Global open-access DEM vertical elevation and along track neighbouring structure evaluations in the Tibetan Plateau using ICESat-2 ATL03 points

Abstract

Global digital elevation models (GDEMs) are critical in the measurement and analysis of Earth's surface, and should be evaluated prior to use. However, existing GDEM evaluations mainly use global statistical metrics to evaluate vertical elevation (VE) differences with reference data, ignoring the relationship between a centre pixel and its neighbouring pixels, which is defined as the GDEM's neighbouring structure (NS). Along track ATL03 points allow evaluation of the along track NS (ATNS). This study comprehensively accesses the VE and ATNS accuracy of 1 arc-second GDEMs, including Copernicus, NASA, AW3D30 and ASTER DEM, using for the first time ICESat-2 ATL03 along track points throughout the Tibetan Plateau, where the rugged terrains and various features make it difficult to maintain its NS's accuracy. This study first introduces continuous and discrete ATNS metrics, then evaluates their effectiveness by analysing their relationships with errors in GDEM terrain derivatives. Finally, the better-performing metric is used for evaluations across various terrain parameters, landforms and land covers. The proposed framework achieved DEM evaluations from pixel-by-pixel statistical analysis of elevation differences to local ATNS assessment. Evaluation results demonstrate that the ATNS errors of the GDEMs are linearly correlated with the RMSE of the vertical errors. Overall, the errors of the VE RMSE and ATNS are ranked as Copernicus< AW3D30 < NASA< ASTER. However, evaluations conducted in the Andes and Alps reveal regional variations in these rankings. This study endeavours to introduce a new framework for large-scale GDEM evaluations, and the conclusions are beneficial for GDEM selection in further applications.