  Decametric (DAM) radio emissions are one of the main windows through which
one can reveal and understand the Jovian magnetospheric dynamics and its
interaction with the moons. DAMs are generated by energetic electrons through
cyclotron-maser instability. For Io (the most active moon) related DAMs, the
energetic electrons are sourced from Io volcanic activities, and quickly
trapped by neighboring Jovian magnetic field. To properly interpret the
physical processes behind DAMs, it is important to precisely locate the source
field lines from which DAMs are emitted. Following the work by Hess et al.
[2008, 2010], we develop a method to locate the source region as well as the
associated field lines for any given DAM emission recorded in a radio dynamic
spectrum by, e.g., Wind/WAVES or STEREO/WAVES. The field lines are calculated
by the state-of-art analytical model, called JRM09 [Connerney et al., 2018]. By
using this method, we may also derive the emission cone angle and the energy of
associated electrons. If multiple radio instruments at different perspectives
saw the same DAM event, the evolution of its source region and associated field
lines is able to be revealed. We apply the method to an Io-DAM event, and find
that the method is valid and reliable. Some physical processes behind the DAM
event are also discussed.
