Overview of the ICESat Mission

Overview of the ICESat Mission - GEOPHYSICAL RESEARCH...

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Overview of the ICESat Mission B. E. Schutz Center for Space Research, University of Texas at Austin, Austin, Texas, USA H. J. Zwally, C. A. Shuman, D. Hancock, and J. P. DiMarzio NASA Goddard Space Flight Center, Greenbelt, Maryland, USA Received 8 July 2005; revised 8 September 2005; accepted 7 October 2005; published 2 November 2005. [ 1 ] The Geoscience Laser Altimeter System (GLAS) on the NASA Ice, Cloud and land Elevation Satellite (ICESat) has provided a view of the Earth in three dimensions with unprecedented accuracy. Although the primary objectives focus on polar ice sheet mass balance, the GLAS measurements, distributed in 15 science data products, have interdisciplinary application to land topography, hydrology, vegetation canopy heights, cloud heights and atmospheric aerosol distributions. Early laser life issues have been mitigated with the adoption of 33-day operation periods, three times per year, designed to document intra- and inter-annual polar ice changes in accordance with mission requirements. A variety of calibration/validation experiments have been executed which show that the elevation products, when fully calibrated, have an accuracy that meets the science requirements. The series of papers in this special ICESat issue demonstrate the utility and quality of the ICESat data. Citation: Schutz, B. E., H. J. Zwally, C. A. Shuman, D. Hancock, and J. P. DiMarzio (2005), Overview of the ICESat Mission, Geophys. Res. Lett. , 32 , L21S01, doi:10.1029/ 2005GL024009. 1. ICESat Mission Science Objectives and Requirements [ 2 ] The primary purpose of ICESat is the determination of inter-annual and long-term changes in polar ice-sheet volume (and inferred mass change) to sufficient accuracy to assess their impact on global sea level [ Zwally et al. , 2002]. A specific objective of ICESat is to reduce the uncertainty in the known ice sheet mass balance through determination of polar ice elevation change with better than 2 cm/yr accuracy over 100 km ± 100 km areas, averaged over three or more years of seasonal and interannual variability. To achieve this objective, ICESat has utilized narrow beam laser altimetry, with state-of-the art instrumentation, to determine the geodetic coordinates of a series of points on the ice sheet with vertical accuracy at the decimeter level. Although ICESat has been designed to meet the demanding requirements of cryosphere applications, its design supports numerous multidisciplinary applications. 2. Measurement Concept and Implementation [ 3 ] The elevation of a spot on the Earth’s surface illumi- nated by a spaceborne laser is determined from the sum of two vectors: the position vector of the laser instrument plus the range vector (the position vector of the illuminated spot centroid with respect to the instrument, alternatively re- ferred to as the altitude vector). The resultant vector is the position of the spot (or footprint), which can be readily transformed into geodetic latitude, longitude and height (or elevation) with respect to a reference ellipsoid. The funda- mental data product consists of this geolocated spot and its surface arrival time (time tag).
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