Working with Landsat Imagery

Table of Contents

  1. Working with Landsat Imagery
  2. Setting Up Your Workspace
  3. Downloading Data from the USGS Earth Explorer
  4. Creating New Imagery Files Using the Composite Bands Tool
  5. Creating True and False-Color Composites
  6. Skill Drill: Creating a Custom False-Color Composite

Creating True and False-Color Composites

When the layer first appeared in the dataframe, the image may have looked a little strange. The coloration has to do with how the computer monitor displays color. The computer monitor emits only three types of colors, red, green, and blue, each assigned to its channel.

An image of the RGB diagram.
The computer has three channels that emit red, green, and blue.

Receptors in the human eye, called cones, perceive color by the way they respond to the combination blue, green, and red wavelengths. The Landsat 8 composite is made up of many more spectral bands, including portions of the electromagnetic spectrum that the human eye cannot see. To visualize this on screen, we have to replace either blue, green, or red with an alternative spectral band.

An image of the RGB diagram with Near Infrared.
It is possible to use a portion of the electromagnetic spectrum you cannot see in either the red, green, or blue channel.

When we first loaded the image in ArcMap, an alternative spectral band is replacing blue, green, and red. It is the reason why the colors appear strange.

An image of Vancouver Island with weird colors.
To view this image in true-color, assign the Landsat 8 bands representing the blue, green, and red to the correct RGB channels.

To learn more about the Landsat 8 bands, navigate to the NASA website. Take a moment to read about each of the Landsat 8 bands. You should become familiar with this information. It will let you know which band combination will give you a true-color image.

An image of the NASA website
The NASA website provides detailed information about the Landsat 8 bands.

The table below indicates the Landsat 8 band numbers, the wavelength, resolution, and description.

Band Number

µm

Resolution

Description

1

0.433–0.453

30 m

Deep blues and violets

2

0.450–0.515

30 m

Visible blue

3

0.525–0.600

30 m

Visible green

4

0.630–0.680

30 m

Visible red

5

0.845–0.885

30 m

Near-infrared

6

1.560–1.660

30 m

Shortwave infrared (SWIR)

7

2.100–2.300

30 m

Shortwave infrared (SWIR)


When you are done reading about the Landsat 8 bands, go back to ArcMap. Right-click on the composite raster layer in the Table of Contents and select properties. Navigate to the Symbology tab. Make sure RGB composite is highlighted on the left. You should see the channels, Red, Green, and Blue with checked boxes next to them. One column over you should see a list of bands with drop-down arrows next to them. For the Red channel, choose band 4. For the Green channel, make sure it is band 3. Assign band 2 to the Blue channel. When ready, click OK.

An image of the True color settings on the symbology tab.
According to NASA, Landsat 8 numbers is red, green, and blue sensors as 4, 3, and 2.

The image should now be in true-color.

An image of Vancouver Island in True-color
By assigning the red, green, and blue bands to the correct red, green, and blue channel, the image now represents true-color.

Because the Landsat imagery captures spectral bands that the human eye cannot see, you can use different band combinations to view these wavelengths. You can accomplish this by creating a false-color composite. A false-color composite is produced by replacing either the red, blue, or green bands (4,3,2) with a band that outside of the range of human vision. In this next step, you will create a false-color composite that will allow you to see into the near-infrared. Take a moment to review the NASA website to find out which Landsat 8 band measures the near-infrared and what kind of mapping application for which it is used.

When you are ready, return to ArcMap. Create a copy of your composite layer in the Table of Contents. You should note that this action is different than creating a copy of the dataset in the Catalog Window. You don’t need to duplicate the data. Instead, you will create a duplicate representation of the data, or layer, in the Table of Contents. Right-click on the composite layer and select copy.

An image of the copy layer option.
Right-clicking on a layer opens a contextual menu with many options.

Then, right-click on the data frame, currently named “Layers,” and select Paste Layer(s).

An image of the Paste layers option.
You can copy and paste multiple layers in the Table of Contents. This action does not create new datasets, but only representations.

The new layer will have the same name and the same symbology settings. To avoid confusion, open the layer properties for the duplicate layer and navigate to the General tab. Name the layer “Near-Infrared False-Color Composite.”

An image of the General tab for near-infrared false-color composite.
You can rename a layer in the General tab of the layer properties.

When you are ready, uncheck the original layer in the Table of Contents. Navigate to the layer symbology tab for the near-infrared false-color composite layer. Assign the near-infrared band to the red channel, the red band to the green channel, and the green band to the blue channel. Then click OK. The result will be a conventional near-infrared false-color composite.

An image of Vancouver Island in near infrared false-color.
In a conventional near-infrared red false-color image, the red and pink areas display healthy vegetation. Click to view the image in a larger size.