Resolving processes of Antarctic Ice Sheet change through innovations in satellite altimetry

• Applicant: Professor Dr.-Ing. Martin Horwath
• Subject Area: Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 562161246

Limitations in our knowledge on present-day responses of the Antarctic Ice Sheet (AIS) to past and present climate change make it difficult to understand and project its future changes and sea-level contributions. While today’s mass change hotspots are known to be related to changing ice-flow dynamics, long-term trends associated to past and current surface mass balance (SMB) changes may compensate for some of the dynamic losses but are poorly constrained. Satellite altimetry has the unique potential to resolve even small surface elevation changes (SEC) in space and time over more than three decades. Yet, the detection of SMB-related long-term trends has been hampered by the large natural SMB fluctuations, by changes in firn structure that cause time-varying radar penetration and thereby compromise the measurements, and by the ambiguous conversion from volume change to mass change. Other mass balance approaches, such as satellite gravimetry, also face systematic uncertainty challenges, and partly disagree with satellite altimetry. Insufficient information on uncertainty budgets have compromised technique-intercomparisons and technique combinations. This project tackles the challenges of satellite altimetry analysis by exploiting and continuing crucial innovations, such as the physics-based convolutional neural network retracking of radar altimetry echoes, the availability of more than 5 years of ICESat-2 laser altimetry to validate radar altimetry analyses, comprehensive uncertainty modeling as well as progress in SMB modeling and firn modeling. The project has the following objectives: (1) develop time series of spatio-temporal SEC over 1993-2025 with unprecedented signal-to-noise ratio and reliability; (2) identify and quantify processes causing SEC and associated ice-mass change due to fluctuations of SMB and firn thickness, effects of recent changes in ice flow dynamics, ongoing long-term trends in SMB and firn structure and long-term ‘memory effects’ of past SMB changes, by utilising results from SMB modeling, firn modeling, ice sheet modeling as well as complementary observations; (3) develop a comprehensive uncertainty budget for altimetric SEC and altimetric ice-mass change in the framework of error covariance modeling, as a basis for resolving processes of AIS change; (4) elaborate schemes for altimetry-gravimetry intercomparisons and aggregated estimates based on consistent uncertainty characterizations; and (5) contribute the altimetric product and its uncertainty characterization to multi-technique inversion case studies. The project will, hence, contribute to resolving processes of AIS change in several ways: clarify which processes are at work and quantify them; unveil the detailed spatial patterns of long-term trends; clarify the comparison and aggregation of different mass balance assessment and thereby facilitate the interpretation and resolution of discrepancies.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1158: Infrastructure area - Antarctic Research with Comparative Investigations in Arctic Sea Ice Areas
• Co-Investigator: Dr. Veit Helm, Ph.D.