Surface rf emitter passive ranging accuracy confirmation algorithm

• US 20090310664A1
• Filed: 10/13/2006
• Published: 12/17/2009
• Est. Priority Date: 10/13/2005
• Status: Active Grant

• Current Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Original Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Inventors: Yannone, Ronald M.
• Granted Patent: US 7,764,217 B2
• Time in Patent Office: Days
• US Class Current: 375/228
• CPC Class Codes: G01S 11/04 using angle measurements
• CPC Class Codes: G01S 5/0294 Trajectory determination or predictive filtering, e.g. target tracking or Kalman filtering
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders

Abstract

Kalman gain is used to calculate range accuracy for a passive angle-of-arrival determining systems, most notably for short-baseline interferometry, in which Kalman gain after arriving at a minimum proceeds to within a predetermined fraction or percent of zero gain, at which time the range estimate accuracy is known.

Claims

1. In a system for passively determining range to an emitter in which angle-of-arrival measurements are made along a baseline and in which a Kalman filter is used in a range-determining element to smooth the range estimates output therefrom, a method for determining the reliability of the range estimates, comprising the steps of:

computing the Kalman gain for the Kalman filter in the range-determining element;

ascertaining when over time a minimum occurs in the Kalman gain; and

,

detecting when after the minimum the Kalman gain is within a predetermined distance of zero, thus to establish that the range estimate at the time that the Kalman gain settles to within the predetermined distance is reliable.

2. The system of claim 1, wherein Kalman gain is determined in two orthogonal directions and wherein the Kalman gain having the deepest minimum is selected for determining when, after a minimum has been detected, the selected Kalman gain is within the predetermined distance.

3. The system of claim 1, wherein the predetermine distance is a fraction of the absolute value of the minimum.

4. The system of claim 3, wherein the fraction is between 1/12^th and 1/16^th.

5. The system of claim 1, wherein the predetermined distance is set so as to assure that the percent range error is 10% at the time that the Kalman gain settles.

6. The system of claim 1, wherein the Kalman gain has both a minima and a maxima and wherein the time at which the predetermined distance is measured occurs after the time of the occurrence of the maxima.

7. A method for eliminating the uncertainty associated with measuring the reliability of a range estimate using sigma range derived from the co-variance matrix of a Kalman filter used in a passive ranging system, comprising the step of:

ignoring the sigma range in favor of determining the reliability of the range estimate from a range-determining element employing the Kalman filter by detecting when the Kalman gain settles out after having first exhibited a minimum.

8. The method of claim 7, wherein the percent range error from the range-determining element is determined to be reliable when the Kalman gain settles out to within a predetermined fraction of the absolute value of the minimum.

9. The method of claim 8, wherein the Kalman gain settles out when the Kalman gain is between 1/12^th and 1/16^th of the absolute value of the minimum.

10. The method of claim 8, wherein when the Kalman gain settles out the percent range error is reliable to within a predetermined percentage.

11. The method of claim 10, wherein the predetermined percentage is approximately 100%.

12. A system for ascertaining the reliability of range estimates available from a passive angle-of-arrival range estimation system in which the transverse bearing spread to an emitter is measured, comprising:

a receiver for receiving signals from said emitter;

at least a pair of spaced-apart collection points along a base leg coupled to said receiver;

a range-determining element including a Kalman filter and coupled to said receiver for calculating a range estimate based on the transverse bearing spread;

a processor for computing the Kalman filter gain, for determining a minimum in the Kalman filter gain, and for ascertaining when, after the Kalman filter gain achieves a minimum, the Kalman filter gain is near zero; and

,

generating a trigger to signify that the range estimate from said range-determining element is reliable.

13. The system of claim 12, wherein said trigger is generated when after a minimum the Kalman gain is within a predetermined percentage of zero.

14. The system of claim 12, wherein said processor computes Kalman gain in orthogonal directions, said processor determining which of the gains associated with the orthogonal directions is deeper and selecting the gain associated with the deeper minimum as a gain on which to generate said trigger.

15. The system of claim 12, wherein said processor for computing Kalman gain and determining a minimum detects when the Kalman gain achieves a maximum after having achieved a minimum, and further generates said trigger when said Kalman gain approaches zero after said maximum.

16. The system of claim 15, wherein said processor includes an algorithm for ascertaining the existence and time of occurrence of a maximum after a minimum, and inhibits the generation of said trigger until a time after the time associated with the occurrence of said maximum.

17. The system of claim 16, wherein said processor computes Kalman gain in orthogonal directions and determines the deeper minimum of the gains associated with the orthogonal directions;

and wherein said trigger generation is dependent upon only gain in the direction which establishes the deeper minimum.