Second EARSeL Workshop on Imaging Spectroscopy, Enschede, 2000 SPECTRAL PROPERITES OF SELECTED DOMINANT SALT CRUSTS

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. The study reported here was conducted for examining spectral reflectance of gypsum, halite, calcium carbonate and sodium bicarbonate and their mixtures. Spectral reflectance was measured with a GER 3700 spectroradiometer in the visible and near infrared region (400-2500 nm), and was compared with the USGS and NASA spectral libraries. 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 by the size of gypsum and halite particles or with their quantities per unit area. However, reflectivites increased with reducing particle sizes or 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. However, the halite spectral pattern eclipses the spectral features of the gypsum in a nonlinear fashion when the mass fraction of gypsum is reduced to about 75 % in mixed salt. It is interpreted that this is due to coating of gypsum with halite crystals. The reflectivity of the mixed calcium carbonate and sodium bicarbonate decrease by increasing the sodium bicarbonate fraction, due to th