HeliFALCON® Airborne Gravity Gradiometer Data Acquisition in Rugged Terrain

Abstract

Fixed-wing Airborne Gravity Gradiometer (AGG) surveying can rapidly provide high resolution gravity data over large areas. Fixed-wing AGG surveys are flown in a smooth drape over the topography in the survey area at a nominal survey terrain clearance. The nominal survey terrain clearance is a function of the chosen line spacing and the expected target depths, and is always subject to flight safety considerations. In areas of moderate topography the nominal terrain clearance for a fixed-wing FALCON AGG survey is of the order of 80m-120m. However, in areas of steep topographic relief, in mountain ranges or near volcanoes, the slow climbing rate of a fixed wing aircraft will often result in a survey drape which does not follow the terrain variations well. In this case large parts of the survey may be flown with an actual terrain clearance exceeding the nominal survey terrain clearance. If the survey target is small (kimberlite pipe) or narrow (banded iron formation), then a large actual terrain clearance may result in the target not being adequately mapped by a fixed wing AGG survey. In such case a helicopter-borne AGG survey should be considered: A helicopter can ascend and descend at a much steeper rate than a fixed wing aircraft. Thus a helicopter-borne AGG system can provide a much tighter drape in areas of steep topography, providing a better adherence to the nominal survey terrain clearance, which again provides more acurate geophysical mapping at higher resolution. The FALCON AGG system is the only commercial AGG system which is sufficiently small and low-weight to be mounted in a light helicopter. We demonstrate an example of the ability of the HeliFALCON ® system to acquire high spatial resolution (100m full wave length), high-accuracy gravity data in areas of steep topography.