HI intensity mapping with MeerKAT: 1/f noise analysis
  The nature of the time correlated noise component (the 1/f noise) of single
dish radio telescopes is critical to the detectability of the HI signal in
intensity mapping experiments. In this paper, we present the 1/f noise
properties of the MeerKAT receiver system using South Celestial Pole (SCP)
tracking data. We estimate both the temporal power spectrum density and the 2D
power spectrum density for each of the antennas and polarizations. We apply
Singular Value Decomposition (SVD) to the dataset and show that, by removing
the strongest components, the 1/f noise can be drastically reduced, indicating
that it is highly correlated in frequency. Without SVD mode subtraction, the
knee frequency over a $20\,$MHz integration is higher than $0.1\,\rm Hz$; with
just $2$~mode subtraction, the knee frequency is reduced to $\sim 3\times
10^{-3}\,{\rm Hz}$, indicating that the system induced 1/f-type variations are
well under the thermal noise fluctuations over a few hundred seconds time
scales. The 2D power spectrum shows that the 1/f-type variations are restricted
to a small region in the time-frequency space, either with long wavelength
correlations in frequency or in time. This gives a wide range of cosmological
scales where the 21cm signal can be measured without further need to calibrate
the gain time fluctuations. Finally, we demonstrate that a simple power
spectrum parameterization is sufficient to describe the data and provide
fitting parameters for both the 1D and 2D power spectrum.
