Measurement of Magnetic Field Gradients

• US 20170075020A1
• Filed: 09/16/2015
• Published: 03/16/2017
• Est. Priority Date: 09/16/2015
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Gann, Matthew E., Barillas, Ender E., Dolgin, Benjamin, Zellner, James C.
• Granted Patent: US 10,338,261 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01C 21/08 involving use of the magnetic field of the earth
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices
• CPC Class Codes: G01D 18/004 Continuous recalibration
• CPC Class Codes: G01R 33/0029 Treating the measured signals, e.g. removing offset or noise
• CPC Class Codes: G01R 33/022 Measuring gradient
• CPC Class Codes: G01V 3/16 specially adapted for use from aircraft G01V3/165 - G01V3/175 take precedence
• CPC Class Codes: G01V 3/165 operating with magnetic or electric fields produced or modified by the object or by the detecting device with electromagnetic waves G01V3/17

Abstract

Technology for performing magnetic field gradient measurements is described. The magnetic field gradient measurements for specific positions on the Earth can be performed from a moving platform. The magnetic field gradient measurements can be identified as being affected by a level of error that exceeds a defined threshold. A correction value can be generated to compensate for the error in the magnetic field gradient measurements. The correction value can be applied to the magnetic field gradient measurements in order to obtain magnetic field gradient measurements with a reduced level of error.

Claims

1. A method for performing magnetic field gradient measurements, the method comprising:

performing the magnetic field gradient measurements for specific positions on the Earth from a moving platform;

identifying that the magnetic field gradient measurements are affected by a level of error that exceeds a defined threshold;

generating a correction value to compensate for the error in the magnetic field gradient measurements; and

applying the correction value to the magnetic field gradient measurements in order to obtain magnetic field gradient measurements with a reduced level of error.

2. The method of claim 1, further comprising performing the magnetic field gradient measurements using a magnetometer that is onboard the moving platform.

3. The method of claim 1, further comprising performing the magnetic field gradient measurements using an inductive coil vector magnetometer that is onboard the moving platform.

4. The method of claim 1, further comprising generating the correction value using a gyroscope that is coupled to a magnetometer onboard the moving platform, the correction value compensating for a misalignment between an orientation of an airframe body coordinate system associated with the moving platform and an orientation of the magnetometer onboard the moving platform.

5. The method of claim 1, wherein the error is caused by high frequency vibrations on the moving platform due to a speed of the moving platform.

6. The method of claim 1, wherein the magnetic field gradient measurements are performed according to a range of approximately 2000 to 50,000 times per second.

7. The method of claim 1, wherein the correction value is a rotation matrix.

8. The method of claim 1, wherein a magnetic field gradient measurement is a projection of a magnetic field gradient tensor into a direction of motion associated with the moving platform.

9. The method of claim 1, wherein the moving platform is traveling at a defined velocity of Mach 0.5 or greater.

10. The method of claim 1, wherein the moving platform is a self-propelled guided weapon or an aircraft.

11. A method for determining a magnetic field gradient, the method comprising:

measuring the magnetic field gradient for specific positions on the Earth using a vector magnetometer onboard a moving platform, the magnetic field gradient being affected by error that is caused by an orientation misalignment of the vector magnetometer and a body coordinate system of the moving platform;

generating a correction value to compensate for the error in the magnetic field gradient using a gyroscope that is onboard the moving platform, wherein the gyroscope is coupled to the vector magnetometer; and

applying the correction value to the magnetic field gradient in order to reduce the error in the magnetic field gradient caused by the orientation misalignment of the vector magnetometer.

12. The method of claim 11, further comprising generating the correction value to compensate for the error in the magnetic field gradient when an error level exceeds a defined threshold.

13. The method of claim 11, further comprising generating the correction value to compensate for the error in the magnetic field gradient when the moving platform is traveling at a velocity that exceeds a defined threshold.

14. The method of claim 11, further comprising generating the correction value to compensate for the error in the magnetic field gradient when the moving platform is traveling at a defined velocity of Mach 0.5 or greater.

15. The method of claim 11, wherein the correction value is a rotation matrix that is provided by the gyroscope onboard the moving platform.

16. The method of claim 11, wherein the error is caused by high frequency vibrations on the moving platform due to a speed of the moving platform.

17. The method of claim 11, wherein the magnetic field gradient is of the Earth'"'"'s magnetic anomaly field.

18. The method of claim 11, wherein the vector magnetometer includes a plurality of coils for measuring the magnetic field gradient, wherein a signal for each coil i is represented as

19. The method of claim 11, further comprising determining the magnetic field gradient by converting the magnetic field gradient from a local coordinate system to a North East Down (NED) coordinate system of the moving platform.

20. A system for determining a magnetic field gradient, the system comprising:

a vector magnetometer operable to measure the magnetic field gradient for specific positions on the Earth;

a gyroscope, coupled to the vector magnetometer, that is operable to generate a correction value to compensate for error in the magnetic field gradient; and

one or more processors operable to;

identify the magnetic field gradient;

identify the correction value; and

apply the correction value to the magnetic field gradient,

wherein the vector magnetometer and the gyroscope are onboard a moving platform.

21. The system of claim 20, wherein the gyroscope is operable to generate the correction value when the error in the magnetic field gradient exceeds a defined threshold and the moving platform is traveling at a defined velocity.

22. The system of claim 20, wherein the error in the magnetic field gradient is caused by a misalignment of a local coordinate system associated with the moving platform and an orientation of the vector magnetometer.