Ocean Optics SpecLine Offline Spectroscopy - Manual (Page 12)

3: Operation
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wavelength and signal. The reference point for stretching and compressing the wavelength is
always the smallest data value. This dialog box remains available until you close it.
2. If the line cursor function is activated, you can change the wavelength at the position of the line
cursor with the menu command Edit | Adjust Wavelength. Execute this command twice to
change the value again, resulting in an adjustment of the dispersion of the spectra. A detailed
description of this function is given in the Adjust Wavelength at Line Cursor dialog box.
Smoothing Data
SpecLine offers several filter functions to smooth noisy data. The Edit | Smooth Data menu command or
the
button opens the Data Smoothing, dialog box in which you can select an appropriate filter
function:
 The Fourier filter (according to the Wiener method) is a low-pass filter, which lets through low
frequencies up to a specified limit and cuts off all frequencies above the limit. The filter function
is a superposition of two functions, which are extracted from the signal range and the noise range
of the data. This filter is applied best to data with white noise.
 The polynomial filter (according to the Savatzky-Golay method) calculates a weighted average
value with the specified polynomial order for a data point from the neighboring points. The
smoothed data is displayed as a new spectrum in the diagram and in the File List dialog box, and
is labeled “smoothed”.
Comparing Spectral Data
For a comparison of spectral data, up to twelve different spectra can be opened and adjusted in a single
diagram window. These spectra can be in different formats.
The File | Overlay File menu command or the button in the tool bar opens a new spectrum and
displays it in the already existing diagram window.
To select a spectrum for evaluation, check the corresponding file name in the dialog File List dialog box.
All functions are available for all spectra.
The File | Close Overlay File menu command or the button in the tool bar closes the selected
spectrum and the entry in the File List dialog box is deleted. If you press the Del key in the File List
dialog box, the file is also closed.
Arithmetic of Spectra
For comparing spectra, it is often very helpful to combine different spectra by arithmetic functions (+, -.
*, /). If at least two spectra are overlaid in the diagram window, you can open the Combine Spectra
dialog box by selecting the Edit | Arithmetic of Spectra menu command or by clicking the
button in
the tool bar.
Select the spectra to combine from the file lists, and then select the operation. You can choose between
addition, subtraction, multiplication and division.