Resources · Dual sensor

EO IR Sensor Pairing: Boresight, Bands and Detectors

Pairing a visible channel with thermal imaging on one line of sight

A dual-sensor payload is only as good as the agreement between its two channels. If the visible and thermal images do not share an aim point, every switch between them costs the operator the target.

Uncooled LWIR
Cooled alternatives
NETD ≤ 40 mK
Boresight on one cage

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An eo/ir sensor pair combines a visible channel, which carries colour and detail, with a thermal channel, which carries heat and works without light. The two bands do not compete: the visible channel answers what something looks like, and the thermal channel answers whether it is there, whether it is running and whether it is occupied. Written as eo ir sensor, eoir sensor or eoir sensors, it is the same pairing of an electro-optical channel with an infrared one. Most eo/ir sensors in production follow that pattern: a 1920 x 1080 visible channel paired with a 640 x 512 thermal detector.

For a uav thermal sensor the defining numbers are detector resolution, lens focal length and noise-equivalent temperature difference. For the pair, the defining number is boresight tolerance: how far the two images can drift apart across temperature and zoom before the operator notices. That is a mechanical and optical property, and it is set at design rather than corrected in software.

Detectors and how they compare

Uncooled microbolometer
Vanadium oxide or amorphous silicon detectors in the 8 – 14 micrometre band, operating at ambient temperature. Light, low power and the mainstay of UAV thermal imaging at 640 x 512 and 1280 x 1024.
Cooled detectors
Mercury cadmium telluride or indium antimonide in the 3 – 5 micrometre band, with better sensitivity and longer range in dry air, at the cost of a cryocooler, weight and power.
NETD
Noise-equivalent temperature difference at or below 40 mK separates a person from a wall that has been in the sun all day. Poorer detectors collapse the same scene into a single shape.
Boresight on one cage
Both optical paths mount on a common structure with matched expansion, aligned at the factory and verified after temperature cycling across the operating band.
Fusion and display modes
Either channel full screen, thermal overlaid on visible as picture-in-picture, or both recorded simultaneously so the mission keeps the frame that mattered.
Shared stabilisation
Both channels sit behind the same stabilised axes, so switching channel does not change the pointing behaviour the operator has learned.

HITS dual sensor gimbal camera payload with a daylight and a thermal aperture in one turret — A daylight and a thermal aperture in one turret: boresight between the two is set and checked on the bench, not in the air.

Serial number and QR label on the rear of a HITS gimbal camera payload tracking it through production — The serial and test record that follows each head, so a replacement unit can be matched to the one it replaces.

Pairing a visible channel with thermal

Indicative combinations across the range, matched to the mission rather than to the sensor.

Pairing	Visible channel	Thermal channel	Typical payload weight	Best for
Entry dual sensor	2688 x 1520 fixed	640 x 512, 19 mm	240 g class	Small aircraft, detection and context
Mid dual sensor	1920 x 1080 with 10x – 30x zoom	640 x 512, 25 – 35 mm	800 g – 1.2 kg class	Patrol and inspection
High-resolution thermal	1920 x 1080 with 30x zoom	1280 x 1024, 75 mm	2.8 – 4.1 kg class	Long-range identification at night
Continuous thermal zoom	1920 x 1080 with 30x – 55x zoom	640 x 512 with 40 – 275 mm zoom	5 – 10 kg class	Surveillance and ISR
Dual thermal with designation	1920 x 1080 with 30x zoom	Dual 640 x 512 with 300 mm + zoom	22 kg class	Targeting and designation

Four dual-sensor payloads

From a 260 g entry head to a 5 kg turret with continuous thermal zoom and 9.5 km ranging.

HQ · 2-axis · EO + IR

HQ-64DA

The lightest dual-sensor head in the range — 2K daylight plus thermal on 260 g.

Visible: 2688 × 1520, 8.5 mm fixed
Thermal: 640 × 512, 19 mm fixed
Laser: —
Weight: ≤260 g

HQ · 3-axis · IR

HQ-125S

A thermal-only head with a 1280 × 1024 sensor — the highest thermal resolution in the series.

Visible: —
Thermal: 1280 × 1024, 50 mm fixed
Laser: —
Weight: ≤1 kg

XQ · 2-axis · EO + IR + LRF

XQ-170TC

1280 × 1024 thermal on a 75 mm lens — the long-range imaging workhorse of the pod range.

Visible: 1920 × 1080, 30x zoom 4.3 – 129 mm
Thermal: 1280 × 1024, 75 mm fixed
Laser: 50 m – 5 km (± 1 m)
Weight: ≤2.8 kg

XQ · 2-axis · EO + IR + LRF

XQ-200T

A continuous-zoom thermal channel from 40 mm to 220 mm plus 9.5 km ranging on a 5 kg pod.

Visible: 1920 × 1080, 30x zoom 4.3 – 129 mm
Thermal: 640 × 512, continuous zoom 40 – 220 mm
Laser: 50 m – 9.5 km (± 1 m)
Weight: ≤5 kg

Compare the range

Model	Series	Axes	Configuration	Visible camera	Thermal imager	Laser rangefinder	Weight
HQ-64DA	HQ series	2-axis	EO + IR	2688 × 1520, 8.5 mm fixed	640 × 512, 19 mm fixed	—	≤260 g
HQ-125S	HQ series	3-axis	IR	—	1280 × 1024, 50 mm fixed	—	≤1 kg
XQ-170TC	XQ series	2-axis	EO + IR + LRF	1920 × 1080, 30x zoom 4.3 – 129 mm	1280 × 1024, 75 mm fixed	50 m – 5 km (± 1 m)	≤2.8 kg
XQ-200T	XQ series	2-axis	EO + IR + LRF	1920 × 1080, 30x zoom 4.3 – 129 mm	640 × 512, continuous zoom 40 – 220 mm	50 m – 9.5 km (± 1 m)	≤5 kg

Specifying a dual-sensor payload

Decide which channel is primary

If the mission runs at night or looks for heat, the thermal channel is primary and the visible channel is confirmation. Size the thermal detector and lens first, then choose the visible channel to match. Doing it the other way round produces payloads with excellent daylight imagery and unusable thermal reach.

The numbers that matter on the thermal side

Detector resolution: 640 x 512 or 1280 x 1024.
Lens focal length, fixed or continuous zoom, which sets the night detection range.
NETD at or below 40 mK for small temperature differences.
Frame rate, which decides whether a moving object can be tracked.

Boresight and drift

Ask how the two channels are aligned, whether the alignment is verified after temperature cycling, and what the tolerance is expressed in: pixels, milliradians or microradians. A payload that quotes no figure has not been measured.

Dual-sensor work connects to the system and product pages.

Electro-optical systemsThe system view above the sensor pair.Read more →
EO sensorsVisible channel formats and lens matching.Read more →
Thermal camerasThirteen thermal configurations in the range.Read more →
EO/IR camerasTwelve boresighted dual-sensor payloads.Read more →

Engineering detail

Why boresight tolerance is expressed in pixels

An operator judges alignment on screen. A tolerance of 0.5 milliradians is invisible at 8 mm focal length and obvious at 129 mm, because the same angular error covers more pixels as the field narrows. Specifying the tolerance in pixels at the operating focal length is the honest way to quote it.

Uncooled or cooled

Uncooled detectors run at ambient temperature, weigh less and need less power, which is why they dominate UAV payloads. Cooled detectors in the mid-wave band reach further in dry air at the cost of weight and a cryocooler. Most airborne missions are better served by a larger uncooled detector and a longer lens than by a cooled detector of the same weight.

Recording both channels

Storage and bandwidth are cheap compared with a lost sortie. Recording visible and thermal at the same time means the frame that mattered is available in whichever band showed it, and the two files can be reviewed side by side after landing.

Designed and manufactured by HITS

Optics, servo hardware, stabilisation firmware and the AI tracking module are developed in house, and every unit is assembled, calibrated and environmentally tested on our own line before it ships.