Wayne Mcrae

• PhD
• Research Associate at University of Strathclyde

Magnetic gradiometers are tools for geophysical exploration. The magnetic gradient is normally calculated by subtracting the outputs of two total field magnetometers which are separated by a baseline. Here we present a unique device that directly measures magnetic gradients using only a single string as its sensing element. The main advantage of a...

Abstract Nighttime ionospheric D-region parameters are found to be ,generally well-modeled bythe,traditional H' and , as ,used by Wait ,and by the ,US Navy in their Earth- ionosphere VLF radio waveguide programs. New comparisons with non-equatorial, mainly all-sea VLF path observations reported over several decades are shown,to be consistent with...

Magnetic gradiometers are powerful tools for mineral exploration. To avoid the problem of heading errors, gradiometers must be made from low susceptibility materials. We compare possible low susceptibility materials for gradiometer use and strategies for minimizing magnetic contamination. In particular, we present the favourable magnetic properties...

Development is continuing on a novel direct magnetic gradiometer that uses a string as its single sensing element. A string driven by an AC current and vibrating in its second order `S' shaped mode is used to directly measure the magnetic gradient. The sensitivity is measured to be 0.4nT/m/&surd;Hz in the laboratory. Long-term drift is very low, an...

A magnetic gradiometer system being developed by the authors uses a vibrating string as its sensing element. The next generation of sensor will use a wide ribbon instead of a string. In order to precisely measure the displacement of the ribbon we have designed a new differential capacitive readout with displacement noise below 10−13m/Hz. Two capaci...

Recently, a novel direct string magnetic gradiometer (DSMG) has been developed, where a vibrating wire, driven by an AC current, is used as a single sensitive element. It is designed to directly measure the local off-diagonal components of the magnetic gradient tensor, Bxz, Byz and Bxy, provided the distance to an object creating magnetic anomalies...

Gravity gradiometry research and development has intensified in recent years to the extent that technologies providing a resolution of about 1 eotvos per 1 second average shall likely soon be available for multiple critical applications such as natural resources exploration, oil reservoir monitoring and defence establishment. Much of the content of...

Recently, a novel Direct String Magnetic Gradiometer (DSMG) has been developed, where a vibrating wire, driven by an AC current, is used as a single sensitive element. It is designed to directly measure the local off-diagonal components of the magnetic gradient tensor, Bxz, Byz and Bxy, provided the distance to an object creating magnetic anomalies...

SUMMARY Gravitec Downhole Instruments Ltd. is in the final stages of adapting its gravity gradiometer technology for deployment in the borehole environment for use in exploration as well as for time-lapse reservoir monitoring. The project, named Scorpius, is in cooperation with partners Kenda Capital and QinetiQ Ltd. Laboratory testing of the senso...

In this paper we report a detailed investigation of a number of different materials commonly used in precision instrumentation in the view of using them as critical components in the magnetic gradiometer. The materials requirement inside a magnetic gradiometer is stringent because the presence of magnetic susceptible material will introduce intrins...

Nighttime ionospheric D region heights and electron densities are determined from an extensive set of VLF radio phase and amplitude observations. The D region parameters are characterized by the traditional H′ (height in kilometers) and β (sharpness in km-1) as used by Wait and by the U. S. Navy in their Earth-ionosphere waveguide programs. The VLF...

Ionospheric perturbations due to solar flares, measured at VLF in both phase and amplitude on long subionospheric paths, are used to determine the accompanying D-region electron density enhancements as a function of the flare X-ray fluxes measured by the GOES satellites. The electron densities are characterised by the two traditional parameters, H′...

Experimental observations of the daytime variations of VLF phase and amplitude over a variety of long subionospheric paths have been found to be satisfactorily modelled with a D-region ionosphere, described by the two traditional parameters, H′ and β (being measures of the ionospheric height and the rate of increase of electron density with height,...

Summary A novel sensor design for measuring magnetic gradient fields has been developed by Gravitec Instruments Ltd, New Zealand. The sensor features a single string element that reacts only to the gradient field, ignoring the much stronger total-field of the Earth. Laboratory tests of the system show the room temperature noise floor is down to 0.1...