Backscatter-type visibility detection

• US 5,663,710 A
• Filed: 07/18/1995
• Issued: 09/02/1997
• Est. Priority Date: 07/18/1995
• Status: Expired due to Fees

• Current Assignee: Jaycor, Inc. (Titan Corporation)
• Original Assignee: Jaycor, Inc. (Titan Corporation)
• Inventors: Fasig, James R., Lutjens, Steven W., Fasig, Harold A., Flanagan, Terry M., Vasel, Edward J., Coakley, Peter G., Mallon, Charles E., Denson, Raymond
• Primary Examiner(s): Swarthout, Brent A.
• Assistant Examiner(s): TRIEU, VAN THANH
• Application Number:
  US08/503,994
• Time in Patent Office: 777 Days
• Field of Search: 340/601, 340/602, 340/901, 340/904, 340/905, 340/968, 340/584, 340/583, 340/903, 73/170.16, 342/26, 342/53, 250/338.5, 250/341.8, 250/339.1, 250/338.1
• US Class Current: 340/601
• CPC Class Codes: B60Q 1/52 for indicating emergencies
• CPC Class Codes: G01N 21/538 for determining atmospheric attenuation and visibility
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 17/95 for meteorological use
• CPC Class Codes: G01S 2007/4975 of sensor obstruction by, e.g. dirt- or ice-coating, e.g. by reflection measurement on front-screen
• CPC Class Codes: G01S 2007/4977 including means to prevent or remove the obstruction
• CPC Class Codes: G01S 7/486 Receivers
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

An improved visibility detector and method emit infrared radiation away from an infrared emitter; detect an amount of infrared radiation backscattered by an airborne visibility impeding agent; and generate a backscatter signal in response to the amount detected. In one embodiment, the detector detects an amount of the infrared radiation that is not backscattered; generates a reference signal in response thereto; determines an actual amount of the infrared radiation backscattered; determines whether the actual amount exceeds a prescribed threshold; and generates an alarm signal in event the actual amount is determined to exceed the prescribed threshold. In other embodiments, the device employs a meniscus barrier between the emitter and the detector; another, lower, threshold in determining when to terminate the alarm signal; a second alarm signal to indicate that backscatter has increased above another, higher, threshold; a calibration scheme for calibrating the detector and/or a running average to avoid anomalous indications of low/high visibility.

Claims

1. A system for detecting an airborne visibility impeding agent comprising:

an infrared emitter positioned for emitting infrared radiation;

an infrared backscatter detector positioned to receive a first portion of the infrared radiation having been backscattered by the airborne visibility impeding agent, the infrared backscatter generating a backscatter signal in response to a detected amount of the first portion of infrared radiation;

an infrared reference detector positioned to receive a second portion of the infrared radiation not having been backscattered by the airborne visibility impeding agent, the infrared reference detector generating a reference signal in response to a detected amount of the second portion of infrared radiation; and

a visibility determination circuit coupled to the infrared emitter, the infrared backscatter detector and the infrared reference detector, for averaging the reference signal and the backscatter signal over time, for scaling the backscatter signal having been averaged using the reference signal having been averaged, for determining a determined amount of the infrared radiation backscattered by the airborne visibility impeding agent as a function of the backscatter signal having been averaged and scaled, for determining whether the determined amount exceeds a prescribed threshold, and for commencing generating of an alarm signal in event the determined amount is determined to exceed the prescribed threshold.

2. The system of claim 1 wherein said visibility determination circuit includes means for determining whether said determined amount is less than a lower threshold, and for terminating said generating of said alarm signal in the event said determined amount is determined to be less than the lower threshold.

3. A system for detecting an airborne visibility impeding agent comprising:

a housing having a surface;

an infrared emitter positioned in the surface, for emitting infrared radiation;

an infrared backscatter detector positioned in the surface to receive a portion of the infrared radiation having been backscattered by the airborne visibility impeding agent;

a meniscus barrier including a ridge, on the surface, interposed between the infrared emitter and the infrared backscatter detector, for preventing diffusion of the infrared radiation through a fluid meniscus on the surface between the infrared emitter and the infrared backscatter detector;

a visibility determination circuit coupled to the infrared emitter and the infrared backscatter detector, for determining an amount of the infrared radiation backscattered by the airborne visibility impeding agent, for determining whether the amount determined exceeds a prescribed threshold, and for generating an alarm signal in event the amount is determined to exceed the prescribed threshold.

4. The system of claim 3 wherein said visibility determination circuit includes means for determining said amount of said infrared radiation backscattered by said airborne visibility impeding agent by averaging said portion of the infrared radiation having been backscattered that is received over time.

5. The system of claim 4 wherein said visibility determination circuit includes means for determining whether said amount is less than a lower threshold, and for terminating said generating of said alarm signal in the event said amount is determined to be less than the lower threshold.

6. The system of claim 4 including:

an infrared reference detector positioned to receive another portion of said infrared radiation not having been backscattered by said airborne visibility impeding agent;

wherein said visibility determination circuit includes means for determining said amount of said infrared radiation backscattered by said airborne visibility impeding agent by averaging said other portion of the infrared radiation not having been backscattered that is received over time, and by scaling said portion of said infrared radiation having been backscattered, having been averaged over time, said means for determining said determined amount using said other portion of said infrared radiation not having been backscattered, having been averaged over time, in said scaling of said portion of said infrared radiation, having been backscattered, and having been averaged over time.

7. The system of claim 3 wherein said infrared emitter includes means for emitting infrared radiation having an intensity of at least 2 watts and a wavelength of 880 nm.

8. The system of claim 3 including:

a timing circuit coupled to said infrared emitter, and said infrared backscatter detector, for periodically activating said infrared emitter, and said infrared backscatter detector.

9. A method for detecting an airborne visibility impeding agent comprising:

emitting infrared radiation away from an infrared emitter;

detecting an amount of a first portion of the infrared radiation having been backscattered by the airborne visibility impeding agent;

generating a backscatter signal in response to the amount of the first portion detected;

detecting an amount of a second portion of the infrared radiation not having been backscattered by the airborne visibility impeding agent;

generating a reference signal in response to the amount of the second portion detected;

determining an actual amount of the infrared radiation backscattered by the airborne visibility impeding agent in response to the backscatter signal and the reference signal including averaging the backscatter signal over time, averaging the reference signal over time, and scaling the backscatter signal having been averaged using the reference signal having been averaged;

determining whether the actual amount exceeds a prescribed threshold; and

generating an alarm signal in event the actual amount is determined to exceed the prescribed threshold.

10. The method of claim 9 including:

determining whether said actual amount is less than a lower threshold; and

terminating said generating of said alarm signal in the event said actual amount is determined to be less than the lower threshold.

11. A method for detecting an airborne visibility impeding agent comprising:

calibrating including;

generating a recalibrate signal;

emitting, in response to the recalibrate signal, infrared radiation away from an infrared emitter;

detecting a baseline amount of the infrared radiation having been backscattered; and

generating a calibration signal in response to the baseline amount of the infrared radiation detected; and

then

determining a prescribed threshold as a function of the calibration signal; and

then

detecting reduced visibility including;

emitting infrared radiation away from the infrared emitter;

detecting a detected amount of the infrared radiation having been backscattered by the airborne visibility impeding agent;

generating a detection signal in response to the detected amount of the infrared radiation including averaging the reference amount over time;

detecting a reference amount of said infrared radiation not having been backscattered by said airborne visibility impeding agent;

generating a reference signal in response to the reference amount including averaging the reference amount over time;

determining a determined amount of the infrared radiation backscattered by the airborne visibility impeding agent by scaling the detection signal using the reference signal;

determining whether the determined amount exceeds the prescribed threshold; and

generating an alarm signal in event the determined amount is determined to exceed the prescribed threshold.

12. The method of claim 11 including:

detecting increased visibility including;

determining a lower threshold as a function of said calibration signal;

determining whether said detection signal is less than the lower threshold; and

terminating said generating of said alarm signal in the event said detection signal is determined to be less than the lower threshold.

13. The method of claim 11 including:

detecting a fault condition, including;

determining whether said reference amount is less than a reference threshold; and

generating a fault signal, indicating the fault condition, in event said reference amount is determined to be below the reference threshold.

14. A method for detecting an airborne visibility impeding agent comprising:

detecting a reduced visibility condition including;

emitting infrared radiation away from an infrared emitter;

detecting a first amount of the infrared radiation emitted during the first period of time having been backscattered by the airborne visibility impeding agent;

generating a first detection signal in response to the first amount of the infrared radiation including averaging the first amount over time;

detecting a first reference amount of said infrared radiation not having been backscattered by said airborne visibility impeding agent;

generating a first reference signal in response to the first reference amount detected including averaging the first reference amount over time, the generating of the first detection signal further including scaling the first amount using the first reference signal;

determining whether the first amount exceeds a first prescribed threshold; and

generating an alarm signal in event the first amount is determined to exceed the first prescribed threshold; and

detecting an increased visibility condition including;

emitting infrared radiation away from the infrared emitter;

detecting a second amount of infrared radiation emitted during the second period of time having been backscattered by the airborne visibility impeding agent;

generating a second detection signal in response to the second amount of the infrared radiation;

detecting a second reference amount of said infrared radiation not having been backscattered by said airborne visibility impeding agent;

generating a second reference signal in response to the second reference amount detected;

determining whether the second amount is less than a second prescribed threshold, the second prescribed threshold being lower than the first prescribed threshold; and

terminating the generating of the alarm signal in event the second amount is determined to be less than the second prescribed threshold.

15. The method of claim 14 wherein:

said generating of said second detection signal includes averaging said second amount over time; and

said generating of said second reference signal includes averaging said second reference amount over time.

16. The method of claim 15 wherein:

said generating of said second detection signal includes;

scaling said second amount using said second reference signal.

17. The method of claim 15 wherein said generating of said first detection signal includes:

determining whether said first reference amount is less than a reference threshold; and

generating a fault signal in event said first reference amount is determined to be below the reference threshold.

18. A method for detecting an airborne visibility impeding agent comprising:

emitting infrared radiation away from an infrared emitter;

detecting an amount of the infrared radiation having been backscattered by the airborne visibility impeding agent;

generating a detection signal in response to the amount of the infrared radiation detected including averaging the amount of infrared radiation detected over time;

detecting a reference amount of the infrared radiation not having been backscattered by the airborne visibility impeding agent;

generating a reference signal in response to the reference amount including averaging the reference amount over time;

scaling the detection signal having been averaged using the reference signal;

determining whether the detection signal having been scaled exceeds a first prescribed threshold;

generating a first alarm signal in event the detection signal is determined to exceed the first prescribed threshold;

determining whether the detection signal exceeds a second prescribed threshold that is higher than the first prescribed threshold; and

generating a second alarm signal in the event the detection signal is determined to exceed the second prescribed threshold.

19. The method of claim 18 wherein said generating of said detection signal includes:

determining whether said reference amount is less than a reference threshold; and

generating a fault signal in event the reference amount is determined to be below the reference threshold.

20. The method of claim 18 including:

determining whether said detection signal is less than a first lower threshold;

terminating said generating of said first alarm signal in the event said detection signal is determined to be less than the first lower threshold;

determining whether said detection signal is less than a second lower threshold; and

terminating said generating of said second alarm signal in the event said detection signal is determined to be less than the second lower threshold.

21. A method for detecting an airborne visibility impeding agent comprising:

emitting infrared radiation away from an infrared emitter;

detecting an amount of the infrared radiation having been backscattered by the airborne visibility impeding agent;

generating a backscatter signal in response to the amount of the infrared radiation detected;

detecting a reference amount of said infrared radiation not having been backscattered by said airborne visibility impeding agent;

generating a reference signal in response to the reference amount;

repeating the emitting, the detecting and the generating at least two times;

determining a running average of the backscatter signal over time;

determining a running average of the reference signal over time;

scaling said running average of said backscatter signal using said running average of said reference signal;

determining the amount of the infrared radiation having been backscattered as a function of the backscatter and determining whether the amount of the infrared radiation having been backscattered exceeds a prescribed threshold; and

producing an alarm signal in event the running average, having been scaled,. is determined to exceed the prescribed threshold.

22. The method of claim 21 including:

determining whether said running average is less than a lower threshold;

terminating said producing of said alarm signal in the event said running average is determined to be less than the lower threshold.

23. The method of claim 22 including:

determining whether said reference amount is less than a reference threshold; and

generating a fault signal in event said reference amount is determined to be below the reference threshold.