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ACOS WMS Images

The ACOS Web Map Service (WMS) at the GES-DISC

Monthly mean Atmospheric Carbon dioxide (CO2) Observations from Space (ACOS) images are available upon submitting an http request to a particular Web Map Service (WMS) at the GES DISC. The server name should be noted as "wms_airs", see example http requests below.

A WMS request defines the geographic layer(s) and area of interest to be processed. The response to the request is one or more geo-registered map images (returned as JPEG, PNG, etc) that can be displayed in a browser application. The interface also supports the ability to specify whether the returned images should be transparent so that layers from multiple servers can be combined or not. This standard is supported by the Open Geospatial Consortium (OGC).

There are six available layers based on the variable dry air mole fraction, Xco2. Five of these layers are screened using simple and advanced screening criteria, while one represents the data "as is", without any quality screening or bias correction. The simple screening approach is using the  quality_flag values "Good" and "Caution", whereas the advanced screening approach is using all the criteria outlined in the Table 2 "Advanced screening criteria" of the  “ACOS Level 2 Standard Product Data Users Guide, v3.3”, and ignores the quality_flag.  Lastly, one of the advanced screened layers is also bias-corrected as advised in the Users Guide. The table below summarizes the available layers.

 

Available Layers
Variable Name quality_flag Advanced Screen Bias Corrected Explanation
ACOS_Grid_xCO2_All - - - No quality screening; no bias correction.
ACOS_Grid_xCO2_Good Good - - quality_flag="Good' only, advanced screening and bias correction not applied
ACOS_Grid_xCO2_Caution Caution - - quality_flag="Caution' only, advanced screening and bias correction not applied
ACOS_Grid_xCO2_GandC Good and Caution - - quality_flag="Good" or "Caution'  only; advanced screening and bias correction not applied
ACOS_GridScreen_xCO2_All - yes - Advanced screening without bias correction;  quality_flag ignored.
ACOS_GridScreenBias_xCO2_All - yes yes Advanced screening and bias correction applied;  quality_flag ignored.

 

The images can be obtained by constructing the appropriate URL and downloading using WGET, a web browser, or they can be viewed in a WMS compatible client like GoogleEarth.

 

Several examples of ways to obtain ACOS monthly images are given below.  Images for different months can be obtained by changing the month or year string in the below examples (e.g., by changing "2009-04" to "2010-05"). The earliest ACOS monthly CO2 is from 2009-04. The simplicity  of the interface does not provide advanced checks of the user input, i.e. the correctness of the syntax of the request. However, in case errors occur, the map server will return an XML file that can be examined for hints on what went wrong.

 

Obtaining monthly images using wget


For example, a portable network graphics (PNG) file called "xco2_2013.04.png" of the monthly mean ACOS CO2 mole fraction (Screened and bias corrected "ACOS_GridScreenBias_xCO2_All") from April 2013 can be obtained by typing the following wget command: 

wget "http://disc1.sci.gsfc.nasa.gov/daac-bin/wms_airs?service=WMS&VERSION=1.1.1&REQUEST=GetMap&SRS=EPSG:4326&WIDTH=720&HEIGHT=360&LAYERS=ACOS_GridScreenBias_xCO2_All&TRANSPARENT=TRUE&FORMAT=image/png&bbox=-180,-90,180,90&time=2013-04-01" -O xco2_2013-04.png

 

A color bar can be obtained using wget as follows:  

wget "http://disc1.sci.gsfc.nasa.gov/daac-bin/wms_airs?version=1.1.1&service=WMS&request=GetLegendGraphic&layer=ACOS_GridScreenBias_xCO2_All&format=image/png&STYLE=default" -O colorbar.png

 

Viewing the image in a web bowser


Alternatively, the image can be viewed in the web browser by just typing the following URL into the web browser:

Example 1: ACOS_Grid_xCO2_All

http://disc1.sci.gsfc.nasa.gov/daac-bin/wms_airs?service=WMS&VERSION=1.1.1&REQUEST=GetMap&SRS=EPSG:4326&WIDTH=720&HEIGHT=360&LAYERS=ACOS_Grid_xCO2_All&TRANSPARENT=TRUE&FORMAT=image/png&bbox=-180,-90,180,90&time=2013-04-01

 

Example 2:  ACOS_GridScreenBias_xCO2_All

http://disc1.sci.gsfc.nasa.gov/daac-bin/wms_airs?service=WMS&VERSION=1.1.1&REQUEST=GetMap&SRS=EPSG:4326&WIDTH=720&HEIGHT=360&LAYERS=ACOS_GridScreenBias_xCO2_All&TRANSPARENT=TRUE&FORMAT=image/png&bbox=-180,-90,180,90&time=2013-04-01

 

Additional WMS capabilities for ACOS v3.3 data:

There are 2 WMS requests can be used for additional information retrieval regarding to the data set. 

a) GETCAPABILITIES: This request will return an XML document with metadata containing WepMap service information. Ex:

http://disc1.sci.gsfc.nasa.gov/daac-bin/wms_airs?service=WMS&VERSION=1.1.1&REQUEST=GETCAPABILITIES

While above command generates all the information available, following request can be used in order to capture only ACOS related service information:

 

wget "http://disc1.sci.gsfc.nasa.gov/daac-bin/wms_airs?service=WMS&VERSION=1.1.1&REQUEST=GETCAPABILITIES" -O - | grep ACOS

 

 

b) GetLegendGraphic: This request will return the color scale information used to create the image; Corresponding color bar. For example 2 see below: 

 

http://disc1.sci.gsfc.nasa.gov/daac-bin/wms_airs?version=1.1.1&service=WMS&request=GetLegendGraphic&layer=ACOS_GridScreenBias_xCO2_All&format=image/png&STYLE=default

 

Viewing the image in GoogleEarth


The ACOS monthly images served from the WMS can be viewed in virtual 3D globes using the GoogleEarth tool. GoogleEarth can play as client that communicates with our WMS and displays ACOS monthly images in "virtual 3D". It is a bit unusual and advanced usage of GoogleEarth. Thus we provide a KMZ example  to serve as a guidance on how to configure your GoogleEarth "places". (You must have GoogleEarth installed to view KMZ). From the properties of the "ACOS xCO2" place, users can see the familiar url syntax from above, and correspondingly get the idea e.g. how to overlay more "places" that can be ACOS images from different time, or even images from different satellites, from  different WMS providers.

 

Other Commands

 More information about interacting with the WMS server can be found at the following page and references therein:

http://disc.sci.gsfc.nasa.gov/services/ogc_wms.

Information about WMS can be found on the OpenGIS Web Map Service web page (http://www.opengeospatial.org/standards/wms/).

 

 

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Last updated: Aug 28, 2013 03:08 PM ET
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