Evaluation Of Landsat, Spot, and Sojuzkarta Data Of Antarctica For Ice and Climate Research

Abstract

Satellite data have proved suitable and cost-effective for ice and climate research in Antarctica. They have been used in numerous research efforts, including: monitoring coastal change, determining velocities of outlet glaciers, defining blue ice areas, tracking the movement of icebergs, and as a base for overlaying radar and other data. This paper reviews the data acquired since 1972 by the Landsat, SPOT and Sojuzkarta space systems and illustrates where good-quality (±10% cloud cover) data are available.

The Landsat 1, 2, and 3 satellites acquired approximately 10 000 multispectral scanner (MSS) (80 m resolution) and return-beam vidicon (RBV) (30 m resolution) photographic and digital images of Antarctica between 1972 and 1983. The quality of these images has been evaluated by USGS to determine the feasibility of using them for glaciological, climatological, and geological research. Results have been plotted on a base map of Antarctica and show about 45% of the nominal scene centers, or about 70% of the geographic area of the continent, to be covered by good-quality imagery. Landsat 4 started acquiring data in 1982 and Landsat 5 in 1984. Together the two satellites acquired more than 4 500 thematic mapper (TM) (30 m resolution) and MSS images of Antarctica through the 1988–89 austral summer season, which may be the last season of Landsat 4 and 5 acquisition. The majority of the scenes have been acquired by two major projects: the West German Institut für Angewandte Geodäsie project to acquire data from the Ronne Ice Shelf area to the Greenwich meridian, and the USGS project to acquire data of coastal Antarctica and the inland boundary of the ice shelves, for use by the Scientific Committee on Antarctic Research (SCAR) community. Landsat 4 and 5 have different orbital parameters from Landsat 1, 2, and 3. As a result Landsat 4 and 5 imagery have different areal coverage. The data also have been archived differently. While the Landsat 1, 2, and 3 data exist in film format, many Landsat 4 and 5 TM images exist only as high-density digital tapes, and, as a result, the scenes cannot be examined and evaluated before purchase. Computer evaluation of the Landsat 4 and 5 data indicate that about 1350 or about 30% of the images have 10% cloud cover or less. However, it is difficult for automatic systems or those unfamiliar with the area to discriminate between clouds and snow. Based on a sampling of the data, it is more likely that 10–15%, or about 500 scenes, are of good quality. Those scenes which have been examined and evaluated as part of the SCAR cooperative acquisition project and are known to be of good quality are plotted and compared with the earlier Landsat data. The combined plot gives accurate and reliable information on the location of good quality Landsat 1–5 data of Antarctica.

More than 7 000 Sojuzkarta scenes have been collected over Antarctica since 1976. The most useful data consist of photography from the KATE-200 system (20 m resolution) and the KFA-1000 system (6 m resolution). The data have been plotted by the U.S. Geological Survey and will soon be available as an open-file report. Those scenes which have been evaluated as having 10% cloud cover or less are plotted separately and overlaid on the Landsat plots. Scenes which have been examined are excellent, but an insufficient number of scenes have been inspected to evaluate the accuracy of the cloud cover estimation.

The Systeme Probatoire d'Observation de la Terre (SPOT) was launched in 1986 and has acquired more than 1200 scenes of Antarctica. SPOT data consist of multi-spectral (20 m resolution) and panchromatic (10 m resolution) photographic or digital imagery. SPOT also possesses a mechanical plane mirror which permits off-nadir imaging and the generation of stereoscopic images. The locations of these scenes are now being plotted by the U.S. Geological Survey. Scenes with 10% cloud cover or less will be combined with Landsat and Sojuzkarta data to provide an accurate summary of the availability and coverage of high-quality satellite data of Antarctica.