System and method for time-to-intercept determination

• US 6,487,519 B1
• Filed: 01/19/2000
• Issued: 11/26/2002
• Est. Priority Date: 01/19/2000
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Wellman, William H., OʼNeill, Mary D.
• Primary Examiner(s): Shah, Kamini
• Assistant Examiner(s): PRETLOW, DEMETRIUS R
• Application Number:
  US09/487,575
• Time in Patent Office: 1,042 Days
• Field of Search: 702/182, 702/176, 702/40, 702/49, 702/127, 702/143, 342/19, 342/62, 342/17, 342/119, 342/203, 342/159, 244/3.15, 244/3.19
• US Class Current: 702/176
• CPC Class Codes: F42C 13/02 operated by intensity of light or similar radiation
• CPC Class Codes: G01S 11/12 using electromagnetic waves other than radio waves

Abstract

A method and system of time-to-intercept determination for a radiation source using passively-sensed irradiance data. The invention provides a plurality of noise reduction features to reduce the noise present in the data and improve the accuracy of the time-to-intercept computation. The method includes reducing data noise by defining an acceptable noise level and eliminating any excessively noisy data from the time-to-intercept computation. The method further includes constantly updating the time-to-intercept computation by using irradiance values that are advanced in time. Other features of the present invention includes averaging of irradiance values over a time interval, filtering of the irradiance data received by the method, and triggering at a predetermined time-to-intercept. The invention also includes a time-to-intercept system and processor implementing the above method.

Claims

1. A method of determining a time-to-intercept for a radiation source using irradiance values of the radiation source, the method comprising:

computing the time-to-intercept using at least three irradiance values; and

reducing noise in the time-to-intercept computation by using a continuously-updated calculation, based upon recent values, and upon initial values;

where, performing the calculation comprises determining a signal-to-noise ratio (SNR) value of each irradiance value and rejecting from the calculation an irradiance value having a SNR value that is less than a threshold SNR value.

2. The invention as set forth in claim 1, wherein each irradiance value is a respective detected irradiance value of the radiation source.

3. The invention as set forth in claim 1, wherein the threshold signal-to-noise ratio value can be 27 decibels.

4. The invention as set forth in claim 1, further comprising:

filtering of each irradiance value to reduce noise in the irradiance values.

5. The invention as set forth in claim 4, wherein:

filtering of the irradiance values is continuous; and

each irradiance value is a respective detected irradiance value of the radiation source.

6. The invention as set forth in claim 1, further comprising:

determining whether a time interval between irradiance values is greater than a minimum time interval;

computing an average irradiance value over the time interval if the time interval is greater than the minimum time interval.

7. The invention as set forth in claim 1, wherein calculating the time-to-intercept further comprises:

using an equation relating the irradiance values to the time-to-intercept.

8. The invention as set forth in claim 7, wherein the equation uses signal strength normalization.

9. The invention as set forth in claim 8, wherein:

signal strength normalization includes having a ratio of the irradiance values;

each irradiance value is a respective radiation intensity value of the radiation source.

10. The invention as set forth in claim 7, wherein the equation is derived using a constant acceleration assumption.

11. The invention as set forth in claim 7, wherein the equation is derived using a constant velocity assumption.

12. The invention as set forth in claim 1, wherein computing the time-to-intercept further comprises:

computing a first time-to-intercept value using first and second irradiance values; and

updating the time-to-intercept by computing a second time-to-intercept value using a third irradiance value taken later in time than the first and the second irradiance values.

13. The invention as set forth in claim 12, further comprising:

repeating the time-to-intercept updating with subsequent irradiance values that are later in time until a predetermined time-to-intercept value is reached.

14. A method for determining a time-to-intercept for a radiation source, comprising:

providing irradiance data relating to the radiating source;

minimizing noise associated with the irradiance data so as to provide usable irradiance data;

computing the time-to-intercept using the usable irradiance data; and

updating the time-to-intercept computation using updated usable irradiance data derived from the updated irradiance data;

where, minimizing noise comprises determining a signal-to-noise ratio (SNR) value of each irradiance value and declaring an irradiance value to be a usable irradiance value if the SNR value is greater than a threshold SNR value.

15. The invention as set forth in claim 14, wherein irradiance data includes a detected irradiance of the radiation source.

16. The invention as set forth in claim 14, wherein irradiance data is provided as one of:

(a) a continuous data stream;

or (b) a periodically sampled data set;

or (c) an aperiodically sampled data set.

17. The invention as set forth in claim 14, wherein computing the time-to-intercept further comprises using an equation having signal strength normalization.

18. The invention as set forth in claim 17, wherein the equation assumes a constant acceleration.

19. The invention as set forth in claim 17, wherein the equation assumes a constant velocity.

20. The invention as set forth in claim 17, further comprising:

computing a time interval between successive usable irradiance data;

comparing the time interval to a minimum time interval; and

averaging the irradiance data over the time interval if the time interval is approximately less than the minimum time interval.

21. A system for determining a time-to-intercept of a radiation source, comprising:

a detection system detecting successive irradiance values of the radiation source;

a calculation module that calculates the time-to-intercept using the irradiance values output from said detection system; and

an update module that updates the time-to-intercept calculation using irradiance values that are advanced in time;

said detection system comprising a noise module for determining a signal-to-noise ratio (SNR) value of each detected successive irradiance value and for outputting to said calculation module only those irradiance values having a SNR value that is greater than a threshold SNR value.

22. The invention as set forth in claim 21, further comprising:

an averaging module that averages irradiance values over a time interval.

23. The invention as set forth in claim 22, wherein the irradiance value is a detected irradiance of the radiation source.

24. The invention as set forth in claim 22, wherein the calculation module uses an equation that assumes constant acceleration.

25. The invention as set forth in claim 22, wherein the calculation module uses an equation that assumes constant velocity.

26. A time-to-intercept processor for determining a time-to-intercept of a radiation source, comprising:

means for providing irradiance values of the radiance source successively in time;

means for reducing noise present in the irradiance values to produce usable irradiance values, said noise reducing means comprising means for determining a signal-to-noise ratio (SNR) value of each irradiance value and declaring an irradiance value to be a usable irradiance value if the SNR value is greater than a threshold SNR value; and

means for calculating the time-to-intercept using the usable irradiance values.

27. The invention as set forth in claim 26, further comprising:

means for averaging the us able irradiance values over a time interval if the time interval is less than a minimum time interval.

28. The invention as set forth in claim 26, further comprising:

an update module for updating the time-to-intercept calculation using irradiance values that are advanced in time.

29. The invention as set forth in claim 28, wherein the means for providing irradiance values is an input module that inputs irradiance values into the time-to-intercept processor.

30. The invention as set forth in claim 29, wherein the input module inputs irradiance values as at least one of:

(a) a continuous data stream;

(b) a periodically sampled data set;

(c) an aperiodically sampled data set.

31. The invention as set forth in claim 26, wherein the means for calculating comprises a calculation module that uses an equation relating the irradiance values to the time-to-intercept.

32. The invention as set forth in claim 31, wherein a constant acceleration is assumed.

33. The invention as set forth in claim 31, wherein a constant velocity is assumed.

34. The invention as set forth in claim 31, wherein the irradiance value is a radiation intensity of the radiation source.

35. A method for determining a time-to-intercept during a time-of-flight of a radiating source, comprising:

computing a plurality of irradiance values from measurements made from the radiating source, each computation of the irradiance value using a substantially constant value of acceleration a of the radiating source;

reducing noise in the irradiance values to provide usable irradiance values; and

computing the time-to-intercept based on usable irradiance values.

36. A method as in claim 35, where reducing noise comprises determining a signal-to-noise ratio (SNR) value of each irradiance value and declaring an irradiance value to be a usable irradiance value if the SNR value is greater than a threshold SNR value.

37. A method for determining a time-to-intercept during a time-of-flight of a radiating source, comprising:

computing, using a substantially constant value of acceleration a of the radiating source, a measured amplitude Z(t) of an irradiance value H(t) from a measurement made from the radiating source;

determining a ratio of the measured amplitude to a change in amplitude dZ(t)/dt; and

relating the determined ratio dZ(t)/dt to the time-to-intercept of the radiating source.

38. A method as in claim 37, where the step of computing includes determining a signal-to-noise ratio (SNR) value of each irradiance value and declaring an irradiance value to be a usable irradiance value if the SNR value is greater than a threshold SNR value.