Normalized Difference Vegetation Index (NDVI)

"The normalized difference vegetation index (NDVI) is a standardized index allowing you to generate an image displaying greenness, also known as relative biomass. This index takes advantage of the contrast of characteristics between two bands from a multispectral raster dataset—the chlorophyll pigment absorption in the red band and the high reflectivity of plant material in the near-infrared (NIR) band.

The documented and default NDVI equation is as follows:

NDVI = (NIR - Red) / (NIR + Red)

    NIR = pixel values from the near-infrared band
    Red = pixel values from the red band

This index outputs values between -1.0 and 1.0." (ESRI, 2018)

Sources

"Indices gallery". ArcGIS Pro, ESRI. 2018. 
http://pro.arcgis.com/en/pro-app/help/data/imagery/indices-gallery.htm.
Accessed February 1, 2019.

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Digital Earth Africa: Agriculture and Food Security

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This learning platform helps users understand the significance of Earth observations, explore Digital Earth Africa datasets through an interactive map, and get started on the basics of python coding for spatial analysis.

Digital Earth Africa makes Earth observation (EO) data readily available, delivering decision-ready products to the African continent. Data generated by Digital Earth Africa will provide valuable insights for better decision-making across many areas, including resource management, food security and urbanisation.

Space-based Solution

Collaborating actors (stakeholders, professionals, young professionals or Indigenous voices)
Suggested solution

Background information on the geology of Kenya

The geology of Kenya was studied to develop several maps with ArcGIS to understand the geological and topographical setting of the locations of the communities. The maps were obtained from the European Commission, Joint Research Centre (see sources). 
The geology of Kenya shows Metamorphic rocks in the western part due to high metamorphic processes. 
Tertiary and Quaternary Volcanic rock are located in the East due to the split of the East African Rift System  causing volcanic activity during these periods. 

Geology map of Kenya
Figure 1: National Atlas of Kenya - Geological Map. (n.d.). European Commission, Joint Research Centre. ​

Location of Samburu in the geological map of Kenya

The geology of Samburu County is mostly magmatic with Quaternary elements (for details see Figure 3). 

 

Geology map of Samburu County Krhoda et al. (2015).
Figure 3: Detailed geological map of Samburu County (Krhoda et al. 2015).

Location of the communities SW of Samburu County 

Map of important community locations
Figure 4: Map of locations of the community, from where water access would be needed in the vicinity.
Legend of the map of community locations

Samburu County's topographic map 

A topographic map from Samburu County was developed to understand where the major recharge zones are located. These zones in arid areas can also be indicated by the Normalised Differentiated Vegetation Index (NDVI). 

  1. Topographic map of Samburu province in Kenya
    Figure 5: Topographic map of Samburu province in Kenya. Credit: Topographic Map (2023)

    Location of water sources

The type and location of water sources in the Samburu District were studied with a map provided by the KSA. With the study of the geological maps and the water sources map, a geological and hydrological comparison was made, to understand where groundwater could be located. 
Fig.6. Samburu District - Type and Location of Water Sources, Key Landforms, and Soils (Symbols - See Map 11). (n.d.). European Commission, Joint Research Centre. https://esdac.jrc.ec.europa.eu/content/samburu-district-type-and-locati… (visited: 19.10.2023)

  1. Map of water sources in Samburu county, Kenya.
    Figure 6: Water sources in the Samburu county. Map provided by Kenya Space Agency. Source: G. de Sourza, Dept. Geography, University of Nairobi, J. Keza, Ministry of Water Development.

Development of the maps 

With the support from datasets obtained from the Kenya Space Agency a  differentiated vegetation map (NDVI), an elevation map (DEM), and a water points map were developed using ArcGIS Pro 3. 

DEM map in ArcGIS Pro3

  1. Add your Samburu county map dataset to the project. You can do this by going to the "Map" tab and using the "Add Data" button to import your county shapefile or feature class.
  2. Add Samburu Elevation Data: To create an elevation map, you need elevation data. Download the  Digital Elevation Model (DEM) data. Once downloaded, add the DEM to your map.
  3. Symbolize Elevation Data: Symbolize the elevation data to represent different elevation ranges. You can do this by right-clicking on the DEM layer, selecting "Symbology," and choosing a suitable color ramp and classification method.
  4. Add Legend: Insert a legend to the map by going to the "Insert" tab and selecting "Legend." Configure the legend properties to display the layers and symbology correctly.
  5. Add North Arrow and Scale Bar: Insert a North arrow and scale bar by going to the "Insert" tab and selecting "North Arrow" and "Scale Bar." Adjust the properties to suit your map layout.
  6. Adjust Map Layout: Go to the "Layout" tab to set up the map layout. Adjust the size of the map, add a title, and organize the legend, scale bar, and north arrow as desired.
  7. Save and Export: Save your project, go to the "Share" tab, and export the map as an image, PDF, or any other desired format.
Samburu county elevation map
Figure 7: Elevation Map made with QGIS. Version 3.32.3 / Version 3.28.11 LTR.

NDVI map in ArcGIS Pro3

ArcGIS Pro involves using the raster calculator to perform the necessary mathematical operations on the input bands. NDVI is typically calculated using the near-infrared (NIR) and red bands from a multispectral image.

  1. Add County Dataset: Add your Samburu county dataset to the map. You can do this by going to the "Map" tab and using the "Add Data" button to import your county shapefile or feature class.
  2. Add Satellite Imagery: import Samburu County Landsat or Sentinel imagery containing the necessary bands (Red and Near Infrared) for NDVI calculation. You can add the imagery by going to the "Map" tab and selecting "Add Data" or using the "Add Raster Data" option.
  3. Calculate NDVI: Open the "Image Analysis" window by going to the "Analysis" tab and selecting "Tools." Use the "NDVI" tool to calculate NDVI from the available bands. 
  4. The equation of NDVI is as follows: NDVI = ((IR - R)/(IR + R)); IR = pixel values from the infrared band and R = pixel values from the red band
  5. Symbolize NDVI: Symbolize the NDVI layer to visually represent vegetation health. Typically, healthy vegetation appears in shades of green, while less healthy or bare areas might be represented in browns or grays.
  6. Add Legend: Insert a legend to the map by going to the "Insert" tab and selecting "Legend." Configure the legend properties to display the NDVI layer and symbology correctly.
  7. Add North Arrow and Scale Bar: Insert a North arrow and scale bar by going to the "Insert" tab and selecting "North Arrow" and "Scale Bar." Adjust the properties to suit your map layout.
  8. Adjust Map Layout: Go to the "Layout" tab to set up the map layout. Adjust the size of the map, add a title, and organize the legend, scale bar, and north arrow as desired.
  9. Save and Export: Save your project, go to the "Share" tab, and export the map as an image, PDF, or any other desired format.
Samburu NDVI map
Figure 8: NDVI made with QGIS. Version 3.32.3 / Version 3.28.11 LTR. 

Water points map in ArcGIS 3

  1. Add County Dataset: Add the Samburu county dataset to the map. You can do this by going to the "Map" tab and using the "Add Data" button to import your county shapefile or feature class.
  2. Add Water Points Dataset: Import your water points dataset into the map. Use the "Add Data" button to add the water points layer. Make sure the dataset contains information about the location of water points.
  3. Symbolize Water Points: Symbolize the water points on the map. Right-click on the water points layer, go to "Symbology," and choose an appropriate symbol to represent water points. You may want to use a distinctive symbol like a blue dot.
  4.  Add Legend: Insert a legend to the map by going to the "Insert" tab and selecting "Legend." Configure the legend properties to display the water points layer and its symbol correctly.
  5. Add North Arrow and Scale Bar: Insert a North arrow and scale bar by going to the "Insert" tab and selecting "North Arrow" and "Scale Bar." Adjust the properties to suit your map layout.
  6. Adjust Map Layout: Go to the "Layout" tab to set up the map layout. Adjust the size of the map, add a title, and organize the legend, scale bar, and north arrow as desired.
  7. Save and Export: Save your project, go to the "Share" tab, and export the map as an image, PDF, or any other desired format.
Map showing the Samburu county water points
Figure 9: Elevation Map made with QGIS. Version 3.32.3 / Version 3.28.11 LTR.

Suggested aquifer location map

  1. Add the geological map of Kenya dataset: You can do this by going to the "Map" tab and using the "Add Data" button to import your county shapefile or feature class.
  2. Add Water Points Dataset: Import your water points dataset into the map. Use the "Add Data" button to add the water points layer. Make sure the dataset contains information about the location of water points. Delete the ones that are not relevant to the communities 
  3.  Add Legend: Insert a legend to the map by going to the "Insert" tab and selecting "Legend." Configure the legend properties to display the water points layer and its symbol correctly.
  4. Add North Arrow and Scale Bar: Insert a North arrow and scale bar by going to the "Insert" tab and selecting "North Arrow" and "Scale Bar." Adjust the properties to suit your map layout.
  5. Adjust Map Layout: Go to the "Layout" tab to set up the map layout. Adjust the size of the map, add a title, and organize the legend, scale bar, and north arrow as desired.
  6. Save and Export: Save your project, go to the "Share" tab, and export the map as an image, PDF, or any other desired format.
Map showing possible groundwater resources in the Samburu County based on the geology
Figure 10. Suggested aquifer locations in Samburu County based on the geology.

Interpretation

An aquifer could be located  in a magmatic/metamorphic basement, which suggests they moderate productivity and low groundwater potential. This is due to the fact that magmatic rocks have low permeability and therefore the groundwater recharge is low. 

Ideal outcome: A possible groundwater source exists near the communities homes and a borehole could be developed.

Conclusion

The communities are located in the SW of the Samburu District. The geology of the area is mostly magmatic and metamorphic. This suggests that the ground has very low permeability. However, near the location of the communities, there are two springs. These springs point to an aquifer in the area, where a well for the communities in the area could be developed. Ideally, various groundwater sources could be located with the maps and the support from space technologies. The next steps to be taken are with external actors, e.g. drilling and pumping tests approved by the local authorities

Future steps

  1. Work with hydrogeologists to prepare a borehole siting report as well as an Environmental Impact Assessment. Groundwater relief has some trusted hydrogeologists in their network in Kenya who could implement that and submit the information to the Kenya Water Resources Agency.
  2. Kenya Water Resources Agency needs to grant permission for drilling.
  3. Drilling and pumping test: A contractor performs drilling and a pumping test. The latter is to identify the appropriate pump to be used.
  4. Study the groundwater level, type of aquifer, groundwater recharge, groundwater vulnerability.
Relevant publications
Related space-based solutions
Sources

Barasa, M., Crane, E., Upton, K., Ó Dochartaigh, B.É. & Bellwood-Howard, I. (2018): Africa Groundwater Atlas: Hydrogeology of Kenya. British Geological Survey. Accessed [22.09.2023]. http://earthwise.bgs.ac.uk/index.php/Hydrogeology_of_Kenya

Kuria, Z. (2013): Groundwater Distribution and Aquifer Characteristics in Kenya. Developments in Earth Surface Processes, Elsevier. 16, 8, p. 83-107.

Krhoda, G., Nyandega, I. & Amimo, M. (2015): Geophysical investigations of Suyien Earthdam in Maralal, Samburu County, Kenya. International Journal of Physical Sciences. 2, p.33-49.

Makinouchi, T., Koyaguchi, T., Matsuda, T., Mitsushio, H. & Ishida, S. (1984): GEOLOGY OF  THE NACHOLA AREA AND THE SAMBURU HILLS, WEST OF BARAGOI, NORTHERN KENYA. African Study Monographs, Supplementary Issue 2, p. 15-44.

Touber, L. (1986): Landforms and solid of samburu District, Kenya. A site evaluation for rangeland use. The Winand Staring Centre for Integrated Land, Soil and Water Research. Report 6. 

Data sources (maps)

National Atlas of Kenya - Geological Map. (n.d.). European Commission, Joint Research Centre. https://esdac.jrc.ec.europa.eu/content/national-atlas-kenya-geological-map (visited: 19.10.2023). 

Samburu District - Type and Location of Water Sources, Key Landforms, and Soils (Symbols - See Map 11). (n.d.). European Commission, Joint Research Centre. https://esdac.jrc.ec.europa.eu/content/samburu-district-type-and-location-water-sources-key-landforms-and-soils-symbols-see-map-11 (visited: 19.10.2023)

Software
QGIS: A Free and Open Source Geographic Information System. Version 3.32.3 / Version 3.28.11 LTR. 
ArcGIS Pro. Version ArcGIS Pro 3.

Keywords (for the solution)
Climate Zone (addressed by the solution)
Dry
Habitat (addressed by the solution)
Region/Country (the solution was designed for, if any)
Relevant SDGs