The Use of Ground-Penetrating Radar to Accurately Estimate Soil Depth in Rocky Forest Soils

Ground-penetrating radar (GPR) is a geophysical tool that has the capability, given favorable soil properties, to improve the accuracy of soil depth estimation, compared with other commonly used methods. This study was conducted on three different physiographic regions across the southern Appalachian Mountains: the Ridge and Valley (n = 9), Cumberland Plateau (n = 6), and Allegheny Plateau (n = 6). At each site (N = 21), a 20- X 20-m measurement plot was scanned using both 200- and 400-MHz antennas to estimate average soil depth. Soil depth estimates obtained from both GPR antennas were compared with each other as well as with soil depth estimations obtained with a soil auger using a paired t test (alpha = 0.05). No significant differences in soil depth were observed for the 200- versus 400-MHz antennas (P = 0.913). Consequently, data recorded from the 400-MHz antenna were used when depth measurements between the GPR and soil auger were compared. This was done because of the smaller and lighter antenna size and better practicality (i.e., can be used by a single operator) compared with the heavier and bulky 200-MHz antenna. Across all plots (N = 21), depth estimations were shallower using a soil auger compared with estimates obtained using GPR across all plots (P = 0.0002). Results from this study demonstrate how current methods can underestimate soil depth in rocky forest soils. Depth estimations from GPR could be used to more accurately quantify site quality in the southern Appalachians by providing the precise data needed to calculate nutrient availability and water-holding capacity. Last, the reduction in size and weight of GPR antennas and computers now provides forest scientists a practical and powerful technology that should be revisited because it has been confined to very specific applications over the last 25 years. FOR. So. 57(1):59-66.