  Collisionless shocks are ubiquitous in the Universe and often associated with
strong magnetic field. Here we use large-scale particle-in-cell simulations of
non-relativistic perpendicular shocks in the high-Mach-number regime to study
the amplification of magnetic field within shocks. The magnetic field is
amplified at the shock transition due to the ion-ion two-stream Weibel
instability. The normalized magnetic-field strength strongly correlates with
the Alfv\'enic Mach number. Mock spacecraft measurements derived from PIC
simulations are fully consistent with those taken in-situ at Saturn's bow shock
by the Cassini spacecraft.
