MAPPING BUILT-UP AREAS USING TWO BAND RATIO ON LANDSAT IMAGERY OF ACCRA IN GHANA FROM 1980 TO 2017

Abstract

Lack of historical land cover and urban growth governance structure makes spatial planning within the economic capitals of developing countries difficult. Monitoring urban built-up growth with insitu methods is complicated. In this paper, long-term Landsat archive is utilised to map the built-up areas of Accra, the economic capital of Ghana, in Africa. Simple two band ratio and band combination is coupled with historic Google Earth imagery to monitor built-up dynamics from 1980-2017. A 10-year period was sub-divided into three parts each; early period, mid period and late periodfor analysis. Maximum Likelihood classifier was used for the classification within the ENVI environment. The results show 11.90% as the highest and 4.63% as the lowest built-up growth rates between 2001-2005 and 1996-2000 respectively. Annual loss of non-built-up areas was 1.31%, and 48.57% over the entire study period. Water bodies lost 0.08% annually but 3.1% over the 37-year period. Highest and lowest overall accuracy were 87.18% and 81.31% respectively, with an average kappa coefficient of 0.7618. Gain in the built-up area was 1676.69 km 2 but non-built up areas lost 1576.10 km 2 while water bodies lost 100.60 km 2 . Results will be of interest to spatial planners, policy makers and land administrators.