WO1998041960A1

WO1998041960A1 - Highway visibility sensor system

Info

Publication number: WO1998041960A1
Application number: PCT/US1998/005037
Authority: WO
Inventors: Takeo Sawatari; Philip A. Gaubis; Clark J. Charnetski
Original assignee: Sentec Corporation
Priority date: 1997-03-18
Filing date: 1998-03-13
Publication date: 1998-09-24
Also published as: AU6555898A; US5982288A

Abstract

A highway visibility sensor system (10) includes a housing (24) having a first hollow opening and a second hollow opening. A first light source (28) is fixed within the housing (24) and directs light through the first hollow opening to a sample volume (30) outside the housing (24). A first light detector (56) receives light reflected from the sample volume (30) through the second hollow opening. A controller (26) is coupled to the first light source (28) and the first detector (56). A controller (26) determines an output indicative of visibility from the light received by the light detector (56). A second light source (64) may be placed near the first detector (56) and a second detector (66) may be placed near the first light source (28). The second detector (66) and the second light source (64) are used for self checking to ensure the functionality of the first light source (28) and the first detector (56) and may be used to determine the amount of deterioration of the first light source (28) and the first detector (56) so that the controller (26) may adjust the measurements accordingly.

Description

HIGHWAY VISIBILITY SENSOR SYSTEM

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under Contract DTRS-57-95- C-00080 awarded by the Federal Highway Administration, United States Department of Transportation. The Government has certain rights in this invention.

BACKGROUND OF THE INVENTION

The present invention relates generally to a sensor system to detect visibility and, more specifically, to a visibility sensor system particularly suited for detecting visibility on a highway.

Reduced visibility on highways due to fog or blowing dust has often been the cause of tragic traffic accidents. Fog, especially in mountainous regions, has a tendency to build up in patchy dense pockets. At highway speeds, in particular, a driver may suddenly find himself within one of these patchy dense fog pockets.

The ability to adequately warn drivers of dense fog is highly desirable. If adequate warning is provided to drivers, drivers may then reduce their speed based on the density of the fog. Adequate warnings will reduce loss of life.

Several optical and non-optical methods for determining the presence of fog are known. Most, however, are not suitable for highway visibility sensors. There are several optical systems that may be used. Radar and lidar systems are used to gather general weather data. Such systems are too expensive, bulky, insensitive and difficult to use on a highway. Closed circuit television has limited use for visibility detection, but it cannot function at night and requires monitoring by an operator. Airports commonly use transmissometers. Transmissometers measure the transmission of a light beam traveling a given path. Transmissometers are very expensive and require considerable maintenance and thus are not suitable to detect patchy highway fog. Coulter counters are often used in clean room monitoring. Coulter counters are very expensive and have high maintenance and power consumption requirements.

Non-optical devices such as triboelectric current sensors depend on the flow of gas rubbing against an electrode. Fog, however, frequently occurs in quiet atmospheric conditions. Spark discharge sensors require sensor electrodes to continually be kept clean and thus maintenance costs are prohibitive. A dosimeter-type particle density measurement device does not provide real-time data.

Another optical device for measuring fog is a nephelometer. Known nephelometers have expensive optical systems and are very large in size. The optical system requires constant maintenance to clean the windows through which the optics are directed.

It would therefore be desirable to provide a highway visibility sensor system that overcomes the drawbacks of the prior art. Particularly, it would be desirable to provide a highway visibility sensor system that is inexpensive, has low maintenance, and is reliable to endure the conditions experienced on a highway.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an improved highway visibility detection system. According to one embodiment of the invention, a highway visibility detector includes a housing having a first hollow opening and a second hollow opening. A first light source is fixed within the housing and directs light through the first hollow opening to a sample volume outside the housing. A first light detector receives light reflected from the sample volume through the second hollow opening. A controller is coupled to the first light source and the first detector. The controller determines an output indicative of visibility from the light received by the first light detector.

In another embodiment of the visibility sensor system, a display may be coupled to the controller to warn drivers of the existence of fog ahead. The display may also indicate a safe driving speed through the fog.

In yet another embodiment of the invention, a means for compensating for the deterioration of the first detector may be included. To compensate for the deterioration of the first detector, a second light source may be placed adjacent to the first detector and illuminate the first detector with a predetermined amount of light. The controller then calculates the deterioration of the first detector in its visibility calculation. In another aspect of the invention, a means for determining deterioration of the first light source may be concluded. The means for compensating for deterioration of the first light source includes a second detector located adjacent to the first light source. The second detector would provide feedback to the controller as to the deterioration of the light source. The controller would then compensation for any deterioration of the first light source in its calculation for visibility.

In yet another embodiment of the invention, a method for detecting visibility comprises the steps of illuminating a sample volume of air from a first hollow opening within a housing using a first light source, detecting the amount of light reflecting from the volume of air with a first detector that receives light through a second hollow opening and calculating a visibility factor based upon the light reflecting from the volume of air.

In one aspect of the method for calculating visibility, the calculation may take into consideration deterioration of the first detector and the first light source.

One advantage of the present invention is that no optics or windows are required within the hollow openings through which light is transmitted and received. This eliminates a major problem for optical sensor systems. That is, eliminating the persistent need for cleaning of the optics or windows.

Another advantage of the present invention is that short periodic onsite inspections for calibration are not required. The sensor system provides a means for compensating for the deterioration of a detector and light source. The sensor system also can provide a self check and report the results to a central monitoring station.

Another advantage of the present invention is that a variety of communication options may be supported. For example, communication to a centrally located communication center may be provided via fiber optics, a cable, RF, telephone, and cellular phones.

Yet another advantage of the present invention is that the system operates using a significantly less amount of energy compared to that of other known fog detection systems. The sample rate for determining fog may be changed depending on whether the conditions around the sensor are changing to make fog more likely. If the conditions are such that fog is likely, the sample rate may be increased. Power use is thereby minimized. Yet another advantage of the present invention is the compactness of the sensor system. A separate post does not need to be installed along the highway for a sensor system. The sensor system may be installed on currently existing posts such as speed limit signs or other highway signs.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become apparent from the following detailed description which should be read in conjunction with the drawings in which:

Figure 1 is a diagrammatic view of a highway warning system employing a visibility sensor according to the present invention;

Figure 2 is a diagrammatic of a visibility sensor head according to the present invention;

Figure 3 is a diagrammatic view of an alternative embodiment of a visibility sensor; and

Figure 4 is a flow chart a method for operating a visibility sensor system to conserve energy.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, like reference numerals are used to identify identical components in the various views. Although the invention will be illustrated in terms of a fog detection visibility sensor, it will be appreciated that this invention may be used with other visibility applications such as detection of blowing dust.

Referring now to Figure 1, a highway visibility detection system 10 has a visibility sensor unit 12, a warning display 14 and a central controller 16. Visibility sensor unit 12 is preferably placed at eye level of a vehicle operator 18 in an automotive vehicle 20. Visibility sensor unit 12, warning display 14 and central controller 16 may all be linked through a communications network. A communication network, for example, may be cellular phone, RF, cable, or optical fiber. As shown, each of visibility sensor unit 12, warning display 14 and central controller 16 has an antenna 22 which may be used for RF or cellular communication between each.

Upon detection of reduced visibility by visibility sensor unit 12, an indication as to the distance of visibility may be displayed on warning display 14. Also, a suggested vehicle speed may also be displayed on warning display 14.

Central controller 16 may be part of an intelligent transportation system (ITS). The central controller 16 may be a manned controller which may perform a number of functions such as initiating self-tests for the sensor unit 12 or sending a maintenance crew to service the sensor in the event of contamination.

Referring now to Figure 2, visibility sensor unit 12 preferably has most of its components sealed within a housing 24. Several visibility sensor units may be coupled within one housing 24. The operation of the system is generally controlled by a microcontroller 26. A sensor head 28 is coupled to and controlled by microcontroller 26. Sensor head 28 transmits light to a sample volume 30 and provides microcontroller 26 an indication of the amount of light reflected from sample volume 30 below sensor head 28. A memory 32 is used to store various information and is coupled to microcontroller 26. Memory 32 is preferably nonvolatile memory. Memory 32, for example, may contain a conversion factor for converting the amount of light received by sensor head 28 to a visibility distance. Memory 32 may also store service and calibration data, security codes, the serial number of the system, and visibility data history.

Various sensors for sensing the atmospheric conditions around the housing 24 of visibility sensor system 12 are coupled to microcontroller 26. Such sensors may include an atmosphere pressure sensor 34, a temperature sensor 36 and a humidity sensor 38.

Microcontroller 26 may also be coupled to a communications link 40 that allows microcontroller 26 to communicate with a central controller 16. Although atmospheric pressure sensor 34 has been shown coupled directly to microcontroller 26, atmospheric pressure sensor 34 may be coupled directly to central controller 16. In such a case, atmospheric pressure data would be provided through communications link 40 to microcontroller 26. Micro controller 26 may be used to calculate the safe speed based upon the visibility detected by the sensor head 28. The calculation of a safe speed may be done at a central controller.

Communications link 40 may be one of a number of types of communications links that may be used to link microcontroller 26 to central controller 16. Because the detector system may be used in a variety of locations and conditions, flexibility for various types of communications is required. Communications link 40 may, for example, be cellular telephone link, an RF link, a fixed cable link, or optical fiber link. Communications link 40 may be used to couple to a warning display (shown as 14 of Figure 1) on the highway.

Sensor head 28 has a first optical port 42 and a second optical port 44. First optical port 42 has a first optical axis 46 and second optical port 44 has a second optical axis 48. First optical axis 46 coincides with the longitudinal axis of first optical port 42. Likewise, the second optical axis 48 coincides with the longitudinal axis of second optical port 44. An angle 50 between first optical axis 46 and second optical axis 48 may be about 150°.

Recessed within first optical port 42 is a first light source 52. First light source 52 is preferably mounted in an end of first optical port 42. First light source 52 is preferably an infrared light emitting diode having a relatively narrow beam width. First light source 52 may, for example, have a total beam width of 10°. Light from first light source 52 emerges from first optical port 42 at a first hollow opening 54. The cone of diverging light from first light source 52 illuminates a sample volume 30 outside first optical port 42.

Second optical port 44 has a first detector 56 located in an end thereof. First detector 56 is sensitive to the wave length of light reflected from the sample volume 30. First detector 56 may have a small surface area such as a five square millimeter surface area. Light is reflected from sample volume 30 into a second hollow opening 58. A light filter 60 may be interposed in the optical path between sample volume 30 and first detector 56. Filter 60 is provided to filter ambient light from first detector 56. First detector 56 provides an output to microcontroller 26 through a low noise amplifier 62 corresponding to the amount of light reflected from sample volume 30.

In one constructed embodiment both second optical port 44 and first optical port 42 were constructed of .5 inch diameter by 3.5 inch tube.

A test light source 64 may be provided in second optical port 44. Test light source 64 is also preferably an infrared LED. Test light source 64 preferably has a relatively wide beam width of approximately 80° so that light may be directed into second optical port 44 to first detector 56. Test light source 64 is coupled to microcontroller 26. Microcontroller 26 controls the operation of test light source 64. Test light source 64 is used during self testing and self calibration as will be further described below.

A compensation detector 66 is coupled within first optical port 42. Compensation detector 66 may have a smaller area such as a 1.5 square millimeter detection area. Compensation detector 66 is coupled to microcontroller 26 through a low noise amplifier 68, compensation detector 66 provides feedback to microcontroller 26 as to the operation of first light source 52 during self test and self calibration.

A heater 70 is coupled adjacent to first light source 52 and first detector 56 to prevent condensation on the optical surfaces. Heater 70 may be a tungsten wire or thermoplastic element. Heater 70 may, for example, maintain a differential temperature of roughly 5 ° C between the optical surfaces and ambient temperature to prevent condensation. A thermistor 72 may be coupled adjacent to the heater 70 to provide feedback to microcontroller 26 so that the functioning of heater 70 may be monitored.

An insect repellant 74 may be placed inside or adjacent to first optical port 42 and second optical port 44. Insect repellant 74 may be a variety of insect repellant means. Insect repellant may, for example, be a chemical known to be poisonous or repellant to the insects of the area into which the highway visibility detector system will be placed.

A power source 76 is used to power the highway visibility detection system 10. Highway visibility detection system 10 is flexible in the sense that it may operate from a variety of sources of power. Power source 76 may, for example, be a solar cell coupled to storage batteries. The power source may also be batteries or be coupled directly to a fixed power line. Referring now to Figure 3, an alternative embodiment for first optical port 42 and second optical port 44 is shown. In this embodiment, first optical axis 46 and second optical axis 48 are not aligned with the longitudinal axis of first optical port 42 and second optical port 44. First optical axis 46 and second optical axis 48 also preferably have an angle of about 150° between them. The embodiment of Figure 3 operates in the same manner as that of Figure 2.

One method for operating a highway visibility detector system of the present invention would be to continuously operate the system so as to constantly provide feedback to the central control and to a warning display or several displays. Operating a fog detection system continuously, however, is unnecessary and consumes power unnecessarily.

Referring now to Figure 4, based upon atmospheric conditions, the potential for fog can be predicted. From meteorology, a saturation surface can be defined in three- dimensional space defined by temperature, humidity and pressure. Fog occurs when the saturation surface is reached. In order to conserve energy, microcontroller 26 performs the following operations. First the atmospheric pressure is measured in step 80. In step 82 the humidity is measured. In step 84 the temperature is measured. Each of the atmospheric pressure, humidity and temperature conditions are preferably measured outside the housing of the highway visibility detector system. From the condition measured in steps 80 through 84, step 86 determines the distance from the saturation surface. In step 88, the distance from the saturation surface is compared with the previous distance from the saturation surface to determine the speed that the saturation surface is being approached. In step 90, the time to reach the saturation surface is estimated. In step 92, the sample rate is changed so that the microcontroller will turn on to determine visibility at a higher rate if the saturation surface is being approached. One method for setting the sample rate may be that if the estimated time to reach saturation is below 3 hours, then the microcontroller will turn on at a rate twice as fast as the normal operation mode. For example, this faster rate may be twice an hour. As the estimated time goes lower, the sample rate can be further increased. By increasing the time of sample only when the saturation surface is being approached, energy is conserved. After executing step 92, step 80 is re-executed and the next sample period determined by the microcontroller.

In this manner, the highway visibility detector system 10 does not operate needlessly. Thus, energy is conserved.

In operation, during visibility sampling, the first light source illuminates a sample volume 30 beneath housing 24. Fog or dust particles cause light to be reflected from the sample volume 30 into first detector 56. The amount of light reflected will be dependent upon the particle size and/or the number of particles of the contaminants within the sample volume 30. The light reflected from the sample volume has a direct correlation to the visibility present around the highway visibility detector. Date acquisition may be taken once or preferably sampled a number of times to statistically ensure satisfactory results. The received voltage level corresponding to the amount of illumination on the first detector 56 may be converted by a microcontroller 26 into a visibility. Microcontroller 26 may also convert the visibility into a safe speed for the roadway. The safe speed may be calculated or looked up in a table stored in memory 32.

The sensor system also has the ability to self calibrate. During manufacturing, a light scattering calibration object may be positioned in the sample volume. The microcontroller, when commanded, can save the measurement and determine a correction factor to be stored in the non-volatile memory. The connection factor will be used to correct subsequent visibility measurements. Calibration may easily be done at the manufacturer and easily confirmed when installed in the field. While the best mode for carrying out the present invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claim. For example, the humidity, temperature and atmospheric pressure sensors may be replaced by a wind velocity sensors if this invention were to be used to measure visibility in blowing dust.

Claims

CLAIMSWhat is claimed is:

1. A visibility sensor system comprising: a housing having a first hollow opening and a second hollow opening; a first light source fixed within said housing and directing light through the first hollow opening to a sample volume outside said housing; a first light detector receiving light reflected from the sample volume through said second hollow opening; and a controller coupled to said first light source and said first detector, said controller determining an output indicative of visibility from light received by said light detector.

2. A visibility sensor system as recited in claim 1, further comprising a display coupled to said controller, said display displaying said output indicative of visibility.

3. A visibility sensor system as recited in claim 2, wherein said controller calculates a maximum safe speed, wherein said display displays a maximum safe speed.

4. A visibility sensor system as recited in claim 1, further comprising compensating means for compensating for a deterioration of said first light source.

5. A visibility sensor system as recited in claim 4, wherein said compensating means comprises a second light detector optically coupled to said first light source, said second light detector coupled to said controller.

6. A visibility sensor system as recited in claim 1, further comprising compensating means for compensating for deterioration of said first detector.

7. A visibility sensor system as recited in claim 6, wherein said compensating means comprises a second light source optically coupled to said first light detector, said second light source coupled to said controller.

8. A visibility sensor system as recited in claim 1 , further comprising a heater coupled to said housing.

9. A visibility sensor system as recited in claim 1, further comprising an insect repellant placed adjacent said housing.

10. A visibility sensor system as recited in claim 1 , wherein said light source comprises an infrared light source.

11. A visibility sensor system as recited in claim 1 , further comprising an optical filter adjacent said first detector for filtering an ambient light from reaching said first light detector.

12. A visibility sensor comprising: a housing having a first optical port having a first hollow opening and a second optical port having a second hollow opening; a first light source recessed within said first optical port directing light through said first hollow opening to a sample volume; a first detector recessed within said second optical port receiving light reflected from said sample volume through said second hollow opening; a second light source recessed within said second optical port, said second light optically coupled to said first detector; a second detector recessed within said first optical port, said second detector optically coupled to said first light source; and a controller coupled to said first light source, said first detector, said second light source and said second detector, said second light source providing an indication of deterioration of said first detector to said controller and said second detector providing an indication of deterioration of said first light source to said controller, said controller determining an output indicative of visibility from light received by using said light detector, by said deterioration of said first detector and by said deterioration of said first light source.

13. A visibility sensor system as recited in claim 12, further comprising a heater coupled to said first optical port and said second optical port.

14. A visibility sensor system as recited in claim 13, further comprising a thermistor coupled adjacent said heater and coupled to said controller, said thermistor providing feedback to said microcontroller regarding a functioning of said heater.

15. A visibility sensor system as recited in claim 12, further comprising an insect repellant placed near an opening in said housing.

16. A visibility sensor system as recited in claim 12, further comprising an optical filter adjacent said first detector for filtering ambient light from said first detector.

17. A visibility sensor system as recited in claim 12, wherein said light source comprises an infrared light source.

18. A visibility sensor system as recited in claim 12, wherein first light source has a first optical axis, wherein said first detector has a second optical axis, wherein said first optical port has a first longitudinal axis and said second optical axis, said first optical axis and said second optical axis forming a predetermined angle.

19. A visibility sensor system as recited in claim 18, wherein said first optical axis is coincident with said first longitudinal axis, said second optical axis is coincident with said second longitudinal axis.

20. A visibility sensor system as recited in claim 12, further comprising a communications link coupled to said controller for communicating with a central controller.

21. A method of detecting visibility comprising the steps of: illuminating a sample volume of air from a first hollow opening within a housing from a first light source; detecting the amount of light reflecting from the volume of air with a first light; detector that receives light through a second hollow opening; and calculating a visibility factor based upon the light reflecting from the volume of air.

22. A method of detecting visibility as recited in claim 21 , further comprising the steps of: measuring the atmospheric pressure outside the housing; measuring the humidity outside the housing; measuring the temperature outside the housing; determining the speed at which a saturation surface is being approached; estimating the time to reach saturation; and setting a sample interval.

23. A method of detecting visibility as recited in claim 21 , further comprising the step of compensating for deterioration of the first light source.

24. A method of detecting visibility as recited in claim 21 , compensating for a deterioration of the first light detector.

25. A method of detecting visibility as recited in claim 21 , further comprising the step of checking the operability of the first light source.

26. A method of detecting visibility as recited in claim 21 , further comprising the step of checking the operability of the first light detector.