Thermal infrared hyperspectral imaging for chemical mapping of an open mine (Conference Presentation)

The hyperspectral chemical mapping of open mines exploited by industries are among the possible applications that could possibly benefit from thermal infrared long-distance survey. More specifically the cement production essential in the constructions of our cities. The cement is made by mixing different raw materials and firing them in order to achieve precise chemical proportions of lime, silica, alumina and iron in the finished product. The quality of cement is therefore directly related to the chemistry of the raw materials used. Approximately 80 to 90% of the raw material is limestone. Clayey raw material accounts for between 10 to 15%, although precise amounts vary. Magnesium carbonate, which may be present in limestone, is the main undesirable impurity. The level of magnesia (MgO) should not exceed 5% and many producers prefer a maximum of 3%; this excludes dolomite or dolomitic limestones for the manufacture of cement. In this work, we conducted thermal infrared (TIR) hyperspectral imaging for mineral mapping and mineralogy identification on a pit wall with Juracement at Cornaux using hyperspectral camera. This passive thermal infrared hyperspectral research instrument based on Fourier transform spectroscopy provides high spectral resolution data. The solid targets such as minerals not only emit but also reflect thermal infrared radiation. Since the two phenomena occur simultaneously, they end-up mixed in the radiance measured at the sensor level. To unveil the spectral features associated with minerals from TIR measurements, the respective contributions of self-emission and reflection in the measurement must be «unmixed» using temperature-emissivity separation (TES) algorithms. We developed a new TES procedure that allowed us to retrieve the spectral emissivity of the different minerals in the investigated scene. The chemical maps of the calcite dolomite mixtures were obtained on the pit wall the investigations were carried out, giving important insights on chemical the quality of the mine.