  Typical geomagnetically induced current (GIC) modelling assumes the induced
quasi-DC current at a node in the transmission network is linearly related to
the local geoelectric field by a pair of network parameters. Given a limited
time-series of measured geomagnetic and GIC data, an empirical method is
presented that results in a statistically significant generalised ensemble of
parameter estimates with the error in the estimates identified. The method is
showcased for different transmission networks and geomagnetic storms and, where
prior modelling exists, shows improved GIC estimation. Furthermore, modelled
networks can be locally characterised and probed without any further network
knowledge. Insights include network parameter variation, effective network
directionality and response. Merging the network parameters and geoelectric
field estimation, a transfer function is derived which offers an alternative
approach to assessing transformer exposure to GICs.
