Patent ID: 7667640

Claim:
A method of determining a geolocation of an emitter from two time-difference of arrival measurements from different times, the method comprising: determining a first time-difference of arrival at an observer between a first signal from the emitter relayed by a first satellite and the first signal relayed by a second satellite, wherein the first time-difference of arrival is observed at the observer at a first time; determining a second time-difference of arrival at the observer between a second signal from an emitter relayed by the first satellite and the second signal relayed by a third satellite, wherein the second time-difference of arrival is observed at the observer at a second time, the second time being different from the first time; and determining the geolocation of the emitter based on the first and second time-difference of arrivals, wherein the first satellite is at a first position at the first time and the first satellite is at a second position at the second time and wherein said determining the geolocation of the emitter based on the first and second time-difference of arrivals comprises defining a virtual satellite position as an average of the first and second positions of the first satellite and applying a closed-form solution to the first and second time-difference of arrivals using the virtual satellite position and positions of the second and third satellites.