Transformation of Shuttle Radar Topography Mission (SRTM) Digital Elevation Data to Nigerian Height System

Abstract

Determination of height information using the classical field surveying and geodetic methods is rather expensive, rigorous and time consuming. It is also limited in the capacity of the earth surface data gathered. These conventional topographic mapping technologies have produced maps with a variety of scales and of uneven quality -some with astounding accuracy, some far less adequate. A good alternative is the Shuttle Radar Topography Mission (SRTM) derived Digital Elevation Model (DEM) which provides an excellent base data for extracting heights for topographic mapping. This will ameliorate the present situation. The SRTM space mission produced the most complete, highest resolution digital elevation model of the Earth. This study is aimed at developing a model for the transformation of the SRTM heights from WGS84 datum to the Nigerian height system (Minna datum) using SRTM derived DEM, topographic map and Global Positioning System (GPS) data of some parts of Lagos state, Nigeria. The chosen site corresponds to the area covered by one map sheet at the scale of 1: 25,000 (13.8km x 13.8km) which is 190.44sq.km. Software such as Globalmapper, Surfer 8.0 and ArcGIS 9.3 were used for specialized data processing and analysis. However, the datasets obtained were first projected to a common system and subsequently harmonized. This was carried out with an overlay of GPS points on the grid based SRTM and topographic DEM surfaces of the environment. Results showed deviation in heights with coinciding planimetry data. The average absolute error of the SRTM DEM for our test site was gotten as +/-0.22087m. Finally, by modelling this vertical shift, a transformation model that is accurate with a standard error of 0.238m was developed.

Visualisation of Uncertainty in 30m Resolution Global Digital Elevation Models: SRTM v3.0 and ASTER v2

“…Digital elevation models (DEMs) are fundamental spatial data infrastructure that supports a wide range of applications in environmental modelling (Nwilo et al, 2012). A DEM is defined as -an ordered or unordered digital set of ground elevations (spot heights) for terrain representation‖ (Zhou, 2017).…”

“…Elevations obtained by highly accurate Differential Global Positioning System (DGPS) survey are commonly used to validate DEM accuracy (e.g. Rexer and Hirt, 2014;Patel et al, 2016).…”

Validation of Global Digital Elevation Models in Lagos State, Nigeria

“…Elkhrachy (2017) submits that global elevation datasets are inevitably subject to errors, mainly due to the methodology adopted in extracting elevation information and the various processing steps the models have undergone. He further noted that errors in DEMs comprise mainly of two components: the horizontal component, often referred as the positional accuracy of the X and Y components; and the vertical component or the accuracy of the attributes.…”

“…Although a number of studies have been conducted in Nigeria (e.g. Ozah and Kufoniyi, 2008;Isioye and Obarafo, 2010;Ojigi and Dang, 2010;Isioye et al, 2012;Nwilo et al, 2012;Nwilo et al, 2017), the available information in the literature on the relative performance of the ASTER, GTOPO30 and SRTM DEMs in the country is still inadequate. This study contributes to the existing knowledge by conducting an accuracy assessment of these DEM products at a test site in Lagos, Nigeria.…”

“…Under those assumptions, vertical accuracy expressed as ±30m linear error at 90% can also be described as a RMSE of 18metres. The estimated absolute vertical accuracy for the areas of GTOPO30 derived from each source, with the method of estimating the accuracy is given in the GTOPO30 Readme (2017).…”