Thermal Imaging Cameras for Trucks: Detection Distances and Use Cases

How a thermal camera sees

A thermal camera uses an uncooled microbolometer detector — in our range a vanadium-oxide array — that responds to long-wave infrared radiation in the 8–14 μm band. Every object above absolute zero emits in that band, and living things emit considerably more than the road or the roadside vegetation. The camera converts that into a greyscale image where warmer objects are brighter.

The key practical consequence: thermal imaging needs no light at all, and it is not confused by headlight glare, oncoming beam patterns or the flare that ruins a normal camera at night.

The four specifications that matter

Why NETD matters more than buyers expect

Resolution tells you how many pixels the image has. NETD tells you whether those pixels contain useful information. A 256 × 192 detector with a NETD of 40 mK produces a clearer, more contrasty image in mild weather than a higher-resolution detector with a NETD of 100 mK, because in mild conditions the temperature difference between a person and the background is small. A camera with poor thermal sensitivity simply shows a uniform grey mush.

Calculating detection distance

The industry rule of thumb is that reliable detection needs the target to occupy three or four pixels across its critical dimension, and identification needs eight to twelve. Worked through for a human target about 0.5 m wide:

Identification — recognising that the target is a person and what they are doing — happens at roughly a third of those distances. When a supplier quotes a single detection distance without stating the lens, the target size and the criterion, the number is not comparable with anything.

Where thermal earns its cost

• Unlit rural routes. Pedestrians, cyclists, livestock and stopped vehicles beyond the headlight beam are detected far earlier than with any visible-light system.
• Mining and quarry haul roads. Dust in the air scatters the light from LED illuminators back into the lens, making them nearly useless. Thermal radiation passes through airborne dust far more effectively.
• Rail and depot movements. Detecting a person on or near the track at long range is a safety requirement, and thermal does it without any lighting infrastructure.
• Agricultural machinery at night. Fields at night contain people and animals that lamps do not reliably reveal.
• Search and marine applications. Finding a person in darkness, haze or light fog.

Where thermal does not help

• Reading detail. A thermal image shows heat, not texture. You cannot read a registration plate, identify a face, or read a sign.
• Warm-weather contrast. On a hot day the useful range drops significantly.
• Replacing a visible camera. Thermal should be a second channel, not a replacement. Run one thermal channel for detection and one visible channel for detail.
• Through glass. Ordinary glass is opaque to long-wave infrared, so a thermal camera must have an unobstructed view — you cannot mount it behind a windscreen or a standard lens cover.

Practical installation

• Mount it clear of the windscreen and of any covering. The lens must see out unobstructed — glass blocks the thermal band entirely.
• Specify the lens for the job. A wide lens is right for low-speed manoeuvring; a narrow lens is right for highway detection. Choosing the wide lens for a highway application wastes most of the camera’s capability.
• Check the defrost function if the fleet operates near or below freezing. A thermal lens ices like any other, and an iced lens is blind.
• Expect AHD output. Our thermal cameras output standard AHD, so they connect to the same monitors and recorders as the rest of the range without special hardware.