Return pulse shape analysis for falling edge object discrimination of aerosol LIDAR
View Patent ↗A LIDAR optical remote sensing system and method analyzes the falling edge profile of a return LIDAR signal that may be indicative of an object or an aerosol cloud, which is generally more diffuse. Using the falling edge profile permits burnthrough to an object that may be obscured by the aerosol cloud. The profile is compared against at least one threshold that may correspond, in various embodiments, to a negative slope of the falling edge, an integrated power under the falling edge, or a range estimate error for varying transmitted power values, varying transmitted pulse lengths and/or varying receiver detector field of view values.
1. A remote sensing system for obtaining range information about an object in a predetermined direction, the system comprising:
a pulsed signal source for emitting at least one pulsed signal;
a transceiver for directing the at least one pulsed signal in the predetermined direction and for receiving at least one return signal associated with the at least one pulsed signal from along the predetermined direction;
at least one detector, each for gathering the at least one return signal from the transceiver; and
a signal processor for:
correlating at least one falling edge of the at least one return signal gathered by each of the at least one detectors, with a falling edge of the at least one pulsed signal and determining therefrom a range from the system to a reflecting entity in the predetermined direction;
comparing a feature of one of the at least one falling edge of the at least one return signal against at least one threshold to characterize the reflecting entity as being from the object or from an obscuring aerosol cloud; and
discarding the range associated with the at least one falling edge of the at least one return signal if the reflecting entity is characterized as being from the aerosol cloud.
2. The remote sensing system according to claim 1 , wherein the range is determined by measuring a time difference between the at least one falling edge of the at least one return signal and the falling edge of the at least one pulsed signal.
3. The remote sensing system according to claim 1 , wherein the feature of the at least one falling edge of the at least one return signal comprises its negative slope.
4. The remote sensing system according to claim 1 , wherein the feature of the at least one falling edge of the at least one return signal comprises an integrated power thereunder.
5. The remote sensing system according to claim 1 , wherein the at least one threshold comprises a minimum threshold below which the feature is characteristic of a reflection from an aerosol cloud.
6. The remote sensing system according to claim 1 , wherein the at least one threshold comprises a maximum threshold above which the feature is characteristic of a reflection from the object.
7. The remote sensing system according to claim 1 , wherein the pulsed signal source is adapted to generate pairs of pulsed signals having different output peak power.
8. The remote sensing system according to claim 7 , wherein the feature of the at least one falling edge of the at least one return signal comprises a difference in the range determined from each pulsed signal in the pair and its corresponding at least one return signal.
9. The remote sensing system according to claim 1 , wherein the pulsed signal source is adapted to generate pairs of pulsed signals having different pulse length.
10. The remote sensing system according to claim 8 , wherein the feature of the at least one falling edge of the at least one return signal comprises a difference in the range determined from each pulsed signal in the pair and its corresponding at least one return signal.
11. The remote sensing system according to claim 1 , wherein a first one of the at least one detector has a narrower field of view than a second one of the at least one detector.
12. The remote sensing system according to claim 11 , wherein the feature of the at least one falling edge comprises a difference in the range determined from the at least one return signal gathered by each of the at least one detectors and its corresponding pulsed signal.
13. The remote sensing system according to claim 1 , wherein the at least one threshold comprises a maximum threshold above which the feature is characteristic of a reflection from an aerosol cloud.
14. The remote sensing system according to claim 1 , wherein the at least one threshold comprises a minimum threshold below which the feature is characteristic of a reflection from the object.
15. The remote sensing system according to claim 1 , wherein the range information comprises the range to the object.
16. The remote sensing system according to claim 1 , wherein if no object is identified, the range information comprises the absence of an object for a predetermined distance in the predetermined direction from the system.
17. The remote sensing system according to claim 1 , wherein the at least one pulsed signal is a LIDAR signal.
18. A method for obtaining range information about an object in a predetermined direction, the method comprising steps of:
emitting at least one pulsed signal in the predetermined direction;
receiving at least one return signal associated with the at least one pulsed signal from along the predetermined direction;
gathering the at least one return signal at at least one detector;
correlating at least one falling edge of the at least one return signal gathered by each of the at least one detectors, with a falling edge of the at least one pulsed signal and determining therefrom a range from the system to a reflecting entity in the predetermined direction;
comparing a feature of one of the at least one falling edge of the at least one return signal against at least one threshold to characterize the reflecting entity as being from the object or from an obscuring aerosol cloud;
discarding the range associated with the at least one falling edge of the at least one return signal if the reflecting entity is characterized as being from the aerosol cloud; and
returning either the range associated with the object or the absence of an object for a predetermined distance in the predetermined direction.
19. The method according to claim 18 , wherein step of correlating comprises measuring a time difference between the at least one falling edge of the at least one return signal and the falling edge of the at least one pulsed signal.
20. The method according to claim 18 , wherein the feature of the at least one falling edge of the at least one return signal comprises its negative slope.
21. The method according to claim 18 , wherein the feature of the at least one falling edge of the at least one return signal comprises an integrated power thereunder.
22. The method according to claim 18 , wherein the at least one threshold comprises a minimum threshold below which the feature is characteristic of a reflection from an aerosol cloud.
23. The method according to claim 18 , wherein the at least one threshold comprises a maximum threshold above which the feature is characteristic of a reflection from the object.
24. The method according to claim 18 , wherein the step of emitting comprises emitting pairs of pulsed signals having different output peak power.
25. The method according to claim 24 , wherein the feature of the at least one falling edge of the at least one return signal comprises a difference in the range determined from each pulsed signal in the pair and its corresponding at least one return signal.
26. The method according to claim 18 , wherein the step of emitting comprises emitting pairs of pulsed signals having different pulse length.
27. The method according to claim 26 , wherein the feature of the at least one falling edge of the at least one return signal comprises a difference in the range determined from each pulsed signal in the pair and its corresponding at least one return signal.
28. The method according to claim 18 , wherein a first one of the at least one detector has a narrower field of view than a second one of the at least one detector.
29. The method according to claim 28 , wherein the feature of the at least one falling edge of the at least one return signal comprises a difference in the range determined from the at least one return signal gathered by each of the at least one detectors and its corresponding pulsed signal.
30. The method according to claim 18 , wherein the at least one threshold comprises a maximum threshold above which the feature is characteristic of a reflection from an aerosol cloud.
31. The method according to claim 18 , wherein the at least one threshold comprises a minimum threshold below which the feature is characteristic of a reflection from the object.
32. The method according to claim 18 , wherein the range information comprises the range to the object.
33. The method according to claim 18 , wherein if no object is identified, the range information comprises the absence of an object for a predetermined distance in the predetermined direction from the system.
34. The method according to claim 18 , wherein the at least one pulsed signal is a LIDAR signal.
35. A signal processor operatively coupled to a remote sensing system for obtaining range information about an object in a predetermined direction, comprising:
a correlator for determining, from a falling edge of at least one pulsed signal emitted in the predetermined direction and at least one falling edge of at least one return signal from a reflecting entity associated with the at least one pulsed signal gathered by at least one detector from along the predetermined direction, a range from the system to the reflecting entity in the predetermined direction; and
a comparator for comparing a feature of each of one of the at least one falling edge of the at least one return signal against at least one threshold to characterize the reflecting entity as being from the object or from an obscuring aerosol cloud, whereupon the range characterized as being from the aerosol cloud is discarded.
36. A non-transitory computer-readable medium in a processor operatively coupled to a remote sensing system for obtaining range information about an object in a predetermined direction, the medium having stored thereon, computer-readable and computer-executable instructions which, when executed by the processor, cause the processor to perform acts comprising:
determining, from a falling edge of at least one pulsed signal emitted in the predetermined direction and at least one falling edge of at least one return signal from a reflecting entity associated with the at least one pulsed signal gathered by at least one detector from along the predetermined direction, a range from the system to the reflecting entity in the predetermined direction;
comparing a feature of each of one of the at least one falling edge of the at least one return signal against at least one threshold to characterize the reflecting entity as being from the object or from an obscuring aerosol cloud; and
discarding the range if the reflecting entity is characterized as being from the aerosol cloud.