Cooled (MWIR) or Uncooled (LWIR) Thermal?

In this article, we will look at the differences between Cooled (MWIR) and Uncooled (LWIR) thermal technologies, and the factors to take into account when choosing between the two.

Simplistically speaking, the difference between cooled and uncooled is a question of sensitivity. The quality of the image viewed is a combination of the sensitivity of the sensor and the amount of IR (infra-red) transferred through the attached lens. The bigger the lens, the less IR it passes to the sensor.

For longer-range applications, such as border security and coastal surveillance, longer focal lengths lenses are required. Therefore, to compensate for the reduction in IR transmitted through the lens, a more sensitive sensor is required which can be found in Cooled (MWIR) thermal.

Fundamentally, this is the key difference – longer range means a larger lens and therefore less IR transmitted to the sensor. So, to get a high-quality image at distance, you need a more sensitive sensor.

Typically, uncooled sensors are about 50mk – this is a measure of the temperature points it can distinguish between. Whereas cooled sensors (MWIR) tend to be around the 10-25mk point.

Another factor to be taken into account is atmospheric conditions. For example, a desert scene with a contrast neutral environment will require higher levels of contrast so a cooled thermal solution will likely be required depending on the range required. Whereas, 

From a performance perspective, cooled thermal will always win against uncooled thermal, however, there is a cost to this…

In order to gain this increased sensitivity, the sensor is cooled down to around 77 degrees Kelvin (about -200°C). These coolers have a limited life span and need to be re-serviced regularly. Typically, this is around the 10,000-20,000 hour mark. Servicing is costly and necessitates specialist equipment, meaning the camera has to be returned to base. In a five year lifetime a cooled system may need servicing two to three times, leading to a significant cost and downtime, whereas an uncooled system will typically run for the five years with no downtime.

We have had a lot of success in pairing uncooled thermal sensors with longer range thermal lenses and using a number of video enhancement techniques to improve the quality of the underlying image provided to the user. We are primarily delivering this through our LR range. The LR range as allowed us to bridge the gap between uncooled and cooled thermal by offering an affordable capability that nears cooled performance, but does not have the same cost and servicing requirement.

Overall, as you can see there are benefits and drawbacks to each technology, and every application will require looking at.