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GEOMAGNETISM PROGRAM
OPERATIONS AND DEVELOPMENTS

The most important product of the USGS Geomagnetism Program is time series of stable magnetometer data having high accuracy and resolution. In this section we briefly describe how these data are collected, transported, processed, managed, and disseminated -- the primary tasks of Program staff.

Observatory Network

The USGS Geomagnetism Program currently operates 13 magnetic observatories. Magnetometer data are collected at these facilities, the data are then transmitted to Program headquarters in Golden Colorado. The geographic distribution of the Program’s observatories, shown below, has been determined by the need to monitor and study the geomagnetic field on a global scale, primarily for purposes of space-weather diagnosis and main field modelling and mapping, as well as the practical issues of availability of land, communication and operational logistics, and the relative locations of observatories operated by other foreign-national programs.

Map of U.S.G.S. magnetic observatory locations. Barrow Sitka Newport Fredericksburg Tucson San Juan Stennis Shumagin College Boulder Del Rio Honolulu Guam Fresno Midway

The geographic distribution of Geomagnetism Program observatories. Click on the observatory name for details of each facility. The Midway observatory is not currently operational. Shumagin is in the process of being installed.

Magnetic Sensors and Infrastructure

The basic sensor package at each observatory consists of a tri-axial fluxgate magnetometer which gathers vectorial data, typically the horizontal intensity, declination, and the vertical component (H,D,Z), plus a proton magnetometer, which measures the total intensity of the field (F). The redundancy between these two measurement systems allows for consistency checks that are useful for troubleshooting. Moreover, a fluxgate sensor-electronics package is prone to deliver data that drift on an absolute scale, primarily as the result of changes in ambient temperature; proton magnetometer data also drift with temperature, but usually much less than fluxgate data. To reduce this baseline drift, the sensors and electronics are housed in well-insulated, thermostatically-controlled buildings, but even then there remains some residual baseline drift. Therefore, each observatory is visited by a Program employee or contractor once a week so that so-called ‘absolute’ measurements can be made using a theodolite coupled to a small magnetometer; these data are used later during data processing to make final adjustments to the data baselines. To preserve sensor orientation, both the fluxgate magnetometer and the theodolite are supported by piers that are firmly anchored into the ground. Finally, the buildings at each observatory are situated on plots of land of sufficient size to help isolate the operations from outside magnetic interference. USGS Geomagnetism Program observatory standards are consistent with those set by Intermagnet, an international consortium which promotes the worldwide collection of high-quality, ground-based magnetometer data, and within which the USGS Geomagnetism Program has an important leadership role.

Observatory sensor package.

The basic sensor package installed at each observatory: (bottom) fluxgate magnetometer, (top left) proton magnetometer, (top right) theodolite with fluxgate coupled to the telescope.

Magnetic-field components.

Magnetic-field components: (X,Y,Z) define the Cartesian components (north, east, down), (H,D,Z) are the components usually measured by the fluxgate (horizontal intensity, declination, down), (I) is the inclination of the field (F) is the total intensity measured by the proton.

Data Acquisition and Transportation

Data are collected at each observatory with a temporal resolution of at least one minute. The existing data-acquisition system, which has been in place for about fifteen years, uses off-the-shelf technology that is similar to that used by (among others) the British, Japanese, and Hungarian geomagnetism programs. One-minute data are transmitted in near-real time to Program headquarters in Golden Colorado via a series of satellite linkages, with a back-up transmission capacity accomplished via ftp. Recently, the Program has begun to deploy a new system (PCDCP), built around a personal computer, that will improve the temporal resolution of data collected at each observatory to one second and permit convenient on-site inspection of the data for trouble-shooting purposes. Collection of one-second data will significantly increase the size of the Program’s customer base, particularly among scientists studying the magnetosphere and making practical space-weather applications. Coincident with the development of the new one-second data-acquisition system has been the development of an internet-based, data-transportation system, namely ‘Magworm’, a modification of the ‘Earthworm’ protocol previously designed and developed by USGS seismologists. This new transportation system affords the Program a great deal of operational flexibility and modularity, as well as data delivery with virtually no time delay, an important consideration for practical space-weather related applications. A schematic of the Program's data acquisition-transportation system is given below.

Satellite and internet data-transportation links.

Data from the Program's remote observatories are relayed through a set of satellite links. The new Magworm data-transportation system relies on the internet.

Data Processing, Management, and Dissemination

Data that are received in Golden in near-real time are ‘variational’ or ‘preliminary’; they are arbitrary to within a baseline offset, which itself may have a slow drift. For many applications, such preliminary data are more than sufficient, particularly for investigators concerned with relatively rapid changes in the magnetic field occurring over time windows of less than a few days. Studies involving longer windows of time usually require absolute data time series. These are obtained through data processing, with adjustments made for baseline drift using the periodic absolute measurements made at each observatory. Specialized data-processing software, namely ‘MagProc’ has been developed in-house, making the production of absolute, so-called ‘definitive’, data relatively efficient. Moreover, since the processing software allows for quick systematic inspection of large quantities of data, it can be used for troubleshooting and quality control. The Program is also developing an Oracle database, which will serve as an interface between the data-collection systems and processing software, as well as help facilitate the dissemination of both new and old observatory data. Through the Geomagnetism Program’s National Geomagnetic Information Center (NGIC), data are disseminated in two forms: variational data, available in near-real time, and definitive data, available after processing and within a year of their collection. Near-real-time preliminary data are disseminated to customers via direct links, automatic email, ftp, and increasingly over the internet through the Program’s website. Definitive data are disseminated through the production of CDs. These are produced in cooperation with Intermagnet, which also helps promote the dissemination of other nations' magnetometer data. To view recent Geomagnetism Program data, see the Observatories page of this website.


U.S. Department of the Interior,  U.S. Geological Survey,
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Page last modified/created:   9 September, 2004
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