Techniques for using a series of magnetic measurements to aide position determination

A program product comprising a non-transitory processor readable medium on which program instructions are embodied, wherein the program instructions are configured, when executed by at least one programmable processor, to cause the at least one programmable processor to execute a process to utilize a magnetic anomaly measurement to aid in determining a geographic position of a body, the process comprising:

• receiving a first magnetic measurement and a first time when the first magnetic measurement was made;
• generating a set of at least one geographic location on a magnetic anomaly map, wherein the set includes each geographic location on the magnetic anomaly map which has a magnetic field strength within a threshold range of the first magnetic measurement;
• determining whether the set or another set of at least one geographic location, on the magnetic anomaly map, includes more than one geographic location;
• determining that the set of at least one geographic location includes the more than one geographic location, then receiving another magnetic measurement and another time when the other magnetic measurement was made;
• determining a vector distance travelled by the body, between where the other magnetic measurement was made and where the magnetic measurement immediately preceding the other magnetic measurement was made;
• for each geographic location of a last determined set of at least one geographic location, determining an offset geographic position on the magnetic anomaly map by adding the vector distance to each geographic location of the last determined set of at least one geographic location;
• generating the other set of at least one offset geographic location on the magnetic anomaly map, wherein the other set includes each offset geographic location on the magnetic anomaly map which has a magnetic field strength within the threshold range of the other magnetic measurement;
• and
• determining that the set of at least one geographic location does not include the more than one geographic location, then transmitting, to a navigation filter, only one geographic location in the set or the other set and a time.

An apparatus for utilizing a magnetic anomaly measurement to aid in determining a geographic position of a body, the apparatus comprising:

• a magnetometer;
• an inertial measurement unit;
• a time source;
• and
• a processing circuitry;
• wherein the processing circuitry is configured to store a navigation filter and a magnetic anomaly map;
• wherein the processing circuitry is communicatively coupled to the time source, the magnetometer, and the inertial measurement unit;
• wherein the processing circuitry is configured to:
• receive a first magnetic measurement from the magnetometer and a first time from the time source when the first magnetic measurement was made;
• generate a set of at least one geographic location on the magnetic anomaly map, wherein the set includes each geographic location on the magnetic anomaly map which has a magnetic field strength within a threshold range of the first magnetic measurement;
• determine whether the set or another set of at least one geographic location, on the magnetic anomaly map, includes more than one geographic location;
• determine that the set of at least one geographic location includes the more than one geographic location, then receiving another magnetic measurement from the magnetometer and another time, from the time source, when the other magnetic measurement was made;
• determine a vector distance travelled by the body, between where the other magnetic measurement was made and where the magnetic measurement immediately preceding the other magnetic measurement was made;
• for each geographic location of a last determined set of at least one geographic location, determine an offset geographic position on the magnetic anomaly map by adding the vector distance to each geographic location of the last determined set of at least one geographic location;
• generate the other set of at least one offset geographic location on the magnetic anomaly map, wherein the other set includes each offset geographic location on the magnetic anomaly map which has a magnetic field strength within the threshold range of the other magnetic measurement;
• and
• determine that the set of at least one geographic location does not include the more than one geographic location, then transmitting, to the navigation filter, only one geographic location in the set or the other set and a time from the time source.