  Time-ordered data (TOD) from ground-based CMB experiments are generally
filtered before map-making to remove or reduce the contamination from the
ground and the atmospheric emissions. However, when the observation region
contains strong point sources, the filtering process will result in
considerable leakage around the point sources in a measured CMB map, and leave
spurious polarization signals. Therefore, such signals need to be assessed and
removed before CMB science exploitation. In this work, we present a new method
that we call "template fitting" and can effectively remove these leakage
signals in pixel domain, not only satisfying the requirement for measuring
primordial gravitational waves from CMB-$B$ modes, but also avoiding
time-consuming operations on TOD.
