- Related Research Areas
- Earth Surface & Interior, Water & Energy Cycles
Whenever it occurs, the end of NASA's ICESat mission will signal the completion of the most comprehensive survey of the Earth's cryosphere ever undertaken. The global elevation data set it has yielded will continue to be explored by scientists in many disciplines for years to come. However, the subsequent gap in this time series of observations, which will persist until the launch of the follow-on ICESat-II mission in 2015, represents a serious challenge to the cryosphere community. The planned launch of Cryosat-2 by the European Space Agency in late 2009 offers an opportunity to extend cryosphere observations for several years, filling at least some of this gap. However, the Synthetic Aperture Radar (SAR) Interferometric Radar Altimeter (SIRAL) that it carries on-board requires careful cross-calibration with the ICESat Geoscience Laser Altimeter System (GLAS) to ensure accurate interpretation of ongoing elevation change. Furthermore, the SIRAL instrument will operate in three different modes over ice: a traditional, pulse-limited low-resolution mode for ice-sheet interiors; a SAR altimetry mode for sea ice; and an entirely new interferometric SAR mode for the highly sloped regions of the ice-sheet margins. To establish a long-term, consistent set of cryosphere observations, the relationship between ICESat and Cryosat-2 data must be well understood. Toward that end, we propose three inter-related investigations: (1) elevation change detection, (2) waveform analysis, and (3) cross-calibration. Together, they address the stated goals of this solicitation by facilitating the "continuation of the time series begun by ICESat", and by studying the "complementary nature of the ICESat and Cryosat-2 observations": (1) Elevation Change Detection: The most dynamic regions of the major ice sheets exist along their margins, which are difficult to assess because of poor spatial coverage, seasonal clouds, and high surface slopes. Three methods of determining elevation change rates will be evaluated: crossover analysis, repeat-track analysis, and overlapping footprints. Ice caps and glaciers in the Arctic will initially be used to quantify the errors associated with each technique, as they are well-surveyed regions that are small enough to make data sets manageable, but have challenges similar to those that exist along the ice-sheet margins. (2) Waveform Analysis: In conjunction with elevation change rates, waveform analysis will improve our understanding of ice dynamics. Again using ice caps and glaciers in the Arctic, we will characterize the response of ICESat and Cryosat-2 to different snow and ice facies, as classified using QuikScat scatterometer data. In addition, small-footprint Airborne Topographic Mapper (ATM) data will be used, along with waveform decomposition and deconvolution to assess ICESat elevation errors. (3) Cross-calibration: We propose to conduct global cross-calibration between ICESat and Cryosat-2 using ocean data and three different techniques: (1) direct inter-comparisons and comparisons with other altimetry, via the mean sea surface; (2) comparisons with other radar altimetry using crossovers, and (3) comparisons with tide gauges. This cross-calibration will yield a link between ICESat and CryoSat-2 to ensure measurement continuity; provide inter-mission validation; and produce a set of calibrated measurements suitable for integration with future missions, such as ICESat-II, and perhaps, with past missions, specifically Geosat and Seasat, to obtain a cryosphere measurement time series spanning more than 30 years.
Project PI: Bob Schutz/University of Texas at Austin
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