Performance Evaluation of Satellite Images and Spectral Indices in Estimating Soil Moisture in Telo Region, Tehran Province

Measuring the moisture content of surface soil, as one of the most important components of the water cycle, plays a significant role in the optimal management of water and soil resources. The aim of this research was to evaluate the accuracy of spectral indices and Sentinel-2 satellite images for estimating soil moisture during the period of 2020-2022 in the Telo region, Tehran Province, Iran. The data used included the daily Sentinel-2 images, 30-Meters Digital Height Model and field measurements using the TDR. The spectral indices used in this study included NDWI, MNDWI, NDVI, NDMI, and SAVI. Analysis of the amount of surface soil moisture recorded showed that the average soil moisture in the area was 14.07%. In terms of time, the maximum amount of soil moisture with a value of 40% was recorded on December 18, 2020, and the minimum value was recorded with a value of 1.3% in early June, 2021. Analysis of the trend of soil moisture values showed that the minimum soil moisture values were recorded in the warm season due to the increase in temperature and evaporation and the decrease in precipitation, while the maximum soil moisture was recorded in the cold season with the beginning of the rainy season in the region and the decrease in temperature. Investigating the relationship between soil moisture values recorded using TDR and spectral indices calculated on Sentinel-2 images showed that there was no clear and significant relationship between NDVI and SAVI indices with TDR soil moisture values; and the maximum correlation was obtained for NDWI indexes with a correlation value of 0.23, NDMI with a value of 0.35 and MNDWI index with a correlation value of 0.59.