Gravity Gradiometry - It's not gravity

All gravimeters are basically a mass on a spring, which is deflected due to the minute variations in the earth’s gravity field. However, the fundamental flaw with conventional gravity systems, when deployed in a high dynamic environment, is that they cannot distinguish between an inertial acceleration (aircraft or boat motion) and a gravitational acceleration. In order to separate the two, an independent measure of inertial acceleration is required. Currently, the best measure of inertial acceleration using dual frequency carrier phase GPS is limited and the resultant signal of limited bandwidth and resolution.

A gravity gradiometer measures the differential acceleration of the earth’s gravity field over a unit distance. The result is that inertial accelerations are common and intrinsically rejected, making a gradiometer the ideal choice for high dynamic environments.

In addition, the earth’s gravity is a 3D spatial field varying in all directions. Conventional gravity is only a point measurement and no direct measurement of how the field is varying is taken. This limits the ability of the data to determine subtle changes in the earth’s structure and derive a unique solution. The gradiometer however measures all nine components (tensors) of the gravity field. The resultant tensors, of which five are independent, mean that gradiometry is inherently more suited to resolving geology.

Gravity gradiometry instrumentation has four major advantages over conventional scalar gravimetry:

• Increased signal bandwidth
• Higher signal to noise
• Ideally suited to high dynamic environments
• Five independent measurements.

The combination of these factors means that Gravity Gradient Imaging (GGI) delivers a more complete geologic picture over a wider bandwidth and with increased resolution.

It is simply not just gravity...