Assessment of Source and Transport Parameters of Relativistic SEPs Based   on Neutron Monitor Data
  As part of the HESPERIA Horizon 2020 project, we developed a software package for the direct inversion of Ground Level Enhancements (GLEs) based on data of the worldwide network of Neutron Monitors (NMs). The new methodology to study the release processes of relativistic solar energetic particles (SEPs) makes use of several models, including: the propagation of relativistic SEPs from the Sun to the Earth, their transport in the Earth's magnetosphere and atmosphere, as well as the detection of the nucleon component of the secondary cosmic rays by ground based NMs. The combination of these models allows to compute the expected ground-level NM counting rates caused by a series of instantaneous particle releases from the Sun. The proton release-time profile at the Sun and the interplanetary transport conditions are then inferred by fitting NM observations with modeled NM counting rates. In the paper the used models for the different processes, the software and first findings with the new software are presented. 
Rolf B\"utikofer, Neus Agueda, Bernd Heber, Dennis Galsdorf, Rami   Vainio
astro-ph.IM astro-ph.HE physics.space-ph