MONITORING SURFACE CHANGES OF BARE SOILS DUE TO SLAKING USING SPECTRAL MEASUREMENTS

The structural degradation of the soil surface due to rainfall makes t he surface more susceptible to erosion. Loamy soils are particularly v ulnerable to staking, seal development, and crusting. The sealing proc ess occurs in different stages. This study examined the possibility of using visible and near-infrared reflectances for detecting these surf ace changes due to rainfall, and for defining optimal conditions for s pectral measurements. Experimentation was conducted under field-contro lled conditions using a SPOT satellite simulation radiometer. Radiomet ric measurements were made at three solar altitudes: 0600, 1200, and 1 800 h GMT, at five different stages of surface degradation following s imulated rainfall. Ground measurements consisting of Munsell color, wa ter content, and surface roughness were made simultaneously to charact erize surface changes. The influence of these various factors on refle ctance was analyzed. Soil water was the main source of variation in re flectance, while surface roughness was a factor of secondary importanc e. Reflectance increased with increased roughness and decreased soil w ater content. A combination of red and near-infrared reflectances made it possible to identify different soil Lines according to soil water content, solar angle, and slaking stage. Optimal conditions for monito ring surface changes were those where the solar altitude is the lowest for dry sails. Different slaking stages can also be detected by refle ctances performed at 1200 h under dry conditions.