Method and system for N-track correlation

• US 5,491,645 A
• Filed: 10/13/1993
• Issued: 02/13/1996
• Est. Priority Date: 10/13/1993
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: International Business Machines Corporation
• Inventors: Kennedy, Eugene T., Hansen, Neils H.
• Primary Examiner(s): Ramirez, Ellis B.
• Assistant Examiner(s): ASSOUAD, PATRICK J
• Application Number:
  US08/136,177
• Time in Patent Office: 853 Days
• Field of Search: 364/516, 364/443, 364/447, 364/456, 235/411, 342/76, 342/95, 342/357
• US Class Current: 701/215
• CPC Class Codes: G01S 13/72 for two-dimensional tracking, e.g. combination of angle and range tracking, track-while-scan radar
• CPC Class Codes: G01S 13/726 Multiple target tracking
• CPC Class Codes: G01S 13/87 Combinations of radar systems, e.g. primary radar and secondary radar
• CPC Class Codes: G01S 13/91 for traffic control G01S13/93 takes precedence

Abstract

A computer system and method for accurately transforming multiple returns received by multiple satellites from multiple targets into a set of single accurate tracks for each target. Observations from multiple satellites create partial or resulting tracks. These resulting tracks are then correlated with pre-existing base tracks by a series of steps in which resulting tracks are paired with pre-determined base tracks according to a series of criteria. Pairs based on: common observation points and time spans, common satellites, and lack of common satellite, are considered sequentially. The final attempt at correlation consists of pairing each remaining track with each base track and using profile dependent piece correlation of the pairs. Any remaining resulting tracks are then added to the set of base tracks.

Claims

1. In a tracking system, comprised of a plurality of satellite tracking stations orbiting above the surface of the earth, operatively connected to a data processing system, a computer method for tracking a plurality of targets, comprising the steps of:

receiving a first plurality of returns from said plurality of satellite tracking stations and using said first plurality of returns to create a plurality of base tracks, each return of said first plurality of returns having an associated time, and each of said base tracks having an associated set of returns;

receiving a second plurality of returns from said plurality of satellite tracking stations and using said second plurality of returns to create a first plurality of resulting tracks, each return of said second plurality of returns having an associated time, and each of said resulting tracks having an associated set of returns;

creating a set of first pairs, each of said first pairs comprised of a first resulting track selected from said first plurality of resulting tracks and an associated first base track selected from said plurality of base tracks, where said first resulting track and said associated first base track have at least one common return;

correlating each of said first resulting tracks with said associated first base track;

removing said correlated first resulting tracks from said first plurality of resulting tracks creating a second plurality of resulting tracks;

creating a set of second pairs, each of said second pairs comprised of a second resulting track selected from said second plurality of resulting tracks and an associated second base track selected from said plurality of base tracks, where said second resulting track and said associated second base track have at least one satellite in common;

for each second pair, calculating an associated time gap where said gap measures the maximum length of time between the time associated with a return from said second resulting track and said time associated with a return from said second base track;

removing from said set of second pair second each second pairs having an associated time gap greater than a first specified value, creating a remaining set of second pairs;

calculating a goodness-of-fit score for each pair in said remaining set of second pairs;

removing from said set of second pairs each second pair having a goodness-of-fit score greater than a second specified value;

correlating each of said second resulting tracks remaining in said set of second pairs with said associated second base track;

removing said correlated second resulting tracks from said second plurality of resulting tracks creating a third plurality of resulting tracks;

creating a set of third pairs, each of said third pairs comprised of a third resulting track selected from said third plurality of resulting tracks and an associated third base track selected from said plurality of base tracks, where said third resulting track and said associated third base track have no satellite in common;

calculating a goodness-of-fit score for each pair in said set of third pairs;

removing from said set of third pairs each third pair having a goodness-of-fit score greater than a third specified value;

correlating each of said third resulting tracks remaining in said set of third pairs with said associated third base track;

removing said correlated third resulting tracks from said third plurality of resulting tracks creating a fourth plurality of resulting tracks;

creating a set of fourth pairs, each of said fourth pairs comprised of a fourth resulting track and a fourth base track, said fourth pairs created by pairing each of said fourth plurality of resulting tracks with each of said plurality of base tracks;

using profile dependent piece correlation to correlate said fourth resulting track with said fourth base track and calculating a goodness-of-fit score for each of said fourth pairs;

if said goodness-of-fit score for a fourth pair is greater than a fourth specified value, including said fourth resulting in said plurality of base tracks.

2. A method as in claim 1 wherein said first set of pairs is further comprised of a three-return set of pairs and a two-return set of pairs, wherein:

said first track of said three return set of pairs and said second track of said three return set of pairs have at least three common returns and at least four scans in common; and

said first track of said two-return set of pairs and said second track of said two-return set of pairs have two common returns and three scans in common.

3. A method as in claim 1 which further includes:

removing said returns associated with said correlated first resulting tracks from said returns associated with each of said resulting tracks in said first plurality of resulting tracks;

removing said returns associated with said correlated second resulting tracks from said returns associated with each of said resulting tracks in said second plurality of resulting tracks; and

removing said returns associated with said correlated third resulting tracks from said returns associated with each of said resulting tracks in said third plurality of resulting tracks.

4. A method as in claim 1 wherein calculating a goodness-of-fit score for each pair in said set of third pairs further includes the steps of:

selecting a third resulting track;

selecting a return satellite tracking station from said plurality of satellite tracking stations for said selected third resulting track;

selecting a base satellite tracking station from said plurality of satellite tracking stations for said associated third base track of said selected third resulting track;

selecting three returns from said selected third resulting track and three returns from said associated third base track of said selected third resulting track;

calculating a coplanarity residual for each of said three returns from said selected third resulting track and three returns from said associated third base track of said selected third resulting track;

calculating an estimate of a three dimensional position vector for each of said three returns from said selected third resulting track and three returns from said associated third base track of said selected third resulting track;

calculating an estimate of velocity of said selected third resulting track and said associated third base track of said selected third resulting track;

using said estimate of said three dimensional position vector for each of said three returns from said selected third resulting track and three returns from said associated third base track of said selected third resulting track and said estimate of velocity of said selected third resulting track and said associated third base track of said selected third resulting track, to calculate a goodness-of-fit between said selected third resulting track and said associated third base track of said selected third resulting track.

5. A tracking system, comprised of plurality of satellite tracking stations orbiting above the surface of the earth, operatively connected to a data processing system, said system comprised of:

means for receiving a first plurality of returns from said plurality of satellite tracking stations and using said first plurality of returns to create a plurality of initial base tracks, each return of said first plurality of returns having an associated time;

means for receiving a second plurality of returns from said plurality of satellite tracking stations and using said second plurality of returns to create a first plurality of resulting tracks, each return of said second plurality of returns having an associated time;

means for creating a set of first pairs, each of said first pairs comprised of a first resulting track selected from said first plurality of resulting tracks and an associated first base track selected from said plurality of base tracks, where said first resulting track and said associated first base track have at least one common return;

means for correlating each of said first resulting tracks with said associated first base track;

means for removing said correlated first resulting tracks from said first plurality of resulting tracks and for creating a second plurality of resulting tracks;

means for creating a set of second pairs, each of said second pairs comprised of a second resulting track selected from said second plurality of resulting tracks and an associated second base track selected from said plurality of base tracks, where said second resulting track and said associated second base track have at least one satellite in common;

means for calculating, for each second pair, an associated time gap where said gap measures the maximum length of time between the time associated with a return from said second resulting track and said time associated with a return from said second base track;

means for removing from said set of second pair each second pairs having an associated time gap greater than a first specified value, creating a remaining set of second pairs;

means for calculating a goodness-of-fit score for each pair in said remaining set of second pairs;

means for removing from said second pairs each second pair having a goodness-of-fit score greater than a second specified value;

means for correlating each of said second resulting tracks remaining in said set of second pairs with said associated second base track;

means for removing said correlated second resulting tracks from said second plurality of resulting tracks creating a third plurality of resulting tracks;

means for creating a set of third pairs, each of said third pairs comprised of a third resulting track selected from said third plurality of resulting tracks and an associated third base track selected from said plurality of base tracks, where said third resulting track and said associated third base track have no satellite in common;

means for calculating a goodness-of-fit score for each pair in said set of third pairs;

means for removing from said set of third pairs each third pair having a goodness-of-fit score greater than a third specified value;

means for correlating each of said third resulting tracks remaining in said set of third pairs with said associated third base track;

means for removing said correlated third resulting tracks from said third plurality of resulting tracks creating a fourth plurality of resulting tracks;

means for creating a set of fourth pairs, each of said fourth pairs comprised of a fourth resulting track and a fourth base track, said fourth pairs created by pairing each of said fourth plurality of resulting tracks with each of said plurality of base tracks;

means for using profile dependent piece correlation to correlate said fourth resulting track with said fourth base track and calculating a goodness-of-fit score for each of said fourth pairs;

means for including said fourth resulting in said plurality of base tracks, if said goodness-of-fit score for a fourth pair is greater than a fourth specified value;

display means for displaying updated base tracks, said updated base tracks comprised of said plurality of base tracks as correlated with said first resulting tracks, said second resulting tracks, said third resulting tracks and said fourth resulting tracks.

6. A system as in claim 5 wherein said first set of pairs is further comprised of a three-return set of pairs and a two-return set of pairs, wherein:

said first track of said three return set of pairs and said second track of said three return set of pairs have at least three common returns and at least four scans in common; and

said first track of said two-return set of pairs and said second track of said two-return set of pairs have two common returns and three scans in common.

7. A system as in claim 5 which further includes:

means for removing said returns associated with said correlated first resulting tracks with said returns associated from said each of said resulting tracks in said first plurality of resulting tracks;

means for removing said returns associated with said correlated second resulting tracks with said returns associated from said each of said resulting tracks in said second plurality of resulting tracks; and

means for removing said returns associated with said correlated third resulting tracks with said returns associated from each of said resulting tracks in said third plurality of resulting tracks.

8. A system as in claim 5 wherein said means for calculating a goodness-of-fit score for each pair in said set of third pairs further includes:

means for selecting a third resulting track;

means for selecting a return satellite tracking station from said plurality of satellite tracking stations for said selected third resulting track;

means for selecting a base satellite tracking station from said plurality of satellite tracking stations for said associated third base track of said selected third resulting track;

means for selecting three returns from said selected third resulting track and three returns from said associated third base track of said selected third resulting track;

means for calculating a coplanarity residual for each of said three returns from said selected third resulting track and three returns from said associated third base track of said selected third resulting track;

means for calculating an estimate of a three dimensional position vector for each of said three returns from said selected third resulting track and three returns from said associated third base track of said selected third resulting track;

means for calculating an estimate of velocity of said selected third resulting track and said associated third base track of said selected third resulting track; and

means for using said estimate of said three dimensional position vector for each of said three returns from said selected third resulting track and three returns from said associated third base track of said selected third resulting track and said estimate of velocity of said selected third resulting track and said associated third base track of said selected third resulting track, to calculate a goodness-of-fit between said selected third resulting track and said associated third base track of said selected third resulting track.