Activities of the DEMIX Subgroup 3 "Platforms and Processing"

Abstract—In recent years, an important number of global Digital Elevation Models (DEMs) have been released publicly, with very permissive licenses. Although beneficial to the scientific field, this profusion of data makes it difficult to choose the most adequate DEM for a given field of application. Since 2020, DEM assessment and comparison methodologies have been standardised under the frameworks of the Earthnet Data Assessment Project (EDAP / EDAP+) led by the European Space Agency (ESA), and the DEM Intercomparison eXercise (DEMIX) initiated by the Committee on Earth Observation Satellites (CEOS). EDAP evaluation guidelines provide a comprehensive set of criteria to assess Earth Observation (EO) missions and products based on their documentation. While initially conceived for missions, these standard guidelines were adapted to the case of DEM products. On the other hand, the DEMIX methodology, based on the Randomized Complete Block Design (RCBD), allows users to rank DEMs according to user-defined areas of interest and criteria. Jointly used, these frameworks give scientists a complete analysis of DEM products, from overall assessments to very specific user criteria. While these evaluation standards are mature, fundamental DEM activities are still performed under EDAP and DEMIX. Most of these works are carried-out and discussed in the DEMIX Subgroup 3 (SG3) called “Platforms and processing”. Since the beginning of DEMIX, this subgroup carried out global DEM quality assessments using spaceborne LiDAR data, DEM planimetric misregistration assessments, extended DEM transformation studies including resampling methods, reprojections and datum changes, and analyses of open local VHR DEMs. The knowledge gained from these studies has been used to develop free DEM visualisation and processing web applications, including VtWeb, QGIS tools, a DEMIX Jupyter Notebook, the DEMIX Operations Platform and DEM4Sentinels-1-2. Thanks to these free tools, public users are now able to visualise and process DEMs in an easy interactive way.