  We present a new characterization of partially coherent electric and magnetic
wave vector fields.This characterization is based on the 36 auto/cross
correlations of the 3+3 complex Cartesian components of the electric and
magnetic wave fields and is particularly suited for analyzing electromagnetic
wave data on board spacecraft. Data from spacecraft based electromagnetic wave
instruments are usually processed as data arrays. These data arrays however do
not have a physical interpretation in themselves; they are simply a convenient
storage format. In contrast, the characterization proposed here contains
exactly the same information but are in the form of manifestly covariant
space-time tensors. We call this data format the Canonical Electromagnetic
Observables (CEO) since they correspond to unique physical observables. Some of
them are already known, such as energy density, Poynting flux, stress tensor,
etc, while others should be relevant in future space research. As an example we
use this formalism to analyze data from a chorus emission in the mid-latitude
magnetosphere, as recorded by the STAFF-SA instrument on board the Cluster-II
spacecraft.
