Soil salinity assessment from satellite data in the Trans-Ural steppe zone (Southern Ural, Russia)

Abstract

Soil salinization is an up-to-date worldwide issue. This problem is especially urgent in the territories of arid and semi-arid regions. The aim of this work was to analyze the relationships between the level of soil salinity and the key spectral indices obtained on the base on Sentinel-2A satellite data. The study has been conducted on an area of 5127 ha in the Trans-Ural steppe zone (Republic of Bashkortostan, Russia). Vegetation index NDVI and 15 salinity indices have been used to analyze the relationships. The salinity index III (G×R)/B using quadratic statistical relation showed the best correlation values with salinity level (R=0.89, R<sup>2</sup>=0.79). In general, it was found that the highest correlation values are observed with indices based on the three channels of visible range: salinity index 2 √(G×R) (R=0.82, R<sup>2</sup>=0.67), salinity index 4 √(G<sup>2</sup>+R<sup>2</sup>) (R=0.82, R<sup>2</sup>=0.67), salinity index VII (G+R)/2 (R=0.82, R<sup>2</sup>=0.67). The vegetation index NDVI showed the absence of a correlation with the values (R=-0.10, R<sup>2</sup>=0.01), due to weak development or dry state of vegetation. The areas of saline soils using salinity index III were calculated. The methods elaborated could be useful for mapping and accounting of saline soils based on satellite data under environmental conditions similar to this study.