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2.4 Sensor XML Files
The specifications of the hyperspectral filters are not exactly the same for every sensor due to
variations in the production process. For every camera, there are corresponding XML files that
detail the calibration values. The structure of the XML file is described in section 1.5.1"Sensor
calibration files" of [TR_hyperspectral_sensors] and in more detail in
[TR_hyperspectral_calibration]. You should have received the calibration files corresponding to
your camera by e-mail. If you have not received them then please request the files by sending
an e-mail to support@photonfocus.com and specifying the serial number of the camera.
Accurate measurements can only be obtained if the information in the calibra-
tion file is take into account.
The images of the camera are vertically flipped and therefore the calibration
files can be applied without modification.
2.5 Lens and Filters
It is important that a suitable lens is used. The most important aspects of the lens choice are
described in section 2.1 of [TR_hyperspectral_sensors].
Factors to consider are
•
An appropriate anti-reflective coating: must have good transmission in the wavelength
range of choice
•
Lens should be image side telecentric
•
F-number of the lens: use a small F-number (i.e. F/2.8) to improve the transmission and
have an accurate spectrum.
•
Small focus error in the sensor spectral range: apochromat or superapochromat lenses are
most suitable
Rejection filters must be used to retain only the wavelengths in the sensor's active range used
for hyperspectral imaging. The filters reduce the spectral leaking and they are needed to
obtain the corrected reflectance values.
Examples of lenses and filters for all camera models can be found in the document
[TR_hyperspectral_sensors] and some practices are listed here [How to get started]
2.6 Spectral and Reflectance Correction
The document [TR_hyperspectral_sensors] describes why second order harmonics are generated
and how they can be corrected.
It is very important to remind that only after spectral correction, the images have
absolute reflectance values.
The calibration process for the raw images is the following:
MAN068 10/2019 V1.3
2.4 Sensor XML Files
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