Infrared sensor

An infrared sensor is a device that detects infrared light, which has a longer wavelength than visible light. Every object gives off infrared light according to its temperature, so by reading this light you can tell how heat is spread out and what the outline of an object is, even in the dark.

It has been used for a long time in the military, in surveillance and in space observation, and recently its use is spreading to the eyes of self-driving cars and robots. An infrared sensor on a satellite is valuable because it can observe other objects in space even in a night orbit with no sunlight.

The detector inside an infrared sensor is made of a material whose electrical signal changes when infrared light reaches it. The strength of the light or a difference in heat becomes a change in voltage or current. When these values are gathered point by point and put together into an image, you get a thermal picture.

For the detector to work well, the heat noise that it makes itself has to be reduced. So some high-performance sensors have a cooling device to lower their temperature. Without it, the sensor's own heat covers up the signal it is trying to measure.

On satellites, it is used to observe the heat signals of the ground or of objects in space, day and night alike. It is also applied where changes in heat must be found quickly, such as wildfire watching, road traffic observation and checking factory equipment for overheating.

The condition for using it is that the target must have a temperature or infrared emission that is clearly different from its surroundings. Materials that absorb or reflect a lot of infrared light, such as glass and water, can distort the values, so the place of installation and calibration are important.

Images taken by an infrared sensor differ from real colors, so they can look different from what a person sees. Their resolution is often not high, so to identify small objects you need to use them with other sensors.

A common misunderstanding is that an infrared sensor sees through walls or darkness. In practice, it reads the heat radiation from an object and the infrared light it reflects, so a thin film or a shield in the way will hide the information.

It is like an infrared camera that senses a pet's body heat at night and picks out the warm body. It is a device that reads the signals heat sends out instead of light.

Because it can find targets even where there is no light, it matters for satellite surveillance and for robot work at night. If you understand how an infrared sensor works, you can see why the night observation mentioned in an article is possible.