The Modulation of a Proton Magnetometer Signal due to Rotation

Expressions for the amplitude and frequency modulation of the signal from a rotating proton precession magnetometer are derived by treating the net magnetization of the proton-rich fluid as a simple dipole. The instantaneous frequency modulation is depicted in two sets of curves either of which can be used dependent upon the choice of angular quantities used to specify the instrument's attitude during rotation. In practice the frequency is measured by counting methods and this results in a mean frequency for the counting interval. An expression for the mean frequency is derived and the method of correction discussed.