© 2007 ASD Inc. 49 TerraSpec® User Manual
Appendix B Reference Information
B.1 Frequently Asked Questions (FAQ)
B.1.1 What is a spectrometer?
Spectrograph - An optical instrument for forming the spectrum of a light
source and recording it on a film. The dispersing medium may be a prism or a
diffraction grating. This term was common prior to the digital age. ASD
instruments do not use film.
Spectrometer - An optical instrument which uses detectors other than
photographic film to measure the distribution of radiation in a particular
wavelength region. All ASD instruments are spectrometers.
Spectroradiometer - An optical instrument for measuring the radiant energy
(radiance or irradiance) from a source at each wavelength throughout the
spectrum. A spectroradiometer is a special kind of spectrometer.
Note: Only the FieldSpec spectrometer is configured as a
spectroradiometer. The reason is that the fiber optic cable
significantly affects the calibration required to measure radiance. The
FieldSpec instrument has a fixed fiber optic cable routed directly
through the front panel to the internal spectrometers, while the other
ASD spectrometers are designed to detach and even interchange fiber
optic cables. To be meaningful, radiance measurements with
non-FieldSpec instruments would have to be performed using the
same fiber optic cable and the same connector orientation
of the plugged in fiber optic cable as the factory calibration.
The SWIR component of the ASD spectrometer is a scanning spectrometer,
while the VNIR component is an array spectrometer.
To Next Page
Loading...