Evaluation of Elevation, Slope and Stream Network Quality of Spot Dems

Abstract

ABSTRACT:Digital elevation models are considered the most useful data for dealing with geomorphology. The quality of these models is an important issue for users. This quality concerns position and shape. Vertical accuracy is the most assessed in many studies and shape quality is often neglected. However, both of them have an impact on the quality of the final results for a particular application. For instance, the elevation accuracy is required for orthorectification and the shape quality for geomorphology and hydrology. In this study, we deal with photogrammetric DEMs and show the importance of the quality assessment of both elevation and shape. For this purpose, we produce several SPOT HRV DEMs with the same dataset but with different template size, that is one of the production parameters from optical images. Then, we evaluate both elevation and shape quality. The shape quality is assessed with in situ measurements and analysis of slopes as an elementary shape and stream networks as a complex shape. We use the fractal dimension and sinuosity to evaluate the stream network shape. The results show that the elevation accuracy as well as the slope accuracy are affected by the template size. Indeed, an improvement of 1 m in the elevation accuracy and of 5 degrees in the slope accuracy has been obtained while changing this parameter. The elevation RMSE ranges from 7.6 to 8.6 m, which is smaller than the pixel size (10 m). For slope, the RMSE depends on the sampling distance. With a distance of 10 m, the minimum slope RMSE is 11.4 degrees. The stream networks extracted from these DEMs present a higher fractal dimension than the reference river. Moreover, the fractal dimension of the extracted networks has a negligible change according to the template size. Finally, the sinuosity of the stream networks is slightly affected by the change of the template size.

Effect of image‐matching parameters and local morphology on the geomorphological quality of SPOT DEMs

“…To assess the quality of a DEM, two validation methods are usually used: internal and external validation (Polidori, ). Internal validation is based on a set of realism requirements that have to be satisfied in the DEM and does not require ground control data (El Hage et al., ; Polidori et al., ). External validation uses field measurements to assess the quality of a DEM using statistical descriptors.…”

“…The RMSE tends to decrease with an increase in the calculation distance of the slope. This means that the quality of the slope depends on the mesh size (El Hage et al., ; ). The 17 × 17 pixel template produces a minimum RMSE for the slope of both profiles.…”

Digital Elevation Model Quality Assessment Methods: A Critical Review

“…. [84,[136][137][138][139][140]), as well as by the local slope and the landcover [84,[140][141][142][143][144][145]. There is an almost linear relationship between the DEM elevation error and the terrain slope [146][147][148][149], although the impact on the landform quality is more severe in low-slope areas [85].…”

“…The elevation error propagates through elevation derivatives like slope, aspect and curvature, leading to erroneous drainage network or watershed delineation for instance [76,77]. Although the computation of the slope or other derivatives may lead to different results according to the selected algorithms [78][79][80][81][82], the error propagation always generates an uncertainty in the resulting product (e.g., slope map) that needs to be evaluated due to its wide use in many applications of DEMs in geoscience [68,[82][83][84]. In general, the elevation derivatives are very sensitive to the spatial autocorrelation of the error [28].…”

Effect of Digital Elevation Model Mesh Size on Geomorphic Indices: A Case Study of the Ivaí River Watershed - State of Paraná, Brazil

“…The quality of the geomorphic indices depends on the production technique and its parameters (El Hage et al 2012), on the terrain morphology and its landcover (El Hage et al 2017) as well as on the mesh size (Thompson, Bell and Butler 2001, Tang 2003, Kienzle 2004, Erskine et al 2007, Vaze and Teng 2007, Wu, Li and Huang 2007, El Hage et al 2010, Vaze, Teng and Spencer 2010, Polidori et al 2012. The mesh size constitutes one of the main DEM characteristics and it is part of the triple scale concept manifested by dimension, extension and spacing, directly controlling the size of objects that could be extracted from DEMs (Blöschl and Sivapalan 1995).…”