Special aspects of outdoor thermography

The IR radiation of the a clear sky is referred to as "cold sky radiation". In a clear sky, cold sky radiation (~ -50 to -60 °C) and warm solar irradiation (~ 5500 °C) are reflected during the day. In terms of area, the sky outstrips the sun, which means that the reflected temperature in outdoor thermography is usually below 0 °C, even on a sunny day. Objects heat up in the sun as a result of absorbing sunlight. This considerably influences the surface temperature – some even hours after the solar irradiation.

Tips and tricks in outdoor thermography

  • Ideally, measure in the early morning hours and/or under dense cloud cover. It should not be raining or snowing. Fog and strong winds are also unfavourable.
  • During the measurement, change your position in order to recognize reflections. Reflections shift, thermal anomalies of the measurement object stay in the same place – even when the angle of view is changed.
  • Avoid measurements close to very hot or very cold objects, or screen them off.
  • Avoid direct solar iradiation, even several hours before the measurement. Take cloud cover into consideration several hours before the measurement.
  • Do not measure if there is air humidity condensing on the thermal imager.
  • Do not measure in extremely contaminated air (e.g. when dust has been freshly disturbed).
Thermography with thermal imagers from Testo

Theoretical principles of thermography

Find out more in our compact tutorial on the physical principles of thermography. A real advantage, for example for setting the right emissivity for every surface.

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