ASD Document 600541 Rev. G 59 TerraSpec® User Manual
www.asdi.com Appendix B Reference Information
Optimization depends on the response to light in a particular spectral region.
A well-optimized instrument will display between 20,000 and 35,000 raw
digital numbers, if the source is within the gain and integration time abilities
of the system. The magnitude of the VNIR raw DN will be directly dependent
on the light intensity.
The Spectralon blank should be used when optimizing and for taking a white
reference measurement.
Note: It is important that the position of the reference sample when taking a white
reference is as similar as possible to the position for capturing data from the
samples.
B.5 Spectrum Averaging (or Sample Count)
If signal levels are low, the only way to increase S/N is by reducing noise
through spectrum averaging. However, spectrum averaging takes more time
per spectrum.
B.6 Temperature Effects
The TerraSpec spectrometer instruments have thermo-electrically cooled
SWIR detectors (to -25 C), significantly reducing noise in those areas.
When the system fails due to extreme temperature, it will fail gradually but
the data won't make perfect sense. Shut down and let the instrument cool
before operating again.
You may also see the TerraSpec spectrometer saturate in the SWIR 2 region if
the instrument is still coming to equilibrium from a cooler environment to a
warmer environment. Frequent re-optimizations will address this problem
until the instrument comes to equilibrium.
The ASD applications provide a warning when the SWIR detectors are out of
thermal regulation.
B.7 Technical Support
If you have any questions or concerns, please contact ASD Inc. by phone, fax,
or email:
Phone: 303-444-6522 X-144
Fax: 303-444-6825
email: support@asdi.com
Web: www.asdi.com
ftp: ftp.asdi.com
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