ASD Document 600541 Rev. G 52 TerraSpec® User Manual
www.asdi.com Appendix B Reference Information
Most of the measurements made by the instrument are ratios where such
values get cancelled out and become irrelevant.
It is far more important to keep the instrument from saturation and to ensure
the (baseline) white reference is fresh.
B.1.8 What are the units of radiance?
Radiance is the radiant power per unit source area per unit solid angle. This is
measured in Watts per square meter per steradian (W/m
2
/sr).
The TerraSpec spectrometer does not measure radiance, because this requires
radiometric calibration files which are dependent on the fiber optic cable and
its connection to the instrument. (The TerraSpec spectrometer can be used
with different accessories and fiber optic cables.)
The TerraSpec spectrometer measures only reflectance and transmission
measurements.
B.1.9 Can I post-process my data?
Yes. ViewSpec is one of many applications that can post-process your data.
Various software packages are available for chemometric model. The spectral
data can be imported into many different applications.
The complete specification of the ASD file format is available upon request.
B.1.10 Why do I see oscillations (sine wave) in my data?
Your light source may use AC power. A single SWIR band is about 100 ms. If
you observe five (5) or six (6) waves in a single SWIR, the AC light source is
the cause.
Waves can also occur if the lamp reflector and/or cover glass behave as a
white-light interferometer. Solution: remove the glass and/or use a more
diffuse reflector.
B.1.11 What are these upward or downward spikes in VNIR
data?
These result from artificial light sources, in particular fluorescent lights.
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