To find a Landsat image of Singapore, you'll use the LandsatLook app to explore the entire database of free Landsat imagery. You want a relatively recent image with minimal cloud cover. To download the image, you'll create a free account for the USGS Earth Resources Observation and Science (EROS) Center, which will allow you to download as much Landsat data as you want.
Landsat imagery can be large. The file you'll download in this lesson has a size of approximately 900 MB. Make sure you have enough disk space on your computer, and enough time to wait for the download, before proceeding.
Create an account
To download Landsat data, you need a USGS EROS account. The account is free, but does require you to give demographic survey data and contact information. If you already have a USGS EROS account, skip to the next section.
- Go to the EROS Registration System.
- Follow the onscreen instructions to proceed through the registration process.
Once you complete your registration, a message is sent to your email address to confirm your registration.
- Click the link in the email to activate your account.
Next, you'll open the LandsatLook Viewer and navigate to Singapore.
- Sign in to your USGS EROS account.
If you created your account in the previous section, you still need to sign in.
- Once signed in, open the LandsatLook Viewer.
The viewer opens to the default extent of the United States. The Load Images window includes parameters to search for Landsat imagery. The toolbar at the top of the viewer includes buttons for additional options and map controls. First, you'll change the map extent to Singapore.
- On the toolbar, click the Search button.
The Load Images window is replaced by the Search window.
- In the Search window, type Singapore. From the list of results, choose Singapore, SGP.
The map extent centers on the city-state of Singapore and the Search window is replaced by the Load Images window. Depending on your browser window size, the windows in the viewer may obscure part of the island.
- Pan the map, and zoom if necessary, to see the entire island.
Most of the island is heavily urbanized, with a few open green areas on the western and central parts of the island. Although the viewer has a scale bar in the lower left corner, at this extent it's difficult to discern Singapore's size relative to other geographic features.
- Zoom out five or six times. Compare Singapore's size to the nearby nations of Malaysia and Indonesia.
- Zoom back to Singapore.
A country the size of a single city presents unique challenges for land use and urban development. Although Singapore has expanded its area by reclaiming land from the sea, its confines remain generally fixed, necessitating stringent planning. But proper planning requires quality data.
Find an image
A real urban planning project would use a variety of data types from many sources. The single image you'll download from the Landsat imagery database will instead serve as a starting point, providing a high quality look at the entire city. Landsat imagery is multispectral, meaning it can be displayed with different bands of visible light to emphasize features such as vegetation, coastlines, or man-made structures. The image will be a good reference to which you can add more specialized data.
- In the Load Images window, for Year, choose to search for imagery between 2011 and the present year.
For accuracy, the image should be relatively recent. You can also search based on days of the year, which is useful for tracking seasonal trends or specific incidents, such as wildfires. For a general reference image, the day of the year doesn't matter.
- For Maximum Cloud Cover, choose 10% or less.
Clouds obscure ground cover and conceal features. Reducing the maximum cloud cover will return results with a clearer view of Singapore.
You can also search for imagery from specific Landsat sensors. All of them capture multispectral imagery, although they use different types of light and have different pixel sizes. They also have different years of operation. The default sensors are Landsat 8 OLI and Landsat 7 ETM+ SLC-off, which are the only sensors operational since 2011. You'll accept the default sensors.
- Click Show Images.
Because new Landsat images are added to the database daily, your search may have returned more images. It may also have a more recent image displayed on the map than in the example images.
All images within the map extent that meet your criteria are returned. Additionally, the most recent images are displayed by default. The Modify Images window, which opened after your search, indicates how many images were returned and how many are currently being displayed. In this example, two out of thirteen images are being displayed, but only one is visible on the current map extent.
- Zoom out until you can see all displayed images.
Depending on the number of active images and the zoom extent of the map, the basemap may disappear (such as in the example shown).
The images cover a larger area than Singapore. Two are currently shown. They are displayed as a mosaic, or a collection of multiple images pieced together. You only want to download one image, so you'll change the display to show one image at a time.
- In the Modify Images window, for Display Image, click Active Date Only.
- Zoom back to Singapore.
The map updates and only the most recent image is shown. This image is the most up-to-date for planning purposes. In this example, however, the most recent image has cloud cover that obscures parts of the city. You'll look at the other images returned by your search to decide the best for download.
- On the Active Date timeline, click the back arrow to display the next most recent image (you may need to wait a few seconds for the image to load).
Alternatively, drag the time slider to view the images.
Your search returned some images that were only partially within the map extent at the time of the search, so some images may not cover Singapore at all.
- Look at each of the returned images.
Some images may have black lines across the image, such as in the image from March 2, 2014:
These black lines are gaps in the sensor data caused by the failure of the Scan Line Corrector in the Landsat 7 satellite. Although these gaps can be filled, an image without significant data gaps is preferred for this lesson.
- From the remaining images, display one with minimal cloud cover that you would like to download.
The image that will be used in the example images is from June 27, 2013:
This image has some cloud cover, but it is focused on a small strip of the southern and eastern sections of the island, leaving most of the island clear. It's possible that a new image has been added since this lesson was written that shows Singapore with even less cloud cover. Feel free to choose a different image if appropriate.
Download an image
Now that you've chosen an image for your development project, you'll download it.
- At the bottom of the viewer, click Show Metadata.
The metadata table allows you to view information about the images your search returned and add them to your virtual cart for free download. You can choose to look at a table of the images currently displayed on the map or of all images returned by the search.
- Click Show Displayed.
The table changes to list images displayed on the map. You only have the image you want to download displayed on the map, so the table has one entry. The table contains other useful information about the image, such as its percentage of cloud cover.
- Check the box next to the table entry.
If you have multiple entries, use the Acquisition Date column to find the one you want.
- Above the list entry, click Zoom To.
The map zooms to the extent of the corresponding image.
- Confirm that the map is zoomed to the image you want to download. In the table, in the Standard Product column, click Download.
A new browser window opens, showing your Item Basket and all scenes pending order from your USGS EROS account. (If you're not signed in to your USGS EROS account, you may be prompted to sign in.) The scene you chose can be downloaded as either a LandsatLook Image or a Level 1 GeoTIFF Data Product. A LandsatLook Image is a PNG image file with no geographic information in its data. A GeoTIFF Data Product, however, contains coordinate information within the image itself. When added to a GIS application such as ArcGIS Pro, a GeoTIFF image will automatically be placed in its coordinate location, ready for analytical use. The GeoTIFF image also contains multispectral bands, allowing you to change how the image looks to emphasize different features on the ground. You'll download the Level 1 GeoTIFF Data Product.
- To the right of the available products for your pending scene, click the download icon.
A window opens, showing your download options and the size of each available download. The Level 1 GeoTIFF Data Product has a file size of several hundred megabytes (the size varies from image to image; the example image is 832 MB). Landsat scenes come in large file sizes and can take a long time to download. Make sure your computer has enough hard drive space before proceeding.
- Next to Level 1 GeoTIFF Data Product, click Download.
- Wait for the download to finish.
The download will probably take more than 15 minutes. You can use your computer for other things while the image is downloading.
In this lesson, you used the LandsatLook app to search Landsat's vast database of multispectral satellite imagery. You then located and downloaded an image that may be useful raw data for future development in Singapore. In the next lesson, you'll open the image in ArcGIS Pro and change its band combination to show Singapore more clearly.