Dipole moment detector and localizer

• US 5,731,996 A
• Filed: 03/05/1996
• Issued: 03/24/1998
• Est. Priority Date: 03/05/1996
• Status: Expired due to Term

• Current Assignee: Hanger Solutions, LLC (IP Investments Group LLC)
• Original Assignee: Hughes Electronics Corporation (AT&T, Inc.)
• Inventors: Gilbert, Harold C.
• Primary Examiner(s): Trammell, James F.
• Assistant Examiner(s): Bui, Bryan
• Application Number:
  US08/611,291
• Time in Patent Office: 749 Days
• Field of Search: 364/449, 364/559, 364/516, 364/571.02, 364/556, 364/561, 364/448, 324/207.11, 324/207.22, 324/207.23, 324/207.26, 324/243, 324/207.13, 324/207.14, 324/207.44
• US Class Current: 702/150
• CPC Class Codes: G01V 3/081 the magnetic field is produced by the objects or geological structures characterised by the method of magnetic field measurement G01R33/00

Abstract

A processing method and apparatus that process magnetometer data derived from an array of magnetometer sensors and outputs the position or location of a magnetic dipole. In the method and apparatus, (a) a set of actual magnetic field measurements of a magnetic dipole is collected using the array of magnetic sensors. Then (b), a location for the magnetic dipole is hypothesized. Then (c), a set of estimated magnetic field measurements is determined that would be formed by a magnetic dipole at the hypothesized location. Then (d), the actual magnetic field measurements are compared with the estimated magnetic field measurements. Steps (b) through (d) are repeated for all hypothesized locations within the detection range of the array of magnetic sensors. The position or location of the dipole is displayed for viewing on a display.

Claims

1. A method of detecting and localizing a magnetic dipole using an array of spatially distributed magnetic sensors, said method comprising the steps of:

a) collecting a set of actual magnetic field measurements of a magnetic dipole using a plurality of magnetic sensors;

b) storing position matrices corresponding to hypothesized locations of the magnetic dipole relative to the array of sensors;

c) estimating the orientation and magnitude of the dipole from the magnetic field measurements using an electromagnetic moment equation that generates a minimum least-squares estimate that minimizes the sum of squared errors between the actual magnetic field measurements and magnetic field measurements that would be generated by a dipole having an optimal orientation and magnitude;

d) computing expected magnetic field measurements that would be generated at the sensors by the dipole having the optimal orientation and magnitude;

e) comparing the actual magnetic field measurements with the expected magnetic field measurements;

f) repeating steps b) through e) for all hypothesized locations within the detection range of the array of magnetic sensors to detect and localize the magnetic dipole.

2. The method of claim 1 further comprising the step of displaying the location data.

3. The method of claim 1 wherein the step of repeating steps b) through e) for all hypothesized locations within the detection range of the array of magnetic sensors comprises the steps of:

correlating the measured magnetic field values with each of the estimated magnetic field values for the array of sensors, by multiplying the estimated magnetic field values with the measured magnetic field values and summing the results over the array of sensors; and

if one of the resulting correlations has a significantly larger value than the others and if it is greater than a predetermined threshold, declaring a detection for the location corresponding to the calculated values that resulted in the larger correlation value.

4. The method of claim 3 further comprising the step of displaying the location data.

8. The method of claim 1 wherein the step of estimating the orientation and magnitude of the dipole comprises the step of:

simultaneously estimating the orientation and magnitude of multiple dipoles to simultaneously detect and localize a plurality of discrete magnetic dipoles.

9. The method of claim 8 further comprising the step of:

comparing the magnitudes and positions of the plurality of discrete magnetic dipoles to predetermined geometric patterns of dipoles that correspond to known complex magnetic objects to classify the plurality of discrete magnetic dipoles as a particular magnetic object.

10. The method of claim 1 wherein the plurality of magnetic sensors comprises a three dimensional array having an arbitrary number of sensors, each of which is positioned in an arbitrary orientation at arbitrary points in space.

5. A method of detecting and localizing a magnetic dipole using an array of spatially distributed magnetic sensors, said method comprising the steps of:

a) collecting a set of actual magnetic field measurements of a magnetic dipole using a plurality of magnetic sensors;

b) filtering the actual magnetic field measurements using a predetermined filter;

c) storing position matrices corresponding to hypothesized locations of the magnetic dipole relative to the array of sensors;

d) estimating the orientation and magnitude of the dipole from the magnetic field measurements using an electromagnetic moment equation that generates a minimum least-squares estimate that minimizes the sum of squared errors between the actual magnetic field measurements and magnetic field measurements that would be generated by a dipole having an optimal orientation and magnitude;

e) computing expected magnetic field measurements that would be generated at the sensors by the dipole having the optimal orientation and magnitude;

f) filtering the expected magnetic field measurements using the predetermined filter;

g) comparing the actual magnetic field measurements with the expected magnetic field measurements; and

h) repeating steps c) through g) for all hypothesized locations within the detection range of the array of magnetic sensors to detect and localize the magnetic dipole.

6. The method of claim 5 further comprising the step of displaying the location data.

11. The method of claim 5 wherein the step of estimating the orientation and magnitude of the dipole comprises the step of:

simultaneously estimating the orientation and magnitude of multiple dipoles to simultaneously detect and localize a plurality of discrete magnetic dipoles.

12. The method of claim 11 further comprising the step of:

comparing the magnitudes and positions of the plurality of discrete magnetic dipoles to predetermined geometric patterns of dipoles that correspond to known complex magnetic objects to classify the plurality of discrete magnetic dipoles as a particular magnetic object.

13. The method of claim 5 wherein the plurality of magnetic sensors comprises a three dimensional array having an arbitrary number of sensors, each of which is positioned in an arbitrary orientation at arbitrary points in space.

7. Apparatus for detecting and localizing a magnetic dipole comprising:

an array of magnetic sensors;

processing means coupled to the array of magnetic sensors, for storing position matrices corresponding to hypothesized locations of the magnetic dipole relative to the array of sensors, for estimating magnetic field values comprising the orientation and magnitude of the dipole at said plurality of hypothesized locations from magnetic field measurements using an electromagnetic moment equation that generates a minimum least-squares estimate that minimizes the sum of squared errors between the actual magnetic field measurements and magnetic field measurements that would be generated by a dipole having an optimal orientation and magnitude, for collecting magnetic field signals indicative of the magnetic field measured at each of the sensors in the presence of the magnetic dipole that is to be detected to provide measured magnetic field values, for removing spatial and temporal variations in the magnetic field measured at each of the sensors by temporally and spatially filtering the measured magnetic field signals, for correlating the measured magnetic field values with each of the estimated magnetic field values by multiplying the estimated magnetic field values with the measured magnetic field values and summing the results over the array of sensors, for identifying the location of the dipole if one of the correlations has a significantly larger value than the others and if it is greater than a predetermined threshold, and if the trajectory location of the dipole corresponds to the location represented by the measured magnetic field signals that produced in the significantly larger value; and

display means for displaying the location of the identified dipole.

14. The apparatus of claim 7 wherein the processing means further comprises:

means for simultaneously estimating the orientation and magnitude of multiple dipoles to simultaneously detect and localize a plurality of discrete magnetic dipoles.

15. The apparatus of claim 14 wherein the processing means further comprises:

means for comparing the magnitudes and positions of the plurality of discrete magnetic dipoles to predetermined geometric patterns of dipoles that correspond to known complex magnetic objects to classify the plurality of discrete magnetic dipoles as a particular magnetic object.

16. The apparatus of claim 7 wherein the plurality of magnetic sensors comprises a three dimensional array having an arbitrary number of sensors, each of which is positioned in an arbitrary orientation at arbitrary points in space.