Patent ID: 7663547

Claim:
A method of determining a geolocation of an emitter from two time-difference of arrival measurements and two frequency-difference of arrival measurements, each from a different time, the method comprising: determining a first time-difference of arrival between a first signal from the emitter relayed by a first satellite and the first signal relayed by a second satellite, wherein the first signal is received at a first time; determining a second time-difference of arrival between a second signal from an emitter relayed by the first satellite and the second signal relayed by a third satellite, wherein the second signal is received at a second time, the second time being different from the first time; determining a first frequency-difference of arrival between a third signal relayed by the first satellite and the third signal relayed by the second satellite, wherein the third signal is received at a third time, the third time being different from the first time and the second time; determining a second frequency-difference of arrival between a fourth signal relayed by the first satellite and the fourth signal relayed by the third satellite, wherein the fourth signal is received at a fourth time, the fourth time being different from the first time, the second time, and the third time; determining a first error in the first time-difference of arrival; determining a second error in the second time-difference of arrival; determining a third error in the first frequency-difference of arrival; determining a fourth error in the second frequency-difference of arrival; determining a first weight for the first error; determining a second weight for the second error; determining a third weight for the third error; determining a fourth weight for the fourth error; and minimizing a weighted errors function based on a combination of the first weight applied to a square of the first error, the second weight applied to a square of the second error, the third weight applied to a square of the third error, and the fourth weight applied to a square of the fourth error to determine the geolocation of the emitter.