Automated L-Band Radar System for Sensing Soil Moisture at High Temporal Resolution

The ground-based University of Florida L-band Automated Radar System (UF-LARS) was developed to obtain observations of normalized radar backscatter (mmbσ⁰) at high temporal resolution for soil moisture applications. The system was mounted on a 25 m manlift with capabilities of antenna positioning for multi-angle data acquisition and ranging. The RF subsystem of UF-LARS was based upon the established designs for ground-based scatterometers employing a vector network analyzer with simultaneous acquisition of V- and H-polarized returns. System integration and automated data acquisition were enabled using a software control system. Fifteen-minute observations of mmb σ⁰ collected over a growing season of sweet-corn and bare soil conditions in North Central Florida, were used to study the sensitivity of mmbσ⁰ to growing vegetation and near-surface (0-5 cm) soil moisture (mmbSM0 - 5). On average, mmb σmmbVV⁰ were observed to be 23% higher than mmbσmmbHH⁰ during the mid- and late-stages of crop growth due to the vertical structure of stems. The correlation between 3-day observations of mmbSM0 - 5 and mmbσmmbVV⁰ reduced by 55% compared to those obtained for ≤ 30-min observations. These findings suggested that data set at high temporal frequencies can be used to develop more realistic and robust forward backscattering models.