How much kaolinite could contain my soil sample?

Now that we have our reference kaolinite near infrared spectrum stored  and studied, we can acquire a we spectrum (unknown) and compare it with the reference material trying to have a clear idea od how much kaolinite could contain. Soils high or very high in kaolinite have disadvantages for agriculture, so looking to the comparison we can take some actions.

We are going to use one spectrum (the first one) from the soilspec package, where we have a data set called:  "rutherglenNIR" which is a subset of soil spectra samples from the Rutherglen Area.

First, we compare the kaolinite reference material spetrum with the spectrum of the unknown sample:

And we have a look to the kaolinite featured spectra region, so we can trimm the spectrum and start to make some comparissons after the normalization processes:

Normalization Step 1 :

Normalization Step 2:

Now we can compare the areas, and  get the conclussion that the unknown soil sample has a relative low content of kaolinite compared to the reference spactrum.

Of course we can confirm this with numbers such as Area, Relative Depth,....

Reference Materials (Kaolinite)

 In the spectra of reference materials there are two kaolinite spectra, one is called kaolinite_114 and the other kaolinite_113. We can take them apart and overplot them in the same scale to see the differences:

One of the characteristics of the kaolinite spectra is the double is the doublet spectra feature in the 2200 nm region, so we can trim this region, take it apart and keep it as a diagnostic spectral feature to compare with our soil samples to determine if our soil samples contain kaolinite and in what proportion.

We can trim the zone of interest for the kaolinite and make calculations for the Area, Depth, Slope, etc. After we calculate the same values for our soil sample and compare the results to estimate  how much of the reference material (in this case kaolinite) could contain our soil sample.

In the next figures we see how the spectrum is trimmed, normalized, and the area is calculated:

Reference Materials for Soil in soilspec package.

 

How "spectra2colour" function from "soilspec" get the colour predicted values

 In the soil spectrum the colour regions are defined, and the mean reflectance value obtained for each. With the three values (RGB) we obtain a colour prediction when proyected on the RGB cube space.

 

Colour predictions with soilspec package

 The soilspec package comes with a data set called specSoilCol, which has 12 spectra of four types (A, B, C and D) of soils at three deferent depthss (Horizons 1, 2 and 3). 

The spectra is a Reflectance scale:

Now we use the function spectra2colour in the soilspec package and we obtain the predicted colours for the 12 samples that we have to compare with the real colours of the samples.

Normally the soil in the Horizon 1 is darker due to a higher quantity of organic matter.