Spectroscopy of evaporites

The presence of salt crusts can provide information on soil salinization. Spectroscopy and remote sensing of salt crusts are useful for assessing the distribution of salt crusts in barren landscapes of arid regions as well as to evaporite accumulation in playa basins. In this study are reported the results of spectral reflectance measurements in the visible and near infrared region of gypsum, halite, calcium carbonate, sodium bicarbonate, and their mixtures. Spectral analyses have shown that the studied samples have diagnostic absorption features between 1000 to 2500 nm which are consistent with the reported values in the libraries. The positions of the absorption bands were not affected significantly quantities of evaporites per unit area. However, reflectivites increased with increasing the weight fraction of evaporite present. The reflectivity of evaporite was related to the mixing ratios in a non-linear fashion. At certain mixing ratios, the spectral reflectance data from evaporites were similar to those of the endmembers. It is interpreted that this is due to crystals coating. The reflectivity of the mixed calcium carbonate and sodium bicarbonate decrease by increasing the sodium bicarbonate fraction, due to the coating of calcium carbonate by sodium bicarbonate. The data of this study point to a possibility that the presence of gypsum, halite, calcium carbonate, sodium bicarbonate, and their mixtures in salt crusts can be assessed quantitatively by examining the position and intensity of the absorption features. The presence of soil particles may affect these results, and this subject is currently being evaluated.