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    • Other sensitivity and resolution analysis

    2018-11-13

    Other sensitivity and resolution analysis operations based on kernel values may as well read in the kernel files, do their analyses and produce output in the ASKI directories, according to the needs of the user (Fig. 2, ). ASKI additionally provides executables for minor auxiliary operations, e.g. to generate a starting model in the format required by ASKI or to create vtk files [25] from kernel, wavefield or model values for plotting with external software such as Paraview [26], VisIt [27], MayaVi [28], or VTK [25] (Fig. 2, ). Also all involved grids or point sets are generated in form of vtk files for visualization, e.g. wavefield points, station/event coordinates, lines between event and station locations, or shorelines. All vtk output files of different quantities can be generated with respect to different geometrical projections, e.g. applying certain rotations or removing curvature in spherical settings in order to create convenient views to inspected objects in a consistent way. Fig. 3 gives an example of the same plot using two different projections. For plotting numerical data on the get better grid, it can additionally be decided whether the vtk files should contain data on the volumetric cell geometry or on a point grid only, namely the center points of the inversion grid cells. The latter can be advantageous when applying some kind of display filters/interpolations by the visualization tools and reduces the overall geometry information in the vtk files, hence the file size. The ASKI project website http://www.rub.de/aski intends to provide basic information and literature recommendation, as well as a reference to ASKI’s source repository (currently https://github.com/seismology-RUB/ASKI). Via the source repository, ASKI and some of its components, as well as documentation and some examples are freely available under terms of the GNU General Public License (version 2 or higher http://www.gnu.org/licenses/gpl).
    ASKI from a programmer’s viewpoint The toolbox-like nature of ASKI requires the individual operations to communicate via input/output of files on hard disk and encourages the toolbox to be implemented in an object-oriented fashion that enables flexible maintenance of the code and convenient extension of the software package. Fig. 4 sketches modularization aspects of ASKI which are discussed in the following in the context of the implementation of ASKI. Using external forward codes requires a suitable interface to ASKI. Since in general there are very different (semi-)analytical or fully numerical seismic forward codes operating in time or frequency domain using very different numerical schemes and we do not want to a priori disallow any, we decided to have a very general, thus flexible interface constructed in an object-oriented fashion (Fig. 4, ): From a particular forward code, all forward-code-dependent quantities such as wavefield points (i.e. the forward grid), kernel reference model (i.e. the background model on the forward grid used to solve the seismic forward problem), kernel displacement (i.e. the spectral wavefields originating from the seismic sources) and kernel Green tensor (i.e. the back-propagations in form of single force Green tensor components originating from the seismic station components) are communicated to ASKI through an individual sub-module. In order to extend ASKI to support another forward code, a specific sub-module needs to be created for each such quantity (as indicated by Fig. 4, ). This way, ASKI allows the forward codes to define their own grid points on which sensor provide the wavefields and they can use their own file formats for points, model, wavefields and other meta information they might use, provided the knowledge of how to access the required information, e.g. how to read any files or to calculate certain data, is implemented in the respective sub-modules. Any particular implementational advantages of a forward code can thus be maintained without imposing unnecessary requests on the code. For instance, grid-based forward codes should choose some subset of the simulation grid as wavefield points for ASKI and the forward code’s standard (parameter) files for grids and meta information can be re-used by the interface sub-modules. However, all forward codes most likely need to be extended or modified in order to provide the required spectral wavefield output, synthetic data in the required frequency discretization, as well as point/model information.