Learn More About Thermal Cameras
What can thermal cameras do?
Thermal cameras detect the thermal radiation that all objects with a non-zero temperature emit. With the ability to pick up small temperature differences and convert them into a visual image, these cameras can distinguish persons and vehicles at very large distances. They keep on performing even in complete darkness and regardless of lighting conditions, camouflaging, vegetation, difficult weather, or other conditions where a visual camera would be insufficient.
What are they used for?
Thermal cameras are widely used in perimeter protection systems. Live video from a thermal camera can reveal individuals around critical locations long before a visual camera has detected anything unusual. The thermal images are automatically analysed directly in the camera, and the security system can be set up to respond in various ways. It can trigger automatic audio alerts in loudspeakers to actively deter the intruders, email alerts to security personnel, and pan and zoom the system's visual cameras to capture and record ordinary video footage in which the intruders can be identified.
Thermal cameras are also installed to monitor the temperature of industrial processes. They can be used to find heat leaks in buildings or determine whether a vehicle was recently used.
It is generally not possible to identify specific individuals from thermal images alone. This makes thermal cameras a valuable option for surveillance in locations where privacy is especially important, such as schools.
NETD is a measure of thermal sensor accuracy
A thermal sensor's ability to detect very small differences in thermal radiation can be characterized by its NETD (noise equivalent temperature difference) value. In general, the smaller the NETD, the better the sensor. However, cameras should not be rated by comparison of NETD specifications only, due to the lack of a standardised measurement protocol.
Rules of thumb for installation guidance
Johnson's criteria describe the relation between the minimum required resolution and the expected detection range, based on whether you want to be able to detect, recognise, or identify vehicles or individuals. Another tool is the nomograph, which shows graphically the relation between detection range and the focal length of the camera lens for specific resolution requirements. However, actual results may differ depending on weather conditions. Also, if analytics applications are used, they may require a larger number of pixels in order to function than what these rules of thumb suggest.
Environmental impact on detection
Rain, fog and smog reduce the detection range. The rate of thermal radiation attenuation depends on the size and concentration of the particles or water droplets in the air. But a thermal cameras range is, for most cases, much less affected by phenomena than a visual camera is. Especially in moderate fog or smoke, thermal cameras detect objects that would be completely invisible to a visual camera.