Spectral responses to plant available soil moisture in a Californian grassland

This study established relationships among plant available soil moisture and reflectance and vegetation indices (VIs) derived from AVIRIS and MODIS data in grassland ecosystem in California. Strong correlations were observed between soil moisture and different forms of reflectance in the red-edge, near infrared and shortwave infrared bands. Both greenness-based and canopy-water-based indices were linearly related with soil moisture during the growing season, the wet and the dry season. The relationship was stronger with antecedent soil moisture, particularly in the dry season. Using plant available soil moisture, which is the difference between measured soil moisture and the wilting point, improved the relationship by reducing the soil property effect. Furthermore, results suggested that the difference in sensors had little impact on the relationships in grassland, but the parameters of relationships were influenced by the spatial resolution of sensors.