Improving the GPR reflection method for estimating soil moisture and detection of capillary fringe and water table in a boreal agricultural field

Abstract

The objective of this thesis was to monitor the soil moisture (SM) and water table depth (WTD) in an agricultural field using ground-penetrating radar (GPR). First, SM was estimated using hyperbola-fitting method (27-50 cm depth range) and compared with vertically installed 30 cm long Time Domain Reflectometry (TDR) probe data. TDR-measured and GPR-estimated SM were not significantly different, and the root mean square error (RMSE) was 0.03 m3 m-3. Second, the depth of the capillary fringe (DCF) was estimated distinguishing the reflections from the top of the capillary fringe in a GPR radargram. A site-specific strong linear relationship (R2 = 0.9778) of DCF and measured-WTD was developed. RMSE between GPR-based WTD and actual WTD was 0.194 m. Proposed average capillary height for the particular site throughout the growing season (0.741 m) agrees with the existing literature and would be beneficial for the agricultural water management in the region.