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Images of Antarctic Ice Shelves




Documentation

Changes in the extent and stability of ice shelves in the Antarctic Peninsula prompted NSIDC to begin a monitoring program using data from the Polar 1-km AVHRR Data Set. NSIDC regularly reviews images of those ice shelves considered susceptible to rapid change due to climatic warming.

In December 2001, NSIDC began monitoring Antarctic ice shelves with Moderate Resolution Imaging Spectroradiometer (MODIS) visible satellite data. MODIS provides global coverage every one to two days in 36 spectral bands. Spatial resolution of the MODIS data varies by band from 250 m to 1000 m. By contrast, the Advanced Very High Resolution Radiometer (AVHRR) sensor has five spectral bands with a spatial resolution of 4 km or 1 km.

The images in this site represent a selected subset of the available scenes, generally the clearest and most informative scenes available. The scenes are derived from either the visible (vis) or thermal (temp) channels, enhanced by combining two channels using principal components processing. Thermal images are derived from AVHRR thermal data, and, since January 2002, from MODIS thermal data. AVHRR thermal images are uncalibrated, and radiometric values are opposite those of MODIS images. In the AVHRR images, dark pixels indicate warm areas and bright pixels indicate cold areas. In MODIS images, dark pixels indicate cold areas and bright pixels indicate warm areas.

The derived MODIS thermal images are processed to retain an accurate approximate skin temperature. MODIS thermal data (from channel 32) are 1 km spatial resolution and 12-bit radiometric resolution initially. In the derived 8-bit thermal images, bright signatures represent warm areas, most commonly leads and exposed sea ice. Dark signatures represent cold areas such as crevasses (where cold air collects) and high plateaus. An exception occurs with temperature inversions, typical of the Antarctic winter. In these cases, cold air settles in valleys, and increased temperatures are seen on adjacent higher terrain. The thermal images also reveal local wind effects at the surface. To convert MODIS-derived thermal images to approximate surface temperature, NSIDC uses the following equation:

TK = DN/5 + 225

where:

DN = 8-bit pixel value
TK = surface temperature in kelvins

Each area covered in this archive has a separate web page that includes a location map, projection information, a grid and placename file, and access to the image archive. To save an image, right-click on the image with your mouse and select "Save image as."

Citing these data

These data are offered free of charge. You may use these data freely, provided that you cite NSIDC as the source, and provide an acknowledgment in any published papers.

The following example shows how to cite the use of this data set in a publication. List the principal investigators, year of data set release, data set title, dates of the data you used (for example, March to June 2004), publisher: NSIDC, and digital media.

Scambos, T., J. Bohlander, and B. Raup. 1996. Images of Antarctic ice shelves. [dates of data used] Boulder, Colorado, USA: National Snow and Ice Data Center. Digital media. http://nsidc.org/data/iceshelves_images/

 

If you have any questions about this data set contact NSIDC User Services.