Phase difference of arrival geolocation
Geolocation is performed by receiving, at a plurality of non-earthbound platforms each moving in a known manner within a spatial coordinate system, a radio frequency (RF) signal transmitted from a transmitter at an unknown location on earth within the spatial coordinate system. For each of the platforms, a phase change of the received frequency carrier is measured over the same duration of time. The measured phase changes are combined to determine the transmitter location.
1. A method of geolocating a transmitter located on earth, comprising:
receiving, at a plurality of non-earthbound platforms each moving in a known manner within a spatial coordinate system, a frequency carrier transmitted from the transmitter at an unknown location on earth within the spatial coordinate system;
for each of the platforms, over a same duration of time, measuring a phase change of the received frequency carrier between the transmitter and an associated platform; and
combining the measured phase changes to determine the transmitter location;
wherein said measured phase changes correspond to respective simultaneous receptions of the frequency carrier at the respective platforms over said same duration of time, and wherein at least three said measured phase changes must be combined to determine the transmitter location.
2. The method of claim 1 , wherein said measuring for each platform includes measuring the respective phase changes simultaneously.
3. The method of claim 1 , wherein said combining includes combining each of the measured phase changes with respective locations of the corresponding platform in the spatial coordinate system at a beginning of said duration of time and at an end of said duration of time.
4. The method of claim 1 , wherein each said platform is one of an airborne platform moving in earth atmosphere and a satellite platform moving in space beyond earth atmosphere.
5. The method of claim 1 , wherein said measuring for each platform is performed at the respective platform.
6. The method of claim 1 , wherein said measuring for each platform is performed at a ground station.
7. A system for geolocating a transmitter located on earth, comprising:
a plurality of phase change measurement units respectively associated with a plurality of non-earthbound platforms that each moves in a known manner within a spatial coordinate system, each of said phase change measurement units configured to measure, over a same duration of time, a phase change of a frequency carrier transmitted from the transmitter and received at the associated platform, wherein the transmitter is at an unknown location on earth within the spatial coordinate system; and
a combiner in communication with said phase change measurement units and configured to combine said measured phase changes to determine the transmitter location;
wherein said measured phase changes correspond to respective simultaneous receptions of the frequency carrier at the respective platforms over said same duration of time, and wherein at least three said measured phase changes must be combined to determine the transmitter location.
8. The apparatus of claim 7 , wherein said combiner is configured to combine each of the measured phase changes with respective locations of the corresponding platform in the spatial coordinate system at a beginning of said duration of time and at an end of said duration of time.
9. The apparatus of claim 7 , wherein each said platform is one of an airborne platform moving in earth atmosphere and a satellite platform moving in space beyond earth atmosphere.
10. The apparatus of claim 7 , wherein said phase change measurement units are respectively located on said platforms.
11. The apparatus of claim 7 , wherein said phase change measurement units are located at a ground station.
12. A method of geolocating a transmitter located on earth, comprising:
receiving a plurality of measured phase changes respectively associated with a plurality of non-earthbound platforms, wherein each said measured phase change is a measurement, over a same duration of time, of a phase change of a frequency carrier that is transmitted from the transmitter and received at the associated platform, wherein the transmitter is at an unknown location on earth within a spatial coordinate system, and further wherein the associated platform receives the frequency carrier while the associated platform is moving in a known manner within the spatial coordinate system; and
combining the measured phase changes to determine the transmitter location;
wherein said measured phase changes correspond to respective simultaneous receptions of the frequency carrier at the respective platforms over said same duration of time, and wherein at least three said measured phase changes must be combined to determine the transmitter location.
13. The method of claim 12 , wherein said combining includes combining each of the measured phase changes with respective locations of the corresponding platform in the spatial coordinate system at a beginning of said duration of time and at an end of said duration of time.
14. The method of claim 12 , wherein each said platform is one of an airborne platform moving in earth atmosphere and a satellite platform moving in space beyond earth atmosphere.
15. The method of claim 12 , wherein said measured phase changes are measurements respectively performed on said platforms.
16. The method of claim 12 , wherein said measured phase changes are measurements performed at a ground station.
17. An apparatus for geolocating a transmitter located on earth, comprising:
an input for receiving a plurality of measured phase changes respectively associated with a plurality of non-earthbound platforms, wherein each said measured phase change is a measurement, over a same duration of time, of a phase change of a frequency carrier that is transmitted from the transmitter and received at the associated platform, wherein the transmitter is at an unknown location on earth within a spatial coordinate system, and further wherein the frequency carrier is received at the associated platform while the associated platform is moving in a known manner within the spatial coordinate system; and
a combiner coupled to said input and configured to combine the measured phase changes to determine the transmitter location;
wherein said measured phase changes correspond to respective simultaneous receptions of the frequency carrier at the respective platforms over said same duration of time, and wherein at least three said measured phase changes must be combined to determine the transmitter location.
18. The apparatus of claim 17 , wherein each said platform is one of an airborne platform moving in earth atmosphere and a satellite platform moving in space beyond earth atmosphere.
19. The apparatus of claim 17 , wherein said measured phase changes are measurements respectively performed by said platforms.
20. The apparatus of claim 17 , wherein said measured phase changes are measurements performed by a ground station.