Sensitivity expresses the ability of an infrared camera to display a very good image even if the thermal contrast in a scene is low. Put another way, a camera with good sensitivity can distinguish objects in a scene that have very little temperature difference between them.
Sensitivity is most often measured by a parameter called Noise Equivalent Temperature Difference or NETD, for example, NETD @ 30 C : 80mK. A Kelvin degree is the SI base unit of thermodynamic temperature equal in magnitude to a degree Celsius, so mK means thousandths of a degree (80mK = 0.080 K).
What is NETD?
NETD is defined as the amount of infrared radiation required to produce an output signal equal to the systems own noise. This is a noise rating of the system and should be as low as possible. We are not talking about how loud the system is here!!! We are talking about electronic noise that we translate into a temperature difference at an object temperature of 30 C (86 F).