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SpectRx NIR Technology
information. This limits the number of moving components and pro- 493
vides a more reliable observation geometry. This is a further advan-
tage that can be added to the three “classic” advantages of FFT spec-
trometry over dispersive spectrometry:
• Multiplexing⎯all wavelengths fall on the detector at all
times
• Throughput⎯the aperture versus resolution limitation is
reduced
• Wavelength accuracy⎯the internal laser ensures stability in
ppm levels
In practical terms, the superiority of the FTIR spectroradiometer
can be seen most clearly in its high spectral resolution and broadband
capability.
The throughput, and thus the sensitivity, of the SpectRx FT Spec-
troradiometer is superior to that of a dispersive spectroradiometer—a
tendency that increases as spectral resolution is increased.
SpectRx FT spectroradiometer has inherent broadband capability.
When no optical filtering is used, the spectral bandwidth of the
instrument is the same as that of the detector used, for example 1 to
5.5 μm in the case of an InSb detector. It is also important to note that
there is no time penalty when acquiring a large bandwidth as opposed
to a narrow one.
Finally, the most useful characteristic of a SpectRx FFT spectrora-
diometer is its flexibility. The spectral resolution of the SpectRx FFT
Spectroradiometer can be instantly changed by computer. Also,
because of the complete separation of spectral information (performed
in the time domain) and spatial information (performed in the spatial
domain), the “Field of View” configuration of the instrument can be
changed in the field, simply by changing telescope modules.

10.5.1 Software Philosophy
Multiple software modules are developed with the SpectRx systems,
including two vital modules: the C++/Visual Basic Windows-based
acquisition module—Research-Acquire; and a Windows-based data
manipulation and processing module.
The Research-Acquire routine provides the functions necessary
for general SpectRx applications. It includes functions to acquire raw
interferograms, uncalibrated spectra, radiometric reference spectra using
calibrated sources, and calibrated spectra. It also acquires Fast Fourier
Transformation—Near Infrared FFT-NIR or FFTIR-type data in trans-
mission, such as raw, reference, transmittance and absorbance spec-
tra, which can be useful for quick diagnostics in such things as the
measuring of stability, the transmission capacity of optical filters, and
a general examination of the spectral content of the source observed.