ASD Document 600540 Rev. J
91
FieldSpec® 3 User Manual
www.asdi.com
Appendix B Reference Information
gains, offsets, and integration time will then appear in the lower left hand
corner. These parameters are set by the optimization routine and cannot be set
manually.
The
Gain Value
is the inverse of actual gain. A decrease in
Gain Value
will
produce a higher gain. The maximum
Gain Value
is 16. Under the low light
levels that create such a gain, small changes in
Offset
will translate into large
changes in dynamic range.
Offset
causes a downward shift (from Y=32,768 DN) in a SWIR spectrum
such that the max value of the spectrum and the minimum value of the
spectrum (Dark Current - off screen) are equidistant from the line y=32,768.
Under ideal conditions, where there's enough light, there will be about 32,768
DN of signal immediately after optimization, +/- 1,000. This means that
optimization “creates” about 16,000 DN of dark current and about 16,000 DN
of dynamic range. But this dynamic range will disappear with either a slight
increase in signal (if the signal started out low to begin with) or a slight
increase in dark current (increases with ambient temperature).
B.4
Light Source
When using ASD's ProLamp illumination source, the less intense the lamp
setting (knob on side of light source), the more diffuse (homogeneous) it will
be. An average spot size of reasonable homogeneity is about 10 cm at a 50 cm
lamp distance. Two lamps improve this geometry significantly, especially for
large targets. If lighting conditions are so poor that you are continually
re-optimizing, try optimizing with a brighter source:
•
For outdoor optimization, tilt the Spectralon® panel directly towards the
sun during optimization.
•
For enclosed illumination of targets requiring contact measurements, we
recommend ASD's High Intensity Reflectance probe.
•
Under low light conditions, consider using a reference panel < 99-100%
white and then post-process out the difference between the white and gray
reference in ViewSpec.
B.5
Optimization
The FieldSpec spectroradiometer must be re-optimized for:
•
Light changes.
•
Any atmospheric changes.
•
Outdoor solar changes at least every 10 to 15 minutes.
•
Indoor use every 30 minutes.
Summary of Contents for FieldSpec 3
Page 1: ...FieldSpec 3 User Manual ASD Document 600540 Rev J 2010 by ASD Inc www asdi com...
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Page 10: ...ASD Document 600540 Rev J x FieldSpec 3 User Manual www asdi com Notes...
Page 50: ...ASD Document 600540 Rev J 40 FieldSpec 3 User Manual www asdi com Chapter 5 Batteries Notes...
Page 90: ...ASD Document 600540 Rev J 80 FieldSpec 3 User Manual www asdi com Appendix A Troubleshooting...
