Infrared Imaging: Seeing the Invisible

Part One:

Physics

What Can You See in These Images?

NIR / SWIR LWIR Visible

Electromagnetic Spectrum:

A Helpful Taxonomy

IR Radiation - Characteristics

• Invisible to the human eye … but not to certain sensors

• Caused by the vibration and rotation of atoms and molecules

• Emitted from all objects with a temperature above 0 K (-273 °C)

• Interacts like other electromagnetic radiation, including:

Reference temps: White hot steel ~1200 °C Melting point of aluminum 660 °C Water boils at 100 °C Uncooled camera at 38 °C Human body at 37 °C, radiates at ~ 10 μm Water freezes at 0 °C

IR Energy vs. Object Temperature

Measuring Temperatures

• Emissivity: ratio of actually emitted energy to energy radiated by a black body at same temperature

– Black body by definition ɛ = 1

– In general the duller and blacker, the closer to ɛ = 1

– The more reflective, the less emissive

• Knowing emissivity permits absolute temperature measurement

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