Basic Processing (from downloading to merging) Landsat 8 Raw Images Using QGIS
In my foregoing article, I explained how to perform various land detections by using various Landsat 8 band combinations. In this article, I’d like to explain how to process Landsat 8 raw images in order to utilize them in detections. To be able to detect various land exposure utilizing band combinations, Landsat 8 raw images needs to be processed. They represent wavelength (some say bandwidth), resulting in grey images for each band with different wavelength and resolution. Landsat 8 raw images consist of 11 band files (B1.TIF – B11.TIF) and a Pre-Collection Level-1 QA Band File (BQA.TIF).
There are several sources to freely gather Landsat 8 images. In this article, I’ll show one of the popular sources of Landsat 8 images, USGS. Two ways to collect through USGS website: earthexplorer and glovis. I prefer the latter since I found it’s simpler than the first for beginners.
- To download Landsat 8 images, you need to have an account on USGS website. Go to glovis.usgs.gov. Point location of Landsat 8 images you want to acquire by moving the map window and adjusting the zoom in and zoom out button. As for example Landsat 8 images of Los Angeles, USA. Click on the image tile you want to download. In the dataset window, choose Landsat 8 OLI/TIRS C1 Level-1. You can change the date image captured and the cloud cover percentage in metadata filter window. Click download if you have located and obtained Landsat 8 image you’re searching for. Select Level-1 GeoTIFF Data Product. Ensure you have good internet connection since the data is big and USGS does not support download resume for its data yet.
- Extract downloaded ZIP GeoTIFF Data into a folder. Add all of TIF files into QGIS by dragging it from explorer to QGIS layer window or by adding then through add raster layer menu on QGIS. You can check all of TIF images are grayscale with different in the exposure as it renders wavelengths.
- We need to merge it in order to be able to create true colour Landsat 8 image and to detect a variety of land exposure. Open merge menu under Raster > miscellaneous > merge.
- On the merge window, click input layers […] > select all layers. Note: if we have not added Landsat 8 raw images into QGIS layer window, we have to add it first by clicking add files(s). Click Ok. Ensure “place each input file into the separate band” is checked. In the merge tab […] click save to file and save the merged Landsat 8 image into a folder. Finally, click run in the background.
Now the merged Landsat 8 image is able to show its band combination. Look at my previous article for band combinations.