Magnetic Field Gradient Navigation Aid

• US 20170074660A1
• 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: Hagopian, Garabed P., Barillas, Ender E., Gann, Matthew E., Zellner, James C., Dolgin, Benjamin
• Granted Patent: US 10,378,900 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B64D 43/00 Arrangements or adaptations of instruments arrangements of cameras B64D47/08; aeronautical measuring instruments per se G01C
• CPC Class Codes: F41G 7/008 Combinations of different guidance systems
• CPC Class Codes: G01C 21/08 involving use of the magnetic field of the earth
• CPC Class Codes: G01C 21/1654 with electromagnetic compass
• CPC Class Codes: G01C 21/18 Stabilised platforms, e.g. by gyroscope
• CPC Class Codes: G01C 21/20 Instruments for performing navigational calculations G01C21/24, G01C21/26 take precedence
• CPC Class Codes: G01R 33/022 Measuring gradient
• CPC Class Codes: G01S 19/48 by combining or switching between position solutions derived from the satellite radio beacon positioning system and position solutions derived from a further system

Abstract

Technology for determining a geographical location is described. A sequence of magnetic field gradient measurements can be identified for specific positions on the Earth that correspond to a path traveled by a moving platform. The sequence of magnetic field gradient measurements for the path can be compared to a reference magnetic field gradient map. A trajectory derived from the reference magnetic field gradient map that correlates to the sequence of magnetic field gradient measurements can be identified. The trajectory can have known geographical coordinates. The geographical location of the moving platform can be determined based on the known geographical coordinates of the trajectory.

Claims

1. A method for determining a geographical location of a moving platform, the method comprising:

performing magnetic field gradient measurements from the moving platform, each magnetic field gradient corresponding to a position on the Earth, the magnetic field gradients being continuously measured while the moving platform is traveling along a path to a destination;

creating a sequence of magnetic field gradient measurements that correspond to the path traveled by the moving platform;

comparing the sequence of magnetic field gradient measurements for the path to a plurality of possible trajectories derived from a reference magnetic field gradient map;

identifying a trajectory derived from the reference magnetic field gradient map that correlates to the sequence of magnetic field gradient measurements, the trajectory having known geographical coordinates; and

determining the geographical location of the moving platform based on the known geographical coordinates of the trajectory.

2. The method of claim 1, further comprising updating an inertial navigation system (INS) of the moving platform with the geographical location in order to mitigate INS drift.

3. The method of claim 1, wherein determining the geographical location includes determining a latitude, a longitude and an altitude associated with the moving platform based on the trajectory identified from the reference magnetic field gradient map.

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

5. The method of claim 1, wherein determining the geographical location further comprises using the known geographical coordinates of the moving platform to mitigate positions errors in a previous inertial navigation system (INS) solution.

6. The method of claim 1, wherein the magnetic field gradient measurements are of the Earth'"'"'s magnetic anomaly field.

7. The method of claim 1, further comprising performing the magnetic field gradient measurements using a vector magnetometer onboard the moving platform, wherein the vector magnetometer includes a plurality of coils for performing the magnetic field gradient measurements, wherein a signal for each coil i is represented as

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

9. A method for determining a geographical location, the method comprising:

identifying a sequence of magnetic field gradient measurements for specific positions on the Earth that correspond to a path traveled by a moving platform;

comparing the sequence of magnetic field gradient measurements for the path to a reference magnetic field gradient map;

identifying a trajectory derived from the reference magnetic field gradient map that correlates to the sequence of magnetic field gradient measurements, the trajectory having known geographical coordinates; and

determining the geographical location of the moving platform based on the known geographical coordinates of the trajectory.

10. The method of claim 9, further comprising updating an inertial navigation system (INS) of the moving platform with the geographical location in order to mitigate INS drift.

11. The method of claim 9, wherein determining the geographical location includes determining a latitude, a longitude and an altitude associated with the moving platform based on the trajectory identified from the reference magnetic field gradient map.

12. The method of claim 9, further comprising measuring each magnetic field gradient according to a defined frequency while the moving platform is traveling along the path to a destination, wherein each magnetic field gradient corresponds to a position on the Earth.

13. The method of claim 9, further comprising measuring each magnetic field gradient using a vector magnetometer that is onboard the moving platform.

14. The method of claim 9, wherein the step of comparing further comprises comparing the sequence of magnetic field gradient measurements for the path to a plurality of possible trajectories derived from the reference magnetic field gradient map.

15. The method of claim 9, wherein the reference magnetic field gradient map is a topographical map of the Earth'"'"'s magnetic anomaly field.

16. A system for determining a geographical location of a moving platform, the system comprising:

a vector magnetometer operable to measure a plurality of magnetic field gradients from the moving platform, each magnetic field gradient corresponding to a position on the Earth, the magnetic field gradients being continually measured while the moving platform is traveling along a path to a destination;

a data store comprising a reference magnetic field gradient map that describes the Earth'"'"'s magnetic anomaly field; and

one or more processors operable to;

identify the plurality of magnetic field gradients;

create a sequence of magnetic field gradient measurements from the plurality of magnetic field gradients that correspond to the path traveled by the moving platform;

compare the sequence of magnetic field gradient measurements for the path to a plurality of possible trajectories derived from the reference magnetic field gradient map;

identify a trajectory from the reference magnetic field gradient map that correlates to the sequence of magnetic field gradient measurements, the trajectory having known geographical coordinates; and

determine the geographical location of the moving platform based on the known geographical coordinates of the trajectory.

17. The system of claim 16, wherein the one or more processors are further configured to update an inertial navigation system (INS) of the moving platform with the geographical location in order to mitigate INS drift.

18. The system of claim 16, wherein the system is installed onboard the moving platform.

19. The system of claim 16, wherein the system is installed onboard a self-propelled guided weapon or an aircraft.

20. The system of claim 16, 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