Correlating overlapping magnetic measurement data from multiple magnetic navigation devices and updating a geomagnetic map with that data

1. A method comprising:

by a computing device, receiving from one or more magnetic-measurement devices one or more trajectories comprising magnetic measurements in an area collected by the magnetic-measurement devices over a period of time;

by the computing device, performing one or more correlation analyses on one or more portions of the trajectories to determine similarities in the trajectories; and

by the computing device, incorporating into a master geomagnetic map portions of the trajectories based on one or more of the determined similarities.

2. The method of claim 1 , wherein performing the correlation analyses and incorporating into the master geomagnetic map portions of the trajectories comprises:

for each of one or more portions of one or more of the trajectories:

comparing the portion of the trajectory with a corresponding portion of a baseline magnetic map according to a correlation analysis to determine similarity between the portion of the trajectory and the corresponding portion of the baseline magnetic map; and

storing the portion of the trajectory based on the determined similarity between the portion of the trajectory and the corresponding portion of the baseline magnetic map;

for each of one or more of the stored portions of the trajectories:

comparing the portion of the trajectory with one or more corresponding other ones of the stored portions of the trajectories according to a correlation analysis to determine similarity between it and the corresponding other ones of the stored portions of the trajectories; and

continuing to store the portion of the trajectory based on the determined similarity between the portion of the trajectory and the corresponding other ones of the stored portions of the trajectories; and

for each of one or more of the portions of the trajectories that is still stored, further continuing to store the portion of the trajectory based on a weighting of the portion of the trajectory.

3. The method of claim 2 , wherein:

the master geomagnetic map comprises the baseline geomagnetic map; and

the baseline geomagnetic map comprises an Earth Magnetic Anomaly Grid with 2-arc-minute resolution (EMAG2) model.

4. The method of claim 2 , wherein the weighting of the portion of the trajectory is based at least in part on a trust coefficient for a magnetic-measurement device that the trajectory was received from.

5. The method of claim 1 , wherein each of one or more of the correlation analyses comprises a similarity correlation analysis that comprises one or more of:

normalized correlation;

cross correlation;

one or more spectral criteria functions; or

one or more difference criteria functions.

6. The method of claim 1 , wherein the magnetic measurements comprise measurements of magnetic susceptibility or magnetic conductivity.

7. The method of claim 1 , wherein the magnetic measurements comprise measurements of a magnetic field.

8. The method of claim 1 , wherein incorporating portions of the trajectories into the master geomagnetic map comprises creating one or more portions of the master geomagnetic map.

9. The method of claim 1 , wherein incorporating portions of the trajectories into the master geomagnetic map comprises updating one or more portions of the master geomagnetic map.

10. The method of claim 1 , wherein:

one or more of the correlation analyses on one or more of the trajectories account for errors in the trajectories; and

one or more of the errors:

comprise noise;

are known;

are in one or more of the magnetic measurements in the trajectories; or

are in one or more determined locations where one or more of the magnetic measurements in the trajectories were made.

11. The method of claim 1 , wherein each of one or more of the correlation analyses comprises determining a correspondence between different gradient profiles associated with the magnetic measurements.

12. The method of claim 1 , wherein incorporating portions of the trajectories into the master geomagnetic map comprises updating one or more trust levels associated with one or more portions of the master geomagnetic map.

13. One or more computer-readable non-transitory storage media embodying software that is operable when executed to:

receive from one or more magnetic-measurement devices one or more trajectories comprising magnetic measurements in an area collected by the magnetic-measurement devices over a period of time;

perform one or more correlation analyses on one or more portions of the trajectories to determine similarities in the trajectories; and

incorporate into a master geomagnetic map portions of the trajectories based on one or more of the determined similarities.

14. The media of claim 13 , wherein, to perform the correlation analyses and incorporate into the master geomagnetic map portions of the trajectories, the software is operable when executed to:

for each of one or more portions of one or more of the trajectories:

compare the portion of the trajectory with a corresponding portion of a baseline magnetic map according to a correlation analysis to determine similarity between the portion of the trajectory and the corresponding portion of the baseline magnetic map; and

store the portion of the trajectory based on the determined similarity between the portion of the trajectory and the corresponding portion of the baseline magnetic map;

for each of one or more of the stored portions of the trajectories:

compare the portion of the trajectory with one or more corresponding other ones of the stored portions of the trajectories according to a correlation analysis to determine similarity between it and the corresponding other ones of the stored portions of the trajectories; and

continue to store the portion of the trajectory based on the determined similarity between the portion of the trajectory and the corresponding other ones of the stored portions of the trajectories; and

for each of one or more of the portions of the trajectories that is still stored, further continue to store the portion of the trajectory based on a weighting of the portion of the trajectory.

15. The media of claim 14 , wherein:

the master geomagnetic map comprises the baseline geomagnetic map; and

the baseline geomagnetic map comprises an Earth Magnetic Anomaly Grid with 2-arc-minute resolution (EMAG2) model.

16. The media of claim 14 , wherein the weighting of the portion of the trajectory is based at least in part on a trust coefficient for a magnetic-measurement device that the trajectory was received from.

17. The media of claim 13 , wherein each of one or more of the correlation analyses comprises a similarity correlation analysis that comprises one or more of:

normalized correlation;

cross correlation;

one or more spectral criteria functions; or

one or more difference criteria functions.

18. The media of claim 13 , wherein the magnetic measurements comprise measurements of magnetic susceptibility or magnetic conductivity.

19. The media of claim 13 , wherein the magnetic measurements comprise measurements of a magnetic field.

20. The media of claim 13 , wherein incorporating portions of the trajectories into the master geomagnetic map comprises creating one or more portions of the master geomagnetic map.

21. The media of claim 13 , wherein incorporating portions of the trajectories into the master geomagnetic map comprises updating one or more portions of the master geomagnetic map.

22. The media of claim 13 , wherein:

one or more of the correlation analyses on one or more of the trajectories account for errors in the trajectories; and

one or more of the errors:

comprise noise;

are known;

are in one or more of the magnetic measurements in the trajectories; or

are in one or more determined locations where one or more of the magnetic measurements in the trajectories were made.

23. The media of claim 13 , wherein each of one or more of the correlation analyses comprises determining a correspondence between different gradient profiles associated with the magnetic measurements.

24. The media of claim 13 , wherein the incorporating portions of the trajectories into the master geomagnetic map comprises updating one or more trust levels associated with one or more portions of the master geomagnetic map.

25. A system comprising:

one or more processors; and

one or more computer-readable non-transitory storage media coupled to one or more of the processors and comprising instructions operable when executed by one or more of the processors to cause the system to:

receive from one or more magnetic-measurement devices one or more trajectories comprising magnetic measurements in an area collected by the magnetic-measurement devices over a period of time;

perform one or more correlation analyses on one or more portions of the trajectories to determine similarities in the trajectories; and

incorporate into a master geomagnetic map portions of the trajectories based on one or more of the determined similarities.

26. The system of claim 25 , wherein, to perform the similarity correlation analyses and incorporate into the master geomagnetic map portions of the trajectories, the one or more processors are operable when executing the instructions to cause the system to:

for each of one or more portions of one or more of the trajectories:

compare the portion of the trajectory with a corresponding portion of a baseline magnetic map according to a correlation analysis to determine similarity between the portion of the trajectory and the corresponding portion of the baseline magnetic map; and

store the portion of the trajectory based on the determined similarity between the portion of the trajectory and the corresponding portion of the baseline magnetic map;

for each of one or more of the stored portions of the trajectories:

compare the portion of the trajectory with one or more corresponding other ones of the stored portions of the trajectories according to a correlation analysis to determine similarity between it and the corresponding other ones of the stored portions of the trajectories; and

continue to store the portion of the trajectory based on the determined similarity between the portion of the trajectory and the corresponding other ones of the stored portions of the trajectories; and

for each of one or more of the portions of the trajectories that is still stored, further continue to store the portion of the trajectory based on a weighting of the portion of the trajectory for.

27. The system of claim 26 , wherein:

the master geomagnetic map comprises the baseline geomagnetic map; and

the baseline geomagnetic map comprises an Earth Magnetic Anomaly Grid with 2-arc-minute resolution (EMAG2) model.

28. The system of claim 26 , wherein the weighting of the portion of the trajectory is based at least in part on a trust coefficient for a magnetic-measurement device that the trajectory was received from.

29. The system of claim 25 , wherein each of one or more of the correlation analyses comprises a similarity correlation analysis that comprises one or more of:

normalized correlation;

cross correlation;

one or more spectral criteria functions; or

one or more difference criteria functions.

30. The system of claim 25 , wherein the magnetic measurements comprise measurements of magnetic susceptibility or magnetic conductivity.

31. The system of claim 25 , wherein the magnetic measurements comprise measurements of a magnetic field.

32. The system of claim 25 , wherein incorporating portions of the trajectories into the master geomagnetic map comprises creating one or more portions of the master geomagnetic map.

33. The system of claim 25 , wherein incorporating portions of the trajectories into the master geomagnetic map comprises updating one or more portions of the master geomagnetic map.

34. The system of claim 25 , wherein:

one or more of the correlation analyses on one or more of the trajectories account for errors in the trajectories; and

one or more of the errors:

comprise noise;

are known;

are in one or more of the magnetic measurements in the trajectories; or

are in one or more determined locations where one or more of the magnetic measurements in the trajectories were made.

35. The system of claim 25 , wherein each of one or more of the correlation analyses comprises determining a correspondence between different gradient profiles associated with the magnetic measurements.

36. The system of claim 25 , wherein incorporating portions of the trajectories into the master geomagnetic map comprises updating one or more trust levels associated with one or more portions of the master geomagnetic map.

37. A system comprising:

means for receiving from one or more magnetic-measurement devices one or more trajectories comprising magnetic measurements in an area collected by the magnetic-measurement devices over a period of time;

means for performing one or more correlation analyses on one or more portions of the trajectories to determine similarities in the trajectories; and

means for incorporating into a master geomagnetic map portions of the trajectories based on one or more of the determined similarities.