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  • 1
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    Interpretation of satellite elevation magnetic anomalies (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The present discussion is based on a study of the magnetic field data obtained with the aid of the magnetic field satellite Magsat, deployed in October 1979, over most of the earth during a 7.5-month mission. Inversions using spherical harmonic coefficients are considered along with the inversion of residual fields. In order to perform the correct operation, it is necessary to add on to the source function produced by the inversion process a magnetization function which has no external field. Such a function is known as an annihilator. The use of the annihilator for Pacific Ocean anomalies is discussed. Attention is given to models of oceanic crustal magnetization, and continental long-wavelength anomalies. It is found that in continental regions the annihilator is also useful if induced magnetizations are thought to be responsible for the long-wavelength anomaly.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 3633-365
    Format: text
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  • 2
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    Modelling the core magnetic field of the earth (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: It is suggested that radial off-center dipoles located within the core of the earth be used instead of spherical harmonics of the magnetic potential in modeling the core magnetic field. The off-center dipoles, in addition to more realistically modeling the physical current systems within the core, are if located deep within the core more effective at removing long wavelength signals of either potential or field. Their disadvantage is that their positions and strengths are more difficult to compute, and such effects as upward and downward continuation are more difficult to manipulate. It is nevertheless agreed with Cox (1975) and Alldredge and Hurwitz (1964) that physical realism in models is more important than mathematical convenience. A radial dipole model is presented which agrees with observations of secular variation and excursions.
    Keywords: GEOPHYSICS
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  • 3
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    A problem in representing the core magnetic field of the earth using spherical harmonics (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Although there are computational advantages to the representation of the earth's magnetic field by spherical harmonic coefficients of the magnetic potential, up to the thirteenth degree and order, the following disadvantages emerge: (1) the use of spherical harmonics of up to a certain degree does not remove wavelengths greater than a certain value from the surface fields, and (2) the total field magnitudes represented by spherical harmonics up to a certain degree have minimum wavelengths equal to the circumference of the earth divided by twice the maximum degree of the harmonic used. The implications of the ways in which surface fields are separated into core and crustal components are discussed, and it is concluded that since field signals are generated in the core, the representation of the core field by spherical harmonics of potential does not adequately represent all core field components.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 9; Apr. 198
    Format: text
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  • 4
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    Abundance and distribution of ultramafic microbreccia in Moses Rock dike - Quantitative application of mapping spectroscopy (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Data from the Airborne Imaging Spectrometer were used to map the distribution and abundance of the serpentized ultramafic microbreccia (SUM) component in the Moses Rock dike, which is a Tertiary diatreme located on the Colorado Plateau in Utah. The geologic setting and composition of Moses Rock dike are discussed together with its texture and the relationship to the bedrock of surface materials. These observations along with laboratory spectroscopic data are used to interpret surface mineralogy of the dike and the surrounding regions from the imaging spectometer data. The spatial distribution and the abundance of the primary surface components were calculated using a nonlinear model for the mixing of spectra from multicomponent surfaces. The derived SUM distribution and abundance data support McGetchin's (1968) model for the emplacement of Moses Rock dike as a fluidized system.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 10376-10
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  • 5
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    Deconvolution of mineral absorption bands - An improved approach (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Although visible and near IR reflectance spectra contain absorption bands that are characteristic of the composition and structure of the absorbing species, deconvolving a complex spectrum is nontrivial. An improved approach to spectral deconvolution is presented that accurately represents absorption bands as discrete mathematical distributions and resolves composite absorption features into individual absorption bands. The frequently used Gaussian model of absorption bands is shown to be inappropriate for the Fe(2+) electronic transition absorptions in pyroxene spectra. A modified Gaussian model is derived using a power law relationship of energy to average bond length. The modified Gaussian model is shown to provide an objective and consistent tool for deconvolving individual absorption bands in the more complex orthopyroxene, clinopyroxene, pyroxene mixtures, and olivine spectra.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 6955-696
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