Installing Semi-Automatic Classification Plugin
To download and visualize Sentinel satellite imagery in QGIS we are using a
plugin which is called
Semi-Automatic Classification Plugin. Therefore firstly we have to install this plugin.
From Plugins menu select Manage and Install Plugins... The
plugin window will appear as in figure 1. In the search field type
semi-automatic, and the plugin will be shown in the available plugin
list. Check the plugin and install it.
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Figure 1. Installing Semi-Automatic Classification Plugin |
After installation, the Semi-Automatic Classification working toolbar as shown
in figure 2 will be added to your QGIS dekstop. If it's not appear in your
QGIS dekstop, go to View menu, select Toolbars and make sure
SCP Working Toolbar is checked.
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FIgure 2. Semi-Automatic Classification Working Toolbar |
In this tutorial we will download Sentinel-2 data around Tokyo area, Japan, as
seen in figure 3. To identify the interest area, add Open Streep Map (OSM) or
Google Map basemap layer into QGIS map canvas. You can add a basemap easily
using
Tile+ Plugin.
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Figure 3. Tokyo Surrounding Area |
Downloading Sentinel-2 Data
Now we are ready to download Sentinel data. Click the most left icon in the
SCP working toolbar. The Semi-Automatic Classification Plugin window will
appear as in figure 4. Select Download products in the left window
menu. On the right menu we'll find three tabs: Login data, Search and
Download Options. Before using this tool to download Sentinel data, we
have to provide a registered user account and password in the
Login data tab menu below the Login Sentinels section. In the
Service option fill in with
https://scihub.copernicus.eu/apihub. If you don't have any user
account, the registration can be done at
scihub.copernicus.eu.
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| Figure 4. The Semi-Automatic Classification Plugin window |
Now move to Search tab, in this tab menu we need to specify some search
parameters like upper-left and lower-right coordinates, maximum cloud
coverage, date range, type of products (Sentinel 1, 2 or 3) and number of
results.
The extent coordinate, Upper Left(UL) and Lower Right(LR) coordinate can be
determined using left click and right click. On the map, point the cursor to
the upper left, then left click and point to the lower right corner, then
right click to get lower right coordinate as shown in figure 5.
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Figure 5. Determine Coordinate Extent |
After defining all download parameters. Click the Find button to start searching all available Sentinel-2 imagery that meet the search parameters. Figure 6 shows the searching result. In the product list we can see some information in seperate columns like Product ID, Acquisition date, Cloud coverage, Zone/Path, etc. Sentinel imagery are divided based on Universal Transverse Mercator(UTM) zone. Therefore you need to select a right zone for your interest area. Might be the interest area is within a zone or consist of multiple zones. To verify you select a right scene, view it in QGIS map canvas by clicking Display preview of highlighted images in map button. The selected image/scene will be previewed in QGIS map canvas as in figure 7. Moreover in selecting the right scene, cloud coverage is another parameter to consider, choose a scene with minimum cloud coverage in your interest zone.
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Figure 6. Sentinel Imagery Searching Result |
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Figure 7. Sentinel-2 Image Preview |
The last tab menu is Download options. In this menu we can specify
which bands to download as seen in figure 8. Downloading all bands will
require big storage capacity. All imagery scenes could have size 800MB-1000MB.
In the bottom options disable Preprocess image, because it will
take some times for doing it, and you can do it later if you want to.
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Figure 8. Download Options |
If you're already satisfied with options setting. Lastly click
Run button to download selected Sentinel-2 Imagery and specify where it
will be stored. Take a cup of coffee and relax while waiting it done.
Visualize Sentinel-2 Imagery
After downloading the Sentinel imagery, now let's visualize it. If you add an
individual band image, you'll see a grayscale image like figure 9a. To make it
more interesting we can visualize it with several bands combination, for
example to view the image in true color as in figure 9b, we combine images
with band 4-3-2.
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| Figure 9. Grayscale and True Color Sentinel-2 Satellite Imagery Visualization |
To make a band combination we have to create a band set, as following:
2. Select images band 1,2,3 and 4. The selected images will be added
into Band set and also into QGIS map canvas layer.
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Figure 10. Sentinel Band set images |
3. Switch back into QGIS Dekstop main window. From the Semi-Automatic
Classification working toolbar, in the field next to RGB option, type
4-3-2 and press Enter.
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FIgure 11. Specify Sentinel Band Combination |
4. The band combination process will be running. When it done a layer which is
called Virtual Band Set will be added into QGIS layer.
Moreover you can play with other band combinations depends on your
application, for example to find geological features: 12-11-2,
Agriculture:11-8-2, healthy vegetation 8-11-2, false color urban: 12-11-4,
etc. Some examples of Sentinel-2 band combination can be seen in figure 12.
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| Figure 12. Some examples of Sentinel-2 band combination |
That's all this tutorial how to download and visualize Sentinel satellite
imagery data in QGIS using Semi-Automatic Classification Plugin. We had learnt
how to install the plugin, searching available Sentinel imagery based on some
criteria and visualize it in natural color band combination. Thanks for
reading!
