Mapping and analysis of land subsidence in Awka south L.G.A using sentinel 1 data

Abstract

This study mapped and analysed land subsidence in Awka South, Anambra State, Nigeria with the view of determining the trend and rate of ground displacements within the study area. Its objectives are to model and analyze time-dependent ground displacements of Awka between 2019 and 2020; ascertain the trend, of the ground displacements between 2019 and 2020; determine the vulnerability of land subsidence in Awka South between 2019 and 2020 and to develop an inventory map to show land subsidence susceptibility areas in Awka South. The methodology involved TopSAR Split to split each sub swath with selected bursts into a separate product, application of Orbit File to acquire the satellite orbit file, back Geocoding to co-registers the four S-1 SLC split products (January and December of 2019 and that of 2020) of the same sub-swath using the orbits of the two products, enhanced spectral diversity to implement the network enhanced spectral diversity (NESD) method for TOPS coregistration, interferogram to compute (complex) interferogram, deburst to limited the results to the burst covering the study area, phase removal to estimate and subtract topographic phase from the interferogram, multilook and Goldstein Phase Filtering and Unwrap Phase to reduce speckle noise the residues in the phase unwrapping step respectively then displacement and range doppler terrain corrections to convert interferometric phase to displacement map. The results showed that subsidence in Awka South was ranging between a minimum of 2.33m to a maximum of 9.76m in 2019 and a minimum of 3.99m to a maximum of 11.22m in 2020. The results also indicated that Awka South had a trend of change of 6.95 % at the annual rate of change of 3.47m/y. The results indicated an expanding/increasing Subsidence in Awka South. The results obtained from the Land Subsidence vulnerability revealed high-risk zone occupied 33% of the entire area, spanning 5634.78 hectares, while Moderate risk zone occupied 16.18% spanning 2763.47 hectares while low risk zone occupied 50.82% spanning of 8678.22 hectares. The maps provided in this study is recommended as a spatial data addition for a decision support system on land subsidence issues.