Relationships between water indexes and soil moisture/crop physiological indexes using ground-based remote sensing and field experiments

The controlling experiment of soil moisture was carried out for the study of crop water spectral features affected by the drought in crop early growth and development stages. The spectra of winter wheat were measured using field spectral radiometer in Gucheng Experiment Station of Heibei Province, and normalized difference water index (NDWI) and simple radio water index (SRWI) were calculated, respectively. Meanwhile, the canopy physiological indexes including chlorophyll concentration (Chl), leaf area index (LAI), plant height (H), leaf relative water content (LRWC) and soil moisture (SM) were measured. The results show that there were significant correlations between canopy physiological indexes of winter wheat and SM, the largest correlation coefficient is 0.657, which indicated that crop early photosynthetic and growth were directly affected by the soil moisture. The correlation coefficient is 0.545 among NDWI/SRWI and SM, which show a weak correlation; whereas, there are not obvious between physiological indexes of winter wheat and WI; especially, the correlation coefficient is just equal to 0.175 among NDWI/SRWI and LRWC. The conclusion was that the water index implied the soil moisture condition instead of crop water content in the low coverage crop growing period.