Patent ID: 7561105

Claim:
A method of determining the location of an emitter disposed proximate to the Earth's surface, the method comprising: (a) receiving a signal from the emitter with a first pair of receivers; (b) measuring the signal time difference of arrival between the receivers; (c) producing a hyperboloid of revolution from the measured signal time difference of arrival between the first pair of receivers, wherein the emitter is within a first isochron defined by the intersection of the hyperboloid of revolution and the Earth's surface, the isochron having a width that is a function of the receiver pair and emitter geometry; (d) repeating steps (a)-(c) with a second pair of receivers to define a second isochron that intersects with the first isochron to form an intersection and repeating steps (a)-(c) with a third pair of receivers to define a third isochron that intersects with the first isochron to form an intersection and second isochron to form an intersection, wherein each intersection defines a parallelogram; (e) measuring the area of each parallelogram and determining the parallelogram having the smallest area; (f) identifying the receiver pairs associated with the two intersecting isochrones whose intersection forms the smallest parallelogram; and (g) determining the emitter location using the identified receiver pairs, wherein each parallelogram has a first pair of oppositely facing angles of equal size, a second pair of oppositely facing angles of equal size, a first diagonal defined by the distance between the first pair of oppositely facing angles and a second diagonal defined by the distance between the second pair of oppositely facing angles, and when the measured area of the two smallest parallelograms is substantially the same, the method further comprises measuring the first and second diagonals, identifying the longer diagonal and the shorter diagonal, determining a ratio of the shorter diagonal over the longer diagonal, and identifying the parallelogram having the maximum ratio of the shorter diagonal over the longer diagonal.