Curious behaviour of a proton magnetometer

Abstract

1. Introduction. This Department has made extensive observations with a proton magnetometer towed behind a ship (Hill (2)). The magnetometer consists of a bottle of water surrounded by a coil of wire through which a current flows and produces a polarizing field of about 100 oersted. A small proportion of the protons in the water are polarized along the resultant field. When the current is turned off they precess about the Earth's field and produce in the coil an e.m.f. whose frequency is a measure of the field.

Earth's field magnetometry

“…The orientation of H perpendicular to H,, is not a critical factor, and simple considerations show that signal amplitude varies as sin2 0, where 0 is the angle between H and H,. Bullard et al (1964) have verified the need for rapid switching off of the last few gauss of the polarizing field, Unless this is achieved distortion occurs in the angular dependence of the signal strength and may result in loss of data in survey operations where the orientation of the sensor relative to the field cannot easily be dictated.…”