26 nov. 2017

Binning function in Prospectr package.

In the NIR spectrum there is a high correlation between most of the wavelengths, so we can reduce the spectra to allow more space between the wavelengths to manage better the spectra matrix.
The comercial softwares has the functions to do it, for example in Win ISI we can configure the wavelengths of a NIR 5000 which has 700 wavelengths if we configure the wavelengths selection to 1100-1498,2 , to 350 if we select 1100-2498,4. In this process we don´t lose relevant information for the development of a calibration, so it is applied quite often.
In the Prospectr there is the Binning, were we select the interval of wavelength selection in two ways:
X.bin <- binning(X, bin.size = 10)
In this case we keep one data point for every ten data points.

X.bin2 <- binning(X, bins = 50)
In this case we reduce the spectra matrix to 50 equal spaced data points.

13 nov. 2017

Bandwidth in the NIR Spectral Region

A question from Gabriela (thanks for your nice words about the blog) about the importance of the  resolution and bandwidth in the NIR instruments, takes me to see the paper from Karl Norris: "Limitations of Instrument Resolution and Noise on Quantitative analysis of Constituents with very Narrow Bandwidth in the NIR Spectral Region".
In this paper Karl Norris conclude that instruments with 10nm bandpass and a good signal to noise level ratio can measure constituents having a bandpass as narrow as 2 nm. It is not necessary to increase the resolution to detect them in case we increase the noise because the quantitative analysis become less accurate.
The experiment has been done with talc (2 nm bandwidth) in Avicel.

2 nov. 2017

Waiting for the instrument to be warming up to calibrate (DS2500)

Before to proceed to the instrument calibration in a DS2500 it is important to check that the instrument is stabilized fine. It is not enough to see that the instrument has pass the diagnostics, yo have to run several times the diagnostics and see that the "deltas" (difference between the nominal and founded values) for the wavelengths checked is stable and it finish drifting due to the warm up of the instrument.
In case that the deltas are close to cero for all wavelengths it is not necessary the calibration with the ERC, but if there is an slope in the values or a systematic difference it is better to calibrate to came with the values close to cero for all the wavelengths.
We don´t want to see drifts in the deltas as the instrument is warming up, and the ideal is to see random differences in the deltas for the several repetitions of the wavelength checks:

At this point we can continue with the calibration of the instrument (video).