Multi-resolution analysis of gravity anomalies: A comparative study of modern and spherical approximation techniques

Analysing gravity anomalies is a key method of understanding the Earth’s shape, structure, and subsurface composition. This is done by modeling the Geoid, an irregular surface, into a regular sphere or ellipsoid for easy computations. These approximations, however, result in some inaccuracies in prospecting for underground minerals using satellite gravimetric data. This study aims to perform a multi-resolution analysis for interpreting satellite-obtained gravity anomalies computed by the modern approach and spherical approximation to determine the performances of both gravity anomaly computation techniques for mineral exploration. The satellite-acquired modern and spherical approximated gravity anomalies over a study area were separated into regional and residual gravity anomaly components using a 2D Discrete Wavelet Transform. The quantity, depth, shape, and density of deposited mineral were computed from their respective residual gravity anomalies using the 2D Continuous Wavelet Transform and Modulus Maxima of the wavelet transform coefficients. The result obtained from using spherical approximated gravity anomalies data was less satisfactory due to its lower Regional-to-Residual Ratio (RRR) and high variance as well as high Root Mean Square Error. Compared with the results of the modern defined gravity anomalies, the use of spherical approximation data gave an over-estimated quantity of mineral deposits by 6.44%. Also, at a 99% confidence level, the computed densities and density variances were overestimated by 1.3% and 0.92%, respectively. Hence, gravity anomaly data computed with modern technique is recommended for an optimum interpretation of gravity anomalies for exploration purposes.