Terrain Corrections are Critical for Airborne Gravity Gradiometer Data

Abstract

Several developments aim to produce airborne gravity gradiometers with sufficient sensitivity to detect mineral deposits of several millions of tonnes at shallow depths. In a conventional ground gravity survey, a Bouguer slab correction is always necessary, with the terrain component of the full Bouguer correction often not needed unless the topography is severe. For airborne gravity gradiometers, however, the slab correction is exactly zero but the terrain corrections prove to be critical even with subdued or moderate topography.This paper reports on research into airborne gravity gradiometer corrections, especially aspects that assessed the importance of regolith and its constraints of surface and bedrock topography, together with predicted target anomalies. Using an example of topography typical of the Western Australian shield, calculations show that densities of both regolith and bedrock need to be determined to better than 0.1 t/m 3 for adequate correction to be made to raw gravity gradiometer data. Topography also needs to be defined to about ±3 m on 10 m pixels for adequate gravity corrections.

3D inversion of airborne gravity-gradiometry data using cokriging

“…Chen and Macnae (1997), Kass and Li (2008), Dransfield and Zeng (2009), and Davis et al (2011) study various aspects of terrain correction. Prevalent methods for interpreting various components of gravity-gradient data are focused on enhancing edges, lineaments, using invariants (Pedersen and Rasmussen, 1990;Murphy and Brewster, 2007;Dickinson et al, 2010), eigenvectors of the gravity tensor (Mikhailov et al, 2007;Beiki and Pedersen, 2010), tilt angle (Salem et al, 2013), and the deconvolution approach (Zhang et al, 2000;Mikhailov et al, 2007).…”

3D inversion of airborne gravity gradiometry data in mineral exploration: A case study in the Quadrilátero Ferrífero, Brazil

“…For instance, Chen and Macnae (1997), Kass and Li (2008), Dransfield and Zeng (2009), and Davis et al (2011) studied various aspects of terrain correction. Inversion of gravity gradient components was developed in conjunction with airborne systems, such as the work done by Vasco and Taylor (1991), Condi and Talwani (1999), Li (2001), andZhdanov et al (2004).…”

Designing a HTEM system for mapping glaciolacustrine overburden thickness

“…Another undesirable effect of overburden topography is the creation of anomalies in potential field data that can be mistaken for a mineral deposit. In gravity data (Figure 1), these anomalies can be of a similar size and amplitude as a signal from a deeper target such as an ore body (Chen and Macnae, 1997). How can the contribution of the overburden, whose density varies laterally with thickness, independent of bedrock topography, be corrected for in remote areas where seismic surveying and boreholes are not an option?…”