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Data Available via OGC Web Coverage Service

Description of how the WCS protocol is used to access data

 

The Open Geospatial Consortium (OGC) Web Coverage Service (WCS) interface standard allows users to access geospatial data over the internet. The GES DISC WCS interface complies with a standard protocol, enabling clients to access data both directly, and time-averaged data utilizing Giovanni-4 capabilities.

How does it work?

OGC WCS works on top of the HTTP protocol, based on the specifications defined by the Open Geospatial Consortium.  The WCS specification defines a number of request types, and for each request type it defines a set of query parameters and associated behaviors. Listed below are the requests available from the GES DISC implementation of WCS:

 
    • service=WCS: Service name
    • version=1.0.0: WCS Version
    • request=GetCoverage: Request name
    • coverage=Time-Averaged.AIRX3STD_006_Temperature_A: Requested coverage
    • crs=epsg:4326: Coordinate Reference System
    • bbox=minx,miny,maxx,maxy: Bounding box corners (lower left, upper right) in CRS units.
    • width=output_width: Width in pixels of output data.
    • height=output_height: Height in pixels of output data
    • format=output_format: Output format of map currently netcdf is supported.
    • time=layer_date: Begin and end date and time of the data requested (YYYY-MM-DD/ YYYY-MM-DD)
    • bands=band_label: Requested bands
 
 

Example

 
 

The following GetCoverage request will return AIRS time-averaged data.

 
    • service=WCS
    • version=1.0.0
    • request=GetCoverage
    • coverage=Time-Averaged.AIRX3STD_006_Temperature_A
    • crs=epsg:4326
    • bbox=-180,-90,180,90
    • width=720
    • height=360
    • format=netcdf
    • time=2004-01-01T00:00:00Z/2004-01-03T23:59:59Z
    • bands=1000 
 

The assembled URL becomes:

http://giovanni.gsfc.nasa.gov/giovanni/daac-bin/wcs_ag4?service=WCS&version=1.0.0&request=GetCoverage&coverage=Time-Averaged.AIRX3STD_006_Temperature_A&crs=epsg:4326&bbox=-180,-90,180,90&width=720&height=360&format=netcdf&time=2004-01-01T00:00:00Z/2004-01-03T23:59:59Z&bands=1000

 

This URL can be placed in a browser which will prompt for the user to download the data, or can be used with a utility such as wget from the command line:

wget "http://giovanni.gsfc.nasa.gov/giovanni/daac-bin/wcs_ag4?service=WCS&version=1.0.0&request=GetCoverage&coverage=Time-Averaged.AIRX3STD_006_Temperature_A&crs=epsg:4326&bbox=-180,-90,180,90&width=720&height=360&format=netcdf&time=2004-01-01T00:00:00Z/2004-01-03T23:59:59Z&bands=1000"  -O output.nc

 

 

 

Time Constraints

 

To avoid time-out issues, we define some time constraints on G4 WCS requests:

 

Temporal Resolution  →      

Spatial Resolution ↓

Monthly

Daily

 

3-Hourly

 

Hourly

 

Half-Hourly

 

 >= 1 °

 <= 9 months

 <= 9 days

 <= 27 hours

 <= 9 hours

 <= 4.5 hours

 >= 0.25° and <1°

 <= 7 months

 <= 7 days 

 <= 21 hours

 <= 7 hours

 <= 3.5 hours

 <= 0.125°

 <= 6 months

 <= 6 days

 <= 18 hours

 <= 6 hours 

<= 3 hours

 

If a G4 WCS request does not comply with these constraints, G4 WCS will report an exception. For example, if a user sends a G4 WCS request to get monthly 0.1° data for 7 months, such as this:

http://giovanni.gsfc.nasa.gov/~pzhao1/giovanni/daac-bin/wcs_ag4?service=WCS&version=1.0.0&request=GetCoverage&coverage=Time-Averaged.GPM_3IMERGM_03_gaugeRelativeWeighting&crs=epsg:4326&bbox=-180,-90,180,90&resx=0.1&resy=0.1&format=netcdf&time=2015-03-01T00:00:00Z/2015-10-31T23:59:59Z

 

G4 WCS reports an exception,

<ServiceExceptionReport version="1.0.0">
  <ServiceException>
     Please select the data less than or equal 6 months
 </ServiceException>
</ServiceExceptionReport>

 



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