Alaska Satellite Facility
Delivering Remote Sensing Data Since 1991

The Goal

Antarctica is the coldest, windiest and on average, highest continent on Earth. Shrouded in darkness during the austral winter and often obscured from view by persistent cloud cover, Antarctica has remained one of the most poorly mapped parts of our planet. The mapping situation changed in 1997 when RADARSAT-1 began to image Antarctica from space. The goal of the project was to create the first, high resolution, radar image of the continent. The resulting map was intended to serve as a benchmark for gauging future changes in the polar ice sheet, to understand more about the behavior of the glacier and its interaction with the polar atmosphere and coastal ocean, and to simply expand our ability to explore the vast, remote, and often beautiful, southernmost continent.

The Approach

The first Antarctic Mapping Mission (AMM-1) was made possible by the unique capabilities of RADARSAT-1 including a steerable antenna that provided a range of radar pointing angles (but only pointing to the right). This steerability was essential for imaging the most ground per satellite track. The satellite was also radically maneuvered in orbit, actually turned upside down, to change the pointing direction to the left. This was necessary to image the center of the continent. These two capabilities permitted acquisitions of the Earth's South Pole and represent technical abilities afforded by no other civilian spaceborne radar.

AMM-1 acquisitions began seven days earlier than the anticipated start of the nominal acquisition plan. The early data constituted an important contingency against anomalies encountered later in the mission. Nominal acquisitions started on schedule shortly after noon Eastern Standard Time on September 26. The nominal plan was designed to obtain complete mapping coverage within 18 days. The plan proceeded nearly flawlessly through completion on October 14. It was executed in parallel with acquisition plans for other RADARSAT-1 users and with CSA's Background Mission. An additional opportunity was realized because of the early start on September 19. Radar data collected after the conclusion of the nominal mission were acquired exactly 24 days after the beginning of the early start data. This schedule repositioned the spacecraft to within a few hundred meters of its position 24 days earlier. Consequently the data are suitable for interferometric analysis - a demonstrated technique for estimating ice sheet surface displacement. Exact repeat data collections started on October 14 and continued through October 20.

Preparations to return the satellite to normal operations began on October 20. Arctic mode operations resumed on October 23. Acquisitions for customers resumed on October 26. This occurred 9 days ahead of the planned schedule.

The Mosaic

The RAMP mosaic, shown here at reduced resolution is truly a new view of Antarctica. There are several new and exciting features seen in the mosaic. First, there are large-scale spatial variations in radar brightness. The bright portion of Marie Byrd Land and the eastern sector of the Ross Ice Shelf probably represent the region where significant melting and refreezing occurred during an early 1990's melt event. Most of the coastal areas and much of the Antarctic Peninsula appear bright also because of summer melt. But unlike Greenland, where most of the large-scale brightness patterns are associated with firn melt facies, the remaining, strong variations in radar brightness are poorly understood.

Many of the thousands of kilometer long curvilinear features across East Antarctica appear to follow ice divides separating the large catchment areas. Ice divides derived from topographic information and overlaid onto the mosaic demonstrate the good, but difficult to explain, correlation between ice divides and radar brightness patterns.

On an intermediate scale, the East Antarctic Ice Sheet appears to be very 'rough'. The texturing is probably due to the flow of the ice sheet over a rough glacier bed. Textures are particularly strong paralleling the flanks of the Transantarctic, Pensacola and Shackelton Mountains and extending deep into adjacent portions of the East Antarctic Plateau. Long linear patterns are strongly suggestive of subglacial geology and may indicate that the ice sheet in this area is resting on relatively resistant basement rocks. The texture changes abruptly across the northernmost section of the Wilkes Subglacial Basin located in George V Land. There the imagery shows remarkable, subtle rounded shapes similar in appearance to the signature of subglacial lakes such as Lake Vostok.

Most intriguing are ice stream and ice stream-like features of the East Antarctic Ice Streams in Queen Maud Land partly described in previous research using optical imagery. Ice streams are made visible by the intense crevassing along the shear margins where chaotic surface roughness results in a strong radar echo. Complexities within the interior of the ice streams are revealed by radar flow stripes that probably originate from subtle variations in topography. Slessor Glacier is located on the northeastern margin of the Filchner Ice Shelf. The upper reaches of the glacier are funnel-shaped with the interior of the funnel punctuated by patches of crevasses. The ice stream is about 450 km long from the grounding line to the upstream area that seems to be characterized by several long scars. The scars are probably shear margins but it is not possible to deduce whether they are recently initiated or relict ice stream flow.

An enormous ice stream, reaching at least 800 km into East Antarctica, feeds Recovery Glacier. It too is fed by a funnel-shaped catchment. Down-glacier, crevasses cascade across the ice stream at several locations suggesting strong variations in basal topography modulates the flow. The confluence of a thin, elongated, 280 km-long tributary ice stream with Recovery Glacier is located approximately 250 km from the constriction where Recovery Glacier enters the Filchner Ice Shelf. The central body of the pipe-like tributary is crevasse free indicating that shear stresses are concentrated only at the margins. The tributary is an enigma in that there is little evidence for ice flow into the tributary from the adjacent ice sheet and there is little if any indication as to the source of ice from the up-glacier catchment region. A less active pipe-like tributary merges with Recovery Glacier just upstream of the grounding line. The uppermost portion of that 300 km long tributary is dark and featureless, similar to the eastern companion. Down-glacier, the tributary surface is similarly mottled to the adjacent ice sheet.

Using RADARSAT SAR imagery obtained during the 1997 Antarctic Mapping Mission, ice velocity vectors were obtained over the East Antarctic Ice Streams (see adjacent figure). The upstream velocity of the Recovery Glacier is about 100 meters/year (light blue areas). Near the grounding line there is a local peak velocity of about 900 meters/year (yellow and red areas).

Get SAR Data

Get SAR Data

Select and download SAR data online using Vertex.

Use the ASF API for downloading SAR data via a command line.