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Emission, Reflexion, Transmission

Thermography: knowledge and practice

The radiation detected by a thermal imaging camera consists of the emission, transmission and reflection of infrared radiation emitted by the objects in the field of view of the thermal imaging camera.

Transmission (t)

Transmission is the ability of a material to let through (transmit) IR radiation.

A thin plastic film, for example, has a very high degree of transmittance - so if you want to use a thermal imaging camera to measure the temperature of a thin plastic film hanging in front of a house wall, you are not measuring the temperature of the film, but rather that of the house wall.

Most materials do not transmit IR radiation, so the transmittance of a material is usually almost 0 and can therefore be neglected.

Connection between emission and reflection

Measurement objects with high emissivity (ε ≥ 0.8):

  • Measurement objects with high emissivity (ε ≥ 0.8): have a low reflectance (ρ): ρ = 1 - ε

  • their temperature can be measured very easily with the thermal imaging camera

Measurement objects with medium emissivity (0.6 < ε < 0.8):

  • have an average reflectance (ρ): ρ = 1 - ε

  • their temperature can be easily measured with a thermal imaging camera

Measuring objects with low emissivity (ε ≤ 0.6):

  • have a high degree of reflectance (ρ): ρ = 1 - ε

  • Temperature measurement with a thermal imaging camera is possible, but you should question the results critically. Correct adjustment of the compensation for the reflected temperature is essential as it plays a large part in the temperature calculation

Thermografie in der Praxis

Erfahren Sie in unserem kompakten Tutorial wie in der Praxis aus theoretischen Grundlagen und der richtigen Wärmebildkamera aussagekräftige Wärmebilder werden.

Thermograhy in Practice