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  • 1
    Publication Date: 2013-08-31
    Description: Data from the MAGSAT spacecraft for November 1979 through April 1980 and from 91 magnetic observatories for 1978 through 1982 are used to derive a spherical harmonic model of the Earth's main magnetic field and its secular variation. Constant coefficients are determined through degree and order 13 and secular variation coefficients through degree and order 10. The first degree external terms and corresponding induced internal terms are given as a function of Dst. Preliminary modeling using separate data sets at dawn and dusk local time showed that the dusk data contains a substantial field contribution from the equatorial electrojet current. The final data set is selected first from dawn data and then augmented by dusk data to achieve a good geographic data distribution for each of three time periods: (1) November/December, 1979; (2) January/February; 1980; (3) March/April, 1980. A correction for the effects of the equatorial electrojet is applied to the dusk data utilized. The solution included calculation of fixed biases, or anomalies, for the observation data.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: NAS 1.15:86133 , NASA-TM-86133 , E84-10170
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  • 2
    Publication Date: 2013-08-31
    Description: The results of a preliminary study to determine the feasibility of using Kalman filter techniques for geomagnetic field modeling are given. Specifically, five separate field models were computed using observatory annual means, satellite, survey and airborne data for the years 1950 to 1976. Each of the individual field models used approximately five years of data. These five models were combined using a recursive information filter (a Kalman filter written in terms of information matrices rather than covariance matrices.) The resulting estimate of the geomagnetic field and its secular variation was propogated four years past the data to the time of the MAGSAT data. The accuracy with which this field model matched the MAGSAT data was evaluated by comparisons with predictions from other pre-MAGSAT field models. The field estimate obtained by recursive estimation was found to be superior to all other models.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: NASA-CR-169696 , E83-10112 , BTS-FR-81-147 , NAS 1.26:169696
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  • 3
    Publication Date: 2013-08-31
    Description: A three-dimensional model of the Kentucky body was developed to fit surface gravity and long wavelength aeromagnetic data. Magnetization and density parameters for the model are much like those of Mayhew et al (1982). The magnetic anomaly due to the model at satellite altitude is shown to be much too small by itself to account for the anomaly measured by Magsat. 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 first using prismatic model sources and then using 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 readily detectable, but by scalar data as readily as vector data.
    Keywords: GEOPHYSICS
    Type: NAS 1.26:175239 , REPT-1047 , BTS07-84-121/RB , NASA-CR-175239
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  • 4
    Publication Date: 2013-08-31
    Description: Data from MAGSAT analyzed as a function of the Dst index to determine the first degree/order spherical harmonic description of the near-Earth external field and its corresponding induced field. The analysis was done separately for data from dawn and dusk. The MAGSAT data was compared with POGO data. A local time variation of the external field persists even during very quiet magnetic conditions; both a diurnal and 8-hour period are present. A crude estimate of Sq current in the 45 deg geomagnetic latitude range is obtained for 1966 to 1970. The current strength, located in the ionosphere and induced in the Earth, is typical of earlier determinations from surface data, although its maximum is displaced in local time from previous results.
    Keywords: GEOPHYSICS
    Type: NASA-TM-85012 , NAS 1.15:85012
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  • 5
    Publication Date: 2013-08-31
    Description: Universal solution of Lambert problem for elliptic, parbolic, and hyperbolic motion
    Keywords: MATHEMATICS
    Type: NASA-TM-X-65306 , X-643-70-302
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  • 6
    Publication Date: 2013-08-31
    Description: Near parabolic solutions of two body problem using Kepler equations
    Keywords: SPACE SCIENCES
    Type: X-643-70-83 , NASA-TM-X-63855
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  • 7
    Publication Date: 2013-08-31
    Description: Power series solutions of Thiele-Burrau regularized planar restricted three body problem
    Keywords: MATHEMATICS
    Type: NASA-TM-X-63417 , X-643-68-461
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  • 8
    Publication Date: 2013-08-31
    Description: Power series inverses of universal form of Kepler equation
    Keywords: SPACE SCIENCES
    Type: X-643-68-40 , NASA-TM-X-63090
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  • 9
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    In:  CASI
    Publication Date: 2013-08-31
    Description: Coefficients calculated for Taylor series expansion about two points - application of Taylor expansion to two-body problem
    Keywords: MATHEMATICS
    Type: X-643-66-567 , NASA-TM-X-55759
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  • 10
    Publication Date: 2013-08-31
    Description: A computer software system is described which computes global numerical solutions of the integro-differential Laplace tidal equations, including dissipation terms and ocean loading and self-gravitation effects, for arbitrary diurnal and semidiurnal tidal constituents. The integration algorithm features a successive approximation scheme for the integro-differential system, with time stepping forward differences in the time variable and central differences in spatial variables.
    Keywords: OCEANOGRAPHY
    Type: BTS-TR-77-41 , NASA-CR-152502
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