Understanding Thermal Cameras for Surveillance Applications

Thermal cameras are widely used in oil and gas and marine from process safety to offshore threat detection. Despite this, they often still retain a certain ‘air of mystery’, leaving many unsure as to where and when they should be used to deliver the most operational value.

Below, we answer some FAQs to help clear things up.

Are Thermal and Infrared (IR) cameras the same thing?

No, the terms are often used interchangeably, which can lead to confusion about where best to use thermal technology.

IR cameras detect light (near-infrared light) reflected from an object, meaning that a light source is necessary in complete darkness - typically an integral infrared LED. Thermal cameras, however, operate by detecting differences in the radiation emitted by an object.

This means that thermal cameras require an entirely different design – most notably using a material such as Germanium instead of glass for the optics to accommodate the operational wavelength. The sensors used also need to be different to respond appropriately to photon detection.

Do thermal cameras operate at greater distances?

Yes, thermal cameras can detect objects at much greater distances than is possible with IR. This is because they operate by measuring emissivity rather than capturing reflected light.

Active illumination with cameras fitted with IR LED illumination only has a limited operational range, typically out to about 200m, and very much depends on the reflectance of the target. As the distance increases and the camera field of view is reduced or zoomed in, the light attenuation increases and a more powerful illuminator is required, so it becomes a law of diminishing returns.

On the other hand, thermal cameras passively operate in the Medium-Wave Infrared (MWIR) and Long Wave Infrared (LWIR) bands with their operational range only limited by the lens and sensitivity of the camera.

What is the Johnson Criteria?

With thermal cameras, the DRI (Detection, Recognition and Identification) is based on the Johnson Criteria, where the resolution is defined by a minimum line pair (lp) or pixel value where a line pair is defined as one white line adjacent to a black line on the thermal image captured. While the minimum lp value for ‘Detection’ is 1, for ‘Recognition’ it is 3, and ‘Identification’ requires 6.

With this criteria, ‘Detect’ confirms that an object is present, ‘Recognition’ enables the type of object or class to be confirmed e.g. person or car, and ‘Identify’ enables a specific object or class to be discerned e.g. type of car.

When should thermal cameras be used?

A few good examples are flare stack analysis in the oil and gas sector or monitoring tank liquid levels. In both of these scenarios, operating capability in poor/no-light conditions remains essential, and the objective itself may be non-visible detection i.e. heat levels, gas compositions (different gases will have different emissivity), but the detection range is shorter, and precision imaging is not the priority. Thermal cameras provide an ideal solution and a more cost-effective option.

What are the disadvantages?

While thermal cameras do offer many advantages, many of those are lost when looking at surveillance for retrospective use only i.e. for recording and review.

Thermal cameras won’t, for example, offer the same detailed evidentiary review capabilities as electro-optical cameras. Their strength lies in proactive surveillance – an early warning mechanism for approaching objects, mechanical failure and process issues. In summary, thermal cameras are an ideal first line of defence in terms of critical detection capabilities in low/no light conditions.

Are thermal cameras more cost-effective than IR Cameras?

Over the long term, they can be. It’s important to mention LED degradation. In as little as five years, LED light sources will typically degrade by approximately 30%, which can significantly impact camera capability and image quality. Thermal cameras will require a more significant initial outlay, but their lifespan is much longer.