"Averaging over wavelengths is used to reduce the number of
wavelengths or to smooth the spectrum. Modern spectrophotometers
typically have an optical resolution beyond 10 nm,
whereas a 10 nm resolution is often sufficient for most applications.
Also, most spectrophotometers provide a better spectral
resolution (often 1–2 nm) than the actual optical resolution;
while this certainly increases statistical processing time it does
not improve the information content of the spectra. Further,
below 1100 nm the bandwidth of absorption peaks is typically
larger than 40 nm (Greensill et al., 2001, and references therein).
Nicola¨ı et al. (2006a) artificially inflated NIR reflectance spectra
of apple with a 2 nm resolution tenfold to 0.2 nm resolution; arti-
ficial reflectance values between two neighbouring wavelengths
in the original spectra were obtained by linear interpolation,
and Gaussian noise was added. The accuracy of the corresponding
PLS model was very low but increased by removing
redundant high resolution information by means ofwavelet compression.
The best results were obtained with compression ratios
of 20–30, loosely corresponding to a wavelength resolution of
about 5 nm."
(Nondestructive measurement of fruit and vegetable quality
by means of NIR spectroscopy: A review
Bart M. Nicola¨ı, Katrien Beullensa, Els Bobelyna, Ann Peirs ,
Wouter Saeys , Karen I. Theron , Jeroen Lammertyna
Postharvest Biology and Technology 46 (2007) 99–118)
"Resolution is one of the measurement parameters involved in obtaining spectra with FTIR.
The resolution can be set to values such as 16 cm-1, 8 cm-1,
4 cm-1, or 2 cm-1. It indicates the degree of fineness of
the data obtained by measurement (i.e., the minimum peak interval that can be
distinguished). For example, if 4 cm-1 is selected, spectra
will be obtained at intervals of approximately 2 cm-1. To obtain
sharper spectra (i.e., spectra with a higher resolution), a value such as 2 cm-1 or
1 cm-1 is set.
In fact, although this works for gaseous samples, there are cases with solid and liquid samples where the resolution of the data obtained does not improve even if a higher resolution is set. This is because the molecules of the solid or liquid are influenced by other molecules around them, causing the actual peaks to broaden.
Also, if the resolution is increased, a smaller aperture is selected in the way described later, and the intensity of the light entering the detector is reduced, increasing the relative amount of noise in the spectra. Therefore, it is undesirable for the resolution to be increased more than necessary.
For this reason, the resolution is usually set to approximately 4 cm-1 for
solid and liquid samples, and to approximately 1 cm-1 or 0.5 cm-1 for
gaseous samples. On some occasions, a low resolution is set for gaseous samples
if the purpose is quantification."In fact, although this works for gaseous samples, there are cases with solid and liquid samples where the resolution of the data obtained does not improve even if a higher resolution is set. This is because the molecules of the solid or liquid are influenced by other molecules around them, causing the actual peaks to broaden.
Also, if the resolution is increased, a smaller aperture is selected in the way described later, and the intensity of the light entering the detector is reduced, increasing the relative amount of noise in the spectra. Therefore, it is undesirable for the resolution to be increased more than necessary.
(http://www.shimadzu.com/an/ftir/support/tips/letter8/tech.html)
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