Purpose: This short tutorial focuses on understanding how to query and download the data from the Goddard Earth Sciences Data and Information Services Center (GES DISC). Since GES DISC consists of 32 projects and missions, we will look into one of the commonly used data – The Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG GPM). For this tutorial, we will look at the extreme rainfall event that took place in Paraguay in 2015.
- If you haven’t already, go ahead and make a login for EarthData Login at https://urs.earthdata.nasa.gov/users/new. The EarthData Login is a common authentication system used across the DAAC and various other NASA sites for downloading the NASA data.If you are already a user, go ahead and login to the EarthData Login at https://urs.earthdata.nasa.gov/home
- Then to read more about the dataset we will be using, head onto https://daac.gsfc.nasa.gov/datasets/GPM_3IMERGDF_06/summary?keywords=gpm.
- In order to download the data, there are several options as shown in the right-side panel of Data Access. Giovanni is popular one, but for this exercise, we will use the one built in. Click on Subset / Get Data. A popup dialog opens.
- Fill in the dialogue as shown below. You can use the bbox -63.984,-27.861,-53.701,-18.369 or draw your own box covering the country of Paraguay.
- Note the precipitationCal has the daily precipitation value, and we will be using netCDF. NASA data are commonly available as netCDF so it’s worth to know how to use them in ArcGIS. Click on Get Data. The link of the data is shown. Click on individual file to download them. If large number of files, click on Download links list; it will download a txt file containing the list of the links. These urls are valid for two days. If you have some programming experience, you can use curl or wget to download those data. The instructions for the same is also available.
Note: If you don’t want to go through and have the downloaded files, go to this link and download the files. All the pain of downloading them has been done.
- Download the shapefile of Paraguay from this url. Or directly click here. If you use the HDX link, make sure you are using Level-0 shapefile.
- Go to ArcGIS pro, make a new project and insert a new map. Go to Map tab, click on Add Data dropdown. Click on Multidimensional Raster Layer.
- Click on Import Variables from File, and browse to your netcdf files. Click on the variable precipitationCal. We only downloaded this variable, so this is the only one available. NetCDF can store multiple data in it (hence called multidimensional raster), click which one is appropriate for you. The process needs to be repeated for all the files we downloaded. What if you have 100 files? You can use arcpy. Any other batch import tools that you can use? I’ll leave it to you to figure out.
- Repeat the process to add other time series files as well.
- Load the Paraguay shapefile that we downloaded earlier. Now clip each of these files to only contain the country. Save the clipped files. We have a clipped TIF file that we can operate as traditionally.
- Next, we want to calculate the average and maximum amount of precipitation between the start date (22nd) and end date (29th). How can we achieve this? (Hint: You can use the entire country as a zone).
- (Bonus): Many times, we are interested in visualizing the time series. Since we already have the data, let’s go about building an animation in form of gif or movie, shall we?
- Go to View tab, in the Animation group, click Add. The Animation tab appears as well as the Animation Timeline panel.
- Load your map view with the one you want it to be captured. For example, you can start with the clipped precipitation layer for 2015.12.22. Then click on Create first keyframe. Once you create your first keyframe, you can view the keyframe gallery. The animation will play in that order.
- Next you can begin adding the map view of subsequent dates. And in no time, you have all your keyframe loaded, and ready to export.
- In the Animation Tab, in the Export group, click on Movie, and you are ready to export your animation map. You can customize your export (frame size, speed etc) using file export settings. Next you can experiment with putting up the overlays like text, title etc. to your animation map. Good luck!