Thermal imaging and radiometry

[ArthurReader]

Can a thermal imaging camera detect a body that is cooler than the detector? Or does the temperature of the detector put an absolute floor on the temperatures of objects that can be detected?

How do radiometers detect radiating bodies that are lower temperature than the radiometer? Or does the radiometer have a similar floor problem where the noise from the radiometer itself overwhelm the signal?

 

[mgb_phys]

How do radiometers detect radiating bodies that are lower temperature than the radiometer? Or does the radiometer have a similar floor problem where the noise from the radiometer itself overwhelm the signal?

it's all a question of signal to noise.
It's not the thermal signal from the detector that is a concern but the uncertainty in it.
If you know the detector had a signal of exactly 100units from it's own thermal emission an you measured a signal of 150units you know there was a target with a signal of 50units and so at a lower temperature.

But if the detector has a thermal signal of 100 +/- 20 then you wouldn't be able to detect a source that only had a signal of 20.
Because thermal emission is statistical for a given temperature there is a minumum uncertainty in that background.

in practice you do things like chopping (have the sensor look at the scene and then a at a fixed temperature reference) any difference in the two signal must come from the target scene, any signal that is the same is from the instrument. And integration to smooth out variations in the signal from the instrument.