DEVELOPMENT OF A NEW BUILT-UP INDEX FOR DELINEATING BUILT-UP LAND FEATURE IN SATELLITE IMAGERY: STUDY AREA BLANTYRE

Impervious surface area (ISA) is a key factor for monitoring urban environment and land development. Automatic mapping of impervious surfaces has attracted growing attention in recent years. Spectral built-up indices are considered promising to map ISA distribution due to their easy, parameter-free implementations. This study explores the potentials of impervious surface area extraction for mapping urban expansion from Landsat imagery using a study area of Blantyre city, Malawi. A new built-up index is proposed in this study. To evaluate its effectiveness, the results from this index was compared to the results from ISEI, NDBI, NBI and UI using the Landsat 8 OIL images of 2016 and 2020. Accuracy assessment was calculated on each and every index by using confusion matrix, and from the results, the overall accuracy for the new index in 2016 image was found to be 89% and from 2020 images is 80.45% and the overall kappa coefficient is 75.49% for the 2016 image and 60.6% for the 2020 image. The indices were also applied on Gaborone and Dodoma cities in Botswana and Tanzania in order to ensure the effectiveness of proposed index. And in additional to these, the area covered by the built-up on RGB image of Blantyre city and from the proposed index results of Blantyre were calculated in hectares and the results were closely related. Although the proposed index shows some good performance on Dodoma and Gaborone cities but the results from our study area are more superior than the results from these cities. Therefore, the proposed method is superior index based on ISA mapping in relatively compared with the other indices. However, to ensure its superiority the index must be tested in other areas other than Gaborone and Dodoma, and on other images captured by other sensors for instance worldview, sentinel- 2 etc.