Copernicus Open Access Hub or from several cloud services like creodias, Mundi web service, Onda, etc. In this tutorial we will see how to download and visualize Sentinel data with QGIS.
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.
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.
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.
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.
|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.
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.
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.
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.
|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.
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.
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.
|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!