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Crop Agriculture

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

The point of this course is to explain how to download ongoing Landsat 8 and Sentinel-2 satellite imagery and to start tracking a field or other area of interest over time. This imagery should be viewed over the high-resolution (1-meter resolution or finer [1 x 1 meter pixels]) base layer imagery from Course 1C. Landsat 8 has a 30 meter resolution, while Sentinel-2 applicable bands have 10 and 20 meter resolution.

 

1) Click the Free Satellite Imagery link on the top menu, then click GloVis Next, or open the Data Sources folder and click the GloVis Next link. CURRENTLY, HOWEVER, OUR PREFERRED SOURCE TO DOWNLOAD LANDSAT IS EARTHEXPLORER, WHILE OUR PREFERRED SOURCE TO DOWNLOAD SENTINEL-2 IS COPERNICUS (BOTH CAN BE ACCESSED FROM THE FREE SATELLITE IMAGERY PAGE AND THERE IS INFORMATION ON THE PAGE DESCRIBING HOW TO DOWNLOAD IMAGERY FROM THOSE SOURCES).

2) If you do not have an account, click "Login" then "Create New Account" and follow the steps to create an account so you can download imagery.

3) The GloVis Next site will open (map may open to different extent than below).

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

4) Navigate to your your area of interest by scrolling or using +/- tool. It may somewhat challenging to find the correct area with the default basemap, but after using other basemaps we feel it is the best option. If you click the gear icon in the upper-right you can change basemaps. The crosshair limits the data that is displayed to that intersecting point (explained more in later steps). Click here for recent GloVis Next release notes (outside page; opens in new tab).

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

5) When you have found the proper location (may take some trial and error), click L8 (Landsat 8) circular icon then enter a date range you are interested in below and click Apply. You will want to keep the crosshair icon over the field or other area of interest; however, for the purposes of this course, we are tracking the field to the right of the crosshair so the crosshair is just to the left of the field. After clicking apply the image with the latest date will likely be visible, click "Previous" to progress to earlier dates (pausing long enought to let new image load). The down arrow icon means you have logged in and you can download. Keep in mind, that Landsat imagery has generous overlap areas with adjacent scenes - a location within an overlap area has a chance at more imagery than a location that is not.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

6) We will download this image from 8/6/16. There is a cloud to the left of the field - the impact of the cloud will be assessed later. Don't download yet, go to Step 7 first. Determining if imagery is assessing crop condition and providing useful information about yield patterns and/or quantity will be described in future courses.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

7) Before downloading, you should have some information about the imagery. Keeping in mind that in order to make a curved surface flat, spatial data needs to be modified or projected. If data is not projected, it will be associated with a geographical coordinate system (GCS), which is most often the World Geodetic System from 1984 (WGS 84) - Google Earth uses this system. Without getting into projections much (a good portion of a college semester can be dedicate to map projections), you should know if the data is projected, and if it is, what the projection is. Click the grid/table icon (highlighted below) to view metadata and find out (see Step 8).

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

8) The map projection (UTM) is shown near the middle of the table along with the Datum (WGS84) and the UTM Zone (17; which is 17 North if in the northern hemisphere and would be 17 South if in the southern hemisphere). Record all this information. Though data can be reprojected, it is helpful if all projected data is in the same projection.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

9) Close the metadata window and progress through the Landsat 8 scenes and download the ones you are interested in by clicking the download icon (highlighted). Keep in mind the downloads will include the natural color image (LandsatLook Images with Geographic Reference below) viewable on GloVis Next, as well as the individual bands (totally 900 MB to 1 GB). Also, as mentioned in previous courses, make sure your browser is set to ask you where to save downloads (as the Mozilla Firefox window shows below). Available Landsat imagery has been processed to different levels: T1 (Tier 1) is the highest available data quality; T2 (Tier 2) is second highest quality; RT (Real-Time) are made available for immediate made for download and are later reprocessed to a higher level (click here for Landsat collection information; outside page, opens in new tab). The faster the internet speed for this and other viewers and downloads, the smoother the process should be. Also, it helps to download during off times.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

10) After downloading the Landsat 8 images, click Sentinel-2 (in this case, the most recent in the data range is completely covered with clouds).

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

11) Download the Sentinel-2 images you are interested in. There may be Sentinel-2 images for the same area that have the same data that have different projections (this is possible with Landsat, but less common). Check the metadata (as explained in Step 8) and try to get an image with the same projection, if there are two for the same location. As is shown below, the projection is the same as in Step 8. It can also, be seen below, that while the file size for a complete tile of Sentinel-2 imagery is less than Landsat 8, it is still substantial. Keep in mind, that it takes awhile to get used to the nuances of viewing Sentinel-2 imagery. We have found that while dates may change when moving through the images, the image on the viewer does not appear to change. Also, it is important to realize that Sentinel-2 is available as entire tiles or parts of tile, so the size of downloads can vary dramatically. It is important to first download the much smaller Full Resolution Browse image, then view it over the background imagery in GIS to make sure you downloaded the correct extent.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

12) If using QGIS, open the Landsat and Sentinel-2 imagery before the background imagery from Course 1C, because the data frame in GIS will be set to the projection of the data first opened. The high-resolution imagery from Step 3 will likely have a different projections (NAD83) than Landsat or Sentinel which use WGS84, but it will line up fine in GIS. We will open Sentinel-2 first. Find the compressed download folder that was saved to your computer. The "Browse" image is not compressed when downloaded. The inside of the folder to which the downloads were saved to should appear similar to the following.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

13) Extract (decompress/unzip) the folder by right-clicking on it and extract it to the same folder. If you need decompression software, we recommend free 7-Zip (outside page; opens in new tab).

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

14) After extracting to the same folder (Extract Here), the uncompressed folder will appear.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

15) For different reasons, we have found it is useful to bring a copy of the image folder within the main folder forward. Open the extracted folder by double-clicking on it. You should see similar folders inside. Double-click on the Granule folder to open it.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

16) After opening the Granule folder, you will find a similar folder inside. Double click on the folder to open it.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

17) After opening the previous folder, you should see similar folders inside. The IMG_DATA contains the Sentinel-2 images; right-click on the IMG_DATA folder and copy it, then navigate back to the original open folder (Step 12) and paste the IMG_DATA folder there.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

18) After pasting the copy, the folder contents should contain the following.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

19) Open QGIS and add a raster layer.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

 

20) After navigation to the Sentinel-2 images, they may be in a format where the band number is not visible. If so, right-click somewhere in window and navigate to View then click List.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

21) The band number will now be visible. To add a layer, double-click or click once and open. You can add two or more by holding down the CTRL key and clicking on layer. You can add consecutive layers by dragging the cursor over them, or by clicking one, holding the shift key, and clicking another.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

22) Below Band 8 (an NIR layer) was added.

Course 1D - Downloading Landsat 8 and Sentinel-2 from GloVIS Next and Opening in QGIS (nearly world coverage)

 

23) For Landsat 8, steps to open in QGIS are simpler because there will not be numerous folders. Follow the same extraction steps as for Sentinel-2. One difference is that the LandsatLook image will be compressed, so that needs to be opened. It is recommended to make a separate folder within the main folder for the LandsatLook download (for organizational purposes), then extract the LandsatLook folder within its own folder. Landsat layers have a capital "B" followed by the band number.

 

Spend time getting used to the software and layers prior to any future courses. See Course 1A and 1B for a modest amount of information about using the software (including modifying the layers panel).

 

Slideshow for Cornfield Above (images automatically transition every 4 seconds or click arrows or dots)

Landsat 8 & Sentinel-2 Imagery for Cornfield Above (right of gear icon) and Vicinity (mostly corn and soybeans)

Keep in mind that the amount of clear imagery for a certain area over time is not only a function of cloud cover, but also whether or not an area is located in an overlap zone. The field above is in an overlap zone. Also, Landsat 7 can be used (but has stripings of missing data), as can Landsat 5 (for past assessment because it is no longer operational).