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Whenever we want to purchase a thermal camera, we wonder: How far can I see with this camera? This is a logical question and a proper answer needs to consider different criteria. Most FLIR thermal cameras can observe the sun, which is located more than 146 mil­lion kilometers away from Earth. Nevertheless, we cannot say these cameras, at such a distance, can detect certain “targets”.
Thermal imaging technology allows to detect people and objects, even in complete darkness and adverse weather conditions. Typical applications for this technology are border surveillance, mining, airports, military vehicles, beach surveillance, etcetera. Funda­mental aspects to be taken into consideration in these cases are,  What visualization reach do these FLIR thermal cameras have? Are they capable of detecting possible threats?
In the industry of thermal image cameras the distance at which targets are detected is called “range”. In order to determine the range, you need to consider several and complex parameters: type of thermal imaging camera, type of lenses, nature and size of objects to be spotted, atmospheric conditions and a precise identification of what we call “seeing the target”. As established by the Johnson’s criteria, a distinction should be made between “different degrees” of target observation, as we mentioned as follows:
Detection: In order to detect whether an object is present or not, its critical dimension needs to be covered by 1.5 or more pixels. 1,5 pixels, in a fixed observation position correspond to 0,7 cycles, an established basic unit to de­termine the Johnson’s criteria resolution.
Recognition: Recognizing an object is defined as seeing what type of target we are talking about. This means being able to tell a person from a car or any other object. In order to recognize an object at least 6 pixels of its critical dimen­sion should be covered.
Identification: This term is commonly used in the international militar industry, which means seeing if someone is “friend or foe”. In order to do this, a minimum of 12 pixels of its critical dimen­sion should be covered.

Cooled and Uncooled Thermal Imaging Cameras
There’s also a difference between the range obtained with a cooled versus an uncooled thermal camera. Cooled systems are more expensive, but  normally, they provide longer range in most conditions than uncooled systems. However, cooled systems are more economical for applications demanding greater distance than uncooled systems, since these need lenses with larger focal distance which turn out to be more expensive.

Atmospheric Conditions
Thermal imaging cameras are capable of  detecting targets in complete darkness, through fog, light rain and snow, this detection capacity is affected by atmospheric conditions. Rain and mist can drastically limit the rang of thermal imaging cameras due to scattering of light off of droplets of water. Fog increases the amount of water droplets suspended in the atmosphere or near the surface of the Earth, which can reduce in many occasions horizontal visibility to less than 1 km. This phenomenon is generated when the air temperature and the dew point of the air are nearly equal, therefore producing sufficient condensation. In addition to this, rain can reduce contrast since it cools down the surface of targets. Although performance can be degraded under these conditions, thermal imaging cameras can see targets that human vision is not capable of detecting.
Engineers at Anixter, your added value distributor, can help you select the most adequate camera for you and establish the range at which it can detect different types of targets, depending on atmospheric conditions and types of applications to be used. Just contact your Account Executive at Anixter and obtain all the technical and business consultancy you need to make the best decisions.