The slope of
the regression equation decreases with frequency (L-band RVI has the lowest slope). These results indicate that the L-band RVI
has the largest range of RVI observations over the crop growing
cycle. The accuracy (lower rmse) of the retrieved VWC for rice
using RVI increases as frequency decreases. There was a slight
improvement in estimating VWC using RVI as compared to
using NDVI and a significant improvement over using LAI (see
Table II).