In the previous lesson, you downloaded an image of Singapore taken by a Landsat satellite. In this lesson, you'll prepare the image for analytical use. First, you'll extract the image from the zipped file format it was downloaded as. Then, you'll add the image to a map in ArcGIS Pro and symbolize it by changing its band combination to better show Singapore's urban features.
Unzip the image
As you could tell from the download time, raw Landsat images have large file sizes. The file size is large partly because you actually downloaded a zipped file that contains more than ten images of the same area, each taken with a different spectral band. Together these images can be combined to create a multispectral image. To view the images, you must unzip the file. You'll also create a new folder to store the data.
- Create a new folder called Singapore Data in an easy-to-remember location on your computer, such as your Documents folder.
- Locate the downloaded file on your computer.
Depending on your web browser, you may have been prompted to choose where the file would be downloaded to before you began the download. Most browsers download to your computer's Downloads folder by default.
The file is named by its identification code on the USGS website, which is a long string of letters and numbers. The file has the extension tar.gz, which is a type of file that has been compressed twice instead of just once. You'll need to unzip the contents twice to view the images.
- Right-click the file and extract it to the Singapore Data folder.
The default process to extract files varies depending on your file compression utility.
- Locate the extracted file.
When extracted only once, the file has the same name, except its extension is .tar instead of .tar.gz. Some file compression utilities recognize .tar.gz files and automatically extract them twice.
- If necessary, extract the .tar file.
Once fully extracted, the .tar file contains 12 images (possibly fewer if you downloaded an image from a different sensor) and a text file. Each image has the same name as the original file except for the number at the very end, such as B1, B2, and B3. The B stands for band; each image shows a different spectral band of the same image. The Landsat 8 spectral bands will be discussed in more detail later in the lesson.
- Double-click the B1 image to open it in your computer's default image viewer.
The image is mostly gray, with some visible clouds. Features such as landmasses and oceans are indistinct and difficult to distinguish. Images of a single spectral band tend to look like this, as they cover only a small wavelength of light. To make an image that looks like what the human eye sees, multiple spectral bands are usually combined into a multispectral image.
- Close the image.
Open the image in ArcGIS Pro
To view the individual bands as a single multispectral image, you'll start a new project in ArcGIS Pro. A project contains databases, toolboxes, styles, and other folders that may be useful when making a map.
- Start ArcGIS Pro. If prompted, sign in using your licensed ArcGIS account.
If you don't have ArcGIS Pro or an ArcGIS account, you can sign up for an ArcGIS free trial.
When you open ArcGIS Pro, you're given the option to create a new project or open an existing one. If you've created a project before, you'll see a list of recent projects.
- Under Create a new project, click Map.aptx.
The Map.aptx template creates a project with a default basemap.
- In the Create a New Project window, change the project name to Singapore Development.
By default, the project is saved to the ArcGIS folder, located in your Documents folder. If you want to save the project elsewhere, browse to a different location.
- Click OK.
The project opens and displays a map view. In default ArcGIS Pro configuration, the Catalog pane is to the right of the map. The Catalog pane contains all the folders, files, and data associated with this project. You'll use this pane to establish a folder connection to the Singapore Data folder you created earlier.
If you've used ArcGIS Pro before, your Catalog pane may be in a different place or not visible at all. To show the Catalog pane, click the View tab on the ribbon at the top of the window. In the Windows group, click Catalog.
- In the Catalog pane, click the arrow next to Folders to expand it.
The default folder associated with the project is Singapore Development, a folder that was made when you created the project and which shares the project's name. The folder contains some empty geodatabases and toolboxes but no actual data.
- Right-click Folders and choose Add Folder Connection.
The Add Folder Connection window opens, showing a directory of your computer's files.
- Browse to and select the Singapore Data folder where you extracted your Landsat image.
The Singapore Data folder is added under Folders in the Catalog pane.
- Expand the Singapore Data folder.
The folder contains the 12 individual spectral bands. As you saw earlier, these images on their own show little useful information about the area they cover. To display a single multispectral image that contains all of the bands, you'll add the last file on the list, which ends with MTL.txt. MTL.txt indicates a metadata text file, but it is actually a raster product that has been generated with the information in the metadata file.
- Drag the MTL.txt file (the one with the raster icon) onto the map.
If a window opens asking to create pyramids for the image, click Yes.
The image is added to the map. It looks darker than the image you previewed on the LandsatLook app, but you can change its appearance to show Singapore more clearly.
Symbolize the image
The image's colors are dark and muted. Additionally, the image has black areas of NoData pixels around the edges of the image to make the image a square grid. You'll change the active spectral bands in the image to show the image with more distinct coloring and symbolize the NoData pixels as transparent to make them disappear from the map.
- In the Contents pane to the left of the map, right-click the multispectral image and choose Symbology.
If you've used ArcGIS Pro before, your Contents pane may be in a different place or not visible at all. To show the Contents pane, click the View tab on the ribbon. In the Windows group, click Contents.
The Symbology pane opens. The Band Combination section lists the bands used to display the image (they are also shown in the Contents pane). By default, the Red, Green, and Blue bands are used. These bands cover parts of the light spectrum visible to the human eye and together approximate a natural view of the landscape. For urban development, a view that emphasizes features relevant to the city may be more appropriate. The following table lists each band and what it shows best:
Number Name What this band shows best
Shallow water, fine dust particles
Deep water, atmosphere
Man-made objects, soil, vegetation
Shortwave Infrared 1
Cloud penetration, soil and vegetation moisture
Shortwave Infrared 2
Improved cloud penetration, soil and vegetation moisture
Black and white imagery, crisper detail
Thermal Infrared 1
Thermal mapping, estimated soil moisture
Thermal Infrared 2
Improved thermal mapping, estimated soil moisture
The Red band would emphasize the man-made objects of Singapore's urban environment, while the Near Infrared band would emphasize its coastlines and tight boundaries. The Shortwave Infrared 1 band would also be useful to mitigate the appearance of the clouds in the image.
- In the Symbology pane, for Band Combination, change the first band to ShortWaveInfrared_1, the second band to NearInfrared, and the third band to Red.
The image on the map changes automatically.
The coastlines are much more defined, and urban areas appear as distinct brown clusters. Next, you'll hide the NoData pixels by symbolizing them to be transparent.
- For Background, check Display background value.
The background, or NoData values, can now be symbolized. The default color for NoData pixels is No Color, which is automatically reflected on the map.
- Close the Symbology pane and zoom to Singapore.
This image gives a decent overview of the whole island, with differences between urban and green areas visible at a glance.
- On the Quick Access Toolbar to the upper left of the application window, click the Save button to save the project.
In these lessons, you searched the vast, 40-year database of imagery captured by Landsat satellites to find one showing the island of Singapore for a potential urban development project. After locating the image, you downloaded it, opened it in ArcGIS Pro, and changed its band combination to better show the city. While no urban development project would use only one image to plan for a city's future, this image (in conjunction with feature layers or other imagery) can provide a good starting point. Additionally, you can run analysis on this image to derive new meaning from what is shown. For some ideas about what you can do with imagery in ArcGIS, try the projects Classify Land Cover to Measure Shrinking Lakes and Assess Burn Scars with Satellite Imagery.