Remote Sensing for the Detection of Salinized Soil Using a Multispectral Sensor in the Zeravshan River Basin

The Aral Sea Basin in Central Asia is a region plagued by a severe water crisis. The Union of Soviet Socialist Republics (USSR); installed a massive scale irrigation project here. This led to a rapid expansion of irrigation in the region from the late 19^th century until the collapse of the USSR in 1991. Extensive irrigation in the Aral Sea Basin has resulted in some emerging environmental problems. Central Asia is not only a region plagued by excessive water loss through low irrigation efficiency but is also faced with increasing soil salinity problems. In order to understand the problem of salinity in farms, this study attempted to detect salinity in the Zeravshan river basin in Uzbekistan. 15 salinity indices were applied for this purpose computed from MODIS bands data. These indices were derived from existing techniques of soil salinity assessment and consist of both the direct and indirect methods. Direct methods involve the reflectance of the bare soil while indirect methods involve the assessment of vegetation type or condition. Results from the assessment of band reflectance, using MODIS data on meshes with different salinity levels showed that all bands have a sensitivity to salinity changes. This is from the evaluation of EC measurements collected from the Zeravshan river basin in August 2017 and MODIS reflectance data. Values for the vegetation indices generally decreased with increase in salinity, while those of reflectance indices showed an increase with increasing salinity levels. All of the indices from literature, however, showed low correlation with EC measured from the site. The R² value for some of the vegetative indices was: 0.0493 for Ratio Vegetative Index (RVI) and 0.0674 for Normalized Difference Vegetative Index (NDVI). That of Salinity Indices was: 0.0674 for Normalized Difference Salinity Index (NDSI), 0.1109 for Salinity Index SI2, 0.0895 for Salinity Index S4 and 0.0899.for Salinity Index S5. These results show that there is some negative impact of salinity on vegetation. Vegetation based indices show some level of decreasing values with an increase in salinity. Reflectance based indices, on the other hand, show an increase with an increase in salinity levels.