How to use ArcGIS Pro and Landsat 8 Imagery to Calculate Chlorophyll Index and Global Environmental Monitoring Index

Jeff Oppong

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The advent of GIS tools and technologies has helped immensely in identifying, quantifying, and solving problems. GIS also provides a proactive way of rendering solutions by researching possible situations and implementing preventive schemes.

Over the years, GIS has improved the quality of lives of individuals through areas like telecom and network services, accident/incident analysis, urban planning, transportation planning, environmental impact assessment, flood damage estimation, natural resources management, environmental health, and safety, vegetation monitoring, among many others. 

Using ArcGIS Pro as a Tool to Develop Vegetation Indexes

ArcGIS Pro is an undeniable tool that pioneers the frontiers of the geospatial world today. It helps us to create, edit, manage, and store geo-data and attribute information in wide range of application areas.

Furthermore, ArcGIS Pro has provided scientific empirical evidence supporting the implementation of various schemes that seek to bridge the gaps among scientific research and the professional industry. ArcGIS Pro has helped to solve problems across several social, physical, environmental, economic and socio-economic strata.


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Vegetation Index Concepts in Geospatial

Considering the immense benefits of vegetation in recent times, there is a need to combine a definite scientific approach with geospatial tools to determine the state and spatial extents of vegetation cover. This prior knowledge will help inform proactive strategies for land use and ecosystem management. A relevant tool to pioneer in determining the eco-balance of the biosphere through vegetation monitoring of plants is satellite imagery.

Although many vegetation index concepts have evolved rigorously considering the role of green infrastructure in improving and sustaining the current demands of the global economy, correction of atmospheric effects is a considerable challenge.

Among the several vegetation indexes, the Chlorophyll Index (CI) and Global Environmental Monitoring Index (GEMI) have evolved. The difference between the Chlorophyll Index and GEMI is that GEMI considers atmospheric effects during the use of vegetation index procedures whereas CI does not.  

GIS Tutorial to Determine Chlorophyll Index (CI) and the Global Environmental Monitoring Index (GEMI)

As a result, this tutorial establishes a base for the improvement and sustenance of green vegetation in the global ecosystem by making use of Remote Sensing and geospatial techniques (ArcGIS Pro) to outline steps to follow to determine the Chlorophyll Index (CI) and the Global Environmental Monitoring Index (GEMI) of Landsat 8 imagery in an area of interest.

Figure 1 below shows a summary of the geospatial methodology employed during the process. 

A flow diagram with arrows and black boxes.
Figure 1: Flow of method for determining CI and GEMI in ArcGIS Pro.

Calculation of Chlorophyll Index 

To calculate the chlorophyll Index from Landsat 8 imagery in ArcGIS Pro, the following steps should be taken:

  1. Open ArcGIS Pro and create a new project. Select blank project from the interface that appears. Select and set output location and name for the new project. Click Ok.

The chlorophyll content in leaves is determined using the ratio of reflectivity in the Near Infrared (Band 5) and Green bands (Band 3). Landsat 8 imagery can be accessed from the USGS Earth Explorer’s website after a free sign up process. 

  1. After, import band 3 and band 5, by selecting the “Add Data” icon on the “Map” tab from the Menu bar.
  2. Navigate to the location of the bands 3 and 5 and click “Open.”
  3. Type and search “Raster Calculator” from the search bar of the geo processing toolbox. 

Chlorophyll Index is determined by the formula;

CI = ((NIR / Green)-1), where NIR represents pixel values of band 5 and Green represents pixel values of band 3 (Gitelson et al., 1996).

  1. Type the formula as shown in figure 3 below into the calculator search box.
Screenshots from ArcGIS Pro showing the raster calculator to calculate CI.
Figure 3: Calculating CI in ArcGIS Pro using the Raster Calculator.
  1. Click Run.

Calculation of Global Environmental Monitoring Index (GEMI)

For the calculation of GEMI, bands 4 (Red) and 5 (NIR) are used. The difference between GEMI and NDVI is that GEMI is able to withstand atmospheric effects. 

The formula for GEMI is given as:

GEMI = Eta*(1-0.25*Eta) – ((Red-0.125)/(1-Red)) for Landsat 8 (Pinty & Verstraete, 1992),

Where Eta = (2*(NIR^2-Red^2) +1.5*NIR+0.5*Red)/(NIR+Red+0.5)

NIR = pixel values from the Near Infrared band (Band 5)

Red = pixel values from the Red band (Band 4)

  1. To start with, import band 4 onto the map canvas using the “Add data” tool. 
  2. Type and search raster calculator from the search bar of the geoprocessing toolbox.
  3. From the calculator bar, input the formula as shown in figure 4 below to compute for “Eta.”
Screenshot of the raster calculator in ArcGISPro to calculate ETA;
Figure 4: Calculation of “Eta” in ArcGIS Pro.
  1. Click Run.

To calculate GEMI from “Eta”:

  1. Type and search raster calculator from the search bar of the geoprocessing toolbox.
  2. From the calculator bar, input the formula as shown in figure 5 below to compute for GEMI. 
Screenshot showing the raster calculator in ArcGISPro for calculating GEMI.
Figure 5: Calculation of GEMI in ArcGIS Pro.
  1. Click Run.

Clipping to Area of Interest

To consider streamlining the Landsat 8 imagery to a specific area of interest, the following steps are helpful:

  1. Type and search extract by mask in the search box of the geoprocessing toolbox.
  2. From the “extract by mask” panel, set “input raster” to be results of CI.
  3. Set “feature mask data” to desired boundary extent.
  4. Set “output raster” to desired location and name of output file.
  5. Click Run.
Screenshot showing the "extract by mask" clipping tool in ArcGIS Pro.
Figure 6: “Extract by Mask” in ArcGIS Pro. 

Project Map Showing the Estimation of Chlorophyll Index of Rhode Island in the United States.

Map showing in orange the areas of high Chlorophyll in Rhode Island.
Figure 7: Estimation of Chlorophyll Index of Rhode Island in the United States. Orange areas have a high Chlorophyll Index.

Project Map Showing the Global Environmental Monitoring Index of Rhode Island in the United States.

Map showing Rhode Island.  Areas in red have a high GEMI index.
Figure 8: Global Environmental Monitoring Index of Rhode Island in the United States.

References

Gitelson, A. A., Kaufman, Y. J., & Merzlyak, M. N. (1996). Use of a green channel in remote sensing of global vegetation from EOS-MODIS. Remote Sensing of Environment58(3), 289–298. https://doi.org/https://doi.org/10.1016/S0034-4257(96)00072-7

Pinty, B., & Verstraete, M. (1992). GEMI: A non-linear index to monitor global vegetation from satellites. Vegetatio101, 15–20. https://doi.org/10.1007/BF00031911

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About the author
Jeff Oppong
Jeff Oppong holds a BSc in Geomatic Engineering and currently a graduate student at Hohai University in China, where he's studying MSc. Harbor, Coastal, and Offshore Engineering. Jeff is a prolific researcher and a GIS/Remote sensing expert who aspires to be a change-agent and a renowned Engineer. Jeff Oppong can be contacted via email