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Towards a new optical system to characterize soils by Visible and Near Infrared Spectroscopy

Abstract : (trad auto)With the objective of reducing the amount of greenhouse gases in the atmosphere, public authorities encourage practices designed to sequester carbon in the soil (reforestation, change in agricultural practices). To assess the real benefits, rapid, accurate and inexpensive analytical tools are needed to accurately account for carbon stocks and their evolution over time. Near infrared spectroscopy is an analytical technology adapted to these specifications but which is still part of the field of soil science research. This thesis focused on the first step of this analytical method: signal formation. Since soils are very complex environments, in terms of chemical composition and physical structure, the spectroscopic signal is negatively impacted by diffusion phenomena. As the conditions of Beer-Lambert's law are no longer met, chemometric models for predicting soil carbon content are less accurate and robust. We offer an original optical system for spectral measurement adapted to highly diffusing media, based on the principle of light polarization. It allows to select the photons that have been less impacted by the scattering phenomenon. This signal is used to calculate an absorbance signal being a good approximation of Beer-Lambert absorbance. This device, called PoLiS, has been experimentally validated on liquid and particulate model media. The PoLiS method was tested on soil samples to predict their organic carbon content. Compared to conventional calibration methods, prediction models perform better with the method developed in this thesis.
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Submitted on : Saturday, May 16, 2020 - 5:19:58 AM
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  • HAL Id : tel-02600787, version 1
  • IRSTEA : PUB00043047


Alexia Gobrecht. Towards a new optical system to characterize soils by Visible and Near Infrared Spectroscopy. Environmental Sciences. Doctorat Génie des Procédés, Centre international d'études supérieures en sciences agronomiques de Montpellier, 2014. English. ⟨tel-02600787⟩



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