Capturing the level of progress in vertical accuracy achieved by ASTER GDEM since the beginning: Turkish and Nigerian examples

Abstract

There is little information on the improvement achieved across all versions of ASTER GDEM in terms of vertical accuracy. This study assessed the vertical accuracies of all three versions in Turkey and Nigeria based on the mean error, root mean square error, mean absolute error, average relative error, residual dispersal patterns and combined error performance rankings. Although the improvements from GDEM v1 onward were obvious, they were rather marginal from GDEM v2 to GDEM v3 when five elevation classes were considered from coastal to high mountain. In the coastal, lowland and upland classes in Turkey, and lowland and upland classes in Nigeria, version 2 was superior to version 1. Compared to SRTM version 3.0, the last version produced relatively similar results, but no version outperformed it at any of the test sites. The same was also true in Nigeria. These results showed that a comprehensive vertical accuracy improvement was only partially realized through the successive development phases of the ASTER GDEM.

Keywords:

• Topography
• ASTER GDEM
• GPS benchmarking
• residual dispersals
• error ranking

Acknowledgements

We thank Ms. Seda ASLAN, Director of Spatial Planning Department, Ilbank General Directorate; Berkay Bektaş YIGIT and Ozgur OZTURK, Geomatics engineers, freelance state contractors and Mr. Vuslat BAKAR, Branch Manager, Land Registry and Cadaster, Istanbul Regional Directorate for supplying the reference GCPs in Turkey. We also thank Professor Francis Okeke, Department of Geoinformatics and Surveying, University of Nigeria, Enugu, Nigeria for sharing the ASTER GDEM v1 tiles for Nigeria from his personal repository. Special thanks to the Lagos State Surveyor General’s Office and the Department of Survey and Mapping at the Federal Capital Development Authority (FCDA) Abuja, and Surv. Ikenna Arungwa (Federal University of Technology Owerri, Nigeria) for providing the GCPs for Lagos and FCT. Deep appreciations are for Oytun Emre SAKICI, PhD, and Onder TOR, PhD, who again helped us bring the study to this level.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability

All GCPs used as ground references in either country were acquired from governmental offices on service/scientific only oriented purposes. Sharing might be possible, granting the release consent from them.