Conventional video surveillance cameras struggle to capture usable images in complete darkness or under challenging conditions such as smoke or fog, or when subjects are hiding or obscured by a complex background. Thermal network cameras provide clear, usable images in all these situations, and represent an important step forward for the security industry. But how does the technology work, and how will it be used?
Effective video surveillance depends on accurately detecting and identifying objects, people or incidents, so that appropriate action can be taken. But all network cameras have a basic physical limitation: they need light to work.
Sure, some network cameras have night and day functionality that allows them to operate in very poor lighting conditions, down to fractions of a lux. And of course, if natural light is not available it can be substituted by electrical light, either visible to the human eye or infrared.
But in some instances these solutions have serious drawbacks – they can be expensive, and energy consuming; and illumination creates shadows where an intruder can hide – to mention a few.
Introducing thermal technology
Visible light, which the human eye can see and standard cameras can detect and display, requires a light source such as the sun or a flood light. Even day/night cameras, which use the near-infrared spectrum, require some light to operate – either natural or a dedicated IR-lamp.
A thermal camera requires no light source, as it works by detecting radiation in the thermal infrared range of the electromagnetic spectrum, producing images of that radiation. Infrared radiation is emitted by all objects – even very cold objects, like ice – based on their temperatures and emissivity. This makes it possible for the camera to detect temperature changes and visualize objects in the dark and in other difficult conditions without any external light source.
The amount of radiation emitted by an object increases with temperature. Therefore a thermal camera allows the user to see variations in temperature. When viewed by a thermal camera warm objects stand out well against cooler backgrounds or vice versa.
Thermal images are sometimes associated with bright, intense colors – which may seem a bit odd considering that the camera works outside the spectrum of visible light. The answer is that the colors are created digitally, so-called pseudo-colors.
Each color or nuance represents a different temperature, usually white and red for higher temperatures, over green, blue and violet for colder ones. The reason is foremost practical since the human eye is better at distinguishing different shades of color than different shades of grey.