Cosmic Dawn and Epoch of Reionization Foreground Removal with the SKA
  The exceptional sensitivity of the SKA will allow observations of the Cosmic
Dawn and Epoch of Reionization (CD/EoR) in unprecedented detail, both
spectrally and spatially. This wealth of information is buried under Galactic
and extragalactic foregrounds, which must be removed accurately and precisely
in order to reveal the cosmological signal. This problem has been addressed
already for the previous generation of radio telescopes, but the application to
SKA is different in many aspects.
  In this chapter we summarise the contributions to the field of foreground
removal in the context of high redshift and high sensitivity 21-cm
measurements. We use a state-of-the-art simulation of the SKA Phase 1
observations complete with cosmological signal, foregrounds and
frequency-dependent instrumental effects to test both parametric and
non-parametric foreground removal methods. We compare the recovered
cosmological signal using several different statistics and explore one of the
most exciting possibilities with the SKA --- imaging of the ionized bubbles.
  We find that with current methods it is possible to remove the foregrounds
with great accuracy and to get impressive power spectra and images of the
cosmological signal. The frequency-dependent PSF of the instrument complicates
this recovery, so we resort to splitting the observation bandwidth into smaller
segments, each of a common resolution.
  If the foregrounds are allowed a random variation from the smooth power law
along the line of sight, methods exploiting the smoothness of foregrounds or a
parametrization of their behaviour are challenged much more than non-parametric
ones. However, we show that correction techniques can be implemented to restore
the performances of parametric approaches, as long as the first-order
approximation of a power law stands.
