Vertical Accuracy Assessment of 20-metre SPOT DEM using Ground Control Points from Lagos and FCT, Nigeria

P.C. Nwilo; C.J. Okolie; J.C. Onyegbula; O.E. Abolaji; M.J. Orji; O.E. Daramola; I.D. Arungwa

P.C. Nwilo Department of Surveying and Geoinformatics, University of Lagos, Lagos, Nigeria
C.J. Okolie
J.C. Onyegbula
O.E. Abolaji
M.J. Orji
O.E. Daramola
I.D. Arungwa Department of Surveying and Geoinformatics, Abia State University, Nigeria

Keywords: Digital Elevation Model, SPOT DEM, Ground Control Points, Accuracy Assessment, Root Mean Square Error

Abstract

Digital Elevation Models (DEMs) are one of the most commonly used datasets for representing variations in terrain
elevation. Technological advancements in satellite remote sensing have led to the proliferation of digital elevation
datasets with near-global coverage such as the SPOT (Satellites Pour L’Observation de la Terre) DEM. SPOT DEM,
which has a spatial resolution of 20m, has a stated absolute vertical accuracy of 10-20m. In 2012, the Office of the
Surveyor General of the Federation (OSGOF) in Nigeria acquired SPOT DEM version 1.0 for use in topographic
mapping. As such, it is necessary to conduct localised assessments of the DEM to validate the stated accuracies. In
line with this, the aim of this study is to conduct an accuracy assessment of the 20m SPOT DEM in Nigeria using
Ground Control Points (GCPs) acquired from sites in Lagos State and the Federal Capital Territory (FCT). In addition,
the DEM’s suitability for topographic mapping is assessed in line with international standards. The DEM for both
sites acquired from OSGoF and the GCPs were harmonised in WGS84 datum within ArcGIS software. Subsequently,
heights were extracted from the DEMs with the GCP locations, for which the following accuracy parameters were
computed – height differences, standard deviation (SD) and root mean square error (RMSE). In the results, the
analysis of the height differences yielded the following – Lagos (SD: 3.367m; RMSE: 3.423m) and FCT (SD: 6.280m;
RMSE: 6.285m). This assessment proves that the SPOT DEM for both sites surpasses the stated absolute vertical
accuracy, and hence can be relied upon as a reliable elevation dataset. It was also shown that the DEM satisfies the
Class 2 accuracy standard by the American Society for Photogrammetry and Remote Sensing, and is suitable for
deployment in small and medium scale topographic maps. To fully exploit the advantages of the DEM, it is
recommended that OSGoF should deploy it for use in other applications beyond topographic mapping.

References

Al-Yami, M.A.M. (2014). Analysis and Visualization of Digital Elevation Data for Catchment Management. PhD Thesis,
University of East Anglia, Norwich.
Arungwa, I.D., Obarafo, E.O. and Okolie, C.J. (2018). Validation of Global Digital Elevation Models in Lagos State,
Nigeria. Nigerian Journal of Environmental Sciences and Technology, 2(1): 78 – 88. ISSN (Print): 2616-051X
| ISSN (electronic): 2616-0501 https://doi.org/10.36263/nijest.2018.01.0058
Authority, T. V. (1998). Geospatial Positioning Accuracy Standards Part 3: National Standard for Spatial Data
Accuracy. National Aeronautics and Space Administration: Virginia, NV, USA.
Ayeni, O.O. (1981). Statistical Adjustment and Analysis of Data. Unpublished Manuscript.
Baudoin, A., Schroeder, M., Valorge, C., Bernard, M. and Rudowski, V. (2004). The HRS-SAP initiative: A scientific
assessment of the High-Resolution Stereoscopic instrument on board of SPOT 5 by ISPRS investigators,
Proceedings of ISPRS 2004, Istanbul, Turkey, July 12-23, 2004.
BudgIT. (2018). What we know about Lagos State Finances. https://yourbudgit.com/wpcontent/uploads/2018/05/LAGOS-STATE-DATA-BOOK.pdf (Date accessed: December 2nd, 2019).
CRISP (2019). SPOT 5 was successfully launched on 3 May 2002!
https://crisp.nus.edu.sg/~research/tutorial/spot5.htm (Date accessed: 2nd December, 2019).
EO4SD (2020). Digital elevation models. http://eo4sd-water.net/portfolio/product/digital-elevation-models (Date
accessed: 25th March 2020).
GISAT (2019). SPOT DEM. http://www.gisat.cz/content/en/products/digital-elevation-model/spot-3d/spot-dem
(Date accessed: 2nd December, 2019).
Harris Geospatial (2020). Digital Elevation Models Explained, Part 3: Which Product is Right for Your
Application?https://www.harrisgeospatial.com/Learn/Blogs/Blog-Details/ArtMID/10198/ArticleID/23636
/Digital-Elevation-Models-Explained-Part-3-Which-Product-is-Right-for-Your-Application (Date accessed:
25th March 2020).
Johnson, L. E. (2016). Geographic information systems in water resources engineering. CRC Press.
Li, Z. and Gruen, A. (2004). Automatic DSM Generation from Linear Array Imagery Data, Proceedings of ISPRS 2004,
Istanbul, Turkey, July 12-23, 2004.
Massera, S., Favé, P., Gachet, R. and Orsoni, A. (2012). Toward a Global Bundle Adjustment of SPOT-5 HRS Images,
Proceedings of the 22nd Congress of ISPRS (International Society of Photogrammetry and Remote Sensing),
Melbourne, Australia, Aug. 25 - Sept. 1, 2012, International Archives of the Photogrammetry, Remote
Sensing and Spatial Information Sciences, Volume XXXIX-B1, 2012
Nwilo, P.C., Ayodele, E.G. and Okolie, C.J. (2017a). Determination of the Impacts of Landscape Offsets on the 30-
metre SRTM DEM through a comparative analysis with Bare-Earth Elevations. FIG Peer Review Journal, 21
pps. ISSN No 2412-916X.
http://fig.net/resources/publications/prj/showpeerreviewpaper.asp?pubid=8560
Nwilo, P. C., Okolie, C. J., and Orji, M. J. (2017b). Applications of the 20m SPOT DEM for Geospatial Mapping in
Nigeria. Paper presented at the Nigeria Association of Geodesy (NAG), Port-Harcourt, Nigeria.
Olusina, J. Okolie, C.J. and Emmanuel, E.I. (2018). Quality Assessment Of Terrain Derivatives From 30m Global DEMs:
SRTM v3.0 and ASTER v2. Paper Presented at the 13th Unilag Research Conference and Fair, University of
Lagos.
Olusina, J., and Okolie, C.J. (2018). Visualisation of Uncertainty in 30m Resolution Global Digital Elevation Models:
SRTM v3. 0 and ASTER v2. Nigerian Journal of Technological Development, 15(3), 77-83.
Onyegbula, J.C. (2019). Quality Assessment of 20-metre SPOT DEM Using Field Data from Lagos State, Nigeria.
(Bachelor of Science BSc. Project), University of Lagos.
Paul, B.V. and Timothy, S. (1994). An evaluation of DEM accuracy: elevation, slope, and aspect. Photogrammetric
Engineering & Remote Sensing, 60(11), 7327-7332.
Reinartz, P., Lehner, M., Müller, R. and Schroeder, M. (2004). Accuracy Analysis from DEM and Orthoimages Derived
from SPOT HRS Stereo Data without using GCP, Proceedings of ISPRS 2004, Istanbul, Turkey, July 12-23,
2004
Rosengren, M. and Willén, E. (2004). Multiresolution SPOT-5 data for boreal forest monitoring. Paper presented at
the Proceedings of ISPRS Congress, Istanbul, July 12.
Satellite Imaging Corporation. (2015). SPOT-5 Satellite Sensor. Retrieved from Satellite Imaging Corporation:
https://www.satimagingcorp.com/satellite-sensors/other-satellite-sensors/spot-5/
SPOT Image (2005). SPOT DEM Product Description. Version 1.2 – January 1st, 2005.
Temme, A. J. A. M., Heuvelink, G. B. M., Schoorl, J. M. and Claessens, L. (2009). Geostatistical simulation and error
propagation in geomorphometry. In T. Hengl, & H. I. Reuter (Eds.), Geomorphometry: Concepts, Software,
Applications (pp. 121-140). (Developments in Soil Science; No. 33).
Wechsler, S. (2007). Uncertainties associated with digital elevation models for hydrologic applications: a review.
Hydrology and Earth System Sciences, 11(4), 1481-1500.
Yu, J.H. and Ge, L. (2010). Digital Elevation Model generation using ascending and Descending multi-baseline
ALOS/PALSAR radar images. FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney,
Australia, 11-16 April 2010. 15pp