Continuing with the tutorial, and using the NIRsoil spectra, this time I want to explain the concept of “Scan” and “Subscan”, being a Scan an average of certain number of Subscans (normally 32).
One subscan is normally noisy, and it is acquired, after a grating or an interferometer moves a complete cycle once, but normally we configure the software to take more scans and to get an average (can be 32 in the case of a grating instrument). After that we get an average of the 32 as the spectrum of the sample.
Every subscan is quite noisy, but because the noise is random, the average is much less noisy.
Let´s check with this simulation:
#We take one spectrum and repeated 32 times
#Now we add different spectra noise to each
subscans<-subscans + noise32
See in the figure the 32 subscans overplotted
#Now let´s do the average to get just one scan, the one we will use #as representative of the sample