Abstract: A method and system for detecting gravitational anomalies comprises measuring surface structures, measuring gravitational field characteristics, and estimating the effect of the surface structures on the gravitational measurements. The estimations are then used to derive a representation of nearby non visible features such as changes in rock density, voids, or oil and gas deposits. The surface structures may be measured by a video camera, with the video sequence being processed to estimate 3D positions of structures relative to the measurement point. Other methods may be used, such as lidar or acoustic techniques as appropriate. The method may be applied above ground and also has efficacy in borehole and sewer surveying applications.