Near-surface geophysical data are essential for a wide range of scientific applications, including precision agriculture, archaeological prospection, and Earth System Sciences. Despite the frequent use of comparable survey methods and sensor technologies across these domains, the semantic description of data, metadata structures, and documentation practices remain highly fragmented. This lack of harmonisation limits interoperability, machine readability, and the reuse of geophysical datasets beyond disciplinary boundaries. To address these limitations, an ontology has been developed, presented here as a metadata description. The ontology provides a formal, semantically explicit representation of key concepts, relationships, and processes involved in near-surface geophysical data acquisition, processing, and archiving. It is therefore a minimal but expandable collection of classes and properties that encompasses both method-independent metadata, e.g. location and operators, and method-specific metadata, currently covering electromagnetic induction (EMI), in particular frequency-domain electromagnetics (FDEM), and magnetics. Further development is an ongoing process and will continue in collaboration with the specialist communities. The metadata model presented here represents an initial development stage from FAIRagro use case 14, which is based on a joint initiative within the NFDI (FAIRagro, NFDI4Objects, NFDI4Earth).