GRID4EARTH: Toward an Ellipsoidal HEALPix Grid for Analysis-Ready Earth Observation and Climate Data

The increasing volume and diversity of Earth Observation (EO) and climate data produced by Copernicus missions and the Destination Earth (DestinE) initiative pose a major challenge for interoperability and large-scale analysis. Today, global datasets are distributed on heterogeneous spatial grids, forcing users to repeatedly perform ad-hoc regridding steps, which are costly, error-prone, and difficult to reproduce.The GRID4EARTH project addresses this issue by promoting a common Discrete Global Grid System (DGGS) as a foundation for analysis-ready Earth data. In this context, HEALPix emerges as a strong candidate due to its equal-area property, hierarchical structure, and long-standing adoption in global modelling and large-scale data analysis. These properties enable efficient multi-resolution workflows, scalable data access, and natural integration with modern cloud-native formats such as Zarr.However, a key limitation remains: HEALPix is formally defined on the sphere, whereas EO are naturally referenced to the WGS84 ellipsoid. While often ignored at coarse resolutions, this mismatch introduces non-negligible area distortions at Copernicus resolutions and may bias zonal or regional analyses.To overcome this limitation, GRID4EARTH explores anextension of HEALPix to the WGS84 ellipsoid using the authalic sphere associated with the ellipsoid. By preserving equal-area properties on the ellipsoid, this approach provides a consistent spatial framework bridging spherical climate models and ellipsoidal EO. It enables a unified representation for DestinE model outputs and Copernicus satellite data, while remaining compatible with existing HEALPix-based tools and workflows.This contribution presents the motivation, principles, and expected benefits of ellipsoidal HEALPix within GRID4EARTH, and discusses its role as a practical and scalable DGGS for next-generation Earth system data infrastructures.