What is the Impact of Roots on GPR Data? A Synthetic Study of the Soil-Plant Continuum

The critical zone is a dynamic and heterogenous environment where a broad spectrum of processes take place ranging from hydrological, chemical and biochemical and interactions of rocks, fluids, soils and biota. The use of non-invasive geophysical tools, such as ground penetrating radar (GPR), to investigate the soil-plant continuum of agricultural crops within the critical zone has become increasingly popular. The continuum's complexity poses challenges, as the different components dynamically influence each other and the interactions and processes are not fully understood. Furthermore, establishing a direct link to geophysical information remains challenging. This study quantifies the impact of root distributions on GPR signals and soil water content (SWC) estimation. We investigated the influence of root volume fraction (RVF) on SWC calculation in a synthetic feasibility study before we performed numerical forward modeling using gprMax. Here, we analyzed GPR traces for different scenarios containing soil, roots and above-ground shoots. Thereby, we included two root distributions related to contrasting soil types based on field root counts. We observed that roots had a higher impact than above-ground shoot. Additionally, not considering roots in the calculation of SWC led to an SWC underestimation, depending on the soil permittivity and root volume fraction.