When there is no water, coarse soils have a lower reflectance than fine soils. The opposite is true when the water content increases. As was mentioned above, water lowers reflectance, so coarser soil which holds less water, has a higher reflectance than fine soil which is holds more water. Another factor in reflectance is the vegetation cover. Scatterometry may also provide information about soils.
Energy is sent at the target and the return energy is measured.
This backscattering is a function of the angle of incidence and depends on the moisture, roughness and texture of the surface. The backscattering of radar, which can penetrate meters into surface material if the material is extremely dry, was used in Egypt to determine the material underlying a sheet of sand. Radar may also be used to penetrate through vegetation to determine the soil moisture content in heavily vegetated areas. They can, however, be used for preliminary mapping, and for grouping soils into sets with similar drainage or clay characteristics. The data was analysed most effectively by using only the first and second principle components of the spectral bands.