Innovative Engineering and Consulting is a leading provider of thermal imaging and infrared imaging equipment for use in surveillance and tracking. As a service to our site visitors, the following glossary provides common definitions for the thermal imaging industry.

S T U V W X Y Z
A-I, J-R, S-Z

S

Sapphire: A material sometimes used as an optical element such as windows or lenses for NIR or MWIR systems. This material transmits well in the visible spectrum, but not at all in the LWIR region.

Short-Wave Infrared (SWIR): The spectral region from about 3-5 microns where some imaging systems operate.

Signal to Noise Ratio: A measurement of how strong the desired target signal is, compared to the level of background noise.

Solar Loading: Heating of objects by solar radiation. Solar loading will cause background objects (for example, trees or roadways) to appear warmer in the day than at night.

Spatial Resolution: The smallest spatial detail in an image that can be resolved. Spatial resolution is described in a variety of ways, including the IFOV or the Airy disk size (both previously defined). As a broad generalization, spatial resolution is sometimes described in terms of the number of pixels in the imager array (angular FOV of the lens and the range to the target must also be considered).

Stefan-Boltzmann Law: Describes the total rate of energy emission per unit surface area. The Stefan-Boltzmann Law is the spectrally integrated form of Planck’s Law (integrated over all wavelengths). This result takes the form E=sT4, where E is the rate of energy emitted per unit area, T is the absolute temperature in Kelvin, and s is a constant.

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T

Target Signature: The spectral, spatial, and thermal features that distinguish a target from the background.

Thermal Clutter: A condition in which multiple objects with thermal intensities similar to that of the desired target are in the same image as that target. Thermal clutter can make interpretation of images more difficult.

Thermal Contrast: The difference in thermal intensity between a target and the background.

Thermal Intertia: The tendency of a target to maintain its instantaneous temperature, even in the presence of an external temperature difference. Objects with large thermal inertia tend to heat up or cool down slowly.

Thermal Imager: An imager or camera sensitive to thermal (‘heat’) emissions, typically either MWIR or LWIR. Often, the terms “infrared imager” and “thermal imager” are used interchangeably.

Thermal Resolution: The smallest thermal difference in an image that can be resolved.

Thermoelectric (TE) Cooler: A cooling system with no moving parts (often used in LWIR systems) based on the Peltier effect, in which the junction between two dissimilar metals can be cooled (or heated) by applying a Voltage potential.

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U

Uncooled Detector: A detector (or imager) in which cryogenic cooling is not required. However, even “uncooled” detectors may still employ a TE cooler (defined previously).

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V

Very Long Wave Infrared: The spectral region from about 15 to about 100 microns. This region is generally not used for imaging systems.

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W

Water Vapor Signature: Water vapor in the atmosphere will absorb radiant energy in certain broad wavebands; this energy absorption is a function of both the amount of water vapor present, and the distance through the atmosphere that is being considered. While other spectral regions of water vapor absorptions exist (particulary in the NIR and MWIR regions), some of the strongest absorption bands exist between 5-7 microns.

White Hot: Infrared (‘thermal’) images are inherently grayscale images. Objects that give the strongest thermal signature can either be displayed as ‘black-hot’, meaning that the strongest thermal signature is displayed in black (or dark colors), or ‘white-hot’, meaning the strongest thermal signature would be displayed in white (or light colors).

Wien’s Law: The wavelength at any given temperature (for a blackbody) that emits the greatest amount of energy is given by Wien’s Law. This can be written as:

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Z

Zinc Selenide, Zinc Sulfide: Materials sometimes used for optical elements such as windows or lenses in infrared systems. Both materials are partially transmissive in the visible region, with a somewhat yellow color.

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