10 Hardware of Near-Infrared Spectroscopy
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Fig. 10.6 The NIR spectral shape (a) and measured signals (b)
A typical waveform of the NIR spectrum is shown in Fig. 10.6a. The noise and
signals measured using the slow scan and FRS methods over a 1 min duration are
shown in Fig. 10.6b.
The signals and noise measured using the slow single scan and FRS methods are
shown in Fig. 10.7.
In the spectrum obtained with the slow single scan, as shown in Fig. 10.7a, the
noise is reduced by smoothing, similar to the time constant circuit. In Fig. 10.7b,
nine repeated data with noise measured using the FRS method are averaged. These
results are shown in Fig. 10.8, which indicate that the FRS scan method has a lower
noise level than the slow single scan.
Karl Norris succeeded in retrieving the spectra with low noise using the FRS
method and could estimate the ingredients of a material using statistics. This method
can be realized only using digitalized technology. Almost all the wavelength scanning
NIR spectrometers available in the market employ the above-discussed FRS method.
Fig. 10.7 The signals and noise measured using the slow single scan (a) and FRS (b) methods