GRASIMU: A Gravimetry Forward Modelling Web App for Arbitrary 3D Density Models

Forward modelling of gravity signals is useful for designing an effective survey over specific targets. Given how ubiquitous gravimetry is in mineral exploration, archaeology, and planetary geosciences, there is a need for a fast, open-source tool that can model any 3D density model of complex geometry in any terrain environment. GRASIMU is a browser-based tool written in Python and designed for professionals and students alike. It contains four main components: i) 3D target model upload and configuration, ii) terrain generation, iii) survey design, and iv) an interactive visualization dashboard. First, the user can either upload a custom STL file representing the 3D target geometry, or select simple shapes such as sphere or cylinders. A density model is constructed by converting the mesh into cubic voxels with a user-determined resolution and density. Finally, the numerical solution for gravitational acceleration is calculated. If simple shapes are used, both the numerical and analytical solution are calculated. Terrain can be generated to simulate different morphologies such as rolling hills or steep ridges, or from a custom digital terrain model. To simulate the position error present in the terrain model used for terrain corrections, the terrain elevation is varied within a user-defined range with the uncertainties increasing with terrain slope. Lastly, the user defines the density of the host rock around the target, and GRASIMU calculates the gravitational acceleration of the terrain on the measurement stations. The user can now enter the gravimeter and survey location uncertainty. Survey points can be placed by clicking on a 2D plot of the scene and a table of the station locations. Lastly, the user selects which method will be used to interpolate between survey points to obtain a 2D grid of gravity results. Finally, the 3D model, a list of simulation parameters, and the results of all calculations are given in an interactive dashboard. Free-air and terrain corrections can be dynamically turned on and off. By clicking on an enlarged version of any of the interpolated 2D gravimetry maps, the user can see a 2D cross-section of the gravimetry data and query it as needed. All results can be exported to a text file for further processing or visualization in an external software.