Through specific applications examples with sample images, this presentation introduces you to the basics of infrared (IR) imaging technology. You will learn that in the IR-world things look different and that you can visualize with an IR camera things which you cannot see with your own eyes. To understand “the why”, we touch on some basics about IR radiation and corresponding imaging sensor technologies.

1. Infrared Imaging: Seeing the Invisible
Part Two:
Camera Technology

2. Structure of an Infrared Camera
Optics
&
Filters
Firmware
Sensor
Sensor Cooling
incl. digitization
(optional)
Background
Correction
Gain/Offset
Correction
(NUC)
Defect
Pixel
Correction
• Feature Control
Interface and
• Image Correction
I/O Control
• Temperature
Calibration
Temp.
Calibration
via
LUT
Drift
Compensation

3. Optics & Filters

4. Image with / without SWIR Lens
SWIR optimized lens
Non-optimized lens

5. MWIR and LWIR Optics
• For wavelengths > 2.5 µm that glass
would block
• Special & costly optics: germanium and
silicon
• Further materials available for high
transmittance
• No standard mounts

6. Filters for SWIR Wavelengths
without filter
with filter
• Filters are used to increase
contrast
• They often correspond to the
absorption spectra of specific
substances.
Example: Water filter 1450 nm

7. How the Water Filter Works
Water color
black
narrow bandpass (1450nm)
dark
• Filters are used to
increase contrast
• They often correspond
to the absorption
spectra of specific
substances.
clear
Visible light
IR SWIR (InGaAs)

8. Sensor Technology

9. Quantum vs. Thermal Detectors
• Quantum Detectors
• Sensitivity dependent on wavelength
• Require cooling to improve S/N ratio especially for
wavelengths beyond 1µm
• High detection performance and fast response
• Thermal Detectors
• Detect IR energy as heat
• In general do not require cooling
• Have a slow response time and detection capability

10. Spectral Sensitivity
for Typical IR Detector Types
V N
I I
S R
LWIR
MWIR
SWIR
Quantum
Detectors
MCT
QWIP
InSb
InGaAs
Si-based
CCD/CMOS
Thermal
Detectors
µ-Bolometer
1
2
3
4
5
6
7
8
9
10
11
12
13
14 [µm]

11. Infrared Detector Selection
Min. Object
Temperature
(self-emissive)
Sensor Type
Sensor wavelength
[µm]
Operating
Temperature
800 °C
CCD/CMOS [Si]
<1
300 K (27 °C)
250 °C
SWIR [InGaAs]
< 1.7
300 K (27 °C)
0 °C
MWIR [InSb]
<6
77 K (-196 °C)
-70 °C
LWIR
[µBolometer]
< 14
300 K (27 °C)
-150 °C
LWIR [MCT]
< 20
77 K (-196 °C)
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

12. Cooling Methods
• Cryogenic Cooling
– dry ice or liquid nitrogen
– mechanical cooling using Stirling
elements
• Thermoelectric Cooling (TEC) using
Peltier elements
– Lower cost
– Solid state – no vibration

13. SWIR Sensor Technology
• Quantum detector
Working principle:
Absorption of photons that
elevate the material’s
electrons to a higher energy
level, so that they can be
counted
• Hybrid array:
IR detector, Si readout
Indium bumps
on each pixel
of array and
readout IC

14. µBolometer Sensor Technology
• Thermal detector
Working principle:
Detection of electrical
resistance changes in a
thermally insulated
absorber material (VOx, a-Si)
• Hybrid array:
IR detector, Si readout
Spectral range:
8 ..14 µm i.e. for LWIR

15. Comparing Camera Performance
• Noise Equivalent Temperature
Difference [NETD]: A measure of
detector sensitivity; influences
precision of temperature
measurement
– Measured in °C or K
– 10 mK – 200 mK typical
• Is equal to temperature
difference which would produce
given noise
Influencing physical variables:
thermal time
constant
f-number
temperature
NETD

16. Various Heat Sources Cause Drift
• Heat comes from:
Scene / object of interest
Lens
Camera housing
–
FPA
–
–
–
Optical
lens
Sensor (FPA)
Heat can´t be “blocked” like visible light
 For temperature measurement, corrections
for the undesired heat effects are essential



17. Image Processing

18. Closer Look at SWIR Sensor Image
• Nonuniformities
• Defect Pixels
• Incorrect flipchip bonding

19. How an Image is Processed
1. Original image of an
uncooled SWIR sensor
2. With Gain-Offset
Nonuniformity Correction
(aka NUC)
3. With Error Pixel
Correction

20. Influence of Exposure Time
@20ms Exposure
@100ms Exposure
after NUC
@40ms Exposure
@100ms Exposure

21. Effect of Sensor Temperature
1. Sensor Temp. +40°C
@100ms Exposure
2. Sensor Temp. -11°C
@100ms Exposure
4. Including NUC
5. Including Defect
Pixel Correction
3. @800ms Exposure

22. Allied Vision Technologies GmbH
Taschenweg 2a
07646 Stadtroda, Germany
Tel.: +49 36428 / 677-0
Fax: +49 36428 / 677-24
info@alliedvisiontec.com
www.alliedvisiontec.com
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