A method to rank global DEMs quality focused on their horizontal accuracy

Currently there are various global digital elevation models (GDEM) and it would be necessary to have measures that help decide which one to use according to the derived product that we need. The DEMIX Project addresses this problem. In this communication we show an automatic measure that assesses the planimetric quality of a DEM product (DEM) and that allows ordering from highest to lowest, according to planimetric quality, any DEM and particularly a set of GDEMs. The planimetric quality of a DEM is assessed by comparing its contours with their homologous ones belonging to a reference DEM (DEMref) of greater accuracy. The area enclosed by homologous contours is an indicator of DEM's accuracy: the smaller the area enclosed by homologous contours, the greater horizontal accuracy. In this study, the area divided by the average length of the contours is used to estimate the DEM horizontal accuracy compared with a DEMref. One of the great advantages of this method is that it is completely automatic (we do not need to identify the homologous curves). Although the method can be used to compare any DEM, in this study we have used 2 GDEMs (ASTER and NASADEM) as DEM which have 30 m of spatial resolution and the DEMref is the Spanish MDT05 (5 m of spatial resolution) generated by the Spanish Instituto Geográfico Nacional (IGN).