Thermography involves the graphical representation of temperature distribution on surfaces using infrared cameras. It detects electromagnetic radiation emitted from objects based on their temperature, rather than detecting temperature directly. To accurately measure temperature from radiation readings, cameras need information about the object's emissivity and reflected temperature, as real objects do not emit and absorb radiation like ideal blackbodies. Key specifications for infrared cameras include thermal sensitivity, field of view, and instantaneous field of view, which determine the camera's ability to detect small temperature differences and resolve objects at varying distances.

1. General Thermography
Testo Product Management
02/05/2016 Author

2. 2/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Thermography is the graphical representation of the
temperature distribution on a “solid” body
=> We always only see the surface!
What is this thing called Thermography?

3. 3/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Thermographers see the world in a
different perspective.....
What is this thing called Thermography?

4. 4/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Visible light...

5. 5/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
... and infrared light:

6. 6/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
 Each body, that is warmer than -273.15 ºC, emits electromagnetic
radiation.
 An IR - camera doesn‟t detect temperature but infrared - radiation.
 The camera doesn‟t emit radiation.
 The possibility of a thermal imager to “see through” materials is very
limited.
Basics of Thermography

7. 7/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
•
•
•
The electromagnetic spectrum
visible light
Visible
Short wave
Long wave

8. 8/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Transmission curves for the atmosphere

9. 9/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Planck‟s curves

10. 10/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Radiation and temperature
The Thermal Imager doesn‟t measure temperature but radiation!
For the calculation of the correct temperature a Thermal Imager needs
certain information.
Most of the information the camera gathers by itself, however, some
parameter must be provided by the user.

11. 11/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
The two most important parameters of the measured object are:
Reflected Temperature –
temperatures that are reflected by the measured object.
Emissivity –
describes the capability of the inspected surface to emit
radiation.
Parameter, that must be provided by the user....

12. 12/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Blackbody (perfect emitter)
Absorbs and emits 100%
(Emissivity = 1)
 Real body
A part of the radiation is
reflected as well as transmitted
(Emissivity < 1)
The inspected object

13. 13/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Reflection, Transmission, Emission
=> Kirchhoff„s Law

14. 14/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Reflection, Transmission, Emission
Most of the materials are not permeable for IR-radiation.
In this case τ = 0 and
ρ + τ + ε = 1 equals to ρ + ε = 1
=> Conclusion: The lower the emissivity, the higher is the share of
reflected
radiation and, therefore, the more difficult is an exact temperature
measurement.

15. 15/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
The emissivity can vary with the surface condition, the material
and the temperature.
With long-wave IR-cameras the emissivity is not depending on
the colour of the inspected object.
Most of the construction materials have an emissivity between
0.85 und 0.96.
Emissivitiy tables can be used. However, these values should be
used only as a guide.
It is also possible to determine the emissivity:
Reference measurements with contact thermometers or surfaces
where ε is known.
Reflection, Transmission, Emission

16. 16/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
IR
Optic
2 dim.
Detector-
Matrix
FPA-Camera
(Focal Plane Array)
I
vertical
scanning
Single
detector
horizontal
scanning
Scanner-
Camera
II
IR – camera systems

17. 17/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Thermal sensitivity
 The most important criterion for building inspections
is the thermal sensitivity or NETD (Noise Equivalent
Temperature Difference) of a thermography system.
 NETD describes the ability to resolve small
temperature differences.
 The NETD in professional building thermography
should not be above 100mK (or 0,1°C).

18. 18/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Field of View
The Field of View describes the
area seen by the detector
The Field of view is independent of:
 the distance to the object
The Field of view is dependent on:
 The size of the array
 The lens used
 The larger the field of view, the more fits on one image at the same
distance to the object.
160 Pixel
120Pixel
32°
24°

19. 19/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Instantaneous Field of View
 Instantaneous Field of View describes the field of view of one single pixel.
 The unit of IFOV is mrad.
160 Pixel
120Pixel
1,3 mrad
1m
1,3mm The smaller the instantaneous field of view, the better is
the geometrical resolution of the system.

20. 20/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Instantaneous Field of View
IFOVgeometric : smallest object that can be detected by
the system at a given distance.
IFOVmeasured : in real life the information of only one
pixel is not sufficient to get a precise
measuring value.
Therefore as a rule of thumb is used:
IFOVmeasured = 3 * IFOVgeometric

21. 21/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Distance and smallest object
Distance D Smallest object
standard lens (32°)
Smallest object
telephoto lens (12°)
0,1 m 1,0 mm -
0,3 m 3,1 mm -
0,6 m 6,3 mm 2,4 mm
1 m 10 mm 4 mm
2 m 21 mm 8 mm
10 m 105 mm 39 mm
Attention: all values are based on edge lengths of 3x3 Pixel!

22. 22/22Testo AG, General Thermography (1.0), 1000len-3956, 02.05.2016, Confidentiality 1
Power Point Template