1. Introduction
Topographic data are an important source of information for the processing of Earth Observation (EO) products and, thus, for developing reliable EO-based services. Within this context, the Copernicus Programme made the important effort of making available a high-quality topographic dataset that can be used as harmonized elevation reference for downstream applications: i.e., the Copernicus Digital Elevation Model (DEM), also known as CopDEM dataset. The latter is a digital surface model (DSM) mainly obtained from the X-band, SAR-derived WorldDEM dataset and locally infilled by other elevation data, like ALOS AW3D30, ASTER GDEM, SRTM etc. (e.g., for gap filling). In order to ensure the CopDEM dataset homogeneity, these data underwent a thorough editing and quality assurance process. Although the WorldDEM is a proprietary product that has a spatial resolution of 0.4 arc seconds (ca. 12 m) and a global coverage, the derived CopDEM dataset is distributed via products that have been processed and resampled to have different pixel sizes (i.e., ca. 10 m, 12 m, 30 m and 90 m), different spatial coverages (i.e., European and global) and different licenses. These different formats of the CopDEM dataset products are defined instances. For example, the 10-and 12-meters products (both referred together as EEA-10 instance; but hereinafter simply individually called EEA-10m and EEA-12m instance, respectively) are available over the European area (i.e., EEA-39 area). The exploitation of EEA-10 data is restricted to eligible users. The EEA-12m instance is the one more similar to the original WorldDEM product. The 30-meters and the 90-meters instances (named GLO-30 and GLO-90, respectively) are available worldwide with a free license (i.e., free, full and open data policy) [1].