Airborne Gravity
Introduction - System
Development & Operations - Data
Processing - Resolution
and Accuracy - Conclusion
The Fugro airborne gravity system arose from a
joint effort by three companies, including a leading U.S.
defense contractor specializing in advanced GPS applications.
The development team incorporated both geophysicists and
geodesists, led by Dr. J. (Christopher) Harrison. Dr. Harrison,
was a lead scientist, along with Dr. Lucien LaCoste in the
world’s first non-military airborne gravity tests, conducted in
a B17 in 19591. Additionally Drs Harrison and LaCoste
pioneered research in the understanding of cross-coupling
effects in dynamic gravimetry measurements2. Many
important aspects of Dr. Harrison’s extensive dynamic gravity
knowledge has been incorporated in the design of the Fugro
airborne gravity system.
Flight-testing included three separate
campaigns, flown over an industry sponsored gravity test range
in Texas. In addition, Fugro was contracted to fly a gravity
test range in Pennsylvania. Tens of thousands of line kilometers
of data, flown in typical real world exploration survey
conditions (rather than waiting for ideal weather for flying)
were collected, processed and analyzed over a period of four
years prior to Fugro conducting its first commercial airborne
gravity survey in 1995.
Safety is the paramount factor in Fugro’s
airborne gravity operations. Fugro is a founding member of the
International Airborne Geophysics Safety Association (IAGSA). In
addition to IAGSA guidelines Fugro utilizes it’s own
comprehensive safety procedures, each project is analyzed and a
full job safety plan activated. Fugro monitors all it’s aircraft
worldwide via the Inmarsat-C satellite service.
System Hardware
Fugro uses a LaCoste & Romberg (L&R) dynamic
gravity meter upgraded to the ZLS UltraSys™ system. The ZLS
model is a modern digital control upgrade of the widely tested
and proven LaCoste and Romberg (L&R) dynamic gravity meter
sensor. Fugro’s airborne gravity system only uses L&R sensors
with the latest generation air dampers (serial number S-88 and
higher), which minimize cross-coupling effects.
| A unique three-stage
vibration isolation platform was developed as a result
of extensive vibration testing at the Boyd More Research
Laboratory. Fugro’s testing revealed a wide range of
significant vibration effects on the gravity meter
sensor, at both long and short periods, which have been
eliminated by careful attention to platform mounting. |
 |
The gravity meter clock is synchronized to GPS
time at the beginning of each flight, and kept in
synchronization (equivalent of 1 millisecond drift in 32 years)
by an extremely stable Rubidium oscillator. The large amplitudes
and short periods of aircraft vertical accelerations make tight
synchronization of gravity and GPS data a necessity.
GPS data is collected using geodetic quality
dual frequency receivers. The system logs full carrier phase
(required for maximum accuracy), dual-frequency (required for
ionospheric effect removal) raw GPS data for up to nine
satellites. |
