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The International Geomagnetic Reference Field (IGRF) is a standard mathematical description of the Earth's main magnetic field and its secular variation. It is the product of a collaborative effort between magnetic field modellers and the institutes involved in collecting and disseminating magnetic field data from satellites and from observatories and surveys around the world. == Spherical Harmonics == Mathematically, the IGRF model consists of the Gauss coefficients which define a spherical harmonic expansion of the magnetic scalar potential. where is radial distance from the Earth's center, is the maximum degree of the expansion, is East longitude, is colatitude (the polar angle), is the Earth's radius, and are Gauss coefficients, and are the Schmidt normalized associated Legendre functions of degree and order . IGRF models are standardized for a particular year, reflecting the most accurate measurements available at that time, and indicating a small-scale, slow time variation of the Earth's overall magnetic field. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「International Geomagnetic Reference Field」の詳細全文を読む スポンサード リンク
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