Data processing: measuring – calibrating – or testing – Measurement system – Measured signal processing
Reexamination Certificate
1998-10-19
2001-07-31
Shah, Kamini (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Measured signal processing
C702S150000, C702S151000, C324S207110, C324S207130, C324S207140
Reexamination Certificate
active
06269324
ABSTRACT:
BACKGROUND
The present invention relates generally to the tracking of magnetic source objects, and more particularly, to a data processing algorithm that permits kinematic tracking in real time of one or more magnetized objects, using a series of magnetic field strength measurements, vector components or total field, collected from one or more magnetometers.
Numerous opportunities exist for sensor systems that can track objects which generate magnetic fields. All types of land vehicles, ships, and aircraft have structural and power systems capable of generating substantial magnetic signatures. Even small inert objects such as firearms and hard tools may exhibit sufficient magnetization to be observed from a distance. Over the past several years, the assignee of the present invention has developed various types of magnetic sensor data processing algorithms and systems capable of localizing, quantifying, and classifying such objects based on their magnetostatic fields. The present invention extends this capability to real time tracking in a way that greatly simplifies solution of the nonlinear field equations.
A magnetostatic field may be generated by any combination of three physical phenomena: permanent or remanent magnetization, magnetostatic induction, and electromagnetic induction. The first occurs in objects that contain metals of the ferromagnetic group, which includes iron, nickel, cobalt, and their alloys. These may be permanently magnetized either through manufacture or use. Second, the Earth's magnetostatic field may induce a secondary field in ferromagnetic structures and also paramagnetic structures if the mass and shape sufficiently enhance the susceptibility. Third, the object may comprise a large direct current loop that induces its own magnetic field. This is often the case with land vehicles that use the vehicle chassis as a ground return.
Tracking objects by sensing and data processing their magnetostatic fields offers several advantages over other methods. One is that the process is passive rather than active. This eliminates potential health and safety hazards that could be associated with some types of active sensor systems, such as those which use various types of electromagnetic radiation. A passive system also permits covert observation, useful to military and intelligence operations as well as law enforcement. Another advantage is that the field is mostly unaffected by natural boundaries, such as space above and the sea or land surface below. It is also unaffected by many adverse environmental conditions such as wind, fog, thunderstorms, and temperature extremes. Yet another advantage is that the magnetostatic field of the tracked object is difficult to conceal or countermeasure, and is therefore useful against hostile subjects.
RELATED ART
As a result of continuing research and development, the assignee of the present invention has previously filed developed inventions relating to magnetic sensor systems and data processing of magnetic field measurements. To date these have been primarily concerned with detecting, locating, and classifying magnetic objects based on a large set of measurements distributed over space and/or time. The first method to be introduced was the dipole detection and localization (DMDL) algorithm disclosed in U.S. Pat. No. 5,239,474, issued Aug. 24, 1993. This algorithm assumes that the field of a magnetic source object is well represented as the field of a magnetic dipole moment at distances far removed from the source. The location of the dipole is determined by maximizing an objective function over a grid of search points that spans the search volume. Two limitations of this method are the assumption of a linear array of sensors and the need to search over all possible dipole orientations if the orientation is unknown.
This original invention was augmented by two subsequent inventions. The first invention, disclosed in U.S. Pat. No. 5,337,259, issued Aug. 9, 1994, provided for three improvements to DMDL processing. The first improves spatial resolution yielding a more definitive localization; the second uses higher order mutipole terms in the Anderson function expansion to increase the signal to noise ratio (SNR); and the third introduces a multiple-pass, multiple-target localization method. The next invention, disclosed in U.S. Pat. No. 5,388,803, issued Feb. 17, 1995, extended the DMDL process to use in synthetic aperture arrays. This method permits a set of magnetic field measurements to be collected from a single moving sensor over a period of time in lieu of a large number of fixed sensors in a single instant.
Subsequent to these inventions, a substantially changed and improved DMDL processing algorithm (IDMDL) was developed by the assignee of the present invention which is disclosed in a U.S. patent application Ser. No. 08/611,291. The Anderson function expansion in spherical coordinates was replaced by a conventional electromagnetic field moment expansion in Cartesian coordinates. This change eliminates the requirement for a linear array of sensors and permits an arbitrary array geometry to be used. Also, range normalization and the search over unknown dipole orientations was eliminated by forming a unique estimate of the dipole moment within the objective function. An extension of the method estimates multiple dipole moment sources simultaneously.
The fundamental algorithm change in IDMDL substantially generalized the process and led rapidly to new processing extensions on several fronts. The first was spatial-temporal processing, disclosed in U.S. Pat. No. 5,684,396 issued Nov. 4, 1997. This extension permits the dipole source to be in motion and solves for the source object location as well as its velocity vector. When applied independently to short time intervals of measurements, it provides an approximate track of the object. The second extension was multipole dipole characterization, disclosed in U.S. Pat. No. 5,783,944 issued Jul. 21, 1998. This second extension replaces the dipole approximation with a set of spatially separated and independently oriented dipoles when the object is close or large. The dipole set provides a means of characterizing or classifying an object in the near field. A third extension permits both the remanent and induced components of the dipole source to be independently estimated as the source object rotates in the earth's magnetic field, and is disclosed in U.S. Patent application Ser. No. 08/789,032, filed Jan. 27, 1997.
Accordingly, it is an objective of the present invention to provide for a data processing algorithm that permits kinematic tracking in real time of one or more magnetized objects, using a series of magnetic field strength measurements, vector components or total field, collected from one or more magnetometers.
SUMMARY OF THE INVENTION
To accomplish the above and other objectives, the present invention provides for an algorithm, which may be implemented as an apparatus or a method, that permits kinematic tracking of magnetized targets (objects) using magnetic field strength measurements from one or more vector or total field magnetometers (magnetic field strength sensors). While kinematic tracking of targets using a variety of observables including range, bearing, Doppler shift, for example, has been well established for many years, the kinematic tracking of magnetized targets using magnetic field strength measurements from one or more vector or total field magnetometers provided by the present invention is unique. The present magnetic object tracking algorithm has been shown to effectively track a maneuvering magnetic dipole target using an extended Kalman filter directly observing real magnetic field strength data.
The present invention comprises a substantial change to algorithms of the prior art discussed above in that it is intended for use in tracking rather than in initially detecting or classifying the object. The present method begins with a source detection and approximate location provided by one of the prior methods and tracks the source continuou
Gilbert Harold C.
Kohnen Kirk K.
Rakijas Michael
Saglembeni Anthony
Alkov Leonard A.
Lenzen, Jr. Glenn H.
Raufer Colin M.
Raytheon Company
Shah Kamini
LandOfFree
Magnetic object tracking based on direct observation of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetic object tracking based on direct observation of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic object tracking based on direct observation of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2561143