Geographical Distribution of Magnetic Observatories and Field Modelling

摘要: This study presents some characteristics of geomagnetic models computed from magnetic observatory data. We first analyse the covariance matrix Gauss coefficients for different data distributions and truncation degrees spherical harmonic expansion. then compute ratio R mean square value diagonal terms this to its off-diagonal terms. Finally, we estimate accuracy two main-field models, using annual values 132 observatories weights series. The effect uneven distribution on global modelling field secular-variation is underlined. such good enough in areas where density high (Europe, North America, East Asia), but it decreases dramatically poorly covered areas.