Magnetic Field Work and IGRF Models for Mexico, Three Examples for the 20th Century

Abstract

The historical field work inside the current Mexican area since the XVII century is presented as an introduction to the comparison study done on three examples of these magnetic surveys during the XX century, in particular the years 1907, 1952 and 1990, in order to find how well the IGRF fits this area. The magnetic declination was used because of the better availability of the magnetic declination maps for the period studied. The values given by the IGRF were compared with the values from magnetic surveys in the Mexican Republic. Results of these comparisons show RMS differences for the magnetic declination of 52.5' for 1907, 115.4' for 1952 and 18.7' for 1990. Means and standard deviations of the residuals are discussed. The isolines shows a possible underestimation of the surface field in 1907 and an overestimation in 1952 by the IGRF. Long-wavelength features were found to be correlated with aeromagnetic and satellite magnetic anomalies, but, in any case, the IGRF seems to be a satisfactory geomagnetic reference model for the area and epochs studied.