Heli‐borne gravity gradiometry in rugged terrain

For airborne gravity gradiometry in rugged terrain, helicopters offer a significant advantage over fixed‐wing aircraft: their ability to maintain much lower ground clearances. Crucially, this provides both better signal‐to‐noise and better spatial resolution than is possible with a fixed‐wing survey in the same terrain. Comparing surveys over gentle terrain at Margaret Lake, Canada, and over rugged terrain at Mount Aso, Japan, demonstrates that there is some loss of spatial resolution in the more rugged terrain. The slightly higher altitudes forced by rugged terrain make the requirements for terrain correction easier than for gentle terrain. Transforming the curvature gradients measured by the Falcon gravity gradiometer into gravity and the complete set of tensor components is done by a Fourier method over gentle terrain and an equivalent source method for rugged terrain. The Fourier method is perfectly stable and uses iterative padding to improve the accuracy of the longer wavelengths. The equivalent source method relies on a smooth model inversion, and the source distribution must be designed to suit the survey design.