Recommended Free Satellite Imagery Sources: EarthExplorer, Copernicus, and GloVis
(EarthExplorer is recommended for Landsat; Copernicus is recommended for Sentinel-2)
The information on this page shows and describes free Landsat and Sentinel-2 imagery sources, including steps to use and download imagery from the viewers - by combining Landsat and Sentinel-2, it is possible to acquire a few images a week of the same location (though clouds affect if clear imagery is available). The imagery can be used in free QGIS, ArcGIS, or other true GIS software. As is mentioned below, Landsat imagery can be downloaded in surface reflectance format - however, both Landsat and Sentinel-2 all can be converted to surface reflectance with the tutorials in the Landsat & Sentinel-2 Surface Reflectance Guides drop-down menu.
EarthExplorer (offsite USGS page; opens in new tab): USGS Viewer that offers free Landsat 8, 7, 5, and 4 digital number (DN) imagery (can be downloaded directly from viewer) that you can convert to surface reflectance (SR) with tutorials on this website, and also offers Landsat SR Imagery (converted by USGS; need to order SR then wait for email). Sentinel-2A Top of Atmosphere (TOA) imagery can also be downloaded (though we recommend using the Copernicus site for Sentinel-2 imagery); see tutorials and courses here to covert Sentinel-2A to surface reflectance. IT IS NECESSARY TO REGISTER THEN LOGIN TO DOWNLOAD IMAGERY; THIS IS A SIMPLE PROCESS THAT STARTS WITH CLICKING LOGIN THEN CREATING A NEW ACCOUNT.
TO LOCATE AND DOWNLOAD IMAGERY FROM EARTHEXPLORER VIEWER (need to be logged in to download imagery): 1) Scroll in and out and pan by clicking and dragging hand icon to area of interest; 2) Left-click on screen to locate area of interest (or enter Path/Row); 3) Enter Date Range; 4) Press Data Sets; 5) Click + Landsat to open folder; 6) For DN imagery, select Landsat Collection 1 Level-1 for digital number (DN) imagery then download; for SR, select Landsat Collection 1 Level-2 (On-Demand) if you would like to order SR; 7) Press Results; 8) Select Download Options to download.
Copernicus (offsite ESA [European Space Agency] page; opens in new tab): ESA Map Viewer that is the source for both Sentinel-2A & 2B imagery downloads. Imagery is in Top of Atmosphere (TOA) format; a downloadable toolkit (convert to surface reflectance by using the free tutorial on this website, or access the toolkit link, and scroll to bottom of page for Sentinel-2 toolkit information) can be used to convert TOA to surface reflectance, or see tutorials and courses on this website to covert to surface reflectance. It is necessary to sign up to to login and download imagery; this is a simple process that starts with clicking on Open Hub, then clicking Sign Up.
TO LOCATE IMAGERY FROM OPEN HUB VIEWER (need to be logged in to download imagery): 1) Scroll in and out and pan by clicking the cursor and moving the screen to locate area of interest; 2) Click Box near the bottom left and left-click to draw box of area of interest; if the Box icon is not visible, click the long ovalish icon below the Map Layers icon near the upper right so the blue circle moves to the bottom, then click and drag to make a rectangle for the area of interest, or click to make a different shaped polygon (finishing with a double-click); 3) Click the three bars next to Insert search criteria near upper left; 4) Change Ingestion Date to Sensing Date on the Sort By drop-down menu (keep Descending on the Order By window); 5) Enter the imagery dates of interest for the Sensing Period; 6) Scroll down and select Mission: Sentinel-2; 7) Select S2MSI1C on Product Type drop-down menu; 8) Click the magnifying glass to start search; 9) Available imagery will appear in window, click link to download.
GloVis (offsite USGS page; opens in new tab): USGS Viewer that offers free Landsat digital number (DN) imagery and Sentinel-2A Top of Atmosphere (TOA) imagery - see tutorials and courses here to covert to surface reflectance. It is necessary to register to login and download imagery; this is a simple process that starts with clicking Login then Create New Account. Viewer has a nice 654 (SWIR, NIR, Red) RGB (Red, Green, Blue) false color imagery: green vegetation appears green because of high NIR reflectance and low SWIR and Red reflectance; water commonly appears blue because of higher blue reflectance than SWIR and NIR reflectance; snow appears aqua because of low SWIR reflectance and high NIR and red reflectance. You can also right-click and select View Browse to view the image of interest.
TO LOCATE IMAGERY FROM THE GLOVIS VIEWER (need to be logged in to download imagery): 1) Scroll in and out and pan by clicking and dragging hand icon to position the crosshair on area of interest; 2) Press button for Data Set (start with Landsat 8 or Sentinel-2); 3) Enter Date Range, and press APPLY; 4) Available images will be viewable and downloadable in the window near bottom right.