PASSIVE ELECTRO-OPTICAL TRACKER

• US 20110261193A1
• Filed: 05/24/2010
• Published: 10/27/2011
• Est. Priority Date: 02/25/2009
• Status: Active Grant

• Current Assignee: Light Prescriptions Innovators, LLC
• Original Assignee: Light Prescriptions Innovators, LLC
• Inventors: Falicoff, Waqidi, Agurok, Ilya
• Granted Patent: US 8,280,113 B2
• Time in Patent Office: Days
• US Class Current: 348/135
• CPC Class Codes: F41H 13/00 Means of attack or defence not otherwise provided for details of radar or sonar systems G01S7/00
• CPC Class Codes: G01J 2005/0077 Imaging
• CPC Class Codes: G01J 5/60 using determination of colour temperature
• CPC Class Codes: G01P 5/10 by measuring thermal variables
• CPC Class Codes: G01S 11/12 using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 5/16 using electromagnetic waves other than radio waves
• CPC Class Codes: G06T 2207/10048 Infrared image
• CPC Class Codes: G06T 2207/30212 Military
• CPC Class Codes: G06T 2207/30241 Trajectory
• CPC Class Codes: G06T 7/20 Analysis of motion motion estimation for coding, decoding, compressing or decompressing digital video signals H04N19/43, H04N19/51
• CPC Class Codes: G06V 10/62 relating to a temporal dimension, e.g. time-based feature extraction; Pattern tracking

Abstract

A passive electro-optical tracker uses a two-band IR intensity ratio to discriminate high-speed projectiles and obtain a time-varying speed estimate from their time-varying temperature, as well as determining the trajectory back to the source of fire. In an omnidirectional system a hemispheric imager with an MWIR spectrum splitter forms two CCD images of the environment. Various methods are given to determine the azimuth and range of a projectile, both for clear atmospheric conditions and for nonhomogeneous atmospheric conditions. One approach uses the relative intensity of the image of the projectile on the pixels of a CCD camera to determine the azimuthal angle of trajectory with respect to the ground, and its range. A second uses a least squares optimization over multiple frames based on a triangle representation of the smeared image to yield a real-time trajectory estimate.

Claims

1. A projectile tracking device comprising:

detector apparatus for converting into electronic form images in at least two infrared wavebands;

optics for projecting onto the detector apparatus an image of a scene in the at least two infrared wavebands;

logic operative to obtain from the images in electronic form apparent brightnesses of the projectile at the optics in at least two infrared wavebands;

logic operative to estimate the speed of the projectile varying over time from the varying ratio at successive times of the measured apparent brightnesses in said at least two infrared wavebands;

logic operative to obtain from the images in electronic form an azimuth of the projectile from the optics at successive times; and

logic operative to estimate the direction of the trajectory of the projectile from the measured azimuths in combination with the ratio between the measured apparent brightnesses.

2. The tracking device of claim 1, wherein the logic operative to estimate the direction of the trajectory of the projectile further comprises logic operative to estimate relative changes over time in the distance from the optics to the projectile from changes in at least one of the apparent brightnesses over time, including logic operative to correct the at least one measured apparent brightness for the change in absolute brightness as a function of temperature as a function of the estimated varying speed of the projectile.

3. The tracking device of claim 2, wherein the logic is further operative to estimate parameters of the projectile trajectory using a method comprising measuring the azimuth of the projectile from the optics at successive times, and estimating the direction of the trajectory of the projectile from the measured azimuths in combination with the ratios between the corrected measured apparent brightnesses.

4. The tracking device of claim 3, wherein the logic is further operative to estimate parameters of the projectile trajectory using at least a method comprising measuring the direction of the projectile from the optics at successive times, and estimating the trajectory of the projectile from the measured directions in combination with the time-varying estimated speed;

and

wherein the logic is operative to choose based on atmospheric conditions between projectile trajectory parameters calculated with at least said two methods of estimating parameters.

5. The projectile tracking device of claim 1, wherein the logic is operative to relate acceleration to speed using a lumped coefficient μ

=−

V′

/V², where μ

is calculated from time dependent projectile velocity data and lumps together parameters that at least initially are not individually known.

6. The tracking device of claim 1, wherein the logic is further operative to estimate parameters of the projectile trajectory using a method comprising measuring the azimuth of the projectile from the optics at more than two successive times, estimating the distances traveled by the projectile between the successive times using the speeds estimated at successive times, and estimating the direction of the trajectory of the projectile as a best fit to the successive distances and azimuths.

7. The tracking device of claim 6, wherein the logic is operative to estimate the best fit by defining imaginary triangles, each triangle formed by radii from the optics to the projectile at two of the successive times, and a segment of trajectory of length calculated using the estimated speed or speeds of the projectile between the said two successive times bounding each triangle.

8. The tracking device of claim 7, wherein the logic is further operative to estimate parameters of the projectile trajectory using a method further comprising measuring the direction of the projectile from the optics at successive times, and estimating the trajectory of the projectile from the measured directions in combination with a sum or integral of the estimated speeds;

and to provide a final estimate using a comparison of estimates from at least two said methods of estimating parameters.

9. The tracking device of claim 1, wherein the detector apparatus images the scene at regular intervals of time, and the successive azimuths and speeds are derived from successive images.

10. The tracking device of claim 1, further comprising logic operative to extrapolate the speed and trajectory of the projectile backwards in time to calculate a starting point at which the projectile would have had a speed corresponding to an initial speed of a weapon consistent with observed characteristics of the projectile.

11. The tracking device of claim 1, wherein the operative logic comprises a general purpose computer suitably programmed to carry out the operations of the logic.

12. A nontransitory computer readable storage medium carrying a computer program that will cause a suitable general purpose computer to carry out a method comprising:

measuring apparent brightnesses of a projectile at an observing location in at least two infrared wavebands at successive times;

estimating the speed of the projectile as a function of time from the ratio of the apparent brightnesses measured in at least two infrared wavebands at successive times;

measuring an azimuth of the projectile from the observing location at successive times; and

estimating the direction of the trajectory of the projectile from the measured azimuths in combination with the ratios at different times between the measured apparent brightnesses.

13. A method of tracking a projectile in air, comprising:

measuring apparent brightnesses of the projectile at an observing location in at least two infrared wavebands at successive times;

estimating the speed of the projectile as a function of time from the ratio of the apparent brightnesses measured in the at least two infrared wavebands at successive times;

measuring an azimuth of the projectile from the observing location at successive times; and

estimating the direction of the trajectory of the projectile from the measured azimuths in combination with the ratios between the measured apparent brightnesses.

14. The method of claim 13, further comprising estimating relative changes in the distance from the optics to the projectile over time from changes in at least one of the apparent brightnesses over time, and correcting the measured apparent brightnesses for the change in absolute brightness as a function of temperature as a function of the estimated varying speed of the projectile.

15. The method of claim 13, further comprising combining the estimated projectile speeds with the estimated projectile trajectory direction for calculating distances from the sensor to the projectile.

16. The method of claim 13, comprising estimating parameters of the projectile trajectory using a method comprising measuring the azimuth of the projectile from the optics at more than two successive times, estimating the distances traveled by the projectile between the successive times using the speeds estimated at successive times, and estimating the direction of the trajectory of the projectile as a best fit to the successive distances and azimuths.

17. The method of claim 13, wherein estimating the best fit comprises defining imaginary triangles, each triangle formed by radii from the optics at two of the successive times, and a segment of trajectory of length calculated using the estimated speed or speeds of the projectile between the said two successive times.

18. The method of claim 13, comprising calculating projectile trajectory parameters by a method comprising measuring the azimuth of the projectile from the observing location at successive times, and estimating the direction of the trajectory of the projectile from the measured azimuths in combination with the ratios between the corrected measured apparent brightnesses.

19. The method of claim 18, further comprising calculating projectile trajectory parameters by at least a method further comprising measuring the direction of the projectile from the observing location at successive times, and estimating the trajectory of the projectile from the measured directions in combination with the estimated speed;

and

choosing based on atmospheric conditions between projectile trajectory parameters calculated with at least two methods of calculating projectile trajectory parameters.

20. The method of claim 13, further comprising extrapolating the speed and trajectory of the projectile backwards in time to calculate a starting point at which the projectile would have had a speed corresponding to an initial speed of a weapon consistent with observed characteristics of the projectile.