High-resolution non-invasive mapping of vertical heterogeneity in sandy soils of the Oak Openings Region using electromagnetic imaging and ground penetrating radar

Traditional soil investigation methods involve laboratory analysis on soil cores or direct measurements of soil properties with in-situ sensors. These methods are, however, destructive, labour-intensive, and ineffective in capturing the spatial variation of soil properties. Geophysical methods provide a non-invasive approach to rapidly characterize soil properties distribution. Gaps, however, exist in the use of non-contact-based geophysical methods such as ground penetrating radar (GPR) and electromagnetic imaging (EMI) for characterizing the vertical variation of soil properties. This study assesses the use of EMI and GPR for quantifying the vertical variation of soil moisture content (SMC), soil organic matter (SOM), and soil texture. Co-located EMI and GPR surveys were conducted along 12 transects at the Stranahan Arboretum research site in Toledo, Ohio. Soil samples collected from nine locations along the transects were segmented into 63 subsamples and analysed for SMC, SOM, and soil texture. Apparent electrical conductivities (EC _a ) from EMI were inverted to obtain lateral and vertical variations of soil electrical conductivity (EC), which captures three major lithostratigraphic units (sand, silty loam, and silt) found in soil cores within the top 2.0 m. Soil EC correlates with SMC, SOM and soil texture, with coefficient of determination (R ² ) ranging from 59–91%. The GPR radargrams show reflectors consistent in delineating sandy and silty clay soils but unable to distinguish between sand and silt. These results validate the effectiveness of using EMI and GPR to delineate vertical variation of soil properties and characterize stratigraphic heterogeneity, expanding the possibilities for non-invasive three-dimensional (3D) soil properties mapping.