Download TESTING THERMAL IMAGERS - Practical Guide

0ºC to 100ºC)
is too narrow for calibration of measurement thermal imagers
designed for non-contact temperature measurement of targets of temperature
variable from about -20ºC to about 300ºC (sometimes up to 1000ºC).
There are on the market some differential blackbodies of extended temperature
range from about -15ºC up to about 150ºC-180ºC [24,30]. Such blackbodies can
be used for calibration, even more for recalibration, of measurement thermal
imagers optimized for temperature ranges no more than only slightly bigger than
the absolute temperature range of these blackbodies. However, upper limit of
temperature range of most thermal imagers is typically much higher than 180ºC.
Therefore several blackbodies of wide combined temperature range are needed to
carry calibration of most measurement thermal imagers.
temperature chamber
thermal
imager
black
body
Fig. 4.25. Concept of calibration of measurement thermal imagers.
4.3.3 Boresighting to a reference optical/mechanical axis
Boresighting is a process to align optical axis of a single system or a series
of optical or electro-optical systems with a certain reference optical axis
or mechanical axis.
Basically the aim of boresighting of a thermal imager is to achieve a situation
when:
a) optical axis of the thermal imager is parallel to axis of other electro-optical
surveillance systems (the case when the thermal imager is a part of a bigger multisensor surveillance system),
b) optical axis of the thermal imager is parallel to a reference mechanical axis.
In other words the aim of boresighting process is to achieve a situation when:
a) all subsystems of bigger electro-optical imaging systems are looking into
the same point (assumption: the distance is hundreds times bigger than the focal
length of the optics of the subsystems),
b) an imaging system (the thermal imager) is looking at a point of exactly known
coordinates relative to the reference mechanical axis).
When the boresighting process is not carried out properly we can get a situation
when:
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