Christopher Turbitt

A technique for estimating the absolute vector geomagnetic field from a marine vessel

We have developed a technique to estimate the absolute strength and direction of the geomagnetic field from a marine vessel. This technique will be of value in the study of marine magnetic anomalies, directional drilling or geomagnetic field modelling. One of the main difficulties in this operation is to correct the data for the magnetic field generated by the vessel itself. Assuming the vessel susceptibility is isotropic, we show that by turning the ship through 360° at a place where the strength of the field is known we can estimate the local direction of the magnetic field. Once this is known, the vessels field at any attitude can be robustly estimated and the measurements of the full magnetic field vector made in a normal surveying mode can be corrected. The ambient magnetic field estimates at the turn locations have proved to be very accurate. In normal surveying mode, these estimates are not as good since they are directly dependent on the accuracy of the vessel attitude measurements. However, when the technique is applied on real data, the total intensity field estimates have a very low level of noise showing that the vessel signal has been well accounted for.

Improvements in Geomagnetic Observatory Data Quality

Geomagnetic observatory practice and instrumentation has evolved significantly over the past 150 years. Evolution continues to be driven by advances in technology and by the need of the data user community for higher-resolution, lower noise data in near-real time. Additionally, collaboration between observatories and the establishment of observatory networks has harmonized standards and practices across the world; improving the quality of the data product available to the user. Nonetheless, operating a high-quality geomagnetic observatory is non-trivial. This article gives a record of the current state of observatory instrumentation and methods, citing some of the general problems in the complex operation of geomagnetic observatories. It further gives an overview of recent improvements of observatory data quality based on presentation during 11th IAGA Assembly at Sopron and INTERMAGNET issues.

A method for the near real-time production of quasi-definitive magnetic observatory data

Magnetic observatory data are widely used in the derivation of time-varying magnetic field models, often in combination with satellite magnetic data, when available. Traditionally the definitive observatory results are used, the availability of which can often lag those of the satellite data by months and even years. The recently defined quasi-definitive observatory data type has been introduced to meet the need to provide observatory data suitable for use in field modeling in a more rapid time frame and for producing Level 2 products planned for the upcoming European Space Agency Swarm mission. A method for producing quasi-definitive data is presented and the essential steps described. To evaluate the method, provisional data published on a next day basis since 2000 are tested against definitive data at five INTERMAGNET observatories. The means and standard deviations of the differences between the candidate quasi-definitive and definitive data are within the accuracy of 5 nT set by INTERMAGNET. Since the tested data were published on-line on a next day basis, they also easily meet the INTERMAGNET requirement of availability within three months. These results demonstrate that prompt production of quasi-definitive data is possible for observatories that already perform to the standards set by INTERMAGNET.

An Investigation into Techniques for Isolating Noise in Observatory Data

In this study, using one-minute definitive data published by a number of INTERMAGNET observatories, we apply a number of time- and frequency-domain techniques to characterise the global, natural geomagnetic signal and isolate the artificial noise at an individual observatory. With the aim of developing an analytical tool that can be used to identify observatory noise against the natural signal, we report on the suitability of these techniques to detect common observatory noise types.

INDIGO: Better Geomagnetic Observatories Where We Need Them

Good magnetic observatories are needed more than ever for global modeling and navigation. Magnetic satellite missions, once said to be the death of ground based observations, are now demanding quality data from fixed observations points on the Earth.