Studying the local magnetic field and anisotropy of magnetic turbulence
  by synchrotron polarization derivative
  Due to the inevitable accumulation of the observed information in the
direction of the line of sight, it is difficult to measure the local magnetic
field of MHD turbulence. However, the correct understanding of the local
magnetic field is a prerequisite for reconstructing the Galactic 3D magnetic
field. We study how to reveal the local magnetic field direction and the eddy
anisotropy on the basis of the statistics of synchrotron polarization
derivative with respect to the squared wavelength $dP/d\lambda^2$. In the low
frequency and strong Faraday rotation regime, we implement numerical
simulations in the combination of multiple statistic techniques, such as
structure function, quadrupole ratio modulus, spectral correlation function,
correlation function anisotropy and spatial gradient techniques. We find that
(1) statistic analysis of $dP/d\lambda^2$ indeed reveals the anisotropy of
underlying MHD turbulence, the degree of which increases with the increase of
the radiation frequency; (2) the synergy of both correlation function
anisotropy and gradient calculation of $dP/d\lambda^2$ enables the measurement
of the local magnetic field direction.
