Performance of a Portable FT-NIR MEMS Spectrometer to Predict Soil Features

NIR spectrometers based on micro-electromechanical systems (MEMS) have become available in the market, with lower prices and smaller dimensions than traditional spectrometers. MEMS technology allows for miniaturizing and reduces the cost of the spectrometers, allowing a wider use for agricultural consultants, technicians, and scientific researchers. The aim of this work was to evaluate an innovative FT-NIR MEMS spectrometer, namely the Neospectra Scanner (NS), covering the range from 1350 to 2500 nm. The assessment was performed by comparing the accuracy of prediction of soil organic carbon, texture fractions, and total calcium carbonate, obtained with NS, with that of a standard full VIS-NIR spectrometer, namely the ASD-Fieldspec Fr Pro (AF). A dataset of 182 soil samples, dried and sieved at 2 mm, collected from 4 different agricultural areas of Italy were scanned with both devices. AF showed slightly higher R2 and lower prediction error (RMSEP) than NS for all soil features, but the accuracy of the two instruments can be considered comparable. Removing the 350-1350 nm range from VIS-NIR spectra of AF, i.e., as to have the same spectral range of NS, made the prediction accuracy of AF reduced spectra (1350-2500 nm) slightly lower than that of NS. This demonstrates that the lower accuracy of the NS in soil features prediction is not due to the lower resolution of the spectra, but probably due to the lack of visible and beginning of the NIR range (350-1300 nm).