Ultra-highresolution topographic modelling of gravitational fields

• Applicant: Dr. Christian Hirt
• Subject Area: Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 276463299

The short-wavelength constituents of the gravitational field are closely related to the topographic masses, so can be modelled from topographic data. Topographic gravity modelling techniques play a key role in geodesy and related disciplines, e.g., for densification and refinement of observed gravity information. In the context of ultra-high resolution gravity modelling, e.g., with km-resolution or better, a critical assessment of topographic modelling methods is required. This research programme proposes a detailed investigation of topographic modelling techniques with ultra-high resolution. Focus will initially be placed on spectral modelling techniques, aiming at a complete assessment of their numerical precision and stability as a function of resolution, which will be studied for the first time at scales as short as 1 km, or harmonic degree 21,600. Shortcomings of the popular residual terrain modelling technique (RTM) - the method of which plays a key role in ultra-detailed gravity modelling with sub-km resolution - will be rectified by developing a new filter approach. This will ensure spectral consistency between topography and gravity, and remove relative errors as large as 10% in topographic gravity. With these and further investigations, the programme will provide a more complete theoretical and practical framework for topographic gravity modelling at ultra-high resolution, thus advancing the knowledge base of the discipline.The improved methods will be applied for a first-ever full transformation of the Earth´s global topography at 90 m resolution to accurate topographic gravity effects. This computationally demanding task (about 200,000 CPU-hours) will be tackled by deploying advanced computational resources and parallelisation. The derived topographic gravity field will be characterised, e.g., in terms of energy curves and signal strengths at different spatial scales, and will be made available to the public. This will confer benefits to geodesy (e.g., as input for future ultra-high resolution gravity fields) and geophysics (e.g., providing an in-situ reduction of observed gravity across the globe) because tedious computations will partially become obsolete. Parts of the modelling techniques will be tested and applied for the Moon too based on high-resolution lunar topography models. In summary, this proposal is significant for physical geodesy, geophysics and parts of the planetary sciences.

• DFG Programme: Research Grants