Sensitivity of the land surface temperature and NDWI index to soil moisture on wheat and barley

Abstract

The spatial monitoring of crop water status is crucial for agricultural purposes. The aim of this study was to analyze the sensitivity and response times of land surface temperature (LST) and the Normalized Difference Water Index (NDWI) to changes in soil moisture (VWC) in barley and wheat crops at plot scale in southeastern Argentine Pampas. VWC and LST were recorded daily by stations installed over the crops, and NDWI from Sentinel 2 (S2). Results showed instantaneous correlations between VWC and LST (r>-0.65) for soil depths explored by crop roots (20-50 cm). Correlations with NDWI were negative, which lacks biophysical meaning from a soil-plant system perspective. However, this index showed lower maximum values during the dry campaign. During the critical period of crops, the relationship between NDWI and VWC at 10 cm was positive, with a high correlation (r≈0.92) when considering responses with a 1-day time lag. This study contributes to the understanding of crops spectral behavior in the optical and thermal spectrum according to their water status, which is key to evaluating the usefulness of these data for monitoring agricultural systems.