During the initial project phase, the main focus was on the integration of the glacier-system model into an adequate data assimilation framework. For this purpose, critical target quantities were selected and suitable observations were identified for the actual analysis steps during the data assimilation. Moreover, particular attention was given to the analysis frequencies, to constraining prior uncertainties as well as to computational efficiency. This substantial development effort resulted in a first successful application to a typical Alpine valley glacier, still using synthetic observations. As observations are sequentially assimilated, an accurate tracing of glacier evolution in the past and a best representation of the glacier state at present was achieved. In this way, we took the first major step for streamlining the information flow from Earth observations into glacier-system models as well as for generating a self-consistent model initialisation into present day for seamless future projections.
Secondary activities relate to a refinement of the energy balance at the glacier surface as well as to improving global ice-thickness mapping by glacier-specific calibration to past retreat. The former comprises a melt-model implementation following a simplified energy-balance approach. For this implementation, we deliberately decided to include topographic shading, indirect radiation as well as clouding. A pending task remains the inclusion of the influence of supraglacial debris on ice melt. An empirical description of snow drift is, however, already available. First tests on regional scales have been conducted in the European Alps and in South America. Turning to thickness mapping, an existing state-of-the-art mass-conservations approach was improved by viscosity re-scaling, which further exploits slope, elevation and outline information. Moreover, it has been shown that glacier retreat can be used as a valuable source for past thickness information. This information is provided by satellite remote sensing and therefore available for each glacier on this planet. Calibration and performance tests have been presented in the Swiss Alps and a new thickness map product was released for the entire European Alps.
