Publicly available soil moisture datasets: an overview and the UB-SMDC portal

Soil moisture is a fundamental environmental variable essential for applications in agriculture, drought assessment, hydrological modeling, and climate research. In recent decades, numerous Soil Moisture Content (SMC) datasets have been produced from in-situ measurements, airborne and spaceborne observations, and model simulations. However, information about these datasets is fragmented across disparate repositories, publications, and portals, making data discovery, comparison, and integration a significant challenge for researchers. This study introduces the University of Bonn Soil Moisture Data Catalog (UB-SMDC), a unified, standards-compliant metadata portal designed to overcome this fragmentation. Two primary objectives drove the project: first, centralizing information on publicly available SMC datasets into a single, user-friendly, web-based interface; and second, conducting a comprehensive statistical analysis of SMC datasets to characterize the global SMC data landscape. The UB-SMDC was developed using a structured, three-phase methodology: (1) comprehensive data discovery, (2) catalog design and implementation, and (3) metadata creation and analysis. Built on the open-source GeoNetwork platform, the catalog aligns with the Geographic information, ISO19139 metadata standard, to ensure consistency and interoperability. To harmonize key attributes, a controlled keyword taxonomy was developed to standardize terms for spatial and temporal resolution, measurement depth, data format, processing level, and data version. Each metadata record is enriched with links to initial data sources and access, and includes map-based previews to visualize dataset coverage. By assessing 373 metadata records, the UB-SMDC streamlines the data discovery and selection process, supports transparent and reproducible research, and facilitates cross-dataset comparison and integration.