Knowledge of the dynamics of soil moisture and organic matter is essential in agricultural, hydrological, and environmental research and engineering as these properties control, at different scales in the soil-plant-atmosphere system, key hydrological processes, plant growth, contamination of surface and subsurface water, sustainability of natural ecosystems, biodiversity and climate change. The recent emergence of drones has opened new research and application avenues for digital soil mapping and monitoring at the farm management scale. Within the frame of the BELSPO RAPAS project, we developed new drone-based soil sensing methods using ground-penetrating radar (GPR) and multispectral spectroscopy to map key soil properties with a high spatial resolution. In particular, we developed a new lightweight ground-penetrating radar (GPR) and advanced radar signal processing methods for soil moisture mapping. In a context of precision agriculture, this technology is expected, e.g., to improve the efficiency of irrigation practices by adapting the applied water quantity to the crop needs. Then, new multispectral processing methods were developed and analyzed to retrieve soil organic carbon. A series of multispectral cameras were tested and compared. Particular attention was dedicated to positioning of the measurements and the cm accuracy was reached without the use of any ground control points. The GPR and multispectral tools that we developed were applied in a series of agricultural fields in the Belgium loess belt. In order to provide further insights regarding larger scale mapping from satellites, the soil moisture results were compared to Sentinel-1 acquisitions. These high-resolution soil property products highlighted the scaling challenge resulting from the inherent, multi-scale spatiotemporal variability of the soil properties.
