Interferometric locating system

• US 4,215,345 A
• Filed: 08/31/1978
• Issued: 07/29/1980
• Est. Priority Date: 08/31/1978
• Status: Expired due to Term

• Current Assignee: Frosch Robert A Administrator of The National Aeronautics and Space Administration With Respect To An Invention of, Peter F. Macdoran
• Original Assignee: Frosch Robert A Administrator of The National Aeronautics and Space Administration With Respect To An Invention of, Peter F. Macdoran
• Inventors: MacDoran, Peter F., Frosch, Robert A. Administrator of the National Aeronautics and Space Administration, with respect to an invention of
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US05/938,581
• Time in Patent Office: 698 Days
• Field of Search: 343/112 R
• US Class Current: 342/465
• CPC Class Codes: G01S 5/0009 Transmission of position information to remote stations involving assistance data G01S5/0236

Abstract

A system for determining the position of a vehicle or other target that emits radio waves, which is of the type that senses the difference in time of arrival at spaced ground stations of signals from the vehicle to locate the vehicle on a set of intersecting hyperbolas. A network of four ground stations detects the radio emissions from the vehicle, and by means of cross correlation derives the relative signal delay at the ground stations from which the vehicle position is deduced. Because the signal detection is by cross correlation, no knowledge of the emission is needed, which makes even unintentional radio noise emissions usable as a locator beacon. By positioning one of the four ground stations at an elevation significantly above the plane of the other three stations, a three dimensional fix on the vehicle is possible.

Claims

1. A method for locating a target that can emit radio waves that aid in its location, comprising:

emitting radio waves from the target;

detecting the same emitted radio waves originating from the target, at a first pair of stations that are spaced apart and located at known geographical positions;

measuring the difference in time of arrival of said waves at said first pair of stations;

detecting the same emitted radio waves originating from said source, at a second pair of stations that are spaced apart and located at known geographical positions;

measuring the difference in time of arrival of said waves at said second pair of stations; and

calculating the geographic location of a point which is located a different distance from the two stations of each pair wherein each difference distance is equal to the time difference in wave arrival multiplied by the speed of light; and

wherein

said step of emitting includes emitting a signal which comprises a radio frequency carrier modulated by an information frequency band of more than a kilo-Hertz width and a second spur signal comprising an unmodulated signal but of a frequency which is a plurality of times greater than the highest frequency of said information band, whereby to enable a determination of the general sector of target location and the specific target location within the sector using a limited amount of broadcast frequency bandwidth.

2. The method described in claim 1 wherein:

said step of emitting includes emitting a voice signal in a channel of a plurality of kilohertz bandwidth, and emitting a spur signal having a frequency at least ten times the highest frequency in said information band.

3. A surveillance system comprising:

at least three radio receiving stations spaced apart, to form at least two pairs of stations with each pair including two stations, each station including a receiver for detecting a modulated high frequency radio wave;

means for comparing the phase of first modulating signals within a first low frequency modulation band of said high frequency radio wave, and for separately comparing the phase of second modulation signals within a second higher frequency modulation band of said high frequency radio wave, for generating signals representing the difference in time of arrival of the same high frequency radio wave at the two stations of the pair; and

means for generating a signal defining the location of a point which is located a different distance from the two stations of each pair, wherein each difference is equal to the time difference in wave arrival multiplied by the speed of light.

4. The system described in claim 3 wherein:

said comparing means comprises means to generate a first difference-indicating signal representing the difference in phase of said first modulating signals whereby to indicate the approximate difference in time of arrival, and to generate a second difference-indicating signal representing the difference in phase of said second modulating signals, whereby to more precisely indicate the difference in time of arrival plus any integral multiple of the duration of one cycle of the second modulating signal; and

said generating means comprises means to generate a signal which defines the location of a point which is located a different distance from the two stations of each pair, wherein each difference distance is approximately equal to the time difference indicated by the first difference-indicating signal multiplied by the speed of light, and is more precisely equal to the time difference indicated by the second difference-indicating signal plus an integral multiple of the duration of one cycle of the second modulating signal.

5. A method for locating a target that emits radio waves, comprising:

detecting the same emitted radio waves originating from the target, at a first pair of stations that are spaced apart and located at known geographic positions;

measuring the difference in time of arrival of said waves at said first pair of stations;

detecting the same emitted radio waves originating from said source, at a second pair of stations that are spaced apart and located at known geographic positions;

measuring the difference in time of arrival of said waves at said second pair of stations;

detecting the same emitted radio waves orginating from the target at a third pair of stations that are positioned at widely space altitudes;

measuring the difference in time of arrival of said waves at said third pair of stations;

calculating the geographic location and altitude of a point which is located a different distance from the two stations of each pair wherein each difference distance is equal to the time difference in wave arrival times the speed of light; and

wherein

said steps of detecting each comprise detecting a train of wideband noise-like signals at each station of the pair, and cross correlating the signals detected by each pair of stations to determine the amount of delay of one train of noise signals relative to the other, at which the trains are matched.

6. A surveillance system comprising:

at least four radio receiving stations spaced apart, to form at least three pairs of stations with each pair including two spaced stations, each station including a receiver for detecting radio waves;

means for comparing the phase of wideband noise-like radio waves received at each pair of signals, for generating a signal representing the difference in time of arrival of the same transmitted radio waves at the two stations of a pair; and

means for generating a signal defining the location of the intersection of at least two hyperbolas, wherein the points along each hyperbola are positioned so they are spaced differently from the two stations of a pair by a distance equal to the difference in time of arrival of the same transmitted radio waves at the two stations of a pair times the speed of light;

at least one of said stations being at a significantly different altitude than a plurality of other stations; and

said signal generating means generating a signal defining the location in three dimensions of the intersection of three hyperboloids of revolution.

7. A method for locating each of a group of vehicles, comprising:

emitting radio signals from each of a plurality of vehicles;

detecting the same emitted radio waves originating from a vehicle, at a first pair of stations that are spaced apart and located at known geographic positions;

measuring the difference in time of arrival of said waves at said first pair of stations;

detecting the same emitted radio waves orginating from said vehicle, at a second pair of stations that are spaced apart and located at known geographic positions;

measuring the difference in time of arrival of said waves at said second pair of stations; and

calculating the geographic location of a point which is located a different distance from the two stations of each pair wherein each difference distance is equal to the time difference in wave arrival times the speed of light; and

wherein

said steps of detecting each comprise detecting a train of wideband noise-like signals at each station of the pair, and cross correlating the signals detected by each pair of stations to determine the amount of delay of one train of noise signals relative to the other, at which the trains are matched; and

said step of emitting includes repeatedly emitting a train of pulses from each of said vehicles wherein each train of pulses from a vehicle defines a number uniquely identifying said vehicle, and wherein each train of pulses has a duration of a small fraction of a second, and successive trains of pulses from each vehicle are spaced apart by a different time period each at least one hundred times longer than the train of pulses from the aircraft, so that systematic interference between pairs of aircraft do not occur.

8. A surveillance system comprising:

a radio transmitter which is constructed to repeatedly generate a train of pulses, with each pulse containing nearly white noise within a limited bandwidth, each train of pulses lasting a fraction of a second, and the train being repeated at intervals spaced apart by a period at least one hundred times longer than the duration of the train;

at least three radio receiving stations spaced apart, to form at least two pairs of stations with each pair including two spaced stations, each station including a receiver for detecting radio waves from said transmitter;

means for comparing the phase of wideband noise-like radio waves received at each pair of signals, for generating a signal representing the difference in time of arrival of the same transmitted radio waves at the two stations of a pair; and

means for generating a signal defining the location of the intersection of at least two hyperbolas, wherein the points along each hyperbola are positioned so they are spaced differently from the two stations of a pair by a distance equal to the difference in time of arrival of the same transmitted radio waves at the two stations of a pair times the speed of light.