Detection of sea-water motion by nuclear precession

The long memory of nuclear-spin Larmor precession can be utilized to detect small changes in precession phase angle. The detection of longrange, slow transport of sea water caused by internal waves or other disturbances would seem desirable. Consider how the transport of a volume element of spins in a liquid through a spatial, inhomogeneous, magnetic field affects the phase of Larmor precession. For simplicity, consider a volume element of spins at position x0 at time t = 0, and assume that this volume element moves with a constant velocity v in an inhomogeneous field H(x). The magnitude and direction of v is to be measured, and it is shown that v as small as 10−8 cm/sec is detectable.