An investigation in the use of satellite data to develop a geomagnetic secular variation model over Southern Africa.

Abstract

Time variations of the geomagnetic field can be classified into two main categories of internal and external origin with respect to the surface of the Earth. It has been found that the variations that take place on longer time scales (~ 1 year and longer) are commonly known as secular variation (SV) and are of internal origin. There is a need to develop SV models using satellite data as the use of ground data is not always possible with many limitations including the limited data points and lack of data over ocean areas that are not easily accessible. Two regional geomagnetic field modelling techniques namely polynomial surface modelling (PolyM) and Spherical Cap Harmonic Analysis (SCHA) were applied to CHAMP satellite data recorded between 2001 and 2005 to investigate the use of satellite data to develop a geomagnetic SV model over southern Africa. The restricted area of investigation is between 10° and 40° South in latitude and between 10° and 40° East in longitude. The resulting regional models of this investigation were validated against the two widely used global field models IGRF 10 and CHAOS using the available ground survey data obtained during the same period over southern Africa. The results suggest that the regional field models can be derived based entirely on satellite data. However, the regional SV models can be improved by combining both high quality satellite and ground survey data, since they lack the high quality of a global field model like CHAOS.