FROM OBSERVATION TO UNDERSTANDING
A better image starts
with a better question.
What is emissivity?
Emissivity describes how effectively a surface emits infrared energy compared with an ideal emitter at the same temperature. A thermal camera uses that emitted radiation as part of its temperature calculation.
Is 0.95 always the right emissivity?
No. Many painted and nonmetallic surfaces may be relatively high-emissivity, while polished metals and other reflective surfaces can behave very differently. The correct value depends on the target and the measurement method.
What is reflected apparent temperature?
A thermal camera can receive infrared energy reflected from the surroundings as well as energy emitted by the target. On low-emissivity surfaces, that reflected component can dominate what the camera sees.
Why does shiny metal look hot or cold in a thermal image?
Often because it is reflecting its thermal surroundings. A bright apparent temperature on polished metal may represent reflected radiation rather than the actual surface temperature.
Why is my thermal camera showing the wrong temperature?
Before blaming the instrument, examine emissivity, reflected temperature, focus, distance, target size, viewing angle, atmospheric conditions and whether enough detector pixels are actually on the target.
THE FIELD REFERENCE
TAKE THE NEXT QUESTION FURTHER
The Environment
Decides.
The Discipline of Defensible Thermography
Explore the physics that makes a temperature meaningful—or misleading.
Environmental history. Measurement physics. Competing explanations. The book explores the discipline behind acquiring, interpreting and defending thermal evidence.
- Before the missionPlan the question and the conditions.
- In the fieldReconsider when the scene changes.
- At the deskExamine what your evidence supports.