Vehicle identification
Magnetometers under the road surface detect variations in the vertical and longitudinal horizontal components of the magnetic field over time in response to passing vehicles. A trajectory of these components in the phase space of these field components is regularized to obtain a magnetic signature. Magnetic signatures are compared using cross-correlation over arc length to identify vehicles. Inductance sensors can be used to detect vehicles and help determine the beginning and end of magnetic signatures.
1. A method of vehicle identification, comprising:
sensing a change in at least two components of a magnetic field at a first location due to movement of a vehicle and producing an event record that includes a vehicle magnetic signature corresponding to the change;
comparing the vehicle magnetic signature to a database of saved records that include stored magnetic signatures;
associating the event record with a saved record in the database when a match is obtained between the vehicle magnetic signature and the stored magnetic signature of the saved record; and
performing an action when the match is obtained between the vehicle magnetic signature and the stored magnetic signature;
wherein the first location is at a road and the stored magnetic signatures are generated by sensing a change in a magnetic field in at least two components at a second location due to movement of vehicles along the road at the second location, the second location being a location past which vehicles travel before reaching the first location.
2. The method of claim 1 in which the change is detected in two components.
3. The method of claim 1 in which the change is detected in three components.
4. The method of claim 1 in which each saved record includes an entry corresponding to one or more of the weight of the vehicle, the speed of the vehicle, and the license number of the vehicle.
5. The method of claim 1 in which sensing comprises sensing changes in the earth's magnetic field.
6. The method of claim 1 in which sensing comprises sensing with synchronized magnetometer pairs.
7. The method of claim 1 in which the sensed change in a magnetic field at a second location is a change in three components of the earth's magnetic field.
8. The method of claim 1 in which the sensed change in a magnetic field at a second location is a change in two components of the earth's magnetic field.
9. The method of claim 1 further comprising sensing at the second location and saving in a corresponding saved record one or more of the weight of the vehicle, the speed of the vehicle, and the license number of the vehicle.
10. The method of claim 1 in which comparing comprises a cross-correlation, and a match is determined by a cross-correlation exceeding a pre-defined threshold.
11. The method of claim 10 in which cross-correlation is performed on a non-linear and/or variance stabilized statistic where such a statistic is constructed to optimize statistical identification.
12. The method of claim 10 in which the cross-correlation is performed on a constructed time and process independent measure.
13. The method of claim 12 in which the constructed time and process independent measure comprises a regularized trajectory of the magnetic signal in the phase space of the sensed components of the magnetic field.
14. The method of claim 13 in which the cross-correlation is calculated over arc-length of the regularized trajectory.
15. The method of claim 13 in which the cross-correlation is calculated over arc-length of the regularized trajectory.
16. The method of claim 12 in which the cross-correlation and measure are both constructed directly from measured magnetic field components in at least two dimensions.
17. The method of claim 12 in which the constructed time and process independent measure comprises a regularized trajectory of the magnetic signal in the phase space of the sensed components of the magnetic field.
18. The method of claim 12 in which the cross-correlation and measure are both constructed directly from measured magnetic field components in at least two dimensions.
19. The method of claim 10 further comprising taking a Fisher-Z of the cross-correlation to compare the signatures.
20. The method of claim 1 in which the magnetic signature is a regularized trajectory of the magnetic signal in a phase space of the sensed components of the magnetic field.
21. The method of claim 1 in which a constant velocity and/or spatially reconstructed equivalent of the vehicle's magnetic field change record is calculated.
22. The method of claim 1 further comprising using additional sensor data in combination with the sensed change in at least two components of a magnetic field at the first location.
23. The method of claim 22 further comprising using the additional sensor data to detect the presence of the vehicle.
24. The method of claim 22 further comprising using the additional sensor data to determine the boundaries of the change in at least two components of a magnetic field at the first location due to movement of the vehicle.
25. The method of claim 22 in which the additional sensor data comprises data generated by an inductance sensor.
26. A method of vehicle identification, comprising:
sensing a change in at least two components of a magnetic field at a first location due to movement of a vehicle and producing an event record that includes a vehicle magnetic signature corresponding to the change;
comparing the vehicle magnetic signature to a database of saved records that include stored magnetic signatures;
associating the event record with a saved record in the database when a match is obtained between the vehicle magnetic signature and the stored magnetic signature of the saved record; and
performing an action when the match is obtained between the vehicle magnetic signature and the stored magnetic signature;
wherein comparing comprises a cross-correlation performed on a constructed time and process independent measure, and the match is determined by the cross-correlation exceeding a pre-defined threshold.