  The strong variations of energetic electron fluxes in the Earth's inner
magnetosphere are notoriously hard to forecast. Developing accurate empirical
models of electron fluxes from low to high altitudes at all latitudes is
therefore useful to improve our understanding of flux variations and to assess
radiation hazards for spacecraft systems. In the present work, energy- and
pitch-angle-resolved precipitating, trapped, and backscattered electron fluxes
measured at low altitude by Electron Loss and Fields Investigation (ELFIN)
CubeSats are used to infer omnidirectional fluxes at altitudes below and above
the spacecraft, from 150 km to 20,000 km, making use of adiabatic transport
theory and quasi-linear diffusion theory. The inferred fluxes are fitted as a
function of selected parameters using a stepwise multivariate optimization
procedure, providing an analytical model of omnidirectional electron flux along
each geomagnetic field line, based on measurements from only one spacecraft in
low Earth orbit. The modeled electron fluxes are provided as a function of
$L$-shell, altitude, energy, and two different indices of past geomagnetic
activity, computed over the preceding 4 hours or 3 days, potentially allowing
to disentangle impulsive processes (such as rapid injections) from cumulative
processes (such as inward radial diffusion and wave-driven energization). The
model is validated through comparisons with equatorial measurements from the
Van Allen Probes, demonstrating the broad applicability of the present method.
The model indicates that both impulsive and time-integrated geomagnetic
activity partly control electron fluxes in the outer radiation belt and in the
plasma sheet.
