DE102008006146A1 - Device for obscuration measurement in monitoring area at road in tunnel, has evaluation unit for selecting light-sensitive pixel element of matrix image sensor, where light source lies in receiving area of element - Google Patents

Abstract

The device has an evaluation unit i.e. controller (24), to calculate an extinction coefficient based on a distance between a light source (26) e.g. halogen lamp, and a light receiving unit and decrease in measured intensity with respect to reference intensity of light incident on the receiving unit. The source is arranged in a monitoring area (22). The evaluation unit selects a light-sensitive pixel element of a matrix image sensor (20) e.g. charge-coupled device sensor chip, where the source lies in a receiving area of the element. The element is provided as the receiving unit. An independent claim is also included for a method for obscuration measurement in a monitoring area.

Description

The The invention relates to a device and a method for measuring visibility in a surveillance area with a matrix-shaped image sensor according to the preamble of claim 1 and 10, respectively.

After a few serious accidents involving fires and associated smoke in European road tunnels, these must be provided with improved safety features. A European Directive EC 54/2004 was transposed into national law by a Road Tunnel Equipment and Operation Directive (RABT2006). These guidelines require that tunnels above a certain risk class be equipped with automatic, camera-based accident detection systems. In addition to smoke, the incidents to be detected include traffic jams, accidents, lost cargo, people lying down, pedestrians on the road and ghost riders.

to Smoke detection in case of fire in known systems the entire Image of the camera evaluated on its image contrast and falls below a specific contrast value triggers an alarm. such Image evaluations recognize smoke in the tunnel, but the realizable False alarm rate is not low enough in practice. Reason are the difficulties, the high contrast differences of the normal Operation, such as light fluctuations, contamination of the optical interfaces, change the scenery by various vehicles, water flags and like to differentiate from contrast attenuation by smoke. Therefore, there are currently hardly any better false-alarm rates than one False alarm every two months and camera reach. Considering the number on cameras per tunnel and the high overhead that a false alarm triggers, on the other hand, an acceptable false alarm rate would be one False alarm per measuring point and a few decades.

In a typical road tunnel does not just have to smoke by fires, but also the visibility turbidity (extinction coefficient) to be monitored in order to improve the quality of Air in the tunnel, for example by controlling a ventilation system to obtain. For this task become conventional Transmissiometer or scattered light meters used, since the increased due to vehicle emissions and abrasion particles Extinction coefficients cause too little contrast differences in the image, which by means of evaluation of the image contrast and / or the structure sharpness are not recognizable.

From the DE 100 11 411 C2 an imaging fire detector is known, which may derive a fire message from changes in the structure sharpness in the image sequences of the camera, if necessary. In this case, in one embodiment, the type of smoke is identified by the particle size of smoke particles is detected by light scattering of these smoke particles that produce a corona around a light source in the image area. In addition, the brightness of this light source is also evaluated. However, the system is not able to detect the impairment of the air outside of a fire even at low smoke levels by the global evaluation of all pixels, and it is not designed as a pure fire detector.

Other Fire detection systems are based on temperature sensors or for example on light guides, the light-conducting properties of which change with temperature.

in view of In this prior art it is the object of the invention to provide a reliable and to provide simple visual haze measurement, which is also low Can detect particle and smoke emissions.

These The object is achieved by a device for measuring visibility according to claim 1 and a corresponding method solved according to claim 10. By pixels be selected by the image sensor which shows the active illumination (s) effectively create one or more transmissiometers, consisting of the active illumination and the selected pixels. This makes it possible, the transmission measurement camera-based make so that about an already existing video surveillance be exploited with additional functionality can, or the images used for the transmission measurement can be reversed for further evaluations Will be provided. Through the transmission evaluation the false alarm rate is significantly reduced, with less than one False alarm every 20 years and measuring point becomes possible.

Becomes more than one lighting used in the device, so are the illuminations advantageously at different distances installed to the light receiving device. This ever arises Illumination of a transmissiometer, each with a different measuring section, wherein each illumination to be assigned to the corresponding selected pixels. By comparing the readings of each of these transmissiometers it is possible the visibility through smoke or To determine vehicle emissions between the individual illuminations such a statement about the spatial distribution to get the visibly opaque substances along the tunnel.

Advantageously, the evaluation unit is designed to determine a measure of a smoke load from image data of the image sensor. Thus, the two tasks, namely a tech nischer view very reliable and fast visual cloud measurement to determine the increasing by vehicle emissions extinction coefficient and smoke detection in case of fire about integrated by contrast differences based image analysis in a single sensor, so that the equipment required without loss of reliability, accuracy or functionality with a corresponding reduction in financial and organizational Expenditure is considerably reduced.

The Evaluation unit is preferably designed to, the Measure from a contrast attenuation of the image data, a comparison with a reference image in free view or a Determine brightness drop, and in particular a plausibility check between the one based on the illuminated selected pixel Extinction coefficient and based on the image data measure. The reliability of the two measurements increases so through plausibility comparisons. The two procedures Image evaluation on the overall picture and transmission measurement by The select pixels can be shared with another Reduction of the false alarm rate are used.

Prefers is the evaluation unit designed for this purpose by means of Image sensor a first image for visibility measurement and a second image changed with respect to the first image Recording parameters, such as brightness, aperture or more, for the Determining the measure to include, in particular the first and second image follow each other in time, the first picture a brightness suitable for overall picture evaluations and the second image has a lower brightness than the first image. This optimizes the images for the respective measurement customized.

advantageously, a light source receiving element is provided nearby Each light source is arranged to match that of the respective light source Check emitted light intensity. This ensures at all times that the active lighting still intact. A possible drop in intensity may occur in the evaluation unit for the selected pixels and the Image analysis are taken into account. Thus, fluctuations or failure of active lighting as sources for one False alarm off and the probability of a false alarm further reduced.

In Another preferred embodiment is the light source designed to emit light that is variable in time, in particular modulated light or a flashing sequence. This can be DC light fluctuations be suppressed in the measurement signal. The evaluation unit is based on the known temporal variation capable of active lighting to distinguish from disturbers.

The Light source preferably has one or more of the following elements on: a semiconductor light source, a laser, a halogen lamp, a gas discharge lamp, a reflector or a reflector strip. Depending on the test section can thus be a desired spatial Extension of active lighting and a desired Intensity distribution can be achieved. Is the light source a passive element, ie an illuminated reflector or a reflector strip, so the actual lighting can be close to the camera or even be integrated into this. This makes maintenance and installation easier.

Prefers Dust protection devices, in particular tubes are provided to protect the device and the image sensor from contamination, and / or it is a detection device for the detection of Impurities or defects of a windscreen of the device and / or the image sensor. This can be a Impairment of the windshield due to contamination exclude or at least limit, as another source of error, and thereby the reliability and the maintenance intervals elevated.

The inventive method can be similar to Be further developed and shows similar benefits. Such advantageous features are exemplary, but not exhaustive in the subsequent claims to the independent claims described. Conversely, the method claims are also analogous configurations for the device conceivable.

Especially it is advantageous in the method according to the invention, when the light sources are in places in the surveillance area be arranged, in which during operation the respective line of sight between light source and image sensor not interrupted especially in a method of detecting smoke in tunnels on the ceiling or a wall above the expected height of Vehicles. This can at any time during operation the Transmission and thus the extinction coefficient are measured. The active illumination thus uses a part of the image sensor, the anyway less interesting for the actual image evaluation would be because it takes up wall or ceiling areas.

Farther is preferred if the signals of the image sensor are preprocessed, in particular low-pass filtered or with increasing operating time be further reinforced to aging processes and / or compensate for creeping pollution. This will turn increased reliability and reduced the false alarm rate and the need for maintenance lowered.

When exceeded a threshold of the extinction coefficient and / or the measure Advantageously, a ventilation system is activated, an alarm is triggered or an evacuation measure triggered. Since according to the invention everything from a slight increase the particles in the tunnel are detected until a fire catastrophe can, in this way, with the appropriate measure responding.

The Invention will also be described below with regard to further features and Advantages exemplary by means of embodiments and with reference to the accompanying drawings closer explained. The illustrations of the drawing show in:

1 a schematic representation of a road in a tunnel with a first embodiment of the device according to the invention for detecting smoke;

2 an exemplary light spot of the active illumination on the image sensor for explaining the selected pixels;

3 a schematic representation according to 1 to a second embodiment, wherein the light source is realized via a reflector; and

4 a schematic representation according to 1 to a further embodiment of the invention, in which a plurality of light sources or reflectors are arranged in the monitoring area.

1 shows a camera 10 standing against a wall in a tunnel 12 with a road 14 is mounted. The camera 10 is shown once more in a detail enlargement represented by dotted lines and circles for better recognition of its components. Through a stylized reception lens 16 with a single lens 18 shown optical system and a protective windscreen light falls on an image sensor 20 , The imager is a pixel-resolved matrix-shaped recording chip, based for example on CCD or CMOS technology. The camera 10 thus generates image data of a surveillance area 22 namely a section of the tunnel 12 , Usually a camera 10 for automatic incident detection arranged so that it essentially considers the traffic area. In addition, there are almost always other permanently static areas in the picture, namely the walls or the ceiling.

To the imager 20 is a controller 24 connected, which controls the camera functions and evaluates the image data. This controller can be housed with the camera in a housing or external. In the surveillance area 22 is at a known distance a light source 26 mounted on a tunnel wall, preferably within one of said static areas. In the immediate vicinity of the light source 26 is a light receiver 28 mounted, such as a photodiode, to the emitted light intensity of the light source 28 to investigate. To the light receiver 28 can light the light source 26 also indirectly, for example via a half-mirror. The line of sight between camera 10 and light source 26 can not be interrupted during operation, because the arrangement is chosen so that either no vehicles cross the line of sight or camera 10 and light source 26 are mounted above the vehicle heights.

The control 24 can evaluate the image data in a conventional manner on the occurrence of smoke to detect a fire. It can also control the surveillance area 22 monitor for the aforementioned incidents such as traffic jams, accidents or lost loads. Via a wireless interface 28 which is based on any standard such as WLAN, UMTS or the like, image data or evaluation results can be sent to the outside for further processing, but also an alarm or control commands to alarms, barriers or tunnel ventilation are generated. Alternatively to a wireless interface 32 can the camera 10 also be wired or integrated into a network, such as direct connections, 4-20 mA current loops with relays, or serial interfaces such as Ethernet, Profibus or RS485

An appropriate wireless or wired interface 32 is with the light source 26 and the light receiver 28 connected. The control 24 In this way it can be the immediate vicinity of the light source 26 measured light intensity of the light receiver 28 query and the light source 26 drive.

2 shows by way of example the pixel arrangement of the image sensor 20 and a spot of light 34 as an image of the light source 26 with a clear view. Those pixels 36 which is directly from the light source 26 be illuminated, that is, under the light spot 34 are selected, are selected for a transmission evaluation. The selection can be learned as part of the installation, at the push of a button or during maintenance. It also the intensity of the light spot 34 In the case of clear view, the reference value has been taught in advance. Changes, including later dynamic changes by dynamically storing further reference values, are monitored in order to determine the transmission, ie the extinction coefficient from the brightness values in the pixels 36 and the known distance to be parameterized between the light source 26 and camera 10 (Strictly speaking, their windshield, because within the Kame ragehäuses no impairment of the visibility is to be expected) to calculate. The selected pixels 36 and the light source 26 thus act as an integrated transmissiometer.

The device is therefore capable of measuring the transmission as well as of evaluating the smoke by means of image evaluations, for example by detecting contrast fluctuations. In this case, combinations of the invention are also included: The use as a transmissiometer, the use as a transmissiometer for visibility measurement with additional smoke detection and also a mutual plausibility check of both measurements to further improve the prevention of false alarms. The pixels 36 can already see a slight increase in the extinction coefficient, which can only be attributed to vehicle emissions. Of course, you will certainly recognize the smoke of a source of fire on the basis of the significantly increased extinction coefficient.

The same imager 20 can therefore be used according to the invention for two evaluations, namely the transmission measurement and smoke detection by image analysis. The pixels 36 can have a dual function, but can also be used exclusively for the transmission measurement. Thus, it is conceivable to evaluate one and the same recorded image both for the measurement of the visual haze and for the smoke detection. Alternatively, separate images for a transmission measurement and own images for a smoke detection can be recorded. Then recording parameters, in particular the image brightness, can be adjusted so that they are optimally adapted for the intended type of measurement. Thus, an image evaluation, as used in the smoke detection or for a video surveillance, usually make at higher brightness than a transmission measurement, because the pixels on the active light source 26 are aligned.

These Pictures for the two different measurements can it is also possible to perform the two measurements in mutually different time intervals.

The selected pixels 36 can also do a self-test of the camera 10 be used, because at least the light source 26 must be detected if the system is still to provide reliable image data. This may be the light of the light source 26 can also be varied to recognize, for example, burned-in "stuck-at-high" pixel errors or other pixel errors such as dead pixels, excessively high-noise pixels, etc.

Such a modulation or variation of the light intensity of the light source 26 can also serve, in the image analysis, the useful light of the light source 26 Distinguished by stray light, such as headlights of the vehicles, and thus to make the evaluation more robust. The alternating light signal of the light source 26 is with the camera 10 synchronized to suppress stray light fluctuations in the measurement signal. A simple solution to temporal variations is an on-off change that can be easily created by controlling an existing trigger signal so that two consecutive shots are taken once with "Illumination On" and then "Illumination Off" become. The modulations can also be used to the light receiver 28 to test.

The light receiver 28 provides a constant intensity of the light source 26 safely or provides signals about its changes, which then from the controller 24 can be compensated or, if this is no longer possible, lead to a maintenance request.

To limit the contamination of the optical paths, so especially the front screen of the camera 10 , protective devices, such as tubes, shall be provided to limit turbidity due to contamination. Alternatively or additionally, the front screen can be examined for defects and impurities by means of additional devices or image evaluation.

All Signals can be low-pass filtered to very slow changes due to slow contamination or aging of the components. It is also possible to amplify the signals adjust accordingly.

3 shows a further embodiment of the invention. Here, and in the following like reference numerals designate the same features. The further embodiment differs in that instead of an active light source 26 in the surveillance area 22 only a passive reflector 38 is provided while light source 26 and light receiver 28 into the camera 10 are integrated. In this case, the image sensor 20 by suitable optical coupling also the task of the light receiver 28 take. The integration of the light source 26 has the advantage of being on an interface 32 be omitted or this can be replaced by a short direct connection. In the surveillance area 22 all that's left is the passive reflector 38 to be assembled.

As a light source 26 According to the invention, a plurality of active light sources, ie semiconductor diodes, halogen lamps or the like, a plurality of geometrically different reflectors such as small, approximately point-like or strip-shaped reflectors or a mixture of all these components are used.

In 4 Yet another embodiment of the invention is shown, which differs in that in the surveillance area 22 several light sources 26a c are arranged such that the light path from each light source 26a -c to the camera 10 is interrupted during operation neither by vehicles nor by internals. The light sources 26a -c may alternatively be formed as reflectors, as in connection with 3 and reflect the light from a shared light source located at the camera. Also the characteristics of related 1 described embodiment can be combined here, such as the measurement of the emitted intensity of the light sources 26a -c with additional light receivers (in 1 reference numeral 28 ). The control 24 selects for transmission measurements those pixels, each one of the light sources 26a -c picture. This makes it possible to obtain information about the spatial distribution of visibly clouding particles, or to obtain better information about the visual haze by means of averaging, further statistical or other mathematical methods than with only one transmission measurement with only one light source. It is also conceivable for each light source separately to record or modulate an image adapted for its evaluation in its acquisition parameters, as described above for a single light source.

According to the invention thus a measuring system, namely the additional Transmissiometer, saved in the tunnel and still a very low false alarm rate achieved for smoke detection in the tunnel by means of image analysis become. This solution is inexpensive, and the Measuring device may be slightly away from the heated area and is therefore able to start the fire Visualize to plan appropriate countermeasures. It is the visualizing system, for example for additional monitoring tasks by operating personnel or for documentation purposes, with the brand recognition System identical. Although the specific embodiments refer to the assembly in a tunnel, the invention also in rooms, assembly halls, on exposed roads or in other environments.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 54/2004 [0002]
• - DE 10011411 C2 [0005]

Claims (18)

Device for measuring visibility in a surveillance area ( 22 ) comprising a light receiving device ( 36 ), at least one light source ( 26 . 38 ) as well as an evaluation device ( 24 ), which is formed from the distance between the light source ( 26 . 38 ) and light receiving device ( 36 ) and a weakening of the respective measured intensity from a desired intensity of the free view without visual clouding on the light receiving device ( 36 ) to calculate an extinction coefficient, characterized in that the light source ( 26 . 38 ) in the surveillance area ( 22 ) and that as a light receiving device ( 36 ) at least one selected photosensitive pixel element of a matrix-type image sensor ( 20 ) is provided with a plurality of photosensitive pixel elements, wherein the evaluation unit ( 24 ) is adapted to select those pixel elements in whose reception area the light source ( 26 . 38 ) lies. Apparatus according to claim 1, wherein a plurality of mutually staggered light sources ( 26a -c) in the surveillance area ( 22 ) and the evaluation unit ( 24 ) is designed for each light source ( 26a -c) to select those pixel elements in whose reception area the respective light source ( 26a -c), for each light source ( 26a -c) calculate a partial extinction coefficient and from this a spatial distribution of the extinction coefficient and / or by different weighting a more accurate extinction coefficient. Apparatus according to claim 1 or 2, wherein the evaluation unit ( 24 ) is adapted to image data from the image sensor ( 20 ) to determine a measure of smoke pollution. Device according to one of the preceding claims, wherein the evaluation unit ( 24 ) is adapted to determine the measure of a contrast attenuation of the image data, a comparison with a reference image in free view or a brightness decrease, and in particular a plausibility check between the selected on the illuminated pixel ( 36 ) and the amount based on the image data. Apparatus according to claim 3 or 4, wherein the evaluation unit ( 24 ) is designed for, by means of the image sensor ( 20 ) to record a first image for the visibility measurement and a second image with respect to the first image changed brightness for the determination of the measure, in particular, the first and second image immediately follow in time, the first image suitable for overall image evaluations brightness and the second image a lower Brightness as the first image. Device according to one of the preceding claims, wherein a light source receiving element ( 28 ), which is close to the light source ( 26 ) is arranged to the from the light source ( 26 ) to check emitted light intensity. Device according to one of the preceding claims, wherein the light source ( 26 . 38 ) is adapted to emit light which is variable in time, in particular modulated light or a flashing sequence. Device according to one of the preceding claims, wherein the light source ( 26 . 38 ) comprises one or more of: a semiconductor light source, a laser, a halogen lamp, a gas discharge lamp, a reflector or a reflector strip. Device according to one of the preceding claims, wherein dust protection devices, in particular tubes are provided to the device and the image sensor ( 20 ) to protect against contamination and / or wherein a detection device for the detection of impurities or defects of a windshield of the device and / or the image sensor ( 20 ) is provided. Method for measuring visibility in a surveillance area ( 22 ), in which the distance between at least one light source ( 26 . 38 ) and a light receiving device ( 36 ) as well as a weakening of the respectively measured intensity from a desired intensity of the light view without Sichttrü advertising on the light receiving device ( 36 ), an extinction coefficient is calculated, characterized in that the light source ( 26 . 38 ) in the surveillance area ( 22 ) and that as a light receiving device ( 36 ) at least one photosensitive pixel element of a matrix-type image sensor ( 20 ) is selected with a plurality of photosensitive pixel elements, so that the light source ( 26 . 38 ) lies in the reception area of the selected pixel element. Apparatus according to claim 10, wherein a plurality of mutually staggered light sources ( 26a -c) in the surveillance area ( 22 ) and depending on the light source ( 26a c) those pixel elements are selected in whose reception area the respective light source ( 26a -c), and for each light source ( 26a -c) a partial extinction coefficient and from this a spatial distribution of the extinction coefficient and / or by a different weighting a more accurate extinction coefficient is calculated. A method according to claim 10 or 11, wherein a measure of a smoke load is determined from image data of the image sensor, and wherein the measure is determined from a contrast attenuation of the image data, a comparison with a reference image in free view or a brightness decrease, and wherein a plausibility check between the extinction coefficient based on the illuminated selected pixel and the amount based on the image data. Method according to one of claims 10 to 12, wherein a first image for the visibility measurement and a second image modified with respect to the first image Brightness recorded for the determination of the measure in particular, the first and second images are temporally immediate one after the other, the first picture with one for overall picture evaluations suitable brightness and the second image with lower brightness as the first picture to be taken. Method according to one of claims 10 to 13, wherein the emitted light intensity in the vicinity of the light source ( 26 ) is checked. Method according to one of claims 10 to 14, wherein temporally variable light is emitted, in particular modulated light or a flashing sequence, and wherein constant light fluctuations due to synchronization between the image sensor ( 20 ) and light source ( 26 . 38 ) are compensated. Method according to one of claims 10 to 15, wherein the light source ( 26 . 38 ) is placed at a location in the surveillance area where, during operation, the line of sight between the light source ( 26 . 38 ) and image sensor ( 20 ), in particular in a method for detecting smoke in tunnels ( 12 ) on the ceiling or a wall above the expected height of vehicles. Method according to one of claims 10 to 16, wherein the signals of the image sensor ( 20 ) are preprocessed, in particular low-pass filtered or further reinforced with increasing operating time to compensate for aging processes and / or creeping contamination. Method according to one of claims 10 to 17, when exceeding a threshold of the extinction coefficient and / or the measure activates a ventilation system, an alarm is triggered or an evacuation measure is triggered.