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Giovanni Online Users Manual: Chapter 20. GLDAS Giovanni

Global Land Data Assimilation System Giovanni instance

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All of the questions below are linked to descriptive answers in this chapter of the Giovanni Online Users Manual regarding the Giovanni GLDAS instance. Click the question of interest.

 

  1. What are the GLDAS products?
  2. What are the land surface models in the GLDAS instance?
  3.  What GLDAS data parameters are available in the GLDAS instance?
  4. How are parameters selected for analysis?
  5. How is the spatial area of interest selected?
  6. How is the time range of interest selected?
  7. Are there any limits on the spatial area or time range that can be selected?
  8. What are the current visualization and analysis capabilities in the GLDAS instance?
  9. What are the plotting preference options for the visualization services?
  10.  How can a generated output image be saved?
  11.  What output formats are available?
  12.  Can I view the output in Google Earth?

 

What are the GLDAS products?

The Global Land Data Assimilation System (GLDAS) data products consist of time series of land surface state (e.g., soil moisture and surface temperature) and flux (e.g., evaporation and sensible heat flux) parameters simulated by four land surface models (CLM, Mosaic, Noah, and VIC). The 1.0 degree resolution data range from 1979 to present for the four models. The 0.25 degree data cover 2000 to present for the NOAH model. For more information about GLDAS, see http://ldas.gsfc.nasa.gov/.
 
 
What are the land surface models in the GLDAS instance?
 
Currently, the GLDAS instance in Giovanni includes four land surface models: Mosaic, Noah, CLM (Community Land Model), and VIC (Variable Infiltration Capacity). More information about the models is available at the Land Data Assimilation Systems (LDAS) and Land Information System (LIS) Web sites.
 
 
What GLDAS data parameters are available in the GLDAS instance?
 
All standard GLDAS parameters are available.
 
 
Water Balance parameters

 

Energy Balance parameters

 

Forcing parameters
 
 
 
How are parameters selected for analysis?
 
Individual parameters are selected by clicking in the check boxes. An entire group may be selected by clicking the group box (leftmost column heading bar, next to the collection name and date range information). If a group is selected, individual parameters within the group can then be deselected by clicking in the appropriate check box(es).
 
 
How is the spatial area of interest selected?
 
The spatial area of interest can be selected by either of the following two methods:
Java applet map: The Java applet map can be utilized to "click and drag" a selection box to designate the spatial area of interest.
Geographic coordinates: The geographic coordinates of the corners of the spatial area box can be input individually. This method can be used if Java is not enabled. Note that decimal and not degree (seconds and minutes) coordinates must be entered.

 

How is the time range of interest selected?
 
The starting date (year/month/day) and the ending date (year/month/day) for the analysis are selected using the calendar menus on the Giovanni interface page. Error messages will be generated if the begin or end dates are out of the data set time range or if the end date is before the begin date.
 
 
Are there any limits on the spatial area or time range that can be selected?
 
No, as long as the selected time range is within the data set time range. The longer the time range, however, the longer it will take for the initial data retrieval from the archive (fetching) and, thus, a longer period of elapsed time for processing.

 

What are the current visualization and analysis capabilities in the GLDAS instance?
 
There are currently seven visualization and analysis services in the GLDAS instance, listed below. More services will be added in the future.

 

What are the plotting preference options for the visualization services?
 
The plotting preference options are described in the Plot Preferences section of the Online Users Manual. After the initial output has been generated, the temporal and spatial ranges (constraints) and plotting preferences can be changed, and a new output generated, using the "Submit Refinements" button.
 
 
How can a generated output image be saved?
 
First select "Download Data" on the output visualization page, then click on the link under "Output Files". On a Windows computer, right-click on the output image and then select "Save Image As." The visualization output is a GIF image.  To download the KMZ file, click on the KMZ icon.   It will automatically be opened in Google Earth if Google Earth is installed on your computer.
 
 

What output formats are available?

 
Three data and two image output formats are available. Data output formats are in HDF, netCDF, and ASCII.  Image output formats are GIF and KMZ.
 
 
Can I view the output in Google Earth?
 
Users can view the output image in Google Earth by downloading the KMZ file(s) under the “Download Data” tab. KMZ is one of the image output formats provided in Giovanni. If Google Earth is installed on a user’s computer, clicking the KMZ icon will allow the immediate loading and display of the visualization in Google Earth.
 

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Last updated: May 27, 2010 04:50 PM ET