Method for determining visibility

The invention relates to a method for determining the visibility of a Detecting means, the at least one sensor for the transmission of in particular pulsed electromagnetic radiation into a monitored zone and to receive from the monitoring area reflected radiation and an evaluation device for evaluating comprises the reflected radiation.

Such detectors are known in principle and are for example, mounted to vehicles in order during the driving operation the vehicle environment in particular for object recognition and to detect tracking.

Problems are occurring during operation disorders eg due to environmental influences such as rain or contamination of the Sensors such as dust which the normal sight of the sensor, which is also referred to as range affect can. In vehicle applications in particular, at high vehicle speeds highest possible visibility and coverage desired thus preceding vehicles or objects on the Road are detected as early as possible.

If, due to interference in a reduction of visibility of the sensor, it is desirable, this limitation of the performance to detect the sensor, to take appropriate measures to be able to, for example, to the speed of the vehicle reduce.

The object of the invention is to provide a method of the type mentioned and to provide a device which make it possible, in the simplest possible Way to recognize a visibility reduction, and it particularly allow quantitative statements about the effect of the disturbance to meet the sight.

This object is achieved by the features of claim 1 and in particular in that the during operation of the sensor Presence of at least one in the field of view of the sensor lying, the Visibility at least regionally debilitating disorder based at least one characteristic property fault is detected, the identifiable by the sensor by evaluating the reflected radiation is from reflected radiation, the at least the out of the interference region includes native interference, determines the strength of the disturbance is, and from the interference power, the current visibility of the sensor is determined.

The sensor is preferably a laser scanner, a comprehensive an angular range of up to 360 ° in at least Scanning emits a laser beam and for each direction in which the laser beam is emitted within the scanning plane, means a Pulslaufzeitmeßverfahrens a distance value and an angle value based supplies to a sensor axis.

According to the invention the detection means itself is capable of the Existence of the sensor to detect visual range debilitating disorder. However, this does not exclude that the fault detection by additional means such as through on a vehicle mounted rain sensor is supported.

In case of faults within the meaning of the invention is not of interest Objects that are to be detected by the sensor - in Vehicle applications, for example to other vehicles to persons or Objects on or at the roadway or road boundaries - But phenomena which the recording of interest affect objects by means of the sensor, at least potentially and thus the actual operation of the sensor interfere.

For fault detection of the sensor, which is capable of serving at least impairing a characteristic property of the Visibility identify interference by the reflected from the monitoring area derived and at least in the field of interference radiation means of the evaluation for the presence of at least one examines interference property back.

According to the invention not only can be detected that a fault is present, but it is also determined to what extent the Visibility of the sensor is affected by the disorder. For example is not only determined <u>that</u> it rains, but also,<u>how strong</u> the rain, whereby a measure is available from the derived the current, reduced by the rain sensor range can be. To this end, the invention first by evaluating at least the reflected from the interference area as raindrops Radiation determines a measure of the strength of the disturbance and then from the interference power determines the momentary sight of the sensor.

For example, a measure of the intensity of the rain from the measured Number of raindrops are derived, which from the rain intensity in turn, determines the instantaneous visibility reduction or is estimated. This determination or assessment can independently take place on the size of raindrops. Alternatively or additionally, at least in principle, the determination of the rain intensity and thus the instantaneous visibility even on the basis of the measured quantity of raindrops occur if the sensor and the evaluation device to distinguish between different droplet sizes in the Able. The same applies to other disorders such as snow, like rain from stochastically occurring individual particles exist. ever can on the performance of the sensor and the evaluation device a distinction between different particle sizes - unless a Such a distinction in the application ever realized is - either within a respective fault type by, for example between different sized raindrops is discriminated or purely occur between different types of noise by as a result of measured particle size only between rain and snow, not but between the rain with small drops and rain with large drops is discriminated.

So according to the invention are used to determine the visibility of the sensor Information used, which can detect even the sensor, that is the fact is exploited that the operation of the sensor impairing Disorder "seen" by the sensor. One does so advantage that the sensor is specifically to ensure, information about his Field of view objects located to procure by from the object "Fault" reflected radiation is evaluated accordingly.

Therefore, it is possible according to the impairing visibility Disorders respond differentiated. In particular, it is not necessary the detection operation for safety reasons and because of the completely set fear that the measurements because of the visibility reduction no relying more is or the reduced visibility for a useful monitoring was no longer sufficient. Rather, According to the invention the actual range of the sensor, for example in rain determined, and for example, the speed of the detection means equipped vehicle are reduced, so that the reduced sensor sight distance a sufficiently reliable detection operation sufficient, ie preceding vehicles or objects on the Roadway are detected in time again despite visibility reduction.

The disturbances that basis of at least a characteristic interference property are detected, it is preferable in the invention to fog, rain, snow, sand, dust, sea spray, fumes, dirt sensor and / or sensor damage. By evaluating the , at least from the respective interference between the reflected radiation the individual faults are distinguished.

The distinction, ie the detection of a particular disorder occurs, based at least one characteristic feature of the disorder. As be disturbance characteristics preferred position, the contour Shape, size, extension, the distance, the structure, consistency, the temporal behavior, the reflection behavior and / or the Near a fault used.

The invention can present, derived from empirical knowledge use has typical characteristics of disturbances. So different for example shower of spray in that the rain drops forming global, that are present in the entire field of view of the sensor, while property "spray" on the one hand is limited in space and on the other only in close proximity to one the spray generating object, as can a vehicle or vehicle tires occur, which in the Around the spray must be "seen" by the sensor, which must move the subject as well. Self gischtartig behaving "objects" on stationary vehicles, for example, have the exhaust fumes be considered, even without the structure of the "object" is investigated.

A distinction between global and localized disorders is already of importance, since the latter, the sight of the sensor can interfere only in a limited angular range and to will not be considered outside of this angular range need.

The detection of global disorders, which consist of individual particles, such as rain or snow, is preferably based on it, that in a Short range, for example up to a distance from the sensor of about 3 m, stochastically occurring individual measuring points are determined that over the total detected by the sensor angle range at least approximately are evenly distributed.

Limited Area or local disturbances such as spray can even at greater distances from the sensor, for example, up to a distance be from 15 m is detected. It may also be that the sensor through a local cloud of mist as it were "sees through" so that behind the cloud of mist contained objects can be detected. It can be considered then, that the sight of the sensor only in the cloud of spray, that is locally reduced.

Each global disturbances, for example, by their temporal Behavior can be distinguished from each other. For example, while it rains, detectable by a stochastic behavior of its means of the sensor Raindrops distinguished, fog is detected by the sensor in that either billowing, cloudlike contours are detected and in things appear temporarily actual interest can (heterogeneous behavior of fog) or - especially with no wind and in case of non-interference of other, moving in particular Items - an at least approximately closed and stationary "Wall" or line is detected (homogeneous behavior of fog) however, in comparison with the contour of an actually measured interest Object, such as another vehicle, substantially is blurred, for example, by a factor of 3-8 (based on the standard deviation in the removal determination).

Further inventively exclusion criteria can be used, under which certain disorders in the context of the application can, from the outset not as coming in question does not occur be considered. Thus, for example occurring at indoors Applications the occurrence of rain or precipitation generally excrete.

According to a preferred embodiment of the invention it is suggested that the presence of interference will only be detected if predetermined combinations of at least two different characteristic disturbance characteristics are identified. hereby are the requirements of a failure to be recognized as such, increased and thereby identifies the interference safer.

Thus, for example spray and fumes that are limited in each case by spatially or "cloud-like" appearance and belonging to a Vehicle distinguish, because of their different structure from each other be distinguished. It can in this case utilized as the fact be that at least detectable approximately spray from individually Water drops is and therefore the extent behaves like rain, while exhaust gases for the sensor more like mist "look".

Further, according to the invention preferably provided that the determination the interference strength and / or the determination of the instantaneous Visibility in dependence on at least one characteristic property disorder takes place.

Here, the one characteristic interference property can be used are the basis of which the problem has been recognized at all. alternative or in addition, at least one additional interference property be used. For example, initially to rain a stochastic behavior individually detectable, with regard to their Size with sufficient probability raindrops appropriate recognize objects and then the intensity of the rain, for example by Determining the number of rain drops per time and angle unit be determined.

Furthermore it can be provided according to the invention that the disturbance directly is recognized by their characteristic interference property. in this connection can reference a single characteristic interference property recognized not only the existence of a fault in itself, but also be, what type of error it is. This is, for example, then questioned if certain ambiguities excluded a priori are, for example, when taking place in an enclosed space applications, where can no precipitation occur and a rain-like Behavior displayed faults only by authorized as possible interference can come irrigation.

According to a further embodiment of the invention it is suggested that when there is a disturbance of these based on characteristic Fault property of at least one of several predetermined Fault types is assigned to the several different faults comprises, on which apply the characteristic interference property.

This allows certain faults under one of the type of fault formed roof be treated. For example, this may in Setting a though rough, but quick visibility determination be useful. For example, different types of rainfall are combined into a fault type "precipitation" which shared by all its faults characteristic Interference property of the global, not spatially limited occurrence distinguished.

In the case of using fault types can be provided that the determination of the interference power and / or the determination of the instantaneous Visibility is made depending on the type of fault. In between the individual, a common type of fault belonging disorders Here is consequently no longer distinguish. Fog, rain and snow for example, then have the determination thereof reduced visibility result, although the actual visibility vary can.

To present, derived from experience knowledge about typical to take advantage of properties of interference, according to a particularly preferred Embodiment of the invention provided that the detection of the disorder, an assignment of a fault type, the determination of the Fault strength and / or determining the current Visibility respectively using empirically obtained in a storage means the detection device in the form of at least one Calibration or reference table or curve experience contained takes place.

In this case, therefore, are not already from the evaluation of the reflected Radiation directly absolute findings as about the disorder, a type of fault, the fault strength and / or the momentary sight reached, but the measured values ​​are used to present to determine empirical values ​​which the measured actual situation N describe.

For example, a calibration or reference table or curve for each characteristic interference property, an appropriate fault be and / or a corresponding type of fault can be removed.

Preferably, a reference table or curve is provided for each type of fault, the question for any disturbance this type characteristic Interference property, an appropriate fault strength is removed. For example, the same as the characteristic interference property measured number stochastically distributed objects per timesAnd Angle unit depending on whether it is of a malfunction Type "global", for example, rain, or a disorder of the type "spatially limited ", for example, spray, is, different strengths and disorder thus in particular results in different momentary visibility.

Further, it is preferable that a calibration or reference table or curve for each determined interference power, a corresponding value for the is momentary sight of the sensor can be removed. Particularly Here for each disorder and / or for each type of fault, a separate Reference or calibration table or curve provided.

The invention is not limited to, statements that already due one identified characteristic interference property to be hit. Thus, provided in a variant be that the detection of the fault, an assignment of a fault type, the determination of the interference power and / or the determination of the instantaneous Visibility based on different, each means of the sensor by Evaluating the reflected radiation characteristic identified Fault properties occurs.

Further, according to a particularly preferred embodiment of the Invention provided that in case a fault is detected by the characteristic interference property, in particular of a type of disturbance, dependent measures to mitigate or eliminate the Interference effect are taken.

In vehicle applications, for example, the action may in made that the presence of a fault is indicated to the driver, that certain vehicle equipment such as headlamps, fog lamps or wipers are activated that cleaning devices at least in parts of the sensor or a sensor surrounding protective cover be put into operation, that such a protecting cover in an appropriate manner in movement is set and / or that interfered with the operation of vehicles, eg by reducing the driving speed or only a predetermined Top speed is allowed.

The solution of the problem underlying the invention also takes place by the features of apparatus claim and in particular characterized in that a detection device, in particular a laser scanner, at least one sensor for the transmission of, in particular pulsed electromagnetic radiation into a monitored region and Receiving from the controlled area and reflected radiation an evaluation device for evaluating the reflected radiation , wherein the evaluation device according to the invention for carrying out a The method is designed.

Preferred embodiments of the invention are also described in the subclaims, the description and the drawing.

The invention will in the following by way of example with reference to the described drawing, the single figure to illustrate the invention schematically several mounted by means of a on a vehicle Laser scanner recognizable, leading to a reduction in visibility Disorders shows.

The vehicle 10 illustrated has on its front side and a sensor Laser scanner 12, as was explained at the outset and in the direction of travel ahead of the vehicle 10 monitoring area in at least an example horizontal scanning with radiation pulses 34 scans. The sensor 12 is an evaluation device 16 for evaluating the from the monitoring area reflected radiation by means of appropriate assigned to algorithms and memory means 18 in which Calibration tables are stored, received the more detail elsewhere becomes.

The normal, undisturbed sight 14 of the sensor 12 is through a part circle indicated. In particular, because of the widening of the scanning beam 34 is the intensity of the lying of out of sight 14 objects at least assuming normal reflectivity reflected radiation is no longer in a position to a predetermined threshold a receiving unit of the sensor 12 to exceed.

The sight or range of the sensor 12 is interference 21-27, will be discussed in more detail in the following, reduced to a value, by a further simplification of the disturbances 21-25 same pitch circle 14 'is indicated. In fact, the trouble caused Reduced Visibility 14 'of the type of fault and 21-27 of the Failure strength dependent.

When faults exemplified is for a to mist 21, rain and snow 22 23. This interference, which, for example a be assigned common disorder type "precipitation" or "global" may have in common that they in the entire field of view of the sensor 12 are available, which in the figure respectively by both at close range arranged and in a more remote area symbolism is indicated.

Further disturbances of the "local" experience, of which in the Figure to a spray 24 of a vehicle ahead 30 are caused is shown and on the other hand exhaust gases 25, which by another vehicle 32 come within view of the sensor 12th

Furthermore, the sight of the sensor 12 by contamination 26 27 or damage of the sensor 12, for example a radiation exit window or the sensor 12 surrounding protective cover, be reduced. This interference 26, 27 can, for example the type of fault "on "Be assigned sensor.

Dirt can eg if they in the form of an on Sensor present 12 lying layer of dust, the entire viewing area affect. In the figure, local sensor faults are only indicated, namely on the one hand an extended contamination 26 eg in the form of vibrated to the sensor 12 dirt or mud and on the other a punctual damage 27 eg in the form of a rockfall-related Crack or tear in the exit window or in a protective cover the sensor 12th

The sensor faults 26, 27 are each of an extent such that in the affected areas of the emitted radiation angle sensor 12 does not or at least not as useful for a scanning beam can leave, so here consequently the visibility of the sensor 12 is reduced to zero.

In one embodiment of the invention, first, the presence of the fault "rain" 22 based on characteristics identified, namely the fact that on the one hand particularly in the vicinity of a Plurality of temporally distributed stochastically occurring raw measurements, each of which a distance and an angle value, ie a direction, is assigned, is detected characterized in that the at least in the vicinity yet relatively little expanded scanning beams 34 to are reflected and detected individual raindrops, and other over the entire angular range of the sensor 12 the same Picture emerges, that is, the fault is considered globally.

In addition to these two properties disorder "stochastic behavior" and "global" can - an appropriate configuration of the sensor or the evaluation provided - as the third property the "Particle size" are taken into account by reducing the size of the radiation reflective "objects" is determined. This can be due to additional Into account the intensity of the reflected radiation done. A stored in the memory device 18 calibration table, the empirical values ​​as part of a before initial performed calibration has been obtained, it is then taken the information for the determined particle size, whether it be in the particles is raindrops or snowflakes. To this Example, the actually existing fault "rain" 22 of which alone due to the two disturbance characteristics "stochastic behavior" distinguished and "global" indistinguishable fault "Snow" 23 will.

Then the intensity of the rain 22 is determined by by Evaluating the reflected radiation as a further characteristic interference property a value for the number of raindrops per unit time and Angle unit is determined. A further, in the memory device 18 stored calibration is then for this way estimated disturbance force, a corresponding value for the current Visibility 14 'of the sensor 12 is removed, at which the normal and undisturbed Visibility is 14 reduced by the rain 22nd

In this example, the time behavior of disturbance "Rain" a plays role here are several changes for the visibility determination used successive scans of the viewing area. According to are in principle also such characteristic Disturbance characteristics for the visibility determination in question, which already are identified by a single scan of the viewing area can.

In an alternative embodiment, first only based the first two above-mentioned characteristic properties disorder "Stochastic behavior" and "global" the existence of an Fault type "precipitation" detected without interference between the "Rain" and "snow", which is associated with this type of disorder distinguished, becomes.

According to the first embodiment is then, in turn, the determined number of particles per unit time and angle unit and for this Value of the disturbance alone type "precipitation" associated calibration directly a value for the current Visibility 14 'of the sensor 12 removed, said calibration knowledge or experience includes respect of several different types of precipitation.

Compared to the first embodiment, here therefore is "coarser" worked by for the additional determination of the particle size waived distinction between different types of precipitation becomes.

Some examples of ways of using knowledge about the typical behavior of certain disorders to distinguish them from each other, were in the above embodiments, and in Introductory part already presented.

As a further possibility is mentioned, for example, that the presence of especially global disturbances such as fog or precipitation also characterized it can be seen that inhomogeneities in the field of view, the Objects not actually of interest such as other road users represent, are detected, such as those of turbulence are formed, the moving se by fog or rain through Vehicles produced. Here, the detection of a moving vehicle the assumption that fog or precipitation is present, support.

Furthermore, spatially limited disorders such as spray 24 or Exhaust gases 25 from the "real" objects, such as vehicles or people by the relatively strong statistical fluctuations of their Shape, contour or expansion can be distinguished.

Self respect other characteristic disturbance characteristics gischt- or exhaust like behaving disorders may further example be recognized by the fact that associated, expected in the immediate vicinity Items such as particular missing vehicles. Misinterpretation a drifted onto the roadway shrub or bush, the most only a short-term deterioration of the sensor RVR means as spray or plume is thus avoided.

Another interference property may also be the distance at which the disorder is detected. Global disorders such as fog or Rainfall, which is not directly related to the available functionality of the sensor 12 can thereby recognize be they in the vicinity of the sensor 12, ie in the direction of propagation of radiation are detected immediately before the sensor 12th

Spray 24 and exhaust 25 can also, for example because of their different Structure or consistency are distinguished from each other because Spray 24 - as indicated in the figure - at least partly particles a size for example of raindrops includes as not in exhaust fumes occurrence.

Furthermore, drawing contaminants 26 or damage 27 the sensor 12 by the fact that they are in the so-called Ultranah area the sensor 12 are.

Such disturbances 26, 27 can also be detected, that of the contamination 26 or damage within the sensor 12 detected 27 reflected back into the sensor 12 radiation becomes. While evidence of such, a predetermined intensity threshold exceeding internal reflections such per se in the presence may indicate disturbances, it is possible, based on the amount of radiation reflected back intensity assessments of the nature or to meet the type of damage or contamination.

Furthermore, located in disturbances can Ultranah-range or short-range Then, when in the vicinity also "real" objects as are eg other traffic, including by recognized be that so-called to the sensor 12 separation edges or mixing distances be measured. Such "ghosts measurements" that no actually present in the measured distance object correspond to, are a consequence of the length of the emitted laser pulses. The Detection "apparent" measuring points between the sensor 12 and a close, regarded as actually existing object object can thus as an indication of the presence of contamination or 26 Damage 27 counted the sensor 12th

Disorders can partially cover "real" objects, which a Object recognition, in the framework of the inventive method is carried out, can affect. According to the invention provided be that in the case of such trouble-induced occlusions this recognized as such and carried out at a within the object detection Occlusion detection are taken into account.

<u>LIST OF REFERENCE NUMBERS</u>

<dl tsize="3" compact="compact"><dt>10</dt><dd>vehicle</dd><dt>12</dt><dd>Sensor, laser scanner</dd><dt>14</dt><dd>visibility</dd><dt>14 '</dt><dd>reduced Visibility</dd><dt>16</dt><dd>evaluation</dd><dt>18</dt><dd>memory device</dd><dt>21</dt><dd>fog</dd><dt>22</dt><dd>rain</dd><dt>23</dt><dd>snow</dd><dt>24</dt><dd>spray</dd><dt>25</dt><dd>plume</dd><dt>26</dt><dd>sensor contamination</dd><dt>27</dt><dd>sensor damage</dd><dt>30</dt><dd>another vehicle</dd><dt>32</dt><dd>another vehicle</dd><dt>34</dt><dd>Radiation pulse, scanning</dd></dl>