A New Methodology for Detecting Ice Sheet Surface Elevation Changes From Laser Altimetry Data

The integrated program Surface Elevation Reconstruction And Change detection (SERAC) was specifically designed and developed for detecting surface elevation and elevation changes from the Ice Cloud and land Elevation Satellite (ICESat). ICESat carried geoscience laser altimeter system (GLAS) with the primary goal of measuring elevation changes of the polar ice sheets to sufficient accuracy to assess their impact on global sea level. GLAS had three lasers that operated sequentially, with two to three campaigns per year. The footprint size was about 70 m and the point-to-point spacing between neighboring laser points reached 170 m. SERAC copes with different scenarios. Originally developed for calculating surface elevation changes of crossover areas, it was extended to along-track areas and the inclusion of non-ICESat laser data, such as Airborne Topographic Mapper (ATM), an airborne laser scanning system developed by NASA Wallops Flight Facility. The adjustment system of SERAC simultaneously computes the shape of surface patches containing laser points of the same time epoch, estimates surface elevation changes, and approximates the time series of elevation changes by a polynomial after removing the seasonal cycle. Results shown in the second part of the paper demonstrate the potential of SERAC for calculating detailed ice sheet elevation and volume change histories. Greenland Ice Sheet volume changes, calculated from a combined ICESat/ATM data set, show good agreement with previously published results and provide improved sampling in the rapidly thinning coastal regions of southern Greenland. Moreover, the polynomial approximation of the time series of surface elevation changes is taken to advantage in the last example of Northwest Greenland, illuminating the intricate thinning/thickening patterns that often vary considerably over short spatial scales.

[1]  Robert N. Swift,et al.  Aircraft laser altimetry measurement of elevation changes of the greenland ice sheet: technique and accuracy assessment , 2002 .

[2]  John F. Burkhart,et al.  High-Resolution Ground-Based GPS Measurements Show Intercampaign Bias in ICESat Elevation Data Near Summit, Greenland , 2011, IEEE Transactions on Geoscience and Remote Sensing.

[3]  Helen Amanda Fricker,et al.  An Active Subglacial Water System in West Antarctica Mapped from Space , 2007, Science.

[4]  R. Alley,et al.  Ice-Sheet and Sea-Level Changes , 2005, Science.

[5]  B. Csathó,et al.  Surface roughness on the Greenland Ice Sheet from airborne laser altimetry , 1998 .

[6]  M. Bevis,et al.  Spread of ice mass loss into northwest Greenland observed by GRACE and GPS , 2010 .

[7]  W. Peltier.  GLOBAL GLACIAL ISOSTASY AND THE SURFACE OF THE ICE-AGE EARTH: The ICE-5G (VM2) Model and GRACE , 2004 .

[8]  B. Smith,et al.  Rates of southeast Greenland ice volume loss from combined ICESat and ASTER observations , 2008 .

[9]  H. Jay Zwally,et al.  Precision and Accuracy of Satellite Radar and Laser Altimeter Data Over the Continental Ice Sheets , 2007, IEEE Transactions on Geoscience and Remote Sensing.

[10]  Ian M. Howat,et al.  Large-scale changes in Greenland outlet glacier dynamics triggered at the terminus. , 2009 .

[11]  Theodore A. Scambos,et al.  An image-enhanced DEM of the Greenland ice sheet , 2002, Annals of Glaciology.

[12]  Jack L. Saba,et al.  Greenland ice sheet mass balance: distribution of increased mass loss with climate warming; 2003–07 versus 1992–2002 , 2011, Journal of Glaciology.

[13]  A. Savitzky,et al.  Smoothing and Differentiation of Data by Simplified Least Squares Procedures. , 1964 .

[14]  T. Scambos,et al.  Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica , 2004 .

[15]  Eric Rignot,et al.  Channelized bottom melting and stability of floating ice shelves , 2008 .

[16]  B. Smith,et al.  An inventory of active subglacial lakes in Antarctica detected by ICESat (2003–2008) , 2009, Journal of Glaciology.

[17]  R. Nerem,et al.  Recent Greenland Ice Mass Loss by Drainage System from Satellite Gravity Observations , 2006, Science.

[18]  S. Ekholm,et al.  A full coverage, high-resolution, topographic model of Greenland computed from a variety of digital elevation data , 1996 .

[19]  T. Scambos,et al.  Rapid Changes in Ice Discharge from Greenland Outlet Glaciers , 2007, Science.

[20]  Sebastian B. Simonsen,et al.  Mass balance of the Greenland ice sheet (2003–2008) from ICESat data – the impact of interpolation, sampling and firn density , 2011 .

[21]  Adrian A. Borsa,et al.  Assessment of ICESat performance at the salar de Uyuni, Bolivia , 2005 .

[22]  H. Zwally,et al.  Overview of the ICESat Mission , 2005 .

[23]  Yushin Ahn,et al.  Surface roughness over the northern half of the Greenland Ice Sheet from airborne laser altimetry , 2009 .

[24]  Richard D. Ray,et al.  A Global Ocean Tide Model From TOPEX/POSEIDON Altimetry: GOT99.2 , 1999 .

[25]  C. Tucker,et al.  NASA’s Global Orthorectified Landsat Data Set , 2004 .

[26]  D. Vaughan,et al.  Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets , 2009, Nature.

[27]  W. Krabill,et al.  Recent changes on Greenland outlet glaciers , 2009, Journal of Glaciology.

[28]  Archie Paulson,et al.  FAST TRACK PAPER: Inference of mantle viscosity from GRACE and relative sea level data , 2007 .

[29]  Karl-Rudolf Koch,et al.  Parameter estimation and hypothesis testing in linear models , 1988 .

[30]  Charles F. Raymond,et al.  Recent elevation changes on the ice streams and ridges of the Ross Embayment from ICESat crossovers , 2005 .

[31]  Pavel Ditmar,et al.  Estimation of volume change rates of Greenland's ice sheet from ICESat data using overlapping footprints , 2008 .

[32]  Eric Rignot,et al.  Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise , 2011 .

[33]  H. Zwally.  ICESat's Laser Measurements of Polar Ice and Atmospheres , 2003 .