Geogravl3 – an Open-Source Python Package for Level-3 Gravity Data Processing

Many users of time-variable satellite gravimetry data from the GRACE and GRACE-FO missions employ gridded Level-3 data for various applications in, e.g., hydrology, glaciology, oceanography, and the climate sciences. Operational Level-3 data products are provided, for example, via GravIS (www.gravis.gfz.de) maintained by GFZ based on Level-2 spherical harmonic solutions, or by the three mascon producers JPL, CSR, and GSFC. Users of these products are, however, limited to the processing choices defined by the data providers.In order to make GRACE/-FO data even more accessible, the open-source Python package geogravL3 enables users to generate Level-3 products from spherical harmonic coefficients using user-defined processing settings. The software supports the generation of domain-specific products for land (terrestrial water storage), oceans (ocean bottom pressure), and the Greenland and Antarctic ice sheets (ice mass change). Implemented processing steps include filtering of spherical harmonic coefficients (Gauss, DDK, and VDK), replacement of low-degree harmonics, and correction for glacial isostatic adjustment (GIA). For land and ocean applications, spherical harmonic coefficients are transformed into surface mass distributions using spherical harmonic synthesis under the thin-layer assumption. Ice mass changes over Greenland and Antarctica are estimated using a sensitivity-kernel approach, which is conceptually similar to a Level-2-based mascon method.The geogravL3 package is openly available via GitLab (https://git.gfz.de/grace_l3/geogravl3) and can be installed through PyPI or conda-forge.