Extract Earth Observations using HydroGlobe

Venkatesh Merwade, Purdue University-Main Campus
Author Profile
Initial Publication Date: November 15, 2017


The objective of this step is to download MODIS evapotranspiration data for a geographic region. This step is created for some testing purposes and should not be used for any instruction at this point.

Conceptual Outcomes

Students will be able to download and plot MODIS evapotranspiration data. Students will be able to describe monthly, seasonal and annual variations in Evapotranspiration over a given geographic region.

Practical Outcomes

Students will be able to interact with the HydroGlobe tool for downloading earth observations for any geographic region.

Time Required

30 minutes.

Computing/Data Inputs

Computing/Data Outputs

Hardware/Software Required


Login to mygeohub.org

This step requires all users to have an account on mygeohub.org or an account at a research and higher education institution which is part of the InCommon Federation to access the HydroGlobe data download interface directly from this page.

Case I: If you have an account on mygeohub.org, you can go to the login page, select Sign in with your mygeohub account, and login using your MyGeoHub account. Then go to the next step.


Case II: If you do not have an account on mygeohub.org but have an OpenID account (such as Google account) or an account at a research and higher education institution which is part of the InCommon Federation (such as Purdue University), go to the MyGeoHub login page and select "Sign in with CILogon".


In the CILogon interface, search and/or select your institution to login as shown below.


After you select your institution and login using your institution's account, you will be asked to create a new MyGeoHub local account or link your CILogon account to an existing MyGeoHub account. Click on "Create New" button, and follow the steps to create a new local account. After you fill out all the required information, you will get an email to activate your local mygeohub account. This is a one-step procedure, which you will not repeat in the future when logging in using your institution account via CILogon.


Case III: If neither Case I or Case II do not work for you, please use this link to create an account. After you fill out all the required information, you will get an email to activate your mygeohub account. After that, go to the login page, select Sign in with your mygeohub account, and login using your new MyGeoHub account.

Downloading ET Data for Cedar Creek Watershed in Indiana from 2010-2015

By completing this task, you will be able to download remotely sensed evapotranspiration (ET) data for any watershed. A watershed may have multiple sub-basins. Therefore, the GIS shapefile of the watershed may have multiple polygons, i.e., one polygon representing the boundary for each sub-basin. Taking such a GIS shapefile as input, HydroGlobe tool will download ET time series for each of the sub-basins within a watershed.

This task will download ET data for the Cedar Creek watershed in Indiana, USA. Click here to get started with the data downloading process for the given shapefile. This shapefile has 51 polygons representing the 51 sub-basins in Cedar Creek watershed.

Once you click on the above link, you will see a message box showing that the shapefile has been downloaded and loaded. Click the OK button. You will see the following information on your screen with a small map window showing the spatial extent of the watershed.


Note the earth observation product type. In this task, you are accessing ET data from NASA's MODIS satellite. The tool also allows you to download soil moisture data from SMAP, precipitation data from GPM among other satellite products.

Change the default time-period for which you want to extract data. Let's select 01/01/2010 – 12/31/2010. Give a name for this data request (e.g. watershedname_MODISET_2010 where "watershedname" needs to be replaced by CedarCreek). Click on the Get Data button.


You will now see a message box showing that the data download request has been submitted. Click on the Status tab. The Status tab lists all the data requests that have been sent from a user account (in this case, yours). The most recent request (i.e. CedarCreek_MODISET_2010 in this example) will appear on top of the list with a "Pending" status. The Pending status means that your request is still being processed.

If it is your first attempt to download remotely sensed data using HydroGlobe, the Status tab on your screen might look different. Note the Requested Time in the Status tab which helps you to visualize a dataset that you might have downloaded previously.


Select the row showing your data request (e.g. the first row in the above screenshot) and click the Refresh button. After a while, you will see that the "Pending" status changed into "Done" which means your data is ready for download and visualization. Time required by the tool to extract the data can vary depending on the size of the watershed and number of sub-basins therein.

If you click the Visualize button, the following map window will appear. Slowly move the sliding bar (left to right) and see how the spatial pattern of ET changes from one season to another.



Put the cursor on the map and select any of the sub-basins. The selected sub-basin boundary will get highlighted as shown below. You will also see the temporal plot of the corresponding time-series data on the lower right corner.


Note, HydroGlobe downloads actual evapotranspiration (ET), potential evapotranspiration (PET), latent heat flux (LE), and potential latent heat flux (PLE) even though you opted only for ET data. Click the Download icon (shown below with a red arrow) to download data for the selected sub-basin (sub-basin 35 in this case).


The data is in csv format and it gets saved in your computer. Use MS Excel to open the file you just downloaded which should look like the following. Note, the MODIS data is in 8-day time-step. An ET value between two consecutive time-steps indicates the total ET in that 8-day window. Importantly, you need to multiply the MODIS ET/PET values with 0.1 to convert them into mmH20 unit. For example, ET=23.1 in day 17 indicates that the total ET from day 10 to day 17 is 23.1 x 0.1 = 2.3 mm.


You can download all the time-series (for each of the sub-basins) together as a zip file using the download icon on the left side of the map window.


OK! You are done!

Additional Activities and Variants

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