Remote sensing techniques are being increasingly applied to investigate soil characteristics. Here we propose an approach that allows the detection of salt-affected soils in arid and semi-arid environments. We test the procedure in Northeast Brazil through a combination of remote sensing and geochemical ground-based measurements. Spectral indices were used to characterize soil salinization features and patterns. The Linear Spectral Unmixing technique (LSU) is applied in this study to improve the prediction of soil salinity. Eighteen indices were extracted from the MODIS Terra data. A moderate correlation was found between electrical conductivity and the spectral indices. An improvement occurs in most of the correlations after applying the LSU method. To generate a predicted salinity map, a multiple linear regression, based on the best correlated indices is conducted. The standard error of the estimate is about 12.1 μS cm ⁻¹ .

Arid and semi-arid regions are susceptible to high levels of erosion. A rapid and cost effective methodological erosion assessment for these regions is required to describe and monitor the processes that control erosion. This study uses remote sensing to describe the contribution of several factors that control erosion. Topography, land use, vegetation density, soil properties and climatic proxies are used to determine erosion risk and to provide basic maps of water and soil conservation practices. A hierarchical decision tree is used to sum and combine the weight of parameters controlling the erosion. The assigned weights of each spatial unit express the susceptibility to erosion. We focus on the catchment basin of the Maleka Wakena reservoir, located in the southeastern portion of the main Ethiopian Rift, where erosion is the major environmental problem.Three different combinations of the dominant controlling factors are yielded in this study. In order to optimize the qualitative erosion risk assessment, each combination is discussed and evaluated depending on the contribution of parameters involved in the erosion process.Maps derived from this qualitative analysis allow the identification and ranking of erosion intensity. These maps enable us to highlight areas in immediate need of conservation strategies in order to control siltation of the SE Ethiopian reservoir and to control further soil degradation