  Magnetoseismology, a technique of magnetic field diagnostics based on
observations of magnetohydrodynamic (MHD) waves, has been widely used to
estimate the field strengths of oscillating structures in the solar corona.
However, previously magnetoseismology was mostly applied to occasionally
occurring oscillation events, providing an estimate of only the average field
strength or one-dimensional distribution of field strength along an oscillating
structure. This restriction could be eliminated if we apply magnetoseismology
to the pervasive propagating transverse MHD waves discovered with the Coronal
Multi-channel Polarimeter (CoMP). Using several CoMP observations of the Fe
xiii 1074.7 nm and 1079.8 nm spectral lines, we obtained maps of the plasma
density and wave phase speed in the corona, which allow us to map both the
strength and direction of the coronal magnetic field in the plane of sky. We
also examined distributions of the electron density and magnetic field
strength, and compared their variations with height in the quiet Sun and active
regions. Such measurements could provide critical information to advance our
understanding of the Sun's magnetism and the magnetic coupling of the whole
solar atmosphere.
