Airborne gravity and precise positioning for geologic applications

Airborne gravimetry has become an important geophysical tool primarily beca use of advancements in methodology and instrumentation made in the past dec ade. Airbome gravity is especially useful when measured in conjunction with other geophysical data, such as magnetics, radar, and laser altimetry. The aerogeophysical survey over the West Antarctic ice sheet described in this paper is one such interdisciplinary study. This paper outlines in detail t he instrumentation, survey and data processing methodology employed to perf orm airborne gravimetry from the multi-instrumented Twin Otter aircraft. Pr ecise positioning from carrier-phase Global Positioning System (GPS) observ ations are combined with measurements of acceleration made by the gravity m eter in the aircraft to obtain the free-air gravity anomaly measurement at aircraft altitude. GPS data are processed using the Kinematic and Rapid Sta tic (KARS) software program, and aircraft vertical acceleration and correct ions for gravity data reduction are calculated from the GPS position soluti on. Accuracies for the free-air anomaly are determined from crossover analy sis after significant editing (2.98 mGal rms) and from a repeat track (1.39 mGal rms). The aerogeophysical survey covered a 300,000 km(2) region in We st Antarctica over the course of five field seasons. The gravity data from the West Antarctic survey reveal the major geologic structures of the West Antarctic rift system, including the Whitmore Mountains, the Byrd Subglacia l Basin, the Sinuous Ridge, the Ross Embayment, and Siple Dome. These measu rements, in conjunction with magnetics and ice-penetrating radar, provide t he information required to reveal the tectonic fabric and history of this i mportant region.