Precise Elevation Profiles Across Antarctic Megadunes

Covering more than 500,000 square kilometers of Antarctica, megadune features are related to persistent, down slope winds and have a subtle but characteristic morphology that is best defined by precise elevation data. In this paper, we will discuss ICESat precision laser altimetry data that details some of these features near an NSF-OPP funded research site occupied during the 2002-2003 and 2003-2004 field seasons. Work there to-date shows megadunes having 1) amplitudes from about 2 to 8 meters, 2) wavelengths of approximately 2 to 6 kilometers, 3) crest lengths of up to 100 kilometers, 4) a steeper and rougher upwind face, and 5) a smoother and longer backslope. See other talks in this session (e.g. Scambos et al.,) for additional details of their characteristics and formation. In this harsh environment, satellite altimetry is an excellent way to gather the elevation data needed to define these features. The ICESat mission acquires elevation data with a measurement spacing of about 172 m along its orbital track and can repeat a track to within approximately 50 meters. When skies are clear, ICESat measures laser spot elevations with 2 to 3 centimeter precision over these slowly-changing, undulating ice sheet features. Clouds, although rare in this area, can degrade the elevation data precision by more than a meter. Data obtained during ICESat's first four operational periods clearly documents the megadune and other ice sheet features in the region and enables the impact of clouds and the overall precision of this data to be quantified. ICESat data calibration and validation is being aided by high-precision GPS data acquired on sled traverses in the field area. The combination of ICESat data with a recently completed Antarctic MODIS mosaic will allow additional aspects of these features to be discussed.