Combined Analysis of InSAR Observations and Empirical Models to Assess Soil Erosion Susceptibility

Soil erosion is a serious environmental problem in Nozhian Watershed, which is located in Lorestan province of western Iran. Relatively steep slope, heavy precipitation, lack of dense vegetation cover and geological properties of the soil have been attributed as the main factors affecting erosion in the region. The aim of this study is to apply both radar interferometry and empirical methods to evaluate soil erosion pattern in Nozhian and its impact on surface deformation.

For the empirical model the following factors were applied to calculate erosion rate: rainfall-runoff erosivity (R), soil erodibility (K), slope length and steepness (LS), cover management (C) and support practice (P). The R-factor was produced from annual precipitation data, K-factor was developed from soil maps and geological information, LS-factors were calculated from digital elevation model (DEM) and C-factor was created from Landsat-7 ETM images and land cover maps. All factors were then integrated in a GIS environment to derive soil erosion map. For the radar interferometry we utilized 9 PALSAR images acquired by the ALOS satellite between 22 July 2007 and 9 November 2009 and processed them using the Small BAseline Subset (SBAS) technique to obtain time-series maps of surface deformation.

The results of InSAR time-series analysis are compared with the information obtained from empirical modeling for quantitative and qualitative assessment of different factors contributing to the erosion. We show that the information obtained by these two independent methods are complemnatry and help us gain a comprehensive and better evaluation of soil loss rate and spatial erosion pattern.