Recent elevation changes of Svalbard glaciers derived from ICESat laser altimetry Geir Moholdt a, ⁎, Christopher Nuth a , Jon Ove Hagen a , Jack Kohler b a Department of Geosciences, University of Oslo, Box 1047 Blindern, NO-0316 Oslo, Norway b Norwegian Polar Institute, Polar Centre, NO-9296 Tromsø, Norway abstract article info Article history: Received 22 March 2010 Received in revised form 18 June 2010 Accepted 21 June 2010 Keywords: ICESat Glaciers Ice caps Svalbard Elevation changes Volume changes Mass balance Sea level change Laser altimetry We have tested three methods for estimating 2003–2008 elevation changes of Svalbard glaciers from multi- temporal ICESat laser altimetry: (a) linear interpolation of crossover points between ascending and descending tracks, (b) projection of near repeat-tracks onto common locations using Digital Elevation Models (DEMs), and (c) least-squares fitting of rigid planes to segments of repeat-track data assuming a constant elevation change rate. The two repeat-track methods yield similar results and compare well to the more accurate, but sparsely sampled, crossover points. Most glacier regions in Svalbard have experienced low-elevation thinning combined with high-elevation balance or thickening during 2003–2008. The geodetic mass balance (excluding calving front retreat or advance) of Svalbard's 34,600 km 2 glaciers is estimated to be −4.3±1.4 Gt y −1 , corresponding to an area-averaged water equivalent (w.e.) balance of −0.12 ± 0.04 m w.e. y −1 . The largest ice losses have occurred in the west and south, while northeastern Spitsbergen and the Austfonna ice cap have gained mass. Winter and summer elevation changes derived from the same methods indicate that the spatial gradient in mass balance is mainly due to a larger summer season thinning in the west and the south than in the northeast. Our findings are consistent with in-situ mass balance measurements from the same period, confirming that repeat-track satellite altimetry can be a valuable tool for monitoring short term elevation changes of Arctic glaciers. © 2010 Elsevier Inc. All rights reserved. 1. Introduction Satellite radar altimetry has been used to measure elevation changes in Greenland and Antarctica since the late 1970s (e.g. Zwally et al., 1989; Wingham et al., 1998; Johannessen et al., 2005). The large footprint size of satellite altimeters has made it difficult to apply these measurements to higher relief glaciers and ice caps. However, newer, higher resolution altimeters like the CryoSat-2 radar altimeter (Wingham et al., 2006) and the ICESat laser altimeter (Zwally et al., 2002) provide elevation data sets that can be compared to maps/ DEMs (e.g. Sauber et al., 2005; Muskett et al., 2008; Nuth et al., 2010), to airborne altimetry (e.g. Thomas et al., 2005) and to each other (e.g. Smith et al., 2005). The most established technique to obtain elevation changes directly from satellite altimetry is to compare elevations at crossover points between ascending and descending satellite passes. This is a very accurate method (Brenner et al., 2007), but the spatial sampling is typically too coarse for volume change calculations apart from in Greenland and Antarctica. Repeat-track analysis provides a much denser sample of elevation change points, but sacrifices accuracy due to the imprecise repetition of satellite ground tracks. Still, ICESat near repeat data have been used to identify grounding zones of ice shelves (Fricker and Padman, 2006), to map subglacial lakes and drainage (Fricker et al., 2007; Smith et al., 2009), and to quantify elevation change rates in Greenland and Antarctica (Howat et al., 2008; Slobbe et al., 2008; Pritchard et al., 2009). Arctic glaciers and ice caps are among the largest contributors to sea level rise (Kaser et al., 2006). In-situ mass balance measurements are sparse in these regions, implying a need for remote sensing data to better understand regional variations in mass balance. The most used techniques to obtain elevation changes in the Arctic have been to compare multi-temporal photogrammetric maps/DEMs (e.g. Nuth et al., 2007; Kääb, 2008) or repeated airborne laser profiles (Abdalati et al., 2004; Bamber et al., 2005). However, airborne campaigns are expensive, and photogrammetry is difficult in the accumulation areas of large ice caps where there are few ground control points and where the image contrast is poor. ICESat altimetry data are freely accessible (Zwally et al., 2008) and provide a dense spatial and temporal coverage of high quality elevation points in these high latitude regions. In this article, we investigate the potential of repeat-track ICESat altimetry to derive short term glacier elevation changes within a semi-alpine high latitude environment like the Svalbard archipelago in the Norwegian Arctic. Two methods of repeat-track analysis are tested, and the results are validated against crossover points and external DEMs. Area-averaged 2003–2008 elevation change rates are estimated for 7 glacier regions as well as for the entire archipelago. Additionally, ICESat's 2–3 observation campaigns per year provide the opportunity to calculate winter and summer elevation changes. The area-averaged seasonal estimates are compared and validated with surface mass balance data from the same period. Remote Sensing of Environment 114 (2010) 2756–2767 ⁎ Corresponding author. Tel.: + 47 99102900. E-mail address: geirmoh@geo.uio.no (G. Moholdt). 0034-4257/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.rse.2010.06.008 Contents lists available at ScienceDirect Remote Sensing of Environment journal homepage: www.elsevier.com/locate/rse