Use of laterally varying crustal density in gravity interpolation at large data gaps: experiment for the continent Africa

Abstract

One of the great challenges that the IAG Sub-Commission on gravity and geoid in Africa faces is the significantly large gravity data gaps. Simple interpolation of the gravity data does not add new information at the large data gaps. In the present study, new and independent signal information is implemented by using the laterally varying density that influences the gravity signal. Consequently, the global crustal density model UNB TopoDens was introduced as an additional source of information covering the whole area of the continent of Africa. This new independent information, entering the process of generating and updating the African gravity data base, has variable laterally varying density values available as a 30″ × 30″ grid. It has been employed in the framework of the non-ambiguous window remove-restore technique, which produces well smoothed reduced anomalies which minimize the interpolation errors. The lateral crustal density model (CDM) assigns extensive water areas with a density value which is equal to 1000 k gm⁻³, and the oceans with density equal to zero. These values are overruled with valid values in order to correctly compute the impact of topographic masses in the window remove-compute-restore (wRCR) technique. Accordingly, a density model compatible with the computation of the effect of topographic masses within the window remove-restore technique has been developed. A set of Digital Density Models is needed for the computation of the effect of the topographic masses. This has been achieved by the block average operator technique. The impact of the variable density by using a lateral density model compared to the traditional use of a constant density value is discussed in detail. The results proved that the variable crustal density has a significant effect on the interpolated gravity at the large terrestrial gravity data gaps over Africa.