  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.
