Target tracking in clutter degraded scenes using central level stereo processing

• US 5,351,056 A
• Filed: 06/21/1993
• Issued: 09/27/1994
• Est. Priority Date: 06/21/1993
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: International Business Machines Corporation
• Inventors: Sawyer, Joseph C.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/080,800
• Time in Patent Office: 463 Days
• Field of Search: 342/59, 342/73, 342/95, 342/97, 342/126, 342/189, 342/195, 342/357, 342/463
• US Class Current: 342/195
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders

Abstract

A computer method is disclosed for extracting data on a target from a clutter degraded environment by using non-time-synchronized results from two sensors stations. The method, which is employed in satellite tracking systems, transforming multiple non-synchronous sensor returns comprised of angles from line of sight observations from passive sensors into target position coordinates. Observations from successive returns of each sensor are paired and a triangulation point is calculated. Successive triangulation points are used to determine points on the projected trajectory of the target. These calculated target position coordinates may then used to project the future path of the target.

Claims

1. In a target tracking system, including a first tracking station and a second tracking station, said first tracking station and said second tracking station operatively connected to a data processing system, a computer method for determining the track of a target comprising the steps of:

(a) receiving at said first tracking station a first return, said first return comprised of first angle measurement of the position of a target as observed from said first tracking station, said first return being received at a first point in time;

(b) receiving at said second tracking station a second return, said second return comprised of second angle measurement of the position of said target as observed from said second tracking station, said second return being received at a second point in time, said second point in time being later than said first point in time;

(c) receiving at said first tracking station a third return, said third return comprised of third angle measurement of the position of said target as observed from said first tracking station, said third return being received at a third point in time, said third point in time being later than said second point in time;

(d) receiving at said second tracking station a fourth return, said fourth return comprised of fourth angle measurement of the position of said target as observed from said second tracking station, said fourth return being received at a fourth point in time, said fourth point in time being later than said third point in time;

(e) calculating a first point by triangulating between said first return and said second return;

(f) calculating a second point by triangulating between said second return and said third return;

(g) calculating a third point by triangulating between said third return and said fourth return;

(h) associating said first point and said second point on the basis that said first point and said second point were each calculated using said second return;

(i) associating said second point and said third point on the basis that said second point and said third point were each calculated using said third return;

(j) determining a first vector whose end points are said first point and said second point;

(k) determining a second vector whose end points are said second point and said third point;

(l) determining a first track point, said first track point being the point on said first vector such that ratio between the distance from said first track point to said first point and the distance from said first track point to said second point is equal to a characteristic ratio; and

(m) determining a second track point, said second track point being the point on said second vector such that ratio between the distance from said second track point to said second point and the distance from said second track point to said third point is equal to said characteristic ratio.

2. A method as in claim 1 wherein said calculation by triangulation of said first point is comprised of the steps of:

(a) determining a first closest approach vector between said first return and said second return, said first closest approach vector comprised of the shortest vector connecting said first return to said second return; and

(b) using as said first point said first closest approach vector'"'"'s midpoint.

3. A method as in claim 1 wherein said characteristic ratio is the ratio of a first time interval and a second time interval, said first time interval comprised of the time difference between said first point in time and said second point in time, and said second time interval comprised of the time difference between said second point in time and said third point in time.

4. A method as in claim 1 wherein said first track point and said second track point are used to calculate a projected trajectory of said target.

5. A method as in claim 1 wherein said target'"'"'s velocity is calculated by dividing the distance between said first point and said second point by the difference between said first point in time and said second point in time.

6. A method as in claim 1 wherein a vertical bias between said first tracking station and said second tracking station is determined by comparing the ratio of the length of said first vector to the length of said second vector to said characteristic ratio.

7. A method as in claim 6 wherein if a clutter point if said determined vertical bias is not equal to a known vertical bias, then said first track point is identified as a clutter point.

8. A method as in claim 1 wherein said first and said second tracking stations comprise a first and second satellite in orbit around the Earth.

9. A target tracking system for determining a track of a target, said target tracking system including a first tracking station and a second tracking station, said first tracking station and said second tracking station operatively connected to a data processing system, said system comprising:

(a) means for receiving at said first tracking station, first-station-return-measurements, said first-station-return-measurements comprised of angle measurement of the position of a target as observed from said first tracking station, each of said first-station-return-measurements being received at an associated point in time, said collection of said associated points in time comprising a first set;

(b) means for receiving at said second tracking station, second-station-return-measurements, said second-station-return-measurements comprised of angle measurement of the position of a target as observed from said first tracking station, each of said second-station-return-measurements being received at an associated point in time which is

     1) different than any of said points in time of said first set and which

     2) lies, in time sequence, between two points in time of said first set;

(c) means for calculating a triangulation point from a first first-station-return-measurement and a first second-station-return-measurement, said first second-station-return-measurement having an associated point in time which immediately follows said associated point in time of said first first-station-return- measurement;

(d) means for calculating a vector between pairs of said triangulation points; and

(e) means for determining a track point on said vector, where the ratio of distance of said track point from a first end of said vector to the distance of said track point to a second end of said vector is a characteristic ratio.