Approaching holistic crop type mapping in Europe through winter vegetation classification and the Hierarchical Crop and Agriculture Taxonomy

The process of crop type mapping generates land use maps, which serve as critical tools for efficient evaluation of production factors and impacts of agricultural practice. Yet, despite the necessity for comprehensive solutions in space and time, the state of research still exhibits significant limitations in these two dimensions: (1) From a temporal perspective, the primary focus of past research in crop type mapping has been on the economically most meaningful, main-season crops, thereby largely neglecting the explicit study of off-season vegetation despite its pivotal roles in year-round management cycles. (2) Viewed spatially, study areas in crop type mapping show distinct limitations from a multi- and transnational standpoint, despite intense cross-regional and international interrelations of agricultural production and an increasing number of countries publishing crop reference data. With a focus on Europe, this research aims to tackle the two described shortcomings (a) by investigating to what extent a selection of major off-season, winter vegetation types in continental Europe can be classified and (b) by analyzing the transnational applicability of the Hierarchical Crop and Agriculture Taxonomy (HCAT) for remote sensing-based crop type mapping across the European Union (EU). This study uses ESA's Sentinel-2 satellite data, EU's administrative farming declarations, and HCAT labels to analyze off-season farming measures, based on a study period from late summer to spring, in Austria, France, Germany, and Slovenia. We demonstrate that deep learning models effectively identify major productive and agroecogically significant winter vegetation in continental Europe. HCAT proves thereby valuable for transnational crop classification, excelling in mixed-country experiments and showing potential for transfer learning. This study's findings provide a solid foundation for advancing transnational as well as winter and all-year crop type mapping, thereby serving as contribution towards temporally and spatially holistic research on agricultural practices’ sociocultural, economic, and environmental impacts.