Ground-Penetrating Radar Water Content Mapping of Golf Course Green Sand Layers

Abstract

Information on the spatial distribution of water content across the sand layer component of a golf course green can be important to golf course superintendents for evaluating drainage effectiveness and scheduling irrigation. To estimate the bulk volumetric water content of the sand layer at point locations across the green, a technique was developed that combined (1) depth (or thickness) of the sand layer measured with a steel shaft tile probe, (2) radar signal two-way travel time from the base of the sand layer obtained using a ground-penetrating radar (GPR) system with 900 MHz antennas, and (3) an empirical equation relating porous media dielectric constant to water content. To test this technique, two GPR surveys were conducted on the Nursery Green at the Double Eagle Golf Club near Galena, Ohio, and two additional GPR surveys were carried out on the 9th Hole Green at the Delaware Golf Club near Delaware, Ohio. For comparison, time-domain reflectometry (TDR) water content values for the sand layer near the ground surface were obtained concurrent with each of the four GPR surveys. Results of the four golf course green GPR/TDR surveys carried out on September 8 and 9, 2014 (Double Eagle Golf Club - before and after irrigation, respectively), and April 21 and 29, 2015 (Delaware Golf Club) show that the sand layer water contents determined with GPR respectively averaged, 18.8%, 25.2%, 12.2%, and 11.3%, which were quite similar to the respective TDR sand layer water content averages of 20.3%, 25.7%, 11.0%, and 14.1%. The spatial correlation coefficients (r) between the GPR-based sand layer water content values versus the TDR sand layer water content values for these four GPR/TDR surveys were 0.76 (September 8, 2014), 0.73 (September 9, 2014), 0.55 (April 21, 2015), and 0.70 (April 29, 2015). Sand layer water content was found to have moderate inverse spatial correlation with ground surface elevation (r = −0.44 to −0.56) and elevation at the base of the sand layer (r = −0.43 to −0.53). Consequently, the findings of this study clearly indicate that if sand layer depth values are available, then GPR can be utilized in a non-destructive manner to accurately map sand layer water content across a golf course green, and conversely, in cases where sand layer water content (hence, radar velocity) spatial patterns are already known, then this information can be employed to provide more accurate GPR-based sand layer depth values.