Continuous Monitoring of Rice Growth With a Stable Ground-Based Scatterometer System

Ground-based polarimetric scatterometers have been effective tools to monitor the growth of rice crop, with much higher temporal resolution than satellite synthetic aperture radar systems. However, scatterometer data obtained in every few days, as were the case for the previously reported studies, were not enough to address the effects of ever-changing weather conditions. In this letter, we constructed a highly stable X-, C-, and L-bands polarimetric scatterometer system in an air-conditioned shelter. The incidence and azimuth angles of the antenna were fixed to 40^° and 0 ^°, respectively, to avoid uncertainty in repositioning error. Season-long daily backscattering coefficients from transplanting to harvesting were compared with rice growth data. Total fresh weight, leaf area index, and plant height were highly correlated with L-HH (0.97, 0.96, and 0.88, respectively) due to the deeper penetration and the dominance of double bounce in lower frequency. High-quality backscattering data clearly revealed the dual-peaked pattern in X-band, among which X-VV correlated best with grain dry weight and gravimetric grain water content (0.94 and 0.92, respectively) due to the better interaction of grain and rice canopy with microwave of higher frequency. These results will be useful in retrieving crop biophysical properties and determining the optimum microwave frequency and polarization necessary to monitor crop conditions.