GROOPS: A software toolkit for gravity field recovery and GNSS processing. - Torsten Mayer-Gürr; Saniya Behzadpour; Annette Eicker; Matthias Ellmer; Beate Koch; Sandro Krauss; Christian Pock; Daniel Rieser; Sebastian Strasser; Barbara Suesser-Rechberger; Norbert Zehentner; Andreas Kvas (Comput. Geosci., 2021)