What is soil moisture?

Soil moisture is a measure of the quantity of water in a sample of soil. A common way of quantifying soil moisture is by using volumetric water content. Volumetric water content is measured based on the volume of the soil sample and the air and the water in the sample compared to the volume of water (alone) in the sample. Most satellite and modeling-based soil moisture products use volumetric water content as a measure of soil moisture.


Why do we measure soil moisture?

Measuring soil moisture gives scientists, government planners, and politicians an idea of the status of land not just locally but also regionally, nationally, and internationally. These data help

  • Monitor Drought  
  • Predict Floods and Landslides  
  • Support Farm Production  
  • Weather Forecasting


Does this product represent the full root zone?

SMERGE vertically extends from the surface to a depth of 40 cm. We realize that in many places plant roots can go much deeper. SMERGE provides insight into soil moisture values in the upper root zone. Which is much greater than the 5 cm penetration associated with most satellite soil moisture products.


How can I see or access SMERGE data?

There are many ways of accessing or seeing SMERGE data. The SMERGE website (https://www.tamiu.edu/cees/smerge/data.shtml) provides links to the SMERGE data page. Data access is available through the following interfaces. Information about how to visualize or download SMERGE data is available on pages 13 to 15 of the full Read Me file (https://hydro1.gesdisc.eosdis.nasa.gov/data/SMERGE/SMERGE) provided with the SMERGE product. Downloading of files is possible using a http archival web page, Earthdata search, or OPeNDAP. Giovanni is recommended for visualization and general analysis.

Finally, customized data sets can be created upon request. Please contact the data producers, Wade Crow (Wade.Crow@ars.usda.gov), Jianzhi Dong (Jianzhi.Dong@ars.usda.gov), and Kenneth Tobin (ktobin@tamiu.edu). Please see https://www.tamiu.edu/cees/smerge/data.shtml for an example of a custom request in which SMERGE data was aggregated on a county basis over a monthly time scale. 


What are the variables present in a SMERGE data file?

A SMERGE data file contains only a few variables as indicated in the table below. Here is an example of SMERGE data for a single date (see pdf file).


What is the duration of the SMERGE product?

Unlike other observational soil moisture products SMERGE spans nearly four decades (1979 to 2016; SMERGE 2.0).


What is the spatial resolution or footprint of SMERGE?

SMERGE has a 0.125o spatial resolution at a daily time step. This is equivalent roughly to 156 square kilometers or 60 square miles.


What are the parent products of SMERGE?

SMERGE is developed based on merging NLDAS Noah-2 land surface model output with surface satellite retrievals from the European Space Agency (ESA) Climate Change Initiative (CCI).


If I want to learn more about SMERGE is there documentation I can refer to?

Yes, a full read me file is provided. https://hydro1.gesdisc.eosdis.nasa.gov/data/SMERGE/SMERGE


How many versions of SMERGE exist?

The initial version (SMERGE 1.0) is considered a beta version and was released in May 2018. An updated SMERGE 2.0 product was released on November 30, 2018.


What future plans are there for updating SMERGE?

The SMERGE science team plans to release an update version of SMERGE (v. 3.0) during the summer of 2019. This product will extend SMERGE into 2018. Any future updates to SMERGE will be contingent on future funding.


How can I contact the SMERGE Science Team with any questions?

Feel free to e-mail Wade Crow (Wade.Crow@ars.usda.gov), Jianzhi Dong (Jianzhi.Dong@ars.usda.gov), and Kenneth Tobin (ktobin@tamiu.edu) with any questions you may have about SMERGE.