  The lensing signals involved in CMB polarization maps have already been
measured with ground-based experiments such as SPTpol and POLARBEAR, and would
become important as a probe of cosmological and astrophysical issues in the
near future. Sizes of polarization maps from ground-based experiments are,
however, limited by contamination of long wavelength modes of observational
noise. To further extract the lensing signals, we explore feasibility of
measuring lensing signals from a collection of small sky maps each of which is
observed separately by a ground-based large telescope, i.e., lensing
reconstruction from a patchwork map of large sky coverage organized from small
sky patches. We show that, although the B-mode power spectrum obtained from the
patchwork map is biased due to baseline uncertainty, bias on the lensing
potential would be negligible if the B-mode on scales larger than the blowup
scale of $1/f$ noise is removed in the lensing reconstruction. As examples of
cosmological applications, we also show 1) the cross-correlations between the
reconstructed lensing potential and full-sky temperature/polarization maps from
satellite missions such as PLANCK and LiteBIRD, and 2) the use of the
reconstructed potential for delensing B-mode polarization of LiteBIRD
observation.
