Home  Spectral Descriptors Predefined Spectral Descriptors |
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Spectral Descriptors - a Few Examples
Spectral descriptors may consist of something as simple as unprocessed intensities at a particular wavelength or mass, or maybe something as complicated as a mathematical function derived from several (if not all) intensities of a spectrum. The following table provides a few examples of spectral descriptors:
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Area: sum of intensities between two reference points with the baseline subtracted. The user has to specify the two reference points b1 and b2 to calculate the baseline. In order to avoid a baseline too sensitive to noise the parameter "Nb" defines the number of surrounding data points to obtain the baseline reference points.
The logarithm of the ratio of two peak areas (with the baseline subtracted) weighted by the area of the second peak. The baseline is calculated separately for each of the two areas. In order to minimize the influence of noise in the data, the parameter "Nb" defines the number of surrounding data points used to obtain the baseline reference point.
Centroid: the position of the centroid of the spectral line within the boundaries b1 and b2. The value of CEN may assume values between 0 and 1.
Raw peak: single unprocessed intensity at a particular wavelength or mass; the baseline is not subtracted. This kind of descriptor is most suitable for baseline corrected spectra.
Significant positive correlation (level of significance = 0.01) with a triangle template peak, multiplied by the signal area. Please note that this descriptor is set to zero if the correlation is either negative or not significant. The signal area is calculated by subtracting the area below the baseline from the integral between the reference points b1 and b2. The height of the triangular template peak is always 1.0, its shape is controlled by the points [b1,0], [a1,1], and [b2,0].