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.

 

[astrokreng]

Thermal imaging and radiometry are techniques used to detect and measure the temperature of objects by capturing the infrared radiation they emit. While both techniques involve the use of a detector to capture the radiation, they work differently and have different limitations.

In thermal imaging, a camera is used to capture the infrared radiation emitted by an object and convert it into a visual image. The camera has a detector that converts the radiation into an electrical signal, which is then processed and displayed as an image. The temperature range that can be detected by a thermal imaging camera is limited by the sensitivity of its detector. In other words, the minimum temperature that can be detected is determined by the capabilities of the detector itself. Therefore, it is not possible for a thermal imaging camera to detect a body that is cooler than its detector.

On the other hand, radiometers work by measuring the intensity of the infrared radiation emitted by an object. The detector in a radiometer is typically a thermopile, which converts the radiation into an electrical signal. The temperature range that can be measured by a radiometer is also limited by the sensitivity of its detector. However, since the radiometer is not producing a visual image, the temperature of the detector does not put an absolute floor on the temperatures of objects that can be detected. The sensitivity of the detector can be adjusted to detect lower temperatures, but this may also increase the noise level in the measurements.

In summary, both thermal imaging and radiometry have limitations in terms of the minimum temperature they can detect, which is determined by the sensitivity of their detectors. While a thermal imaging camera cannot detect a body that is cooler than its detector, a radiometer can potentially detect lower temperatures if the sensitivity of its detector is optimized. However, this may also result in higher levels of noise in the measurements.