The Landsat Explorer Web Mapping Application, Revisited

In four years since we last wrote about what was then the “Landsat thematic bands application,” many features have been added to this tool. Furthermore, as it is, I believe, one of the very most useful mapping tools for research and instruction, ’tis time for an updated review. Now known as the Landsat Explorer app, this web mapping application is now part of the Living Atlas set of apps, a very useful set of tools that includes the Wayback imagery (which we have written about here), the water balance app, and others. I have used the Landsat Explorer app for research and also in a wide variety of instructional settings, from upper primary to university level, and in remote sending and GIS courses, but also in geography and environmental science courses. You could also use it for research purposes. With this app, Landsat images for the whole world are available to you at your fingertips, over a 45 year span of time. Truly amazing.

The Landsat Explorer app’s main tools are its renderer, identify, time-swipe-change, mask, save layer to ArcGIS Online, export, and add data from ArcGIS Online.

The renderer allows you to choose from about 10 band combinations, from agriculture to vegetation index to geology and more. This is incredibly responsive and useful. The only slight misgiving I have from an instructional standpoint is that I wish the band combinations would be visible, so students and others understand some of remote sensing theory. To the app’s credit, though, you can choose your own custom bands and indicate the band number you wish to display, shown below.

Identify allows you to learn the image scene ID, acquisition date, and cloud cover.

Most likely, most users will use this application for understanding change over time via imagery. You can use the swipe tool and the change detection tool for this. Before you can compute change, you will need to select Primary and Secondary Dates. Use the Time Slider to select an earlier date and click the Set as Secondary Layer button. Then, select a later date and move to the Swipe tool or the Change Detection tool to compare them. The Swipe tool for the Mt St Helens area for 1990 and 2019 are shown below. The swipe tool is my favorite but admittedly sometimes a frustrating tool to use, to get exactly the images you wish to have on the left and right side. It is also a bit confusing in the app to understand which image corresponds to which dates. All I can say here is to go through the very helpful tutorial, available on the lower left via the ‘graduation cap’ symbol, and carefully follow the steps.

The change detection tool can calculate changes in vegetation health (NDVI or SAVI), burned area (Burn Index), water content (Water Index), and urban area (Urban Index). Three items of interest: First, I am using the vegetation index, but you can use this drop-down to change to the soil adjusted vegetation index, the burn index, the water index, and the urban index. Second, the sliders can be used in your change detection. Third, you can define your own area of interest rather than take the default scene that is in your browser window.

Save allows you to save the top layer to your ArcGIS Online account (a log in to your own account is required). Export allows you to extract whatever map (the top layer in the app) you have built as a local file–a high resolution TIFF with customizable pixel sizes and spatial reference. This is a file that you can then bring into ArcGIS Pro or any GIS software for further analysis.

As the name implies, “Add data from ArcGIS Online” allows you to bring in your content from your own ArcGIS Online account into the Landsat viewer (a log in to your own account is required). After doing so, however, it wasn’t clear how to obtain a list of layers so I could turn my added layer off, so in my view this is the only tool I would probably would not use much. “Stories” shows a selection of 5 areas around the world where Landsat imagery is applied to solve real-world challenges, including in flood analysis. The “points of interest” choice here is particularly useful for instruction, guiding you to numerous places around the planet with explanations of each human-built and natural feature with a specific combination of Landsat bands.

Finally, if you wish to create your own similar type of app in the ArcGIS platform, go to the GitHub imagery zone and to the ArcGIS Developers site. Give this tool a try and I look forward to your comments.

–Joseph Kerski