Patent NZ-580039-A (NZ)
Title: Determining a geolocation solution of an emitter on earth using satellite signals
Inventor: HO DOMINIC K
IPC: G01S5/12
Filed: 2008-04-11
Abstract: A method of determining a geolocation of an emitter (110) comprises a) determining a first time-difference of arrival at an observer between a first signal from the emitter relayed by a first satellite (S1) and the first signal relayed by a second satellite (S2) with the first time-difference of arrival being observed at the observer at a first time and b) 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 (S3) with the second time-difference of arrival being observed at the observer at a second time and the second time being different from the first time. The method further comprises either c) determining the geolocation of the emitter based on the first and second time-difference of arrivals with the first satellite being at a first position at the first time and the first satellite is at a second position at the second time and the determining the geolocation of the emitter based on the first and second time-difference of arrivals comprising 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 or d) determining a first calibration factor from a third time-difference of arrival at the observer between a first calibration signal relayed by the first satellite and the first calibration signal relayed by the second satellite with the first calibration factor being computed as a difference between the third time-difference of arrival and a value predicted for the third time difference of arrival, the value predicted for the third time-difference of arrival being based on a known location of an emitter of the first calibration signal; determining a second calibration factor from a fourth time-difference of arrival at the observer between a second calibration signal relayed by the first satellite and the second calibration signal relayed by the third satellite with the second calibration factor being computed as a difference between the fourth time-difference of arrival and a value predicted for the fourth time-difference of arrival, the value predicted for the fourth time-difference of arrival being based on a known location of an emitter of the second calibration signal subtracting the first calibration factor from the first time-difference of arrival and the second calibration factor from the second time-difference of arrival to reduce effects of satellite position and velocity errors on the determined geolocation of the emitter; and determining the geolocation of the emitter based on the first and second time-difference of arrivals or e) determining the geolocation of the emitter based on the first and second time-difference of arrivals by applying a Taylor-series estimation to an initial estimate of the geolocation of the emitter based on a closed form solution to the first and second time-difference of arrivals. In the above method a first frequency-difference of arrival at an observer can be determined and used in determining the geolocation of the emitter instead of determining and using the second time difference of arrival at the observer.