Pos-4 Vector Overhauser Magnetometer: Results at Magnetic Observatories and Development Prospects as an Alternative to Di-Flux

Abstract

This paper presents the results of the development and test operation of the POS-4 vector Overhauser magnetometer, capable of competing with well-known semi-absolute GEM dIdD variometer [1,2]. The key difference is the use of a Garrett vertical solenoid wound on a durable titanium cylinder with a groove for the wire, as well as perpendicular rings that generate switchable bias fields with high uniformity. Such design ensures long-term measurement stability and dimensional integrity. This magnetic system configuration allows the measurement of absolute values of field components (XYZ) and DI angles in addition to standard scalar measurements (T). Metrological testing and operational deployment at numerous Russian magnetic observatories, as well as several Arctic expeditions, have demonstrated that the basic version of POS-4 provides the necessary stability and accuracy. A simple method and formula for determining and accounting for the measurement error of the vertical component Z due to the mismatch of the mechanical and magnetic axes are presented. This is based on the rotation of the solenoid while holding the end of the solenoid in two liquid levels or an electronic level. Absolute accuracy is achieved up to 0.1 nT and is stable for a long time over a wide temperature range. The compactness of the magnetization system is ensured by the use of a small-sized Overhauser sensor with an original working substance providing high sensitivity due to Heisenberg hyperpolarization ODNP that is presented. A new version of POS-4Theo equipped with parts of standard mid-accuracy theodolite is presented. This theodolite feature: a non-magnetic duralumin central axis, which in the future will allow for absolute measurements of declination angle (D) without the need for specialized non-magnetic theodolites and fluxgate magnetometers (described in INTERMAGNET TRM).