Comparison vegetation indices and tasseled cap transformation for estimates of soil organic carbon using Landsat-8 OLI images in a semi-steppe rangelands

In this research, the capability of Landsat-8 OLI data for generating a soil organic carbon (SOC) map is investigated in a semi-steppe rangeland of Chaharmahal-va- Bakhtiari province. To do so, in the June 2013 ground sampling was performed based on a systematic-random scheme in 24 sampling sites within each site 3 transects was established and along each transect 5 soil samples were chosen and collected from 0 to 20 cm depth and SOC content of the samples was measured. In order to compare, on ground sampled values of SOC with the corresponding and Landsat-8 OLI data (June 2013), vegetation indices and tasseled cap transformation bands were calculated and extracted from the study area. The values of vegetation indices and tasseled cap transformation bands (dependent variable) were regressed against organic carbon values (independent variable) at site level in SPSS software. Finally, the SOC map was drawn based on the best-fitted model between the independent and dependent variable. The results showed that amongst vegetation indices, PVI and Brightness band have the most significant correlation with SOC. Finally, the SOC maps of the study area were drawn by the quadratic linear regression after finding the best regression fit between SOC and vegetation index as well as the tasseled cap. The results of the validation test show that between vegetation indices the PVI index (R=0.53) and tasseled cap transformation bands (R=0.63) showed the highest correlation with soil organic carbon (SOC). Finally, by calculating the fitting of binary linear regression, organic carbon maps were prepared. The validation results of the model indicate that there is no significant difference between ground sampled SOC and extracted values of vegetation indices and tasseled cap. Therefore, the spectral data of the Landsat-8 satellite images (OLI) are a valuable source for determining the soil organic carbon changes in such areas.