Glossary

The visible-light channel of a multi-sensor system: a daylight camera working in roughly the same band the human eye sees. It gives colour and fine detail in good light and loses usefulness as light falls away.

See alsoThermal imagerDRI (detection, recognition, identification)

A camera that forms an image from emitted infrared radiation rather than reflected light, so it works in total darkness, through smoke and against camouflage. It sees temperature difference, not colour.

On this siteThermal Imagers

See alsoLWIR (long-wave infrared)MWIR (mid-wave infrared)

The 8–14 µm infrared band. LWIR detectors are usually uncooled, which makes them smaller, cheaper, quieter and instantly available at power-up; they cope better with smoke and dust than MWIR.

See alsoMWIR (mid-wave infrared)Uncooled detector

The 3–5 µm infrared band. MWIR detectors are cooled, which costs size, power, noise and a cool-down wait, and buys longer range and finer thermal contrast in hot, dry, clear conditions.

On this siteChoosing the Thermal Channel — Uncooled LWIR or Cooled MWIR

See alsoLWIR (long-wave infrared)Cooled detector

An infrared detector held near cryogenic temperature by an integrated cooler so that its own thermal noise does not swamp the scene. It reaches full performance only after a cool-down period and the cooler is a wear item with a rated service life.

See alsoUncooled detectorMWIR (mid-wave infrared)

A microbolometer array that works at ambient temperature. No cooler means no cool-down wait, no acoustic signature and a longer maintenance-free life, at the cost of sensitivity compared with a cooled detector.

See alsoCooled detectorLWIR (long-wave infrared)NETD (noise-equivalent temperature difference)

The smallest temperature difference a thermal detector can distinguish from its own noise, quoted in millikelvin. A lower figure means the sensor separates a target from a background of nearly the same temperature. It describes the detector alone, not what an operator can actually see.

See alsoMRTD (minimum resolvable temperature difference)

The temperature difference at which a human observer can resolve a standard bar pattern through the complete system — detector, optics and display together. Unlike NETD it is measured with an observer in the loop, so it describes the system rather than the component.

See alsoNETD (noise-equivalent temperature difference)

The centre-to-centre distance between neighbouring detector elements, in micrometres. A smaller pitch packs the same pixel count into a smaller sensor, which allows shorter, lighter optics for the same field of view.

Calibration that removes the fixed pattern caused by each detector element responding slightly differently. Without it the image drifts towards a visible grid or blotching as the sensor warms. Automatic NUC does this without operator action, usually with a brief shutter event.

The angular width of the scene the sensor covers, in degrees. Wide field of view finds and tracks; narrow field of view identifies. Optical zoom moves between the two.

See alsoOptical zoomDRI (detection, recognition, identification)

Magnification achieved by moving lens elements, which narrows the field of view while keeping full sensor resolution. Digital zoom instead enlarges pixels already captured and adds no detail; only the optical figure describes real reach.

See alsoField of view (FOV)

Three ranges that describe what an imaging system can do with a target of a stated size: detect that something is there, recognise its class, and identify the specific object. The three distances differ by a wide margin, so a single "range" figure without the letter in front of it says little.

See alsoField of view (FOV)Thermal imager

A device that measures distance to a target by timing a laser pulse’s return. Its quoted range depends on target size, reflectivity and atmospheric conditions, so the figure is always tied to a stated test case.

See alsoLaser designator (LD)

A laser that marks a target so that a seeker on a guided munition can home on the reflected energy. Designators emit coded pulse trains so that several designators can work in the same area without a seeker following the wrong mark.

See alsoLRF (laser rangefinder)Pulse coding

The pattern of intervals between designator pulses, set to an agreed code so that a seeker accepts only its own designator. It is what keeps two designators from confusing each other in the same engagement area.

See alsoLaser designator (LD)

A two-axis mount that rotates a payload horizontally (pan) and elevates or depresses it (tilt). It is the mechanical link between a sensor and whatever the sensor has to look at.

On this sitePan-Tilt & Positioning Systems

See alsoGimbalRotator

A pan-tilt assembly whose axes carry the sensors inside the moving structure, so that the whole optical package is pointed and, in a stabilised gimbal, isolated from platform motion.

See alsoPan-tilt positionerLine-of-sight stabilisation

A single-axis positioner that turns a payload about one axis only, usually azimuth. Used where elevation is fixed or handled elsewhere in the system.

See alsoPan-tilt positioner

A precision angular positioning device, used where a payload must be set to an exact angle and held there rather than swept continuously.

Holding the sensor’s line of sight fixed in space while the platform beneath it moves. Quoted as a residual angle: the jitter that remains after correction, not the disturbance the system can absorb.

On this siteWhat a Line-of-Sight Stabilisation Figure Actually Costs

See alsoGimbalJitter

The small, rapid angular movement that remains on the line of sight after stabilisation. At long range a fraction of a milliradian of jitter translates into metres of movement on the target, which is why the figure matters more than magnification alone.

See alsoLine-of-sight stabilisation

Three different numbers that are often confused. Accuracy is how close a commanded position lands to the true angle; repeatability is how closely the axis returns to the same place on repeated attempts; resolution is the smallest step the axis can be commanded to make. A system can be repeatable without being accurate.

On this siteAccuracy, Repeatability and Resolution Are Not the Same Number

The lost motion in a gear train when the direction of travel reverses — the angle the input turns before the output starts to move. It sets a floor under pointing accuracy that no amount of encoder resolution can remove.

See alsoAccuracy, repeatability and resolution

The sensor that reports an axis’s angular position back to its controller. Its bit count sets how finely position can be known; a 22-bit encoder divides a full turn into just over four million steps.

See alsoAccuracy, repeatability and resolution

A rotating electrical joint that carries power and signal across a continuously turning axis, so the axis is not limited by a cable loop. Line count determines how many circuits can cross, and the assembly has a rated number of revolutions.

On this siteThe Axis That Never Stops: Slip Rings, Line Count and Service Life

Nominal torque is what an axis can deliver continuously without overheating; peak torque is what it can deliver briefly, for acceleration or against a gust. Sizing on the peak figure alone produces a positioner that stalls in steady wind.

A brake on each axis that holds position when drive power is removed, rather than relying on gear friction. It keeps a payload from drifting or falling under its own weight when the system is unpowered.

A multi-section column that raises a payload to a working height and collapses to a much shorter length for transport. Retracted height, extended height and payload are the three figures that decide whether one fits a platform.

On this siteMast Systems

See alsoPayload rangeWind load

The span of payload mass a mast or positioner is rated for. It is a range rather than a single maximum because the figure falls as height rises: the same mast carries less at full extension than part way up.

See alsoTelescopic mastWind load

The wind speed a mast is rated to withstand while extended and carrying its payload, usually stated together with a reference sail area. Without that area the speed figure cannot be compared between suppliers.

On this siteSizing a Mast — Payload, Height and Wind Are One Problem

See alsoTelescopic mastPayload range

A mast held upright by tensioned lines anchored to the ground. Guying lets a lighter structure reach greater height, at the cost of a larger footprint and a longer set-up.

See alsoTelescopic mast

A three-legged support that gives a payload a stable base on unprepared ground. Its rating depends on both the mass carried and the height at which that mass sits, because leverage grows with height.

On this siteTripods

A US defence standard describing environmental test methods — temperature, vibration, shock, humidity, rain, salt fog, sand and dust, altitude. A bare claim of compliance means little: what matters is which method, which procedure and at what severity the equipment was tested.

On this siteMIL-STD-810G — What a Qualification Claim Does and Does Not Prove

The US defence standard for electromagnetic interference: how much a device may emit, and how much it must tolerate, on its cables and through the air. It governs whether a system will work beside a radio rather than jam it.

See alsoEMI / EMC

Electromagnetic interference is the unwanted energy a device radiates or conducts; electromagnetic compatibility is the discipline of making devices coexist. Shielding, filtering and grounding are what turn one into the other.

On this siteIntegrating an EO/IR System on a Vehicle — Power, Bus and EMC

See alsoMIL-STD-461

A two-digit code for enclosure protection: the first digit is solid ingress, the second is water. IP65 means dust-tight and protected against water jets from any direction. It describes the enclosure, not survival of the electronics inside under shock or temperature.

The document that fixes how two subsystems meet — mechanical ICDs cover bolt patterns, envelopes and mass properties; electrical ICDs cover connectors, pinouts, voltages and grounding; software ICDs cover protocol, message formats and timing. Integration schedules slip when these are agreed late.

The vertical measure of 19-inch rack equipment; one U is 44.45 mm. A cabinet’s U size states how much equipment height it accepts, which together with depth decides what will physically fit.

On this siteAccessories & Integration Components