# How to calculate the normalized difference vegetation index in ArcMap

Institute for Environmental and Spatial Analysis...University of North Georgia

## 1   Vegetation and the electromagnetic spectrum

Plants absorb red (R) and blue (B) lights to generate energy and create chlorophyll. This process is called photosynthesis. They reflect green (G) lights and near-infrared (NIR, invisible). This reflection of green lights makes vegetation look green.

During a growing season, chlorophyll in leaf cells actively absorb red and blue lights (decreasing red reflectance) and reflect green and infrared (increasing infrared reflectance), which leads to an increased ratio of $\def\NIR{\text{NIR}} \def\R{\text{R}} \frac{\NIR}{\R}.$

## 2   What is the normalized difference vegetation index (NDVI)?

The range of $\frac{\NIR}{\R}$ is from 0 to infinity, which is not ideal to handle. This spectral ratio can be transformed into the following form: $\frac{\NIR}{\NIR+\R}$ which ranges from 0 to 1.

Finally, the NDVI is defined as $\def\NDVI{\text{NDVI}} \NDVI=\frac{\NIR-\R}{\NIR+\R}$ which varies from -1 to 1.

## 3   Landsat 8

Landsat 8 is a satellite that orbits the Earth and collects spectral data in 11 different bands.

Band no.SpectrumWavelength ($\mathrm{\mu m}$)Resolution ($m$)
1Deep blues and violets0.433–0.45330
2Visible blue (B)0.450–0.51530
3Visible green (G)0.525–0.60030
4Visible red (R)0.630–0.68030
5Near infrared (NIR)0.845–0.88530
6Shortwave infrared (SWIR) 11.560–1.66030
7Shortwave infrared (SWIR) 22.100–2.30030
8Panchromatic (PAN)0.500–0.68015
9Cirrus (clouds)1.360–1.39030
10Thermal infrared (TIR) 110.6–11.2100
11Thermal infrared (TIR) 211.5–12.5100

### 4.1   Search criteria

Use the Use Map button to set your study area in the EarthExplorer and move to the Data Sets tab.

### 4.2   Data sets

Select Landsat 8 OLI/TIRS C1 Level-2. Level-1 data is called top of atmosphere (TOA) and not corrected atmospherically while level-2 data is called bottom of atmosphere (BOA) and provides surface reflectance data. Since we are trying to calculate a vegetation index, we need level-2 surface reflectance. However, it will take time to complete our request for level-2 data.

### 4.4   Results

Once you submit your request for level-2 data, you will receive a confirmation email followed by an email with a download link. It can take long depending on the size of your study area. The level-2 data will be in the tar.gz extension. You can use 7-zip to extract this file format. For this exercise, download the level-2 data for the UNG Gainesville campus at LC080190362020040401RT-SC20200407210432.zip. tar.gz is recompressed as zip.

## 5   Extract the Landsat 8 data

Using the File Explorer, extract the ZIP file.

## 6   Start ArcMap

Click Cancel because you want to create a new map.

## 7   Add the red and infrared bands

Drag and drop bands 4 (R) and 5 (NIR) from the File Explorer into ArcMap.

Add a basemap to find and zoom to the campus. Turning off the band layers will help.

## 9   Start the raster calculator

Find and start the raster calculator.

## 10   Calculate the red surface reflectance

SetNull("LC08_L1TP_019036_20200404_20200404_01_RT_sr_band4.tif", "LC08_L1TP_019036_20200404_20200404_01_RT_sr_band4.tif",
"VALUE < 0 OR VALUE > 10000") * 0.0001

## 11   Calculate the near infrared surface reflectance

SetNull("LC08_L1TP_019036_20200404_20200404_01_RT_sr_band5.tif", "LC08_L1TP_019036_20200404_20200404_01_RT_sr_band5.tif",
"VALUE < 0 OR VALUE > 10000") * 0.0001

## 12   Calculate the NDVI

("NIR" - "R") / ("NIR" + "R")