Figure 1.
Topographic map of Mali. Mapping software: Generic Mapping Tools (GMT) scripting toolset. The area of the Inner Niger Delta is indicated by green rotated square. Data source: GEBCO/SRTM. Cartography source: authors.
Figure 2.
Flowchart summarising general steps of data processing. Diagram source: authors (R library ‘DiagrammeR’).
Figure 3.
The location of the Landsat 8–9 satellite image in Mali, Mopti region of the Inner Niger Delta. The images were downloaded from the EarthExplorer repository, USGS. Background image: ESRI World imagery.
Table 1.
Metadata of the satellite images used in this study: Landsat 8–9 USGS1.
| Date | Spacecraft / ID | Path/Row | Entity Product ID | Scene ID | Cloud/Coverage |
|---|---|---|---|---|---|
| 2013/11/10 | Landsat 8 | 197/50 | LC08_L2SP_197050_20131110_20200912_02_T1 | LC81970502013314LGN01 | 0.12 |
| 2015/11/16 | Landsat 8 | 197/50 | LC08_L2SP_197050_20151116_20200908_02_T1 | LC81970502015320LGN01 | 1.12 |
| 2018/11/24 | Landsat 8 | 197/50 | LC08_L2SP_197050_20181124_20200830_02_T1 | LC81970502018328LGN00 | 0.00 |
| 2020/11/29 | Landsat 8 | 197/50 | LC08_L2SP_197050_20201129_20210316_02_T1 | LC81970502020334LGN00 | 0.00 |
| 2021/11/16 | Landsat 8 | 197/50 | LC08_L2SP_197050_20211116_20211125_02_T1 | LC81970502021320LGN00 | 0.00 |
| 2022/11/11 | Landsat 9 | 197/50 | LC09_L2SP_197050_20221111_20221113_02_T1 | LC91970502022315LGN00 | 0.00 |
1 The Sensor ID is common for all the scenes: Landsat OLI/TIRS (Operational Land Imager and Thermal Infrared Sensor), Collection 2 Level-2. Image courtesy of the U.S. Geological Survey (USGS). Product DOI: 10.5066/P9OGBGM6.
Figure 4.
Landsat 8–9 images of Inner Niger Delta in natural colour RGB values showing floodplain for six years (always November): (a) 2013, (b) 2015, (c) 2018, (d) 2020, (e) 2021, (f) 2022.
Figure 5.
Concept flowchart of the remote sensing data processing and analysis. Flowchart is prepared using R library ‘DiagrammeR’. Source: authors.
Figure 6.
Processing Landsat satellite image in RStudio for extracting NDVI.
Figure 7.
NDVI based on Landsat 8–9 images of Inner Niger Delta: (a) 2013, (b) 2015,(c) 2018, (d) 2020, (e) 2021, (f) 2022. Mapping: RStudio. Source: authors.
Table 2.
Results of the NDVI, SAVI and EVI computations of the Landsat 8–9 images.
| Time | NDVI Extreme Values | SAVI Extreme Values | EVI Extreme Values | |||
|---|---|---|---|---|---|---|
| minimal | maximal | minimal | maximal | minimal | maximal | |
| 10 November 2013 | −0.2311377 | 0.5879165 | −0.2235105 | 0.4281315 | −0.3576084 | 0.6849960 |
| 16 November 2015 | −0.2619293 | 0.5245128 | −0.1681281 | 0.2896889 | −0.2689985 | 0.4634939 |
| 24 November 2018 | −0.2603942 | 0.5258653 | −0.1830571 | 0.2938004 | −0.2928849 | 0.4700728 |
| 29 November 2020 | −0.2496693 | 0.4980780 | −0.1384092 | 0.2833834 | −0.2214491 | 0.4534074 |
| 16 November 2021 | −0.2522458 | 0.5417392 | −0.1564469 | 0.2790245 | −0.2503089 | 0.4464335 |
| 11 November 2022 | −0.3072812 | 0.5237642 | −0.1810541 | 0.2929085 | −0.2896799 | 0.4686475 |
Figure 8.
Histograms of the NDVI of the Landsat 8–9 images on Inner Niger Delta: (a) 2013, (b) 2015, (c) 2018, (d) 2020, (e) 2021, (f) 2022. Plots: RStudio. Source: authors.
Figure 9.
Soil Adjusted Vegetation Index (SAVI) based on the Landsat 8–9 images of Inner Niger Delta for November: (a) 2013, (b) 2015, (c) 2018, (d) 2020, (e) 2021, (f) 2022. Mapping visualisation: RStudio. Source: authors.
Figure 10.
Histograms of SAVI based on the Landsat 8–9 images of Inner Niger Delta: (a) 2013, (b) 2015, (c) 2018, (d) 2020, (e) 2021, (f) 2022. Plots: RStudio. Source: authors.
Figure 11.
Enhanced Vegetation Index (EVI) based on the Landsat 8–9 images of Inner Niger Delta for November: (a) 2013, (b) 2015, (c) 2018, (d) 2020, (e) 2021, (f) 2022. Mapping visualisation: RStudio. Source: authors.
Figure 12.
Histograms of EVI based on the Landsat 8–9 images of Inner Niger Delta for November: (a) 2013, (b) 2015, (c) 2018, (d) 2020, (e) 2021, (f) 2022. Plots: RStudio. Source: authors.
Figure 13.
Clustering based on the Landsat 8–9 images (bands 4-3-2): (a) 2013 RGB in true colour composites (TCC), (b) 2013 clusters, (c) 2015 RGB in TCC, (d) 2015 clusters, (e) 2018 RGB in TCC, (f) 2018 clusters. Mapping: RStudio. Source: authors.
Figure 14.
Clustering based on the Landsat 8–9 images of Inner Niger Delta: (a) 2020 RGB in TCC (4-3-2), (b) 2020 classification, (c) 2021 RGB in TCC, (d) 2021 classification, (e) 2022 RGB in TCC, (f) 2022 classification. Mapping: RStudio. Source: authors.
Figure 15.
Correlation plot showing probability cases for land cover classes in the Inner Niger Delta between 2013 and 2022 based on the results of the clustering of the Landsat 8–9 images using Kendall correlation method. Mapping: Python. Source: authors.