Always wanted to use satellite imagery, but werenâ€™t sure where to start? This blog shows you the five simple steps to find, download and view free imagery from the United States Geological Survey (USGS) Landsat satellite. Within fifteen minutes of reading this post you could have images from Landsatâ€™s 40 year global archive on your computer, like the one at the top of this blog of Plymouth Hoe from the 25th July 2014. So what are we waiting for, letâ€™s get started â€¦
Step One: Register!
Register for a user account with the USGS who, along with NASA, manages the Landsat data archive. Itâ€™s free to create an account, although you will need an email address and answer a quick few questions to help USGS assess their users. Once the account is activated, youâ€™re ready to go and you can download as much data as you need.
Step Two: Selecting your data download tool
USGS offers three tools for downloading data: Landsat LookViewer, Global Visualisation Viewer (GloVis) and EarthExplorer. Whilst all three offer options to view Landsat data, weâ€™d suggest you use GloVis as itâ€™s the easiest tool for new users to navigate. GloVis has a main screen and a left sidebar; the sidebar controls which Landsat image is displayed in main screen.
Step Three: Selecting the image
At the top of the sidebar is a map centred on the US, and the red dot indicates the position of the displayed image. To choose another location use the mapâ€™s scroll bars to wander the world, and simply click on the area you want to see. The four arrow buttons on the sidebar allow you to fine-tune the precise location.
Finally, select the month and year youâ€™re interested in, and the Landsat image that most closely matches your selection will appear in the main window. As Landsat is an optical sensor, it cannot see through clouds. If the chosen image has clouds obscuring the view, use the Previous Scene and Next Scene buttons to move easily around the closet images to your preferred date.
It is worth noting, the Max Cloud dropdown option, which allows you to choose the maximum percentage of the image you are willing to have covered by cloud. For example, if you select 40%, GloVis will only give you images that have 40% or less cloud coverage.
Step Four: Downloading the Landsat image
Once you have an image you like, simply click on Add at the bottom of the sidebar, and then click Send to Cart. This will take you to the download screen.
Your image will have entity ID, which was also visible in the Scene Information Box on the previous screen, consisting of 21 characters such as LC82040252014206LGN00, where:
- The first three characters describe the Landsat satellite the image is from and LC8 refers to Landsat 8.
- The next six (204025) are a Landsat catalogue number known as the Worldwide Reference Systems. If you remember the numbers for your area of interest, entering them in GloVis can be a quick way of navigating to that location.
- The following seven characters give the year (2014) and the day of year (206) the image was taken; the day of the year is a numerical count starting with 001 on 1st January, and so 206 is 25th July.
- A three-digit ground station identifier is next, in this case LGN indicates that the USGS Landsat Ground Network received this data.
- Finally, the last two-digits are a version number (00).
Clicking the download button, gives you options to download any of the Landsat products available for the image youâ€™ve selected. The LandsatLook Natural Colour Image is a jpeg version of the image you were looking at in GloVis, and is the easiest one to use. Click on download and the image youâ€™ve chosen will be downloaded to your computer.
Step Five: Viewing, and using, the Landsat image
The easiest way to view the image is to use the Windows Photo Viewer tool, where you will be able to see the image and zoom in and out of it. You can also open the image in Windows Paint, and use its basic tools to resize and crop the image. For example, the image on the right is a zoomed in version of the image at the top of this post.
Landsat images are free, and they carry no copyright; however, NASA does request you attribute them appropriately â€“ â€śLandsat imagery courtesy of NASA Goddard Space Flight Center and U.S. Geological Surveyâ€ť or â€śUSGS/NASA Landsatâ€ť â€“ which means you, can use Landsat images on your website or other materials. The full information on Landsat copyright can be found here.
Next week, weâ€™ll talk more about the other products you can download from Landsat. We hope these five simple steps have inspired you to find, download and use some Landsat data.