To discover the capabilities of imagery, you'll travel around the world and look through the lenses of several band combinations on the electromagnetic spectrum, including some invisible to the human eye.
Monitor mangroves in the Sundarbans
Your first destination will be the Sundarbans mangrove forest on the border of India and Bangladesh. With Landsat's imagery capabilities, you'll monitor the health of the mangroves in an ecosystem highly susceptible to change.
- Open the Esri Landsat app.
The app opens to the location of Esri headquarters in Redlands, California. Icons on the left side of the image represent the various spectral band combinations you can use to view the imagery. The default band combination is Natural Color, which is how you normally see the world. There are no mangrove forests here, so you'll navigate to the Sundarbans next.
To learn more about the Esri Landsat app, click About in the lower left corner of the app.
- In the lower left of the app, click the Bookmarks button.
A window opens, containing a list of bookmarks to interesting locations around the world.
- In the Bookmarks window, click Sundarbans.
The map extent changes from Redlands to the Sundarbans.
Since satellites can't capture the entire world in one picture, they take multiple pictures which are then stitched together into a patchwork image called a mosaic. In the current extent, you can see the diagonal line that divides two different images.
- Close the Bookmarks window.
Just from observing the area with the default Natural Color band combination, you can see a clear distinction between the heavily-forested Sundarbans and the highly urbanized Kolkata to the northwest. Much of the original mangrove forest was cut down, but what remains is protected by the Indian and Bangladeshi governments.
- In the upper left corner of the map viewer, click the plus button once to zoom in.
You can also zoom in or out using the mouse's scroll wheel.
- Zoom in two more times.
Now you can see the mangrove forest in more detail. Over the broad delta region, the forest is broken up by several rivers and complex tidal waterways. Many of its small islands are accessible only by boat, which hinders on-the-ground observation and intensifies the need for satellite imagery to monitor the forest.
Before you zoomed in, the forest looked like a solid green block of vegetation, but now you can see a variety of colors, ranging from green to purple to black. Is all of this forest cover? You'll find out with a spectral band combination. Spectral bands are ranges of wavelengths on the electromagnetic spectrum. Satellites and other image-capturing devices combine these bands to observe specific features that are more easily seen at those wavelengths. You'll learn more about the different bands later. For now, you'll use the Color Infrared band combination, which combines wavelengths on the light spectrum reflected by vegetation. Healthy vegetation appears bright red in Color Infrared imagery.
- On the list of band combinations to the left of the map viewer, click the Color Infrared band combination.
Almost the entire land area becomes red. While the identity of features in Natural Color imagery can be unclear, using the appropriate spectral band combination can remove the confusion and make for more accurate observations.
The Color Infrared band combination also allows you to monitor vegetation health. Healthier vegetation appears brighter red. Although most of the vegetation in the current view is pretty bright, some parts are brighter than others.
- Click and drag the map to pan around the Sundarbans area. Look for areas that appear unhealthy or are missing forest cover.
Although the area is protected by national governments, mangrove forests are highly susceptible to changes in sea level and water salinity. Loss of mangroves would not only compromise the habitat of the diverse species of flora and fauna that live here (including many endangered species such as the Bengal tiger), but also remove an important shield against monsoons for the neighboring localities. It's important to maintain the health of the forest, and imagery can help do that.
Find an oasis in the Taklamakan Desert
Vegetation is not the only thing imagery can monitor. Next, you'll travel to China's Taklamakan Desert and observe moisture levels in the arid locale.
- In the lower left corner of the app, click the Bookmarks button. Click the Taklamakan Desert bookmark.
The map extent changes.
- Close the Bookmarks window.
The boundaries of the oval-shaped desert are fairly clear. Since the Taklamakan Desert is primarily made up of sand dunes, its surface appears smooth and uniform from above, with few mountains or geological features. While the desert appears dry, you'll find moisture using spectral bands.
Landsat imagery is updated on regular intervals. Your images may appear different than the example images due to cloud cover or weather patterns.
- To the left of the map viewer, click Moisture Index.
Unlike Color Infrared, which was only a combination of three different spectral bands, the Moisture Index is a calculation that adds and divides the values of various bands to find moisture-rich areas. As such, it's not showing visible moisture (the blue areas in the above image are not bodies of water, for instance), but rather highlighting areas where moisture is likely to be. In fact, the Moisture Index uses many of the same bands as the Color Infrared band combination you used in the Sundarbans, as vegetation cover tends to coincide with moisture.
The Moisture Index reveals a few places in the Taklamakan Desert that aren't as dry as they seem. Now you'll take a closer look.
- Zoom to the area of moisture on the left side of the desert, outlined in the image below:
To zoom to a specific extent, hold the Shift key and draw a box around the area you want to zoom to.
You zoom to a place labeled on the map as Shache.
Shache, also known as Yarkant, is an oasis settlement fed by a river that runs down the nearby mountains. The Moisture Index shows that this area is abundant in moisture, but does not reveal what that moisture is being used for. You'll find out using a spectral band combination.
- To the left of the map viewer, click the Agriculture band combination.
The Agriculture band combination highlights agriculture in bright green. Most of the moisture-rich area you saw when you used the Moisture Index coincides with the agriculture you see using the Agriculture band. You can also see the location of the river that irrigates this valley.
It's important to be judicious when making visual analysis of satellite imagery. The Moisture Index indicated some areas of the desert as moisture-rich due to cloud cover rather than agriculture on the ground. Additionally, the Moisture Index may have missed areas with plentiful groundwater that had not been tapped for agriculture. When done properly, interpretation of satellite imagery can uncover truths about the world, but it is important to understand the limitations of imagery as well.
See submerged islands in the Maldives
Landsat imagery can see under water to a limited degree, creating images of shallow seafloor. To explore this capability, you'll travel to the Maldives, a small island nation off the coast of India. The Maldives is made up of over a thousand small, low-lying islands. So low, in fact, that the entire nation is in danger of disappearing beneath the ocean if sea levels continue to rise. With the bathymetric imagery capabilities of Landsat, you'll see the submerged islands—and the ones in danger of being submerged.
- In the lower left corner of the app, click Bookmarks. Click the Maldives bookmark.
- Close the Bookmarks window.
The imagery shows many small islands. The islands are formed out of coral and grouped into ring-shaped clusters called atolls. Unlike the previous bookmarks, which showed you a location with the Natural Color band combination, the Maldives bookmark has automatically made the Bathymetric band combination active. The Bathymetric band combination emphasizes underwater features. At the default extent, however, it's hard to tell what's underwater and what isn't.
- Zoom to the area labeled on the map as Malé, outlined in the following image:
Malé (alternatively spelled Maale) is the capital and main city of the Maldives. After you zoom, you may be able to see built-up urban environments on some of the islands. If not, you can zoom in further.
- Pan and zoom to the two islands directly west of Malé.
The smaller island to the right is Villingili, while the larger island to the left is Gulhifalhu. Villingili is a resort island, while Gulhifalhu is an uninhabited and partially submerged reef. The whiter portion on the left end of Gulhifalhu remains above water, while the blue side of the island is submerged. From this image, you can see the difference between features that are above and below water. Next, you'll explore islands that have been completely submerged.
- Pan north from Malé to see a large number of submerged and partially-submerged islands.
With Landsat imagery, you can monitor how sea level rise affects these low-lying islands. Although more mathematical measurements of sea level rise would be a more exact indicator, satellite imagery can paint a persuasive and compelling picture of the real situation on the ground (or in the water). Islands are sinking worldwide due to recent sea level rise; eventually, low-lying island nations like the Maldives may become uninhabitable.
Track development on the Suez Canal
Until now, you've explored imagery that is a snapshot of a single instant. But what if you wanted to track trends over time? What if you wanted to see how mangrove health today compared to ten years ago, or see if some of the submerged islands in the Maldives were above water in the past? The first Landsat satellite was launched in 1972, meaning that more than forty years of Landsat imagery is available for comparison. While older satellites were not equipped with all of the capabilities of later satellites, including the ability to see certain bands, their imagery can still be important for seeing how the world has changed. For now, you'll take a look at something that changed only in the past few years: construction on the Suez Canal in Egypt to expand its traffic capacity.
- In the lower left corner of the app, click Bookmarks. Click the Suez Canal bookmark.
- Close the Bookmarks window.
The map shows a portion of the Suez Canal that was extended in 2014. There are actually two canals that run parallel to each other. The canal on the left is the original Suez Canal, opened in 1869. The canal on the right is the addition.
- On the lower left of the app, click the Time button.
The Time Line opens. The Time Line shows all available imagery from as far back in time as Landsat satellites captured imagery of this area, and allows you to filter the imagery based on cloud cover or seasonality. The oldest image of this area is from November 10, 2000. Since Landsat imagery is updated periodically, the most recent image may be different than in the example image.
You can click and drag the Time Line to move it anywhere in the app.
- For Cloud Filter, choose 25% Cloud.
The Cloud Filter allows you to choose how much cloud cover is acceptable when searching for imagery. In this case, any imagery with more than 25 percent cloud cover will be excluded.
- Click the left side of the Time Line, above the date 10/11/00. Pan the map to better see the canal.
In the year 2000, no trace of the second canal existed. You'll scroll through the Time Line to watch the second canal's development as it occurred.
- On the right side of Time Line, click the plus sign to move to the next image of the area chronologically.
You may move through other dates as the Landsat App shows imagery close by. Continue until you see imagery that covers the same area as the canal.
The next date with canal imagery is August 23, 2006, still long before the second canal's construction.
- Continue clicking the plus sign until you reach December 12, 2014.
Although faint, you can see the foundation of the second canal to the right of the first.
- Continue clicking the plus sign to observe the canal's development over time.
By when does the canal appear to be completed? How long did its construction take? By accessing the deep compendium of Landsat imagery, you can answer these questions as well as other change-related questions across the world. Landsat imagery can track sea-ice extent, lake water-level fluctuation, and urban development. It can also monitor seasonal changes, such as crop cycles and vegetation bloom. When combined with spectral band combinations, it increases the potential for imagery analysis even further.
- When you are finished exploring, close the Time Line.
Create your own spectral view
You're not limited to using the preconfigured spectral band combinations. You can also build your own band combination in order to look at a place of interest to you in a new light.
- Use the Find a place search bar at the upper left of the map viewer to navigate to a location of interest to you.
When using the search bar, type the desired location using the following format: City, State or Region, Country.
While you are encouraged to use any location in the world, the example images use the default extent of Redlands, California. You can use the home extent by clicking the Home Extent button below the zoom button.
- To the left of the map viewer, click the Build button.
The Build Your Own window opens. To create a band combination, you'll input the three bands to be combined. You'll also adjust the stretch and gamma, which changes the contrast and brightness in the image.
Landsat imagery measures ranges of wavelengths of the electromagnetic spectrum, including some like infrared that are invisible to the human eye. These ranges are called spectral bands. The bands you can combine are described in the following table:
Number Name What this band shows best
Shallow water, fine dust particles
Deep water, atmosphere
Manmade objects, soil, vegetation
Near Infrared (NIR)
Shortwave Infrared (SWIR) 1
Cloud penetration, soil and vegetation moisture
Shortwave Infrared (SWIR) 2
Improved cloud penetration, soil and vegetation moisture
Bands 2, 3, and 4 (Blue, Green, and Red) make up the spectrum of light visible to the human eye. The Natural Color band combination, which your imagery currently uses, combines these three bands to approximate how imagery would look to a person. So what bands should your combination use? It depends on what you want to see. For instance, if you wanted to emphasize vegetation, you might use the Near Infrared, Red, and Green bands—which happen to be the bands that make up the Color Infrared combination you used in the Sundarbans.
- Set the first band to NIR(5), the second band to Red(4), and the third band to Green(3). Click Apply.
The imagery highlights vegetation as red, just like in the Color Infrared band combination. The order of the bands is also important, however. Band combinations are created by using each band as a composite of red, green, and blue colors. The first band is used for the red colors, the second band is used for the green colors, and the third band is used for the blue colors.
- Set the first band to Green(3), the second band to Red(4), and the third band to NIR(5). Click Apply.
The same features (vegetation) are emphasized, but they are emphasized with blue instead of red. In general, the bands used determine what kinds of features are shown more clearly, while the order of the bands determines the color. Next, you'll try a completely new set of bands.
- Using the table above as a guide, put in your own combination of bands and click Apply.
What features are emphasized in the image? Are these the same features you would expect to see emphasized based on the bands you chose? If you reorder the bands, how does the color change?
- Try as many band combinations as you like. Adjust the stretch and gamma to see how the image brightness and contrast changes.
With the ability to make all sorts of band combinations, look at any location in the world, and tap into images extending back many years, the possibilities of Landsat imagery seem infinite.
- Close the Build Your Own window.
Explore more locations
The Landsat app comes with several more bookmarked locations from around the world. These locations display dramatic or unique landscapes viewed through particular band combinations that highlight each location's most intriguing features. The remaining bookmarks include:
- Eye of the Sahara, Mauritania
- Gosses Bluff, Australia
- Exumas, the Bahamas
- Buradah-Riyadh, Saudi Arabia
- Gibraltar, the United Kingdom
- Lake Chilwa, Malawi
- Andasol Solar Power Station, Spain
- Dubai, the United Arab Emirates
- Banks Peninsula, New Zealand
- Mount Fuji, Japan
This lesson won't take you through each bookmark, but you can discover them on your own or navigate to other areas around the world you may want to explore with spectral imagery. What can you find using the app?