Digital elevation model validation with no ground control: application to the topodata dem in Brazil

Abstract

Digital Elevation Model (DEM) validation is often carried out by comparing the data with a set of ground control points. However, the quality of a DEM can also be considered in terms of shape realism. Beyond visual analysis, it can be verified that physical and statistical properties of the terrestrial relief are fulfilled. This approach is applied to an extract of Topodata, a DEM obtained by resampling the SRTM DEM over the Brazilian territory with a geostatistical approach. Several statistical indicators are computed, and they show that the quality of Topodata in terms of shape rendering is improved with regards to SRTM. Keywords: Digital Elevation Model; Topodata; SRTM DEM. RESUMO INTRODUCTIONDigital elevation models (DEMs) are commonly used to describe the 3D geometry of the Earth surface for a variety of applications such as landscape synthesis, hydrologic modelling or geological hazard assessment. Satellite images have been increasingly used in the past two decades to provide DEMs, mainly through photogrammetry or radar interferometry (TOUTIN and GRAY, 2000). The quality of these data has been regularly studied, both to improve the mapping methods and to evaluate their applicative potentialities. Most experiments carried out for the validation of a single DEM or a DEM production method consist in comparing the obtained data with a reference data set, generally a set of ground control points. This comparison may be based on statistical accuracy indicators such as mean difference, standard deviation or RMSE (root mean square error), and when the GCPs are numerous and well distributed the error can be interpolated and mapped. This validation approach is very relevant to evaluate the positional accuracy of the DEM. However, many applications require a good rendering of terrain shapes and a high positional accuracy does not guarantee that his requirement is fulfilled, since accurate slopes are required rather than accurate elevations. In this article, we propose several quality criteria to validate DEMs in terms of shape rendering. The characteristic of these criteria is that they are difficult to implement with ground control, and they can rather be based on reasonable hypotheses concerning geomorphological rules that all topographic surfaces are supposed to fulfil.Among the attempts to provide a world wide elevation data base, the most noticeable one is the Shuttle Radar Topography Mission (SRTM) that resulted in a homogeneous DEM with a 3 arc seconds (around 90 m) grid mesh (FARR and KOBRICK 2001).In Brazil, the Instituto Nacional de Pesquisas Espaciais has proposed another DEM called Topodata, obtained by resampling the SRTM DEM to create a 1 arc second (~30 m) grid with a geostatistical interpolation approach (VALERIANO and ROSSETTI, 2012). Since the selection of geostatistical coefficients for this interpolation considered the likelihood of DEM features relative to natural terrain shape, it was relevant to evaluate the improvement achieved with regards to the input SRTM in terms of shape realism.

Artefact detection in global digital elevation models (DEMs): The Maximum Slope Approach and its application for complete screening of the SRTM v4.1 and MERIT DEMs

“…Villa Real et al (2013) presents an algorithm for detection of vertical artefacts in DEMs that relies on comparisons against reference data. Polidori et al (2014) noted the dependency of elevation derivatives on artefacts and tested the directional distribution of slopes that could possibly reveal artefacts in the data. Hirt et al (2014) used extreme gravity values derived from topography to detect artificial depressions in SRTM elevation data.…”

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.…”

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

“…These small differences are related to the production techniques and methods of these DEMs (Polidori, El Hage and Valeriano 2014). This figure also shows that the increase of the mesh size does not affect the elevation histogram for the both DEMs.…”

“…Indeed, the canopy modify the morphology on the DEM and the geomorphic indices that arise from are affected specifically with a small mesh. According to Polidori, El Hage and Valeriano (2014), TOPODATA carries the advantage of extending SRTM geomorphologic properties to a rather local scale, since the oversampling method of SRTM from 90 m to 30 m is based on geomorphologic assumptions and that is why the effect of the canopy is low in TOPODATA. The increase of the mesh size decreases the effect of the canopy in GDEM and with a mesh size higher than 120 m, the difference between GDEM and TOPODATA becomes very small.…”