Imaging characteristics of thermal detectors
The magnitude of the heat radiation energy of an object is directly related to the temperature of the object surface. The characteristics of thermal radiation so that people can use it to objects without contact temperature measurement and thermal state analysis, thus saving energy for industrial production, protect the environment, and provide an important means of detection and diagnostic tools.
The atmosphere, cloud, and so forth absorb visible and near infrared rays, but are transparent to 3~5 microns and 8~14 microns of thermal infrared. Therefore, these two bands are called "hot infrared" atmospheric windows". The use of these two windows allows people to clearly observe the situation on a completely dark night or in a smoke filled battlefield. Because of this characteristic, thermal infrared imaging technology provides advanced night vision equipment, and provides all-weather forward looking systems for aircraft, ships and tanks. These systems played a very important role in the Gulf war.
Modern thermal imaging devices operate in the mid infrared region (wavelength 3~5um) or far infrared region (wavelength 8~12um). By detecting infrared radiation from an object, a thermal imager generates a real-time image that provides a thermal image of the scene. The invisible radiation image is transformed into the visible and clear image of the human eye. Thermal imager is very sensitive, can detect a temperature difference of less than 0.1 degrees celsius.
Infrared detectors fall into two categories: photon detectors and thermal detectors. After absorbing infrared energy, photon detectors directly produce electrical effects. Thermal detectors produce temperature changes after absorbing infrared energy, thus producing electrical effects. The electrical effect caused by temperature changes is related to material properties.Photon detectors are very sensitive, and their sensitivity depends on their temperature. To maintain high sensitivity, the photon detector must be cooled to a lower temperature. The coolant is usually used Sitailin (Stirling) or liquid nitrogen.Thermal detectors generally do not have as high sensitivity as photon detectors, but have good performance at room temperature, so cryogenic cooling is not required
When working, the thermal imager optical device using infrared energy is focused in the scene from objects in infrared detectors, infrared data from each detector element and then converted into a standard video format that can be displayed in the standard video monitor, or recorded on videotape. Since the thermal imaging system detects heat rather than light, it can be used all day long; it is not entirely exposed to light or radio frequency energy because it is completely passive, so it does not expose the user's position.
