Table of Contents
- Working with Landsat Imagery
- Setting Up Your Workspace
- Downloading Data from the USGS Earth Explorer
- Creating New Imagery Files Using the Composite Bands Tool
- Creating True and False-Color Composites
- Skill Drill: Creating a Custom False-Color Composite
Downloading Data from the USGS Earth Explorer
In previous courses, you learned how to acquire data from public sources. Here you will download digital elevation models from the USGS Earth Explorer. Navigate to the Earth Explorer website at http://earthexplorer.usgs.gov/.
If you don’t already have an account, use the Register link located on the upper right of the page. Fill out the User Registration form to create an account.
If you are already registered, click the Login link located on the upper right of the page.
On the map, use the scroll wheel on your mouse to zoom to the region just north of the United States along the Pacific Coast. For this activity, the area of interest will be the region around Vancouver in British Columbia, Canada. Place a marker just north of Vancouver by clicking the map. The geographic coordinates appear on the Search Criteria tab on the left, and a corresponding pin gets placed on the map.
Next, to Search Criteria, click the tab that says Data Sets. Expand the plus sign next to Landsat, then Landsat Collection 1 Level-1. On the list of data sources, check the box for Landsat 8 OLI/TIRS C1 Level-1. When you are ready, click the Results button near the bottom.
The Results tab opens with a list Landsat 8 images that match the criteria. The images are listed in chronological order. In a previous activity, you learned how to browse through the results on Earth Explorer. For this activity, don’t worry about the specific location. Any of the images from the search results will work fine as an area of interest.
Because the area around Vancouver experiences frequent cloud cover, you need to search for the best image you can find. Ideally, one with little or no cloud cover. Make sure the image is nice and bright. If you recall, you can preview the images by clicking on the thumbnail.
The preview also provides additional metadata information. Once you have chosen your image, take a moment to find out what kind of metadata is available.
Try to find the answer to the following questions:
- On what date was the image taken?
- Does the image use a map projection? Which one?
- What spatial reference does the image use?
- What is the resolution or cell size of the image?
When done, close the metadata window. Click the download link for the best Landsat 8 image.
When the download options appear, click the download button next to Level 1 GeoTIFF Data Product.
The file may take a few minutes to download. In previous activities, you downloaded directly to your original folder. In this instance, the data automatically saves to your downloads folder on your computer. You will have to locate the compressed tar.gz file in the downloads folder and manually move it to your original folder.
This type of file, sometimes referred to as a tarball, uses double compression. You will have to use the 7zip software twice. Use the 7zip software to decompress the tar.gz file inside your original folder. Then, use the 7zip software again on the file that ends only with the extension .tar.
Remove both the compressed tar.gz and tar file when done. This step is especially important when working with imagery because the files are so large. Removing saves space and helps to prevent confusion later.