  The relic neutrinos are expected to acquire a bulk relative velocity with
respect to the dark matter at low redshifts, and neutrino wakes are expected to
develop downstream of the dark matter halos. We propose a method of measuring
the neutrino mass based on this mechanism. This neutrino wake will cause a
dipole distortion of the galaxy-galaxy lensing pattern. This effect could be
detected by combining upcoming lensing surveys with a low redshift galaxy
survey or a 21 cm intensity mapping survey, which can map the neutrino flow
field. The data obtained with LSST and Euclid should enable us to make a
positive detection if the three neutrino masses are quasidegenerate with each
neutrino mass of $\sim$0.1 eV, and a future high precision 21 cm lensing survey
would allow the normal hierarchy and inverted hierarchy cases to be
distinguished, and even the right-handed Dirac neutrinos may be detectable.
