The 2020 Vening Meinesz Medal is awarded to Willi Freeden for his pioneering work in combining a comprehensive mathematical theory with fundamental geodetic problems and advanced applications in Earth system sciences and global change studies.
During the last 20 years geodesy has made remarkable advancements in determining the Earth’s geometric and gravimetric figure as well as its rotation in space, mainly due to new satellite missions and enormous improvements in measurement technologies. The quantity and quality of these new data are reflected in high-resolution and high-accuracy models as well as reliable analyses and forecasts often reached by revising established mathematical modelling techniques and developing modern numerical methods.
Willi Freeden is one of the most outstanding architects in this respect. Two examples of research areas that were sustainably influenced by him are regional and multiscale modelling. These topics have become more and more important, for example, due to the locality of the effects of climate change, the irregularity of data sets, the challenges in the handling of big data, the multitude of physical effects that have to be taken into account at various temporal and spatial scales, as well as regional variations of noise.
Freeden’s seminal contributions to these subjects are particularly given by his spherical spline method from the early 1980s and his spherical wavelet analysis techniques, which he started to develop in the 1990s. Both methods, which continue to be enhanced by him, have provided the foundations for the use of radial basis functions in geodetic models today. The tools based on Freeden’s work are being applied increasingly and in manifold ways. He also established more advanced methods that are suitable for the real Earth’s topography instead of the sphere as a domain. He has also contributed to various sections of Earth sciences besides geodesy, like geomagnetics, oceanography and geothermal energy modelling.
Freeden’s outstanding role in putting the interplay of Earth sciences and mathematics into practice was recognised by the members of the German Geodetic Commission, which elected him, as a mathematician, as one of their fellows. Freeden served the community by being a member of the editorial boards of several journals, including ‘Journal of Geodesy’ and ‘Journal of Geodetic Science’. Furthermore, he set standards for the interdisciplinarity between mathematics and geodesy by founding the ‘International Journal on Geomathematics’, of which he is still an editor-in-chief, and by authoring and editing numerous groundbreaking textbooks like ‘Constructive Approximation on the Sphere – with Applications to Geomathematics’ as well as several handbooks on geomathematics and mathematical geodesy that are in very active use today.
Most of Freeden’s ideas were developed and worked out together with students or in cooperation with international teams. Several of his former students are today highly successful in academia, economy and industry. Freeden cooperated and published jointly with prominent geodesists, and initiated international geodetic meetings, workshops and schools. This all explains the great impact and the high relevance of Willi Freeden’s work in modern geodesy.