, it is true, but there are solutions for most of these problems. Operating at higher altitudes in cold and dry environments and cooling your telescope will solve a lot of the interference problems. Though I suppose there isn't any purely optical way of totally canceling out foreground heat from the final image.