Remote sensing of glacier and ice sheet grounding lines: A review

The precise positioning and long-term monitoring of the grounding line, forming the boundary between grounded and floating ice of marine ice sheets and tidewater glaciers, is critical for assessing ice sheet/glacier stability, ice sheet/glacier mass balance calculations and numerical ice modelling. However, mapping of the grounding line is a challenging task, since it is a subglacial and transient feature. Remote sensing techniques do not map the grounding line directly but locate surface features in the grounding zone that serve as proxies for the true grounding line position. The large variety of methods, products and publications, as well as an inconsistent use of terminology additionally complicate the topic. We present the first detailed review of existing remote sensing techniques and data for grounding line mapping. Benefits and limitations of the different techniques and data sources are discussed and illustrated with examples. We identify a present tradeoff between accuracy and both spatial coverage and temporal resolution of the derived grounding line products. Rather new methods like Sentinel-1-SAR (Synthetic Aperture Radar) Differential Range Offset Tracking (DROT) and Pseudo Crossover Radar Altimetry (PCRA) offer the potential for recent measurements and to fill gaps in some areas. Nevertheless, there is a high demand of new spaceborne radar sensors that provide time series of very short repeat pass data to enable regular grounding line monitoring with most accurate Differential SAR Interferometry (DInSAR) on a continental scale.