A Fortran computer programme for spherical harmonic analysis of geomagnetic field by numerical integration
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A computer program in Fortran IV language for evaluating the spherical harmonic coefficients from grid values of the field componentsX, Y andZ over the surface of a sphere and for separating the harmonic coefficients into ‘internal’ and ‘external’ part is detailed. The method of “Numerical integration” using orthogonality relations of the associated Legendre functions is adopted wherein arbitrary relative weights for observations generally used in the method of “least squares” is eliminated and the derived coefficients are independent of the number of terms retained in the series. The computer program is tested for correctness using the charted values of the field components for two epochs 1945·0 and 1965·0.
KeywordsField Component Legendre Function Fortran Computer Programme Orthogonality Relation Harmonic Coefficient
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