The Effect of Urbanization and Associated Climate Change on GNSS Signal (A Case Study in Addis Ababa City)
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Date
2020-09
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Addis Ababa University
Abstract
Fast urbanization and the associated micro-climate change in the urban setting is a subject of interest, as it will affect the day to day life of contemporary urban dwellers in different parts of the world and the future generation. Since urban climate change affects the atmosphere and because the atmosphere acts as a medium through which the GNSS signal travels from the GNSS satellites to the receivers, it is logical to expect that urbanization has an impact on the propagation of GNSS signal. The assumption that urbanization can affect the accuracy of positioning was the basis for this research activity. The main objective of this study was therefore, to investigate the association between urbanization, change in the urban climate, and the long-term change on the propagation of GNSS signal through the atmosphere. The study was conducted in Addis Ababa city and used different data sources such as that from Landsat, MODIS Normalized Difference Vegetation Index, MODIS Land Surface Temperature, and GNSS data. The IGS station ADIS GNSS daily solutions were computed for the duration 2008-2019 to monitor possible residual change in the three-dimensional location of the station. Similarly, the Landsat built-up index, the Normalized Difference Vegetation Index, and the Land Surface Temperature were computed for the duration 2000-20019. Since the different data sets have different resolutions and are dominated by seasonal effects, long-term variations were computed using least squares curve fitting and these were compared using a linear correlation technique. The result showed that there is a very high correlation between the long-term changes in vertical location of the GNSS station and the built-up expansion, the vegetation coverage, and land surface temperature with correlation value amounting to -0.9227, 0.9489, and -0.9862 respectively. Even though, the level of impact is not quantified a conclusion is drawn that urbanization and its impact on climate change has an effect on the propagation of the GNSS signal.