Prospects for clustering and lensing measurements with forthcoming
  intensity mapping and optical surveys
  We explore the potential of using intensity mapping surveys (MeerKAT, SKA)
and optical galaxy surveys (DES, LSST) to detect HI clustering and weak
gravitational lensing of 21cm emission in auto- and cross-correlation. Our
forecasts show that high precision measurements of the clustering and lensing
signals can be made in the near future using the intensity mapping technique.
Such studies can be used to test the intensity mapping method, and constrain
parameters such as the HI density $\Omega_{\rm HI}$, the HI bias $b_{\rm HI}$
and the galaxy-HI correlation coefficient $r_{\rm HI-g}$.
