The National Geomagnetic Initiative (1993) / Chapter Skim
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B1: Operational Platforms
B1: Operational Platforms
Pages 155-189
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From page 155... ...
; · secular-variation sources at the CMB; · main field origins; · morphology of ionospheric and magnetospheric current systems and plasma distributions; · sources of pulsations (ultra-Iow frequency [ULF] waves)
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From page 156... ...
The technology is available today for implementation of a global network of geomagnetic observatories and magnetometer arrays to address critical problems in the solid Earth and space physics.
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From page 157... ...
. Magnetic observatories are primarily distinguished from variation stations by the use of independent absolute instruments at the observatories to accurately determine baselines in order to establish long-term trends (secular variation)
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From page 158... ...
. No permanent platforms have been established, and no absolute measurements have been made to establish secular variation of the vector components of the Earth's magnetic field, although there is a nascent Japanese program.
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From page 159... ...
In a recent experiment to see how promptly annual means were sent to WDC-A, for example, it was learned that many observatories were 3 years late. Under the newly established INTERMAGNET program, geomagnetic data from participating geomagnetic observatories are transmitted in near real time via geostationary satellites or computer links to collection and distribution centers know as Geomagnetic Information Nodes (GINs)
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From page 160... ...
These array magnetometer systems may be used in regional arrays to discover and map anomalous electrical resistivity structures in the continental crust and upper mantle. By augmenting these array magnetometer systems with electric field sensors, MT soundings can later be made over regional structures mapped by the array magnetometer studies.
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From page 161... ...
Although 2,000-km spacing will satisfy main fields modeling, it does not quite meet the needs of secular-variation source studies. The need for 700-to I,400-km spacing could be satisfied by temporary ocean bottom instruments around a permanent "anchor" observatory.
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From page 162... ...
These data, in conjunction with long-period geomagnetic data, can be used to study deep-Earth resistivity structure. · Where islands are not available, geomagnetic observatories utilizing three-component magnetometers and total field absolute magnetometers should be established on the ocean bottom.
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From page 163... ...
· Selected geomagnetic observatories with {ow-noise magnetometers should compute dB/dt at I-second intervals for electric power companies on a campaign basis. Should these data prove useful, consideration should be given to computing a dB/dt index on a permanent basis and transmitting it in real time to electrical power companies to warn of potential damage to electrical power systems from geomagnetic storms.
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From page 164... ...
INTERMAGNET and Solar-Terrestrial Energy Program (STEP) should cooperate closely in establishing complementary global geomagnetic data bases.
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From page 165... ...
Achievement of these objectives will require the identification of key resource people in the respective organizations. National Airborne Survey The existing digital magnetic data set of the United States and its continental shelves cannot adequately address many scientific and societal problems.
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From page 166... ...
For example, Canada has collected more than 9 million line kilometers of magnetic data at a spacing of 0.8 km, has published more than 9,500 aeromagnetic anomaly maps, and has distributed 30,000 aeromagnetic anomaly maps per year (the most requested item of the Geological Survey of Canada)
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From page 167... ...
, it should be possible to cover the continental United States at an altitude of about 20 km and comparable line spacing in a cost-effective way. Data thus acquired would bridge the gap between low-level and satellite data, define regional magnetic fields, and provide coverage of the continental shelf extending out to a few hundred kilometers offshore.
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From page 168... ...
program. Rock Properties Rock magnetic studies are commonly conducted independently of the required mineralogical, geochemical, and petrological background for linking magnetic property data to interpretation of magnetic anomalies.
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From page 169... ...
Ideally the direction of survey lines should be based on the orientation of geological structure and, most importantly at low latitudes, by the orientation of the magnetic field. Gradiometer data should be routinely collected to avoid problems with diurnal corrections and external fields at high and low latitudes.
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From page 170... ...
The routine collection of marine magnetic data has not evolved to provide information compatible with the resolution of swath bathymetry systems. As such, information on oceanic crustal structure and processes is lost by the inability to exploit the detailed information contained in the bathymetry in conjunction with analysis of the magnetic anomaly data.
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From page 171... ...
Further, gradient data can be used to improve interpolation from flight lines onto a regular grid and to relax survey specifications and reduce costs. Combinations of vector and gradient data have not yet been explored from either an instrumentation or a computational point of view.
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From page 172... ...
Pragmatic concerns with regard to communications systems, power grid reliability, navigational ability, and satellite and general space survivability necessitate the continuous measurements of magnetic fields not only in the proximity of the Earth, but also and perhaps even more importantly throughout the magnetosphere and in the solar wind. The central theme is the monitoring and ultimately prediction of the magnetospheric condition through the modeling and understanding of dynamic processes.
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From page 173... ...
The tens of millions of amperes of horizontal ionospheric currents from this March 13, 1989, event overloaded the entire power grid of Quebec and a partial section of Scandinavia's grid, disrupting power for more than 9 hours; similar events disrupt general communication, particularly via satellite. Specific Scientific and Societal Issues The following section presents a discussion of the role of satellite platforms in addressing specific scientific issues itemized in the working group reports in this appendix.
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From page 174... ...
174 _ ~ ~ ~ < 3 ~ > I: c£ :E on ~ C~]
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From page 176... ...
Separation of charges in the moving magnetospheric plasma creates electric fields that are projected onto the ionosphere along highly conducting field lines. These fields drive electrical currents in the ionosphere which—in regions of electric field in conductivity gradients couple to the magnetosphere through field-aligned currents.
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From page 177... ...
These models can be used in magnetospheric research to help operational platforms mitigate the adverse effects of space weather or to subtract magnetospheric "noise" from data used in studies of the solid Earth. Scientific Issue A2: Lithospher~c Fields The first crustal magnetic anomaly maps from Magsat revealed previously unmown, long-wavelength anomalies (400 to 4,000 km)
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From page 178... ...
Scientific Issue A3: Electromagnetic Induction The electrical conductivity of the crust and upper mantle is probed by the response of these layers to low-frequency electromagnetic waves, magnetic impulses, and electrical currents in the magnetosphere and ionosphere. The magnetic signatures observed with arrays of magnetometers on the Earth's surface are a summation of signals generated in the ionosphere and magnetosphere and of the induced signals generated in the conducting layers below the Earth's surface.
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From page 179... ...
As input, this requires data from satellites that continuously monitor the Earth's magnetic field on a global scale, in the altitude range of 300 km to 1,000 km. ARISTOTELES in the near term and DMSP/POGS and the NOAA polar satellites upgraded to Magsat quality in the long term will provide the necessary observational platforms for main field and secular field analyses.
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From page 180... ...
Continuous time series would not only record secular variations but, in addition, the elusive short-term (~-year) main field changes or "jerks." Low-Altitude Surveys There have been numerous attempts to study the lithospheric magnetic anomaly field with Magsat data (about 500 hen altitude)
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From page 181... ...
Three or more spacecraft equipped with magnetometers, located at different local time orbits, would show the first-order features of these currents as the solar wind fluctuates. This in turn would help in understanding these complex processes and would provide valuable input to models specifying the state of the magnetosphere and ionosphere (see Figure Bl-1~.
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From page 182... ...
Its lifetime is expected to be 3 years; follow-on missions are planned. The purpose of the mission is to provide scalar data for the 1995 epoch DOD world magnetic mode} of the main field and its secular variation.
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From page 183... ...
ISTP. At the time this report was written, the NASA International Solar Terrestrial Program spacecraft were scheduled as followed: Geotail, launch July 1992, equatorial, 100 Re; Polar, launch scheduled for 1993, polar, 4 Re; Wind, launch also scheduled for 1993, first Lagrangian point (~-1 point)
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From page 184... ...
It would have a biaxial vector magnetometer and an Overhauser scalar magnetometer for absolute total field measurements. It would also have a high-energy particle detector array and star imagers for accurate attitude determination.
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From page 185... ...
Furthermore, the simultaneous acquisition of gravity data will allow synergistic potential field interpretations. The high-altitude second phase of the mission, in which the orbit will progress through all local times every ~ months, will provide valuable data on the main field, secular variation, and external fields.
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From page 186... ...
The DMSP and NOAA Polar orbiting satellite systems provide ideal platforms for continuous measurements of the low-Earth magnetic fields. Interagency cooperation would ensure the optimal applications of these operational environmental satellites to provide routine monitoring of main field and secularvariation field, in addition to ionospheric fields, during both solar quiet and disturbed times.
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From page 187... ...
The mapping of geomagnetic field lines from the Earth's surface to the outer regions of the magnetosphere is not adequate to accurately transfer magnetic disturbance vectors from the magnetosphere to the ionosphere. To solve this problem, a survey of the magnetic field between low-Earth orbit and magnetospheric altitudes is needed.
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From page 188... ...
Navy. In the case where attitude information of a few arc minutes is available, the vector data are very useful in mapping fields from fieldaligned currents and ionospheric currents, though not for main field modeling.
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From page 189... ...
However, the measurements are not subject to drift and hence are better for main field modeling. A major shortcoming is that the measurements can make no contribution to the study of fields from field-aligned or ionospheric currents.
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