In the past, magnetic observatories relied on a combination of Overhauser, fluxgate and theodolite instruments for obtaining measurements. GEM then introduced the dIdD (delta Inclination/delta Declination) system for high precision results. Next, dIdD was enhanced significantly with the development of the Suspended dIdD system.
GEM Systems latest development in this field is the Absolute Magnetic Declination & Inclination (DI) Meter. This instrument is being designed to provide a measurement of Declination and inclination at a given location on the globe. This system is an adaptation of the dIdD vector magnetometer, this system will eliminate the need for a theodolite, by determining declination and inclination (not just changes in inclination / declination).
GEM’s declination-inclination instrument is an Overhauser magnetometer with 2 sets of bias coils (horizontal & vertical) in the magnetic north plane.
The new instrument (DI) simplifies setting observatory magnetometers by eliminating the need for fluxgate magnetometers and thermal insulating structures as before, and now a theodolite system.
As described by the Israeli Nuclear group, Soreq, the dIdD is a vector magnetometer offering monitoring of the inclination and declination as well as total intensity of the earth’s magnetic field. Resolution is 0.01 nT with a recording interval of 5 samples per second.
The Suspended dIdD instrument provides key benefits;
The Suspended dIdD takes advantage of many of the benefits of the Overhauser system. In addition, it offers its own unique benefits for observatory work:
Proven construction for high reliability. GEM’s systems are designed for robustness from electronics to sensors. Ultimately, the system also exceeds specifications set by Intermagnet – the global network of observatories monitoring the Earth’s magnetic field (www.intermagnet.org).
Remote Observatory Station
The Suspended dIdD is a vector magnetometer for continuous monitoring of the inclination, declination and total intensity of the Earth’s magnetic field. It is this combination of measurements that sets it apart from fluxgate instruments (i.e. fluxgates only provide inclination and declination).
GEM’s dIdD employs a mutually orthogonal coil system that measures one unbiased and four biased values of total magnetic fields. The axes of the coil system are arranged so that the axes of the mutually orthogonal coils are themselves perpendicular to the Earth’s magnetic field vector, F, in the horizontal plane and vertical geomagnetic meridian plane.
The measurement process is as follows:
The pulsed sequence preserves power; in practice, users acquire readings on demand and save batteries. The continuous sequence polarizes continuously and stops with very small interruptions of a few tens of miliseconds; users can acquire data without losing any interval and obtain full coverage of the terrain.
The dIdD data aquisition/display software is an interactive Windows 95/NT interactive interface supplied with the dIdD vector magnetometer system. It functions as the instrument’s bi-directional RS-232 terminal. The dIdD software offers the user the option to save the instrument readings to a disk file, while displaying the incoming data in text and graph modes.
Total Field, Vertical Field, East Field, North Field, Inclination and Declination
The dIdD chart recorder displays the incoming data versus time. The vertical and horizontal scales are calculated automatically so as to display the data within the window. The user can change both the vertical and horizontal increments. The window is divided into ten horizontal and ten vertical increments (by dashed lines). The displayed profile can be scrolled both horizontally and vertically. These changes can be achieved by selecting the appropriate item from the Chart Recorder menu, or alternatively, by using shortcut keys.
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