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Development of a versatile, commercially proven, and cost-effective airborne gravity system

Fugro-LCT, Houston, Texas, U.S.

Corresponding author: jmacqueen@lct.com

Editor's Note: Several new systems have been recently developed for acquiring airborne gravity data and airborne gravity gradiometry data. Therefore, the Meter Reader is currently running a series of articles that feature all commercial systems now available to the exploration industry. This is the third article in this series.

The first 20% of the full text of this article appears below.

The Fugro airborne gravity system was developed and continues to evolve in accordance with the following design criteria:

• reliability and aircraft independence
  
• measurement of geodetic-quality GPS velocities, rather than using less accurate velocities computed from GPS position
  
• use of exhaustive gravity sensor and platform modeling along with rigorous processing corrections to minimize filtering
  
• evaluation of system resolution and accuracy based on data acquired in "real-world" exploration conditions.
  

Aircraft independence required that the gravity system not depend on flight characteristics of any specific aircraft and that the aircraft not require any extensive aircraft airframe or system modifications. The system has been installed on six aircraft that have been used to fly successful gravity airborne gravity surveys: Cessna 208, Cessna 404, Cessna 421, Rockwell AeroCommander 500 Shrike, Piper Aztec, and Airship Industries R-300 airship (i.e., a blimp).

This aircraft versatility and ease of gravity system installation (typically requiring less than one day) simplify mob/demob operations and reduce survey costs.

Measuring geodetic-quality GPS velocities required state-of-the-art dual-frequency GPS receivers and development of customized postmission GPS-processing software. The system tracks aircraft kinematics with extreme accuracy, thus reducing demands for extreme flight stability.

The guiding philosophy for the system could be summarized as "model, measure, and correct—don't overfilter." The goal is to minimize filtering by applying an extensive suite of corrections derived from GPS velocities, sensor, and platform modeling measurements prior to filtering.

Finally, we established that system resolution and accuracy were satisfactory by performing three independent analysis methods on data acquired in real-world exploration conditions.

	System development and operations

 
The Fugro airborne gravity system is the result of a joint effort by three companies, including a leading U.S. defense contractor specializing in advanced GPS applications. The development team, which included geophysicists and geodesists, was headed by J. Christopher Harrison who directed, along with the late Lucien LaCoste, the . . . [Full Text of this Article]