Magnetic navigation system

• US 8,311,767 B1
• Filed: 07/13/2009
• Issued: 11/13/2012
• Est. Priority Date: 07/13/2009
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Stetson, John B.
• Primary Examiner(s): Charioui, Mohamed
• Application Number:
  US12/501,587
• Time in Patent Office: 1,219 Days
• Field of Search: 702/90, 702 92- 95, 702150-152
• US Class Current: 702/152
• CPC Class Codes: G01C 17/00 Compasses; Devices for ascertaining true or magnetic north for navigation or surveying purposes using gyroscopic effect G01C19/00
• CPC Class Codes: G01C 21/08 involving use of the magnetic field of the earth
• CPC Class Codes: G01R 33/032 using magneto-optic devices, e.g. Faraday or Cotton-Mouton effect

Abstract

A magnetic navigation system senses the three-dimensional magnetic fields of the Earth and compares them with a model of the Earth'"'"'s magnetic fields. An initial guess as to system location is corrected toward the actual location by accessing magnetic amplitude from library pages in response to corrected location. Error detectors determine amplitude error, which is processed with magnetic gradient information from gradient models to generate the new attitude and location correction values. The correction values are subtracted from the guess to generate the new updated location. The system iterates to continually tend toward the actual location.

Claims

1. A magnetic navigation device, comprising:

a three-axis magnetometer including first, second and third single-axis channels oriented mutually orthogonally, in which each of said first, second and third channels comprises;

a photoresponsive solid-state crystalline device with lattice imperfections, where electrons of said lattice imperfections resonate at a given wavelength;

a source of timed sequential pairs of light pulses at said given wavelength, said source being directed toward said device, wherein;

(a) a first of said pulses raises an energy state of said electrons over a ground state, thereby creating distinct quantum spin state populations, and

(b) a second of said pulses occurs at a time such that the energy state of said electrons is reduced to said ground state, whereby the reduction of said energy state generates photons which exit said device, the number of photons exiting said device being related to the magnitude of a component of the magnetic field through said device; and

a photon detector for responding to said photons and for generating an electrical signal in response to said photons, said electrical signal being proportional to the component of the magnetic field in the direction of the channel;

wherein at least one of a latitude location and a longitudinal location of said device are determinable from said electrical signals of said first, second and third single-axis channels.

2. A magnetic navigation device according to claim 1, further comprising a source of reference Earth magnetic field component information, and a processor executing instructions for comparing said reference Earth magnetic field component information with said at least one of a latitude location and a longitudinal location determined from said electrical signals of said first, second and third single-axis channels.

3. A magnetic navigation device according to claim 2, further comprising first, second and third error detectors for receiving said electrical signals from the first, second and third channels, subtracting from said electrical signals corresponding components of said reference Earth magnetic field component information to generate magnetic field difference signals representing a difference between the measured magnetic fields at the location and the reference Earth magnetic field component information at the location.

4. A magnetic navigation device according to claim 1, further comprising an analog-to-digital converter, for converting said electrical signal into digital form.

5. A magnetic navigation device according to claim 1, wherein said given wavelength is 532 nm.

6. A magnetic navigation device according to claim 1, wherein said photoresponsive solid-state crystalline device comprises a nitrogen-vacancy diamond crystal sensor.

7. A magnetic navigation device according to claim 1, further comprising a wavelength selective mirror disposed between said photoresponsive solid-state crystalline device and said source of timed sequential pairs of light pulses.

8. A method for navigation, said method comprising the steps of:

sensing the Earth'"'"'s magnetic fields at a current location, to thereby generate measured three-dimensional magnetic fields;

addressing a reference library of magnetic values with at least a portion of a column vector representing a corrected estimate of location and attitude of the current location, to thereby obtain library values of the magnetic fields at the corrected estimated location;

generating three scalar quantities representing error signals by taking the differences between said measured three-dimensional magnetic fields and said library values of the magnetic fields at the corrected estimated location;

converting said three scalar quantities representing error signals into column vector form;

multiplying, using a processor, said column vector representing difference signals by a gradient correction matrix, to thereby produce a column vector representing the correction to the corrected estimated location and attitude;

estimating a current location, to thereby generate an estimated location and attitude column vector; and

subtracting said column vector representing the correction to the corrected estimate of the location and attitude, from said column vector representing estimated location and attitude, to generate said column vector representing a corrected estimate of said location and attitude.

9. A method according to claim 8, wherein the step of sensing the Earth'"'"'s magnetic fields is performed using a photoresponsive solid-state crystalline device with lattice imperfections, where electrons of said lattice imperfections resonate at a given wavelength.

10. A method according to claim 9, wherein said given wavelength is 532 nm.

11. A method according to claim 8, further comprising the steps of:

forming said library values of the magnetic fields at the corrected estimated location into a library value column vector;

generating a magnetic field gradient correction matrix representing correction of the gradient of the column vector representing the library values;

assembling said magnetic field gradient correction matrix and said library value column vector, to thereby generate a differential correction matrix including a skew-symmetric submatrix which is the skew-symmetric matrix of said library value column vector and also including a submatrix which is the product of the magnetic field gradient correction matrix multiplied by said Cartesian magnetic field column vector; and

performing Moore-Penrose pseudoinverse processing on said differential correction matrix to generate said gradient correction matrix.

12. A magnetic navigation device, comprising:

a three-axis magnetometer including first, second and third single-axis channels oriented mutually orthogonally, in which each of said first, second and third channels is responsive to Earth'"'"'s magnetic field for generating a measured signal proportional to the component of the magnetic field in the direction of the channel;

a source of reference Earth magnetic field component information responsive to a corrected device location and attitude signal;

first, second, and third error detectors, each including a sum input port and a difference input port, and each also including an output port, said sum input ports of said first, second, and third error detectors being coupled to receive said measured signals from said first, second and third channels, said difference input ports of each of said first, second, and third error detectors being coupled to receive said reference Earth magnetic field component information, for subtracting from said measured signals the corresponding component of said reference Earth magnetic field component information to thereby generate, in each of said first, second and third channels, magnetic field difference signals representing the difference between the measured magnetic fields at the location and the reference Earth magnetic field component information at the location;

a first processor for assembling said magnetic field difference signals into a difference column vector representing the magnetic field differences between the measured magnetic field and the reference magnetic field values at said location;

a source of inverted differential correction matrix responsive to a corrected device location and attitude vector, said inverted differential correction matrix representing the pseudo inverse of an attitude and location sensitivity matrix of the reference magnetic field;

a vector matrix multiplier including a first input port coupled to said first processor, for receiving said difference column vector at said first input port, and also including a second input port coupled to receive said inverted differential correction matrix, for multiplying said difference column vector by said inverted differential correction matrix, for generating a column vector representing corrections to the corrected device location and attitude vector;

a source of ancillary signals, said source of ancillary signals generating one of (a) initial estimated device location and attitude and (b) estimated device location and attitude from an independent navigation location estimator;

a vector differencing processor including an inverting input port and a noninverting input port, said inverting input port being coupled to said vector matrix multiplier for receiving said corrections to said corrected location and attitude vector, said noninverting input port being coupled to said source of ancillary signals, for taking the difference between said corrections to said location and attitude vector and said ancillary signals, for thereby generating a column vector representing the corrected device location and attitude.

13. A magnetic navigation device according to claim 12, wherein said source of inverted differential correction matrix further comprises:

a magnetic field gradient correction matrix processor responsive to the corrected device location and attitude vector, for generating a magnetic field gradient correction matrix representing the spatial or 3-dimensional rate of change of the Earth'"'"'s magnetic field as a function of the corrected device location and attitude;

a scalar-to-column-vector processor coupled to said source of reference Earth magnetic field component information for converting said reference Earth magnetic field component information from scalar form into column vector form;

a matrix assembly processor coupled to said or magnetic field gradient correction matrix processor for receiving said magnetic field gradient correction matrix, and coupled to said scalar-to-column-vector processor for receiving said column vector, for forming a skew-symmetric matrix of said column vector, and for multiplying said column vector by said magnetic field gradient correction matrix to form a product, and for column formatting said skew-symmetric matrix with said product to form a magnetic field gradient correction matrix;

a Moore-Penrose pseudoinverse processor coupled to said matrix assembly processor for generating the Moore-Penrose pseudoinverse of said magnetic field gradient correction matrix to thereby generate said inverted differential correction matrix.

14. A magnetic navigation device according to claim 12, wherein said three-axis magnetometer comprises:

first, second and third single-axis channels, in which each of said first, second and three channels includes;

a photoresponsive solid-state crystalline device with lattice imperfections associated with certain electrons, which lattice imperfections electrons resonate at a given wavelength;

a source of timed sequential pairs of light pulses at said given wavelength, said source being directed toward said device, whereby (a) the first of said pulses of each pair of light pulses raises the energy state of said electrons over a ground state, thereby creating distinct quantum spin state populations, and (b) said second of said pulses of each pair of pulses occurs at a time such that the energy state of said electrons is reduced to said ground state, whereby (c) the reduction of said energy state generates photons which exit said device, the number of photons exiting said device being related to the magnitude of a component of the magnetic field through said device;

a photon detector for responding to said photons and for generating an electrical signal in response to said photons; and

an analog-to-digital converter, for converting said electrical signal into digital form.

15. A magnetic navigation device, comprising:

a three-axis solid-state magnetometer including first, second and third single-axis channels, in which each of said first, second and three channels includes;

a photoresponsive solid-state crystalline device with lattice imperfections associated with certain electrons, which lattice imperfections electrons resonate at a given wavelength;

a source of timed sequential pairs of light pulses at said given wavelength, said source being directed toward said device, whereby (a) the first of said pulses of each pair of light pulses raises the energy state of said electrons over a ground state, thereby creating distinct quantum spin state populations, and (b) said second of said pulses of each pair of pulses occurring at a time such that the energy state of said electrons is reduced to said ground state, whereby (c) the reduction of said energy state generates photons which exit said device, the number of photons exiting said device being related to the magnitude of a component of the magnetic field through said device; and

a photon detector for responding to said photons and for generating an electrical signal in response to said photons;

an analog-to-digital converter, for converting said electrical signal into digital form;

said magnetic navigation device further comprising;

a source of reference Earth magnetic field component information responsive to corrected device location and attitude signal;

first, second, and third error detectors, each including a sum input port and a difference input port, and each also including an output port, said sum input ports of said first, second and third error detectors being coupled to receive said electrical signals in digital form from said analog-to-digital converters of said first, second and third channels, said difference input ports of each of said first, second, and third error detectors being coupled to receive said reference Earth magnetic field component information, for subtracting from said electrical signals the corresponding component of said reference Earth magnetic field component information to thereby generate, in each of said first, second and third channels, magnetic field difference signals representing the difference between the measured magnetic fields at the location and the reference Earth magnetic field component information at the location;

a first processor for assembling said magnetic field difference signals into a difference column vector representing the magnetic field differences between the measured magnetic field and the reference magnetic field values at said location;

a source of inverted differential correction matrix responsive to a corrected device location and attitude vector, said inverted differential correction matrix representing the pseudo inverse of an attitude and location sensitivity matrix of the reference magnetic field;

a vector matrix multiplier including a first input port coupled to said first processor, for receiving said difference column vector at said first input port, and also including a second input port coupled to receive said inverted differential correction matrix, for multiplying said difference column vector by said inverted differential correction matrix, for generating a column vector representing corrections to the corrected device location and attitude vector;

a source of ancillary signals, said ancillary signals being one of (a) initial estimated device location and attitude and (b) estimated device location and attitude from an independent navigation location estimator;

a vector differencing processor including an inverting input port and a noninverting input port, said inverting input port being coupled to said vector matrix multiplier for receiving said corrections to said corrected location and attitude vector, said noninverting input port being coupled to said source of ancillary signals, for taking the difference between said corrections to said location and attitude vector and said ancillary signals, for thereby generating a column vector representing the corrected device location and attitude.

16. A magnetic navigation system according to claim 15, wherein said source of inverted differential correction matrix further comprises:

a magnetic field gradient correction matrix processor responsive to the corrected device location and attitude vector, for generating a magnetic field gradient correction matrix representing the spatial or 3-dimensional rate of change of the Earth'"'"'s magnetic field as a function of the corrected location and attitude;

a scalar-to-column-vector processor coupled to said source of reference Earth magnetic field component information for converting said reference Earth magnetic field component information from scalar form into column vector form;

a matrix assembly processor is coupled to said or magnetic field gradient correction matrix processor for receiving said magnetic field gradient correction matrix, and coupled to said scalar-to-column-vector processor for receiving said column vector, for forming a skew-symmetric matrix of said column vector, and for multiplying said column vector by said magnetic field gradient correction matrix to form a product, and for column formatting said skew-symmetric matrix with said product to form a magnetic field gradient correction matrix;

a Moore-Penrose pseudoinverse processor coupled to said matrix assembly processor for generating the Moore-Penrose pseudoinverse of said magnetic field gradient correction matrix to thereby generate said inverted differential correction matrix.

17. A method for navigation, said method comprising the steps of:

sensing the Earth'"'"'s magnetic fields at the current location, to thereby generate measured three-dimensional magnetic fields ({circumflex over (B)}x(kt), {circumflex over (B)}y(kt), and {circumflex over (B)}z(kt));

addressing a reference library of magnetic values with at least a portion of a column vector

18. A method according to claim 17, further comprising the steps of:

forming said library values (Bx(kt), By(kt), and Bz(kt)) of the magnetic fields at the corrected estimated location into a library value column vector

19. A method for navigation, said method comprising the steps of:

sensing the Earth'"'"'s magnetic fields at a current location, to thereby generate measured three-dimensional magnetic fields ({circumflex over (B)}x(kt), {circumflex over (B)}y(kt), and {circumflex over (B)}z(kt));

addressing a reference library of magnetic values with at least a portion of a column vector

20. A method according to claim 19, further comprising the steps of:

forming said library values (Bx(kt), By(kt), and Bz(kt)) of the magnetic fields at the corrected estimated location into a library value column vector