  We investigate how observations of synchrotron intensity fluctuations can be
used to probe the sonic and Alfv\'enic Mach numbers of interstellar turbulence,
based on mock observations performed on simulations of magnetohydrodynamic
turbulence. We find that the structure function slope, and a diagnostic of
anisotropy that we call the integrated quadrupole ratio modulus, both depend on
the Alfv\'enic Mach number. However, these statistics also depend on the
orientation of the mean magnetic field in the synchrotron emitting region
relative to our line of sight, and this creates a degeneracy that cannot be
broken by observations of synchrotron intensity alone. We conclude that the
polarization of synchrotron emission could be analyzed to break this
degeneracy, and suggest that this will be possible with the Square Kilometre
Array.
