Estimation of spatio-temporal variability of soil water content in agricultural fields with ground penetrating radar

摘要

Efficient water management, crop yield variability estimation and prediction of contaminant transport require some measurement of soil water content variation through time and space. This study focused on the estimation of spatio-temporal variability of volumetric soil water content (θ_v) in raised bed agricultural fields using ground penetrating radar (GPR), comparison of GPR method with gravimetric sampling data and development of 2D maps of θ_v. The GPR system (pulse EKKO Pro) with 200MHz antennas was used to collect data on approximately 1.0m wide and 13.0m long raised beds of about 0.1m height cultivated with vegetables. Transillumination Zero Offset Profile (Trans ZOP) and Transillumination Multiple Offset Gather (Trans MOG) GPR survey modes which are classically used as borehole GPR method were employed as a surface GPR method. In each of these survey modes, the direct ground wave travel time was measured. The θ_v at each Trans ZOP and Trans MOG location was calculated by first converting the electromagnetic (EM) wave velocity into soil dielectric permittivity and then to θ_v using a standard empirical relationship. The results revealed that the spatio-temporal variability of θ_v in raised bed agricultural fields could be estimated using the Trans ZOP and Trans MOG GPR survey modes. The GPR estimated θ_v and gravimetrically measured soil water content (θ_g) were not significantly different (P=0.272). The correlation coefficient was 0.87, the root mean square error was 0.0184m~3/m~3 and the average error was 0.20% between the two methods. The Trans MOG survey data allowed us to create plan view maps (2D) of the θ_v variation which could not be obtained from the Trans ZOP data. No statistical difference (P=0.053) was found between the Trans ZOP and average Trans MOG values.