Accessing Data through the Antarctic Cryosphere Access Portal (A-CAP)

This tutorial gives step-by-step instructions for accessing data through the Antarctic Cryosphere Access Portal (A-CAP). A-CAP is a geo-visualization and data download tool developed at the NSIDC Antarctic Glaciological Data Center (AGDC). The portal includes AGDC data and other Antarctic-wide parameters, including glaciology, ice core data, snow accumulation, satellite imagery, Digital Elevation Models (DEM's), sea ice concentration, and many other cryosphere-related scientific measurements.

The first section of this tutorial explains the capabilities of A-CAP. The second and third sections provide step-by-step instructions on searching for data using the layer menu and map interface. The final section describes how to obtain data and documentation through A-CAP.

Note: A-CAP is currently under development. Further functions and data sets will become available over time. For current information on A-CAP’s capabilities, please see the A-CAP News Web page. For automatic notification of new functions, sign up for the A-CAP RSS Feed.

Section I: Understanding A-CAP
Section II: Using the A-CAP Layer Menu
Section III: Using the A-CAP Map Interface
Section IV: Accessing Data and Documentation

Section I: Understanding A-CAP

A-CAP is a geo-visualization and data download tool. The portal offers an interactive Web interface and customizable map images. Source data are also accessible via the Open Geospatial Consortium (OGC) Web Map Service (WMS), Web Feature Service (WFS), and Web Coverage Service (WCS). For more details and instructions for accessing these services, see the A-CAP: OGC services Web page. These international specifications provide an interoperable framework for sharing maps and geospatial data over the Internet, enabling users to access data through OGC-compliant software applications such as ArcGIS, Google Earth, and ENVI.

A-CAP provides a variety of functions that allow users to interactively access data and map images through the map interface. The portal allows users to view one or more layers from a variety of overlays, basemaps, and sea ice climatologies. Users can adjust the map to their preferences or to fit specific data sets. The portal provides access to data and documentation.

Note: Not all functions are available in the Beta version. For the latest information on available functions, see the A-CAP News Web page.

Currently, A-CAP contains basemaps including satellite imagery, overlays including basic geographical information, and data sets including sea ice and some data from the AGDC Data Catalog. Eventually, A-CAP will provide access to all the data sets in the AGDC Data Catalog.

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Section II: Using the A-CAP Layer Menu

The layer menu allows users to select basemaps, overlays, and data sets to view in the map interface. Users can view multiple layers simultaneously, and obtain detailed information about each layer by querying points on the map. The AGDC NSF PI data set layer menu is also searchable by specific data sets by subject, title, or principle investigator. The following section explains how to select basemaps, overlays, and data sets to view on the A-CAP map. Refer to Figure 1.

Figure 1. A-CAP Interface with Layer Menu Highlighted

Layer Menu Icons

The icons following each layer option provide further information, including citation information, automatic map zoom, and direct access to the data. Below, find a list of icons and their functions.

Note: To view layer information, users must configure their browsers to enable pop-up windows.

•  = Fit map to layer: Zooms to the map extent for the selected layer. This is especially helpful when a layer covers a small spatial extent.
  
• i = Layer information: Displays citations, high-level background information, and links to data and documentation.
•  = Download data: Access the FTP site where the source data for this layer are archived.
• ! = Warning: Important information regarding the selected layer.

Working with Basemap Layers

A-CAP basemaps include a variety of backdrops upon which a user can display data. Basemaps are typically images, such as raster data sets, that cover the entire ice sheet, and include satellite imagery. Basemaps also include DEM's and maps of climate variables such as snow accumulation. Refer to Figure 2.

Figure 2. Two Basemaps Overlayed on A-CAP Map

In this section, you will select and display basemap layers. Refer to Figure 3.

1. Click to expand the basemap menu.
   Note: The default setting automatically displays the MODIS mosaic of Antarctica (MOA) image map.

2. Select the desired basemap
   Note: Multiple layers may obscure each other. To view several basemaps simultaneously, adjust the opacity of each basemap to less than 100 percent.

3. Click the update map button

Figure 3. Layer menu with Basemap Option Expanded

Adding Overlay Layers

A-CAP overlays typically include vector data sets that provide geographic context, such as coastlines, research stations, territorial boundaries, and other information. Overlays display on top of basemaps. Refer to Figure 4.

Figure 4. A-CAP Map with Overlay Layers

In this section, you will select overlay layers to facilitate data viewing. Refer to Figure 5.

1. Click on overlays to view the available overlay layers.

2. Select desired overlay layers.
   Note: The NSIDC label and Geographic South Pole display automatically.

3. Click the update map button to display the selected layers.

Figure 5. Layer Menu with Overlay Options Expanded

Displaying AGDC Data Layers

In this section, you will search for and display an AGDC data set using the A-CAP layer menu.

1. Click on AGDC NSF PI data sets to expand the AGDC data set list. Refer to Figure 6.
   Note: The list automatically displays data sets by subject. Click on title, id, or investigator to search for a specific data set using that parameter.
   

2. Click on a subject to view the sub-categories and data sets within the subject.

3. Check the box next to the desired data set and click the Update Map button to display the data set on the map, or click on the   Fit map to layer icon to update the map and zoom to the appropriate map size for that layer.

Figure 6. Layer Menu Showing AGDC PI Data Sets

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Section III: Using the A-CAP Map Interface

The A-CAP map interface allows users to zoom in and out, view a map legend, define map parameters, and query points to find spatial information and data values associated with that point for each displayed layer. In the future, users will also be able to save the map as a GeoTIFF file, zoom to an area of interest by drawing a rectangle on the map, and download the source data for each of the layers displayed in the map.

Adjusting Map Parameters

The A-CAP map server provides a variety of basic functions for viewing layers and obtaining data and documentation. In this section, you will become familiar with the map options and tools. Refer to Figure 7.


Figure 7. Left Menu: Map Interface Options

Map Options

The click-on-map menu, located to the left of the A-CAP map, provides the following functions:

• Re-center: When selected, clicking on the map re-centers it around that point
• Query: When selected, clicking on the map displays a pop-up window with information about each layer of the current map. For more information, see map query below
• Zoom in: When selected, clicking on the map zooms in by a factor selected by the user. Users can select a factor between 2 and 25
• Zoom out: When selected, clicking on the map zooms out by a factor selected by the user. Users can select a factor between 2 and 25

The information menu, located to the left of the A-CAP map, provides the following functions:

• View map legend: Displays the map legend as a pop-up window—the legend contains information for each relevant displayed layer
• Save map or data:
  • To save a map, click on save map or data, and follow the instructions on the resulting pop-up screen. This function saves the current map as an image file in a variety of formats, including PNG, JPG, GeoTIFF, KMZ (Google Earth), and others. The save function also provides the capability to save the underlying data.
  • To save data, click on save map or data. From that pop-up window, click on save data to open the save interface. For more information, see Accessing Data and Documentation, below.
    
• Reset all defaults: Resets the map using default settings
• View help page: Displays A-CAP user manual.

Image Options

The basic image menu, located above the A-CAP map, provides the following functions:

• Zoom to: Zooms to specific locations and regions
• Image size (px): Resizes the image to a variety of sizes, in pixels
• Pixel size (m): Defines the size of map pixels, in meters
• Bgcolor: Provides different background color options

The advanced image options menu is located at the bottom of the page. This form allows the user to numerically select the map center, extent, pixel size, map and image size, and background color. Refer to Figure 8.

Figure 8. Advanced Image Options

• Map projection: Displays a pop-up window with information about the WGS 84/Antarctic Polar Stereographic projection
• Center (x,y): Centers the map using coordinates in meters
• Center (lon, lat): Centers the map on a geographic point using longitude and latitude
• Map extent: Allows the user to define the map extent using coordinates
• Pixel size: Allows the user to numerically define the pixel size, in meters
• Image size (x,y): Numerically define the image size in pixels
• Bgcolor (RGB): Select a custom background color using RGB values

Map Query

Users can query specific points in a layer to find spatial information and data values associated with that point. The query information box displays information for each selected layer, including links to data and documentation. For more information about obtaining data and documentation using the map query function, see Accessing Data and Documentation Using the Map Interface, below.

In this section, you will use the map query function to obtain information about multiple layers, for a selected point.

Note: Not all A-CAP layers can be queried. Furthermore, if you click outside the spatial extent of a given layer, it will not be included.

1. To query a point on the map, select query in the menu on the left side of the screen, and click the desired point on the map. Refer to Figure 9.
   Note: Pop-up windows must be enabled for the query results to appear in the browser.

Figure 9. A-CAP Interface Showing Map Options

2. The query results appear as a pop-up window. Refer to Figure 10. Table 1 provides the spatial information for the selected location.

3. Table 2 provides the data values associated with that location for currently selected layers.
   Note: To query several different layers at the same time, such as all available DEM's, but not include them in the map, set the opacity to 1 percent for each of those layers before performing the query.
   

Figure 10. Map Query Results Pop-up Window

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Section IV: Accessing Data and Documentation

The A-CAP interface provides multiple ways to obtain data and related documentation.

Saving Data Directly from the Map Interface

Users can save data or maps directly from the map interface. To save data,

1. Click on save map or data in the A-CAP information menu. This pulls up the save map or data pop-up window. Refer to Figure 11.

Figure 11. Save Map or Data Pop-up Window

2. To save a map, select the desired output format and other options.

3. To save data, click on save data on the bottom half of the menu. This will display the save data pop-up window. Refer to Figure 12.

Figure 12. Save Data Pop-up Window

4. A-CAP allows users to save both vector and raster data files. To save data, select the desired layer and settings, and click on save raster or save vector to begin the download.

5. Depending on the size of the resulting data file, download could take anywhere from a few seconds to several minutes. The resulting file(s) will be compressed into a ZIP file.

Accessing Data and Documentation Using the Layer Menu

1. To obtain data and/or documentation from the layer menu, click on the information icon ( i ) to the right of the data set title. A pop-up window, or "note card," with basic information and references appears in the layer menu. Refer to Figure 13.

Figure 13. Pop-up Reference Window (Note Card)

2. To obtain data directly, click on the ftp link next to Access Data.
   Note: This option will bypass the data documentation and optional user registration options.
   

3. To access the data via the NSIDC catalog page, click on the NSIDC reference for the data set. This link will take you to the NSIDC catalog page for that data set, which provides documentation and links to the data.

Accessing Data and Documentation Using the Map Interface

To obtain data and documentation using the map interface, use the map query function. For more information on how to select and query a point on the map, see Map Query, above. The steps below describe how to use the Map Query Results pop-up window to access data and documentation. Refer to Figure 14.

Figure 14. Map Query Results Pop-up Window

1. Click on the desired data set in Table 2 to pull up the reference pop-up window, or note card, for that data set. Refer to Figure 13, above.

2. To obtain data directly, click on the ftp link next to Access Data.
   Note: This option will bypass the data documentation and optional user registration options.
   

3. To access the data via the NSIDC catalog page, click on the NSIDC reference for the data set. This link will take you to the NSIDC catalog page for that data set, which provides documentation and links to the data.

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Page last updated: 05/07/09