Near‐station topographic masses correction for high‐accuracy gravimetric prospecting

The expanding role of gravity prospecting in mineral and hydrocarbon exploration as well as seismic and volcanic risk studies will be related to its ability to provide high‐resolution anomalies. To achieve this goal it is necessary to consider the errors resulting from the topographic corrections, in particular near‐station effects. Such errors are relevant not only for severe topographies but also for relatively flat surfaces involving microgravity applications and large‐scale surveys. Indeed, the errors introduced by low‐resolution digital elevation models can be of the same order of magnitude as the anomalies of interest. This basic fact is demonstrated by tests on synthetic models. The results of this analysis are summarized in an intuitive graph that can be used to estimate what near‐station topographic resolution is necessary for a specific survey. For the Vulcano Island test site (in Southern Italy), we also compare results obtained using three different representations of the topographic surface with different horizontal resolutions and vertical precisions: one from existing photogrammetric data, the second from a digitized map and the third from a very high‐resolution laser scanning system. Among the three methods, laser scanning is shown to obtain the highest resolution topographic reconstructions in the shortest time. Some weaknesses of the laser scanning methodology are discussed and we suggest ways of overcoming them.