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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Survey Parameters and Availability of Low-level Aeromagnetic Data for Geomagnetic Field Modelling

Since aeromagnetic surveying started immediately after World War II, a considerable area of the earth's surface both onshore (in excess of 25 million sq. km) has been magnetically surveyed. For about the first 15 years or so, fluxgate magnetometers were employed in aeromagnetic surveys, but the introduction of proton free-precession magnetometers resulted in absolute readings being recorded. Proton precession magnetometers have now been replaced to a large extent by the more sensitive optical absorption magnetometers. Some care has to be taken to calibrate aeromagnetic survey systems and this is best done using a calibration range tied to a magnetic observatory so that accuracies of 10nT or better are achieved for the total field values recorded. Survey navigation has always posed a problem for aeromagnetic surveys, especially offshore. Over land, vertically pointed 35 mm cameras were initially used to recover the aircraft track using a combination of aerial photos and topographic maps. Over featureless areas, it was necessary to utilize existing electronic positioning systems such as Loran C or set up special navigation systems. The advent of the satellite-based Global Positioning Systems (GPS) has to a larger extent solved the navigational problem because there is now almost continuous worldwide coverage to 10 m accuracy in the differential mode. The resultant aeromagnetic data is normally compiled into contour maps in which the diurnal variation and aircraft heading effects are removed. The resultant digital data are normally made publicly available both in gridded and profile form along with the published contour maps. Most aeromagnetic coverage has been obtained in the developed western countries, but elsewhere a considerable amount of surveying has been carried out; as an example, some 80 percent of Africa has been surveyed mostly as a result of aid programs. The data is usually held by the national geological survey or equivalent organizations, but in a number of cases the data (e.g., for the Magnetic Anomaly Map of North America) is also held by the World Data Centres.

Hood, Peter↗
NASA NTRS1971

An aeromagnetic survey in the Valley of Ten Thousand Smokes, Alaska

Geologic and magnetic studies of the Katmai area have further demonstrated the close relationship between the Katmai Caldera, Novarupta plug, and the pyroclastic flows in the Valley of Ten Thousand Smokes. The magnetic fields observed appear to be associated with the thickness of the pyroclastic flow and the different rock units within it for lower flight levels, and also the contrast between the valley fill and the rock units at the Valley margins. Consistent magnetic anomalies are associated with the larger fumarole lines, which were presumably sites of large scale activity, while the smaller fumaroles are not usually seen in the aeromagnetic map. A possible correlation between low positive anomalies and nuee ardente deposits was revealed by the aeromagnetic survey, but was not strong. A ground survey was also carried out in several parts of the Valley with a view to detailed delineation of the magnetic signatures of the pyroclastic flow, as an aid to interpreting the aeromagnetic date.

Anma, K.↗
NASA NTRS1982

A preliminary comparison of the Magsat data and aeromagnetic data in the continental U.S.

A preliminary regional scale magnetic anomaly map derived from the Magsat data over the continental U.S. shows reasonably good correlations when compared with the corresponding aeromagnetic map. This conclusion is based upon the analysis of the fine attitude scalar Magsat data of about a two-month duration starting November 2, 1979 and the analysis of the Project Magnet U.S. aeromagnetic data in the same region.

Won, I. J.↗
NASA NTRS1980

Compatibility study of the Magsat data and aeromagnetic data in the eastern Piedmont of US

Data from a 2 day period recorded by Magsat were used to produce world magnetic maps of the scalar total field and three vector component total fields. Subtracting the reference field of Magsat 6/80, a scalar anomalous field and three vector component anomalous fields were also mapped. After removing 718 bad points from the original data, every fifth point was picked for contouring. While the main geomagnetic field of the Earth is surprisingly well mapped considering the short data period, the anomaly maps suffer from data sparseness. The entire Magsat file collected at altitudes of 500-700 m in nonmountainous terrain and at 900-1,000 m in mountainous terrain was averaged to reduce the total data to 6,500 measurements, yielding a 0.1 deg sampling interval along the flight path. A U.S. aeromagnetic anomaly surface map was produced and the field was upward continued to a 300 km altitude. Differences in anomaly structure between the POGO data and the map produced were attributed to insufficient removal of the reference field. Reprocessing of the data using the GSFC reference field (9/80-2) should remove the low harmonic field and improve the anomalous field structure.

Won, I. J.↗
NASA NTRS1981

Detailed aeromagnetic investigation of the Arctic Basin. II

Remote sensing techniques must be employed to determine the nature of the regional geologic and tectonic structure of the Arctic Basin. Magnetic measurements from aircraft are the most commonly used method. Since 1972 the U.S. Navy has been engaged in a long-term program of mapping, in relative detail, the earth's magnetic field over that portion of the Arctic Basin accessible to the P3 aircraft. A description is presented of the results of the 1977 and 1978 field efforts. The description represents a continuation of an investigation reported by Vogt et al. (1979). The efforts currently considered were directed towards understanding the nature, age, and origin of the major physiolographic features of the western Arctic Basin. Particular attention was given to the Canada and Makarov basins (Fletcher Abyssal Plain) and the Alpha Ridge. The aeromagnetic data are interpreted with respect to the theory of origin presented by Carey (1958).

Taylor, P. T.↗
NASA NTRS1981

Compatibility study of the MAGSAT data and aeromagnetic data

The results of (1) an analysis of the fine attitude MAGSAT data covering the continental U.S., (2) analysis of the Project MAGNET U.S. aeromagnetic data in terms of its compatibility with the corresponding MAGSAT data, and finally, (3) analysis of MAGSAT data in the Pacific region and comparison with satellite gravity data are presented. All data reduction procedures are described and the resulting magnetic maps are given. The results indicate a general compatibility between the MAGSAT data and the MAGNET and gravity data.

Won, I. J.↗
NASA NTRS1981

MAGSAT and aeromagnetic data in the North American continent

Problems were encountered in deriving a proper reference field to be subtracted from the aeromagnetic data obtained from Project MAGNET. Field models tried thus far do not seem to eliminate properly the main field. The MAGSAT data in the North American continent for the period November 1 to December 22, 1979 are being compiled and compared with MAGNET data. Efforts are being made to eliminate the orbital bias errors. A computer program was developed and successfully tested which computes a topographic profile of the Curie depth isotherm which fits best to the observed vector or scalar field magnetic data.

Source record↗
NASA NTRS1982

MAGSAT and aeromagnetic data of the continental US

The MAGSAT data were used to produce a scalar anomaly map of the U.S. In order to remove the east-west striping anomalies, which are believed to be caused by the low-order polynomials used to reduce the orbital bias errors, a 2-D spectral filtering using the Fourier transform method was applied. The resultant low-pass filtered map, with the east-west stripings removed, resembles much closer the surface aeromagnetic map based on the U.S. MAGNET data. The spectral filtering was also applied to the MAGSAT vector data. Department of Defense gravity data was processed to produce a filtered U.S. gravity map whose spectral contents are comparable to those of the MAGSAT magnetic map.

Won, I. J.↗
NASA NTRS1984

US Aeromagnetic and Satellite Magnetic Anomaly Comparisons

Scalar aeromagnetic data obtained by the U.S. Naval Oceanographic Office (NOO) Vector Magnetic Survey of the conterminous U.S. were screened for periods of intense diurnal magnetic activity and reduced to anomaly form, filtered, and continued upward. A number of correlations between the NOO, POGO and preliminary MAGSAT data are evident at satellite elevations, including a prominent transcontinental magnetic high which extends from the Anadarko Basin to the Cincinnati Arch. The transcontinental magnetic high is breached by negative anomalies located over the Rio Grande Rift and Mississippi River Aulacogen. Differentially reduced-to-pole NOO and POGO magnetic anomaly data show that the transcontinental magnetic high corresponds to a well-defined regional trend of negative free-air gravity and enhanced crustal thickness anomalies.

Vonfrese, R. R. B.↗
NASA NTRS1988

Structural geology and regional tectonics of the Mineral County area, Nevada, using Shuttle Imaging Radar-B and digital aeromagnetic data

SIR-B and aeromagnetic lineaments show a correlation with known faults within the Walker Lane of the western Basin and Range Province. Walker Lane faults can be extended based on SIR-B data and unmapped Walker Lane features are identified. South of the Pancake Range lineament, Walker Lane faults are seldom recognized but SIR-B data have the potential for delineating structural features in this area. Earthquake hypocenter distribution in profiles across a SIR-B lineament is consistent with that expected from a vertical fault. Field examination indicates that the lineament is an unmapped neotectonic Walker Lane feature.

Borengasser, Marcus X.↗
NASA NTRS1973

Analysis of three-component aeromagnetic data

The numerical method of obtaining three field components from total field measurements, using double Fourier series expansion, is presented. The expressions for moments of the anomalous field components over a finite area are given. The magnitude and direction of the magnetization vector indicate that the vertical component of the magnetic field calculated from total field observations is more accurate at higher geomagnetic latitudes than at lower latitudes. The opposite is true for the horizontal components. The error in determining the magnetization vector directions are significantly large over most of the range of variation of declination and inclination of the vector, demonstrating the practical limitations of computing field components from total field data even under the best of conditions.

Bhattacharyya, B. K.↗
NASA NTRS1973

Photointerpretation of Skylab 2 multispectral camera (S-190A) data: Advance report of significant results

The author has identified the following significant results. A significant and possible major economic example of the practical value of Skylab photographs was provided by locating on Skylab Camera Station Number 4, frame 010, SL-2, an area of exposures of limestone rocks which were thought to be completely covered by volcanic rocks based upon prior mapping. The area is located less than 12 miles north of the Ruth porphyry copper deposit, White Pine County, Nevada. This is a major copper producing open pit mine owned by Kennecott Copper Corporation. Geophysical maps consisting of gravity and aeromagnetic studies have been published indicating three large positive magnetic anomalies located at the Ruth ore deposits, the Ward Mountain, not a mineralized area, and in the area previously thought to be completely covered by post-ore volcanics. Skylab photos indicate, however, that erosion has removed volcanic cover in specific sites sufficient to expose the underlying older rocks suggesting, therefore, that the volcanic rocks may not be the cause of the aeromagnetic anomaly. Field studies have verified the initial interpretations made from the Skylab photos. The potential significance of this study is that the large positive aeromagnetic anomaly suggests the presence of cooled and solidified magma below the anomalies, in which ore-bearing solutions may have been derived forming possible large ore deposits.

Jensen, M. L.↗
NASA NTRS1973

Facilitating the exploitation of ERTS imagery using snow enhancement techniques

The author has identified the following significant results. Detection and analysis of fracture systems can be more effectively conducted utilizing snow cover as an enhancement tool. From analysis within the Great Barrington Test Site it appears that the use of aeromagnetic data effectively supplements lineament data acquired using ERTS imagery. Coincidence of lineaments derived from aeromagnetics with lineaments interpreted from ERTS imagery apparently indicate the presence of mineralized fracture systems and dikes. Utilizing both tools can increase the speed and efficiency of mineral exploration and geological mapping in areas where bedrock is obscured by a thick unconsolidated sediment cover.

Wobber, F. J.↗
NASA NTRS1985

Magnetization models for the source of the 'Kentucky anomaly' observed by Magsat

Both the aeromagnetic data and magnetic anomaly data obtained by Magsat indicate the presence of a very magnetic source region within the crust beneath Kentucky and Tennessee. A source model was previously developed to fit surface gravity and long-wavelength aeromagnetic data, using limited seismic constraint. For the present study the model was further developed, and it is demonstrated that the source region for the satellite anomaly is considerably more extensive than the Kentucky body sensu stricto. The extended source region is modeled using both prismatic model sources and dipole array sources. Magnetization directions for the source region found by inversion of various combinations of scalar and vector data are found to be close to the main field direction, implying the lack of a strong remanent component. It is shown by simulation that in a case (such as this) where the geometry of the source is known, if a strong remanent component is present its direction is determinable, but by scalar data as readily as vector data. Magnetization magnitude for the extended source region is about 3 A/m if the vertical extent of the source includes the whole of the crust.

Mayhew, M. A.↗
NASA NTRS1986

Crustal structure of the Archaean granite-greenstone terrane in the northern portion of the Kaapvaal Craton

Recent investigations of the electrical resistivity, gravity and aeromagnetic signatures of the various granite-greenstone units in the northern portion of the Kaapvaal craton have revealed three features of significance: (1) the Archean greenstone belts are shallow features, rarely exceeding 5 km in depth; (2) the high resistivity upper crustal layer typical of the lower grade granite-greenstone terranes is absent in the granulite facies terrane; and (3) the aeromagnetic lineation patterns allow the granite-greenstone terrane to be subdivided into geologically recognizable tectono-metamorphic domains on the basis of lineation frequency and direction. A discussion follows.

Debeer, J. H.↗
NASA NTRS1986

Magsat equivalent source anomalies over the southeastern United States - Implications for crustal magnetization

The Magsat crustal anomaly field depicts a previously-unidentified long-wavelength negative anomaly centered over southeastern Georgia. Examination of Magsat ascending and descending passes clearly identifies the anomalous region, despite the high-frequency noise present in the data. Using ancillary seismic, electrical conductivity, Bouguer gravity, and aeromagnetic data, a preliminary model of crustal magnetization for the southern Appalachian region is presented. A lower crust characterized by a pervasive negative magnetization contrast extends from the New York-Alabama lineament southeast to the Fall Line. In southern Georgia and eastern Alabama (coincident with the Brunswick Terrane), the model calls for lower crustal magnetization contrast of -2.4 A/m; northern Georgia and the Carolinas are modeled with contrasts of -1.5 A/m. Large-scale blocks in the upper crust which correspond to the Blue Ridge, Charlotte belt, and Carolina Slate belt, are modeled with magnetization contrasts of -1.2 A/m, 1.2 A/m, and 1.2 A/m respectively. The model accurately reproduces the amplitude of the observed low in the equivalent source Magsat anomaly field calculated at 325 km altitude and is spatially consistent with the 400 km lowpass-filtered aeromagnetic map of the region.

Ruder, M. E.↗