Enhancement of sensors for airborne operation

• US 20050160815A1
• Filed: 03/12/2003
• Published: 07/28/2005
• Est. Priority Date: 03/18/2002
• Status: Active Grant

• Current Assignee: Bhp Billiton Innovation Pty., Ltd. (BHP Group Ltd.)
• Original Assignee: Bhp Billiton Innovation Pty., Ltd. (BHP Group Ltd.)
• Inventors: Lee, James Beresford
• Granted Patent: US 7,181,967 B2
• Time in Patent Office: Days
• US Class Current: 73/514.150
• CPC Class Codes: G01V 7/16 specially adapted for use on moving platforms, e.g. ship, aircraft

Abstract

Gravity gradiometers (or gravity gradient instrument, GGI) measure one or more components of the gradient of gravity which is expressed as the gradient of a gravity vector. One or more feedback loops extend from the instrument output to one or more of the accelerometers (1-4) to compensate for errors. The feedback loops include one or more inputs in addition to the instrument output. The additional inputs include signals representing one or more of: components of attitude, velocity and acceleration, the physical environment and flight conditions, taken alone or in combination.

Claims

1. A gravity gradient instrument, comprising:

a first, second, third and fourth accelerometer equally spaced around the circumference of a circle, with their sensitive axes tangential to the circle, and arranged in opposing pairs with the first accelerometer opposite the second, and the third accelerometer opposite the fourth;

in use the accelerometers are spun around an axis normal to the circle and passing through its centre;

a summing amplifier which receives the outputs of the accelerometers and combines them in a manner to cancel the common mode output signals, to produce an instrument output; and

one or more feedback loops extending from the instrument output to one or more of the accelerometers to compensate for errors;

wherein the feedback loops include one or more inputs in addition to the instrument output, the additional inputs including signals representing one or more of;

components of attitude, velocity and acceleration, the physical environment and flight conditions, taken alone or in combination.

2. A gravity gradient instrument according to claim 1, wherein the additional inputs include signals measuring one, two or three components of the acceleration environment of the gravity gradient instrument.

3. A gravity gradient instrument according to claim 2, wherein the signals are derived from accelerometers used on the inertial platform on which the gravity gradient instrument is mounted.

4. A gravity gradient instrument according to claim 1, wherein the additional inputs include signals measuring one, two, or three components of the acceleration environment of the gravity gradient instrument rotor.

5. A gravity gradient instrument according to claim 4, wherein the signals measuring the acceleration components in the plane of the gravity gradient instrument accelerometers come from those accelerometers.

6. A gravity gradient instrument according to claim 1, wherein the additional inputs include signals measuring the attitude of the aircraft.

7. A gravity gradient instrument according to claim 1, wherein the additional inputs include signals measuring the rotational rates of the gravity gradient instrument.

8. A gravity gradient instrument according to claim 1, wherein the additional inputs include signals measuring the physical environment of the gravity gradient instrument.

9. A gravity gradient instrument according to claim 1, wherein the additional inputs include signals representing the flight conditions of the airborne instrument.

10. A gravity gradient instrument according to claim 9, where the conditions include fuel levels on survey.

11. A gravity gradient instrument according to claim 9, where the conditions include turns between survey lines.

12. A gravity gradient instrument according to claim 9, where the conditions include take-off.

13. A gravity gradient instrument according to claim 9, where the conditions include climb or descend.

14. A gravity gradient instrument according to claim 9, where the signals are automatically determined from flight instruments.

15. A gravity gradient instrument according to claim 1, wherein the enhanced feedback loops are implemented as a part of the gravity gradient instrument and its support electronics.

16. A gravity gradient instrument according to claim 1, wherein the enhanced feedback loops are implemented by means of an external processing unit connected to the gradient instrument.

17. A gravity gradient instrument according to claim 1, wherein the additional inputs are used to determine the performance of a feedback loop and the gain or operation of that feedback loop is then adjusted.

18. A gravity gradient instrument according to claim 1, wherein the sensitivity of the gravity gradient instrument to an acceleration stimulus is determined by correlating the instrument output with a measurement of the stimulus and then applying feedback to an accelerometer to remove that sensitivity on the basis of the determined correlation.

19. A gravity gradient instrument according to claim 1, wherein the sensitivity of the gravity gradient instrument to its environment, as measured by the additional inputs, is determined by a correlation process, then the contribution these sensitivities make to the output of the gravity gradient instrument is determined and this component is subtracted from the instrument output as it is applied to the feedback loop to reduce the noise of this primary input to the feedback loops and in turn to further reduce the noise on the gravity gradient instrument output.