Method and device for traffic monitoring using road vibrations and laser vibrometry

Abstract

Method for detecting a vehicle (1) approaching on a roadway (2), wherein vibrations of the roadway (2) are detected, wherein the vibrations of the roadway (2) are detected by laser vibrometry, wherein a laser beam (7) is directed onto the roadway and a portion (8) of the laser beam returning from the roadway (8) is analyzed, characterized in that the vibrations of the roadway (2) are detected by laser vibrometry from another vehicle (9).

Description

TECHNICAL AREA OF INVENTION

[0001] The invention relates to a method for detecting a vehicle approaching on a roadway, wherein vibrations of the roadway are detected.

[0002] More specifically, the invention aims to detect a vehicle approaching on a collision course on the road in order to prevent an imminent collision with another vehicle.

[0003] Many vehicle collisions occur because neither the drivers nor any vehicle assistance systems recognize that the vehicles are on collision courses in their shared lane. This failure to recognize can be caused by obstructed views of the road ahead due to curves or bumps. Furthermore, mutual visibility between vehicles can be impaired, for example, at intersections, by buildings or other obstructions, or, regardless of the road's shape, by weather conditions such as fog or heavy rain. While there are driver assistance systems that use radar or infrared light, outside the range of visible electromagnetic waves, to detect approaching vehicles, these systems also require a direct line of sight to detect an approaching vehicle. STATE OF THE ART

[0004] From Hostettler R, Birk W, Lundberg Nordenvaad M. Feasibility of Road Vibrations-based Vehicle Property Sensing. Intelligent Transport Systems, IET. 2010 December; 4(4):356-364, it is known to detect vehicle properties based on vibrations of a road surface induced by the vehicles. For this purpose, the road surface vibrations are detected using accelerometers mounted directly on the road surface. The signals from the accelerometers can be used to specifically identify the axes of passing vehicles.

[0005] From Ma W, Xing D, McKee A, Bajwa R, Flores C, Fuller B, Varaiya P. A Wireless Accelerometer-Based Automatic Vehicle Classification Prototype System. IEEE Transactions on Intelligent Transportation Systems, Vol. 15, No. 1, February 2014, a vehicle classification system is known that incorporates wireless accelerometers and magnetic sensors. The accelerometers detect vibrations of a roadway on which the vehicles to be classified are traveling. The automatic vehicle classification system is capable of counting the axles of the vehicles and determining their distances.

[0006] From Ye Z, Wang L, Xu W, Gao Z, Yan G. Monitoring Traffic Information with a Developed Acceleration Sensing Node. Sensors 2017, 17, 2817, it is known to acquire traffic information using an accelerometer node that registers vibrations of a road surface over which traffic is traveling. Using the accelerometer node, quantities such as the respective vehicle speed and the wheelbase can be determined.

[0007] From Dräbenstedt A. Diversity Combining in Laser Doppler Vibrometry for Improved Signal Reliability. AIP Conference Proceedings 1600, 263 (2014), it is known how the signal reliability of a heterodyne laser Doppler interferometer for non-contact vibration measurement, i.e., in laser Doppler vibrometry, can be improved when the signal reliability is impaired, for example, because a surface whose vibrations are to be measured moves transversely. The transverse movement of the surface leads to variations in the speckle pattern of a laser beam directed at the surface, so that a portion of the laser beam returning from the surface and being recorded exhibits intensity fluctuations.To suppress the negative effects of these intensity fluctuations on the laser Doppler vibrometry results, several statistically independent components of the laser beam reflecting from the surface are recorded and pre-evaluated separately. The results of these pre-evaluations are then combined. Since simultaneous intensity jumps, particularly abrupt changes in intensity, are unlikely in the separately recorded, statistically independent components of the light reflecting from the surface, only very short gaps in the observations remain. Specifically, the separate recording and pre-evaluation of such components of the laser beam reflecting from the surface that are spatially distinct or exhibit different polarizations is described.

[0008] German patent application DE 102016 108 273 A1 discloses a method for evaluating signals from at least one vibration sensor connected to a railway track. The signals are fed to an evaluation unit where the signal's power spectral density is analyzed. From this, the distance of a train from the vibration sensor's position and / or the train's speed can be derived. Alternatively, the signal power and / or the temporal change in signal power at one or more characteristic frequencies and / or within a frequency range around these characteristic frequencies can be evaluated to derive the expected time of the train's arrival at the vibration sensor's position and / or the time elapsed since the train passed the vibration sensor's position and / or the train's speed.The vibration sensor can detect vibrations without contact, for example using optical measurement methods with a laser. With two vibration sensors, the train's direction of travel can be determined. TASK OF INVENTION

[0009] The invention is based on the objective of demonstrating a method for detecting an approaching vehicle that does not require a direct line of sight to the vehicle and that can be carried out from another vehicle in order to warn of collisions with the approaching vehicle. SOLUTION

[0010] The object of the invention is achieved by a method with the features of independent claim 1. Dependent claims 2 to 14 relate to preferred embodiments of the method according to the invention. Claim 15 relates to a vehicle for carrying out the method according to the invention. Claims 16 and 17 relate to preferred embodiments of the vehicle according to the invention. DESCRIPTION OF THE INVENTION

[0011] In a method according to the invention for detecting a vehicle approaching on a roadway, vibrations of the roadway are detected by laser vibrometry from another vehicle, wherein a laser beam is directed onto the roadway and a portion of the laser beam returning from the roadway is analyzed.

[0012] Where the term "roadway" is used here, it refers, for example, to an entire road or the section of a highway, particularly a motorway, assigned to a specific direction of travel, which has a continuous road surface or other continuous road structure. The term "roadway" here does not refer to a single lane of a multi-lane road. The term "roadway" also covers multiple roads connected by junctions and / or intersections, as long as these multiple roads are linked by a continuous road surface or other continuous road structure. This continuous road surface or other continuous road structure does not necessarily have to be constant throughout, i.e., it does not need to have a constant composition or thickness.

[0013] Furthermore, the term roadway also covers taxiways for aircraft, and the term vehicle covers any objects moving on a roadway, including aircraft performing taxi services.

[0014] Every road surface is set into vibration by the vehicles traveling on it, causing the road surface to move perpendicular to its main plane of extension. A significant portion of these vibrations originates from the wheels of the vehicles rolling on the road surface. The vibrations propagate along their main plane of extension across the road surface at a speed considerably higher than the speed of sound in air. The vibrations of the road surface attenuate according to 1 / √r, where r is the distance from the point of excitation. In other words, the vibrations of the road surface can still be detected at a considerable distance from their point of excitation. Simultaneously, the vibrations at any given point on the road surface are dominated by the vibrations that are closest to that point.

[0015] The method according to the invention uses the vibrations of the road surface caused by the approaching vehicle to detect that vehicle. This detection can, in particular, also include recognizing whether the vehicle is on a collision course where a collision with, for example, another vehicle is imminent. The information required for this is extracted from the temporal and spatial evolution of the detected vibrations of the road surface.

[0016] In the method according to the invention, the vibrations of the road surface are detected by laser vibrometry, i.e. contactlessly and at least one point on the road surface, which is defined by an impact point of the laser beam directed onto the road surface during laser vibrometry.

[0017] The method according to the invention does not require a direct line of sight to the approaching vehicle. Information is transmitted from the approaching vehicle via the road surface. As long as the vibrations of the road surface on which the approaching vehicle is traveling can be detected by laser vibrometry, the method according to the invention is functional.

[0018] The method according to the invention is insensitive to other excitations of the roadway to vibrations than those caused by vehicles driving on it, since vehicles driving on a roadway excite the roadway to vibrations with a specific frequency spectrum in the range of typically a few hundred Hertz, and because the vibrations develop spatially and temporally in a specific way as the vehicle approaches.

[0019] To accurately capture the spatial and temporal evolution of road vibrations as a basis for detecting an approaching vehicle, it is preferred to record the vibrations at multiple points on the road. It is particularly preferred to record the vibrations at these multiple points simultaneously or at least quasi-simultaneously, that is, with rapid switching between the points. From the temporal and spatial evolution of the road vibrations, the location and, in particular, changes in the location of the approaching vehicle, and thus its speed and direction of approach, can be determined.While simultaneous detection of vibrations at multiple points on the roadway requires directing several laser beams, or at least a laser beam divided into several partial beams, quasi-simultaneous detection of vibrations at multiple points can be achieved by using a single laser beam that is directed at the multiple points on the roadway as quickly as possible, allowing for the detection of vibrations at each point.

[0020] The laser beam can, in principle, have a constant intensity. However, it can be advantageous to pulse the laser beam in order to concentrate its energy into individual pulses, during which the vibrations of the road surface are then detected. Concentrating the energy of the laser beam into individual pulses can be particularly useful if the portion of the laser beam returning from the road surface is small because the road surface absorbs a significant portion of the laser beam and / or the laser beam strikes the road surface at a relatively shallow angle. Furthermore, both the absorption of the laser beam by the road surface and the angle at which the laser beam strikes the road surface can vary considerably when carrying out the method according to the invention.To compensate, the intensity of the laser beam can be varied depending on the intensity of the reflected component of the laser beam from the road surface, so that this reflected component reaches a predetermined minimum intensity. This minimum intensity must be set so that it is sufficient for a meaningful analysis of the reflected component with respect to the vibrations of interest in the road surface.

[0021] To compensate for the potentially unfavorable boundary conditions under which laser vibrometry is performed in the method according to the invention, several statistically independent components of the laser beam reflecting off the road surface can be analyzed at least partially separately, with the results of the separate analyses then being combined. In particular, variations in speckle patterns formed by the laser beam striking the road surface can thus be controlled. The statistically independent components of the laser beam can, for example, be spatially distinct or differ in their polarization.

[0022] Specifically, the laser vibrometry used in the method according to the invention can be heterodyne laser Doppler vibrometry. In heterodyne laser Doppler vibrometry, the component of the laser beam returning from the road surface is superimposed with a reference beam whose frequency is shifted by a frequency difference relative to the frequency of the laser beam. This results in an interference signal with a fundamental frequency of the frequency difference, the fundamental frequency being modulated by varying Doppler shifts of the component of the laser beam returning from the road surface. The varying Doppler shifts indicate the movements of the vibrating road surface in the direction of the laser beam, that is, its vibration component in precisely this direction. Accordingly, the vibrations of the road surface can be extracted from the interference signal.

[0023] As already indicated, in the inventive method for detecting the approaching vehicle, the vibrations of the road surface, which are excited by the wheels of the vehicle rolling on the road surface, can be specifically considered.

[0024] In addition to detecting an approaching vehicle, including its direction and speed, the recorded vibrations of the road surface can also be analyzed to determine the type of vehicle. In particular, the mass of the approaching vehicle can be estimated.

[0025] Furthermore, the method according to the invention makes it possible to evaluate the vibrations of the roadway with respect to the surface condition of the roadway. The interactions between the roadway and the wheels rolling on it, which lead to the excitation of the roadway vibrations, depend on the surface condition of the roadway, for example, whether the roadway is dry, damp, wet, icy, or snow-covered. Thus, the method according to the invention provides valuable information about the condition of the roadway.

[0026] This information is often particularly valuable because, in the method according to the invention, the vibrations of the road surface are detected from another vehicle using laser vibrometry. By having the method according to the invention carried out from another vehicle to detect the approaching vehicle, an assistance system is provided for the vehicle that can alert the driver of the vehicle or the control system of an autonomous vehicle to the approaching vehicle in order to evade it and / or avoid a collision by braking, or at least limit the potential consequences of an unavoidable collision. It is understood that, in the method according to the invention, the relative movement of the approaching vehicle with respect to the other vehicle, i.e., the approach of the vehicle to the other vehicle, is of particular interest.

[0027] At least one point on the roadway where the vibrations from the other vehicle are detected can be positioned at a distance in front of the other vehicle in the direction of travel. A certain distance between the point where the vibrations are detected and the vehicle from which they are detected is generally advantageous because the other vehicle, when traveling on the same roadway, itself induces vibrations in the roadway. While these vibrations can generally be separated from those in the roadway caused by the approaching vehicle, this separation is easier if the vibrations caused by the other vehicle are not significantly stronger than those caused by the approaching vehicle.Furthermore, vibrations are more easily detected at a point on the roadway in front of the respective other vehicle, which are excited by a vehicle approaching via a branch of the roadway.

[0028] If, in the inventive method carried out from the other vehicle, the point of impact of the laser beam on the road surface moves across the road surface with the other vehicle, a frequency shift of the component of the laser beam returning from the road surface can occur due to a structured road surface. This shift is not due to vibrations of the road surface but rather to a surface profile of the road surface. It may therefore be preferable if the laser beam directed onto the road surface from the other vehicle is pivoted relative to the other vehicle, depending on its speed and steering angle, such that the laser beam remains directed at a constant point on the road surface for a period of time when vibrations are detected.It is understood that in this embodiment of the method according to the invention, the changing angle of incidence of the laser beam on the road surface, which changes when the laser beam is swiveled relative to the other vehicle, must be taken into account. This applies not only in geometric terms. Variations in the intensity of the portion of the laser beam returning from the surface at different angles are also appropriately compensated. Furthermore, it is understood that the swiveling of the laser beam relative to the vehicle must be carried out depending on the speed of the other vehicle. However, this speed of the other vehicle is typically measured anyway and can therefore be assumed to be known.

[0029] To extract the relevant road vibrations from the laser vibrometry signal, it is useful to detect the vibrations of the other vehicle and take them into account when measuring the road vibrations using laser vibrometry. For example, the vibrations of the other vehicle can be detected with an accelerometer to compensate for their effect on the laser vibrometry.

[0030] In one embodiment of the method according to the invention, which is carried out from the other vehicle, the vibrations of the road surface are correlated with the position of the other vehicle on a road network, determined by satellite navigation, upon detection of the approaching vehicle. With a specific known position of the other vehicle on the road network, the vibrations of the road surface detected by laser vibrometry can be more easily assigned to a specific direction of travel of the approaching vehicle than without this knowledge.

[0031] Furthermore, in the method according to the invention, when detecting an approaching vehicle, the vibrations of the road surface can be correlated with signals from other methods for detecting approaching vehicles from the other vehicle. That is, in the method according to the invention, several assistance systems, including an assistance system implementing the method according to the invention, can be combined with one another in order to detect the approaching vehicle as accurately as possible, particularly with regard to its speed and direction of travel.

[0032] A vehicle according to the invention has a laser vibrometer, which, including its evaluation devices, is designed to carry out the method according to the invention from within the vehicle.

[0033] The laser vibrometer of the vehicle according to the invention can in particular have a scanner to direct the laser beam of the laser vibrometer specifically to a certain point of the respective roadway.

[0034] In particular, the laser vibrometer is a heterodyne laser Doppler vibrometer. To avoid the need for a Bragg cell to provide the frequency difference between the laser beam and the reference beam, two coupled lasers with different laser frequencies can be used to provide the laser beam and the reference beam, respectively.

[0035] Advantageous further developments of the invention result from the patent claims, the description and the drawings.

[0036] The advantages of features and combinations of features mentioned in the description are merely exemplary and can have an effect alternatively or cumulatively, without the advantages necessarily having to be achieved by embodiments according to the invention.

[0037] Regarding the disclosure content—not the scope of protection—of the original application documents and the patent, the following applies: Further features can be derived from the drawings—in particular, the geometries depicted and the relative dimensions of several components to one another, as well as their relative arrangement and functional connection. The combination of features from different embodiments of the invention or from features of different claims is also possible, deviating from the chosen cross-references of the claims, and is hereby encouraged. This also applies to features that are illustrated in separate drawings or mentioned in their description. These features can also be combined with features from different claims.Likewise, features listed in the patent claims may be omitted for further embodiments of the invention, but this does not apply to the independent patent claims of the granted patent.

[0038] The features mentioned in the claims and the description are to be understood, with regard to their number, as meaning that exactly that number or a greater number than the stated number is present, without the need for the explicit use of the adverb "at least". Thus, for example, if a laser beam is mentioned, this is to be understood as meaning that exactly one laser beam, two laser beams, or more laser beams are used. The features listed in the claims may be supplemented by further features or may be the only features that the respective method or device possesses.

[0039] The reference numerals contained in the patent claims do not constitute a limitation of the scope of the subject matter protected by the patent claims. They merely serve the purpose of making the patent claims easier to understand. BRIEF DESCRIPTION OF THE FIGURES

[0040] The invention will now be further explained and described with reference to preferred embodiments shown in the figures. Fig. Figure 1 illustrates a method not covered by the patent claims using a stationary laser vibrometer. Fig. Figure 2 illustrates an embodiment of the method according to the invention with a laser vibrometer arranged on a vehicle and thus mobile. Fig. Figure 3 illustrates a variant of the in Fig. 2 illustrated methods according to the invention. Fig. Figure 4 illustrates an application of the in Fig. 2 illustrated procedures. Fig. Figure 5 illustrates another variant of the in Fig. 2 illustrated procedures. Fig. Figure 6 shows a heterodyne laser Doppler vibrometer for carrying out the method according to the invention. Fig. Figure 7 illustrates the signal processing of the output signals of the laser Doppler vibrometer according to Fig. 6. Fig. Figure 8 illustrates an application of the method according to the invention at an airport. FIGURE DESCRIPTION

[0041] Fig. Figure 1 shows a vehicle 1 traveling on a roadway 2. The wheels 3 of the vehicle 1 roll on the roadway 2. This rolling motion of the wheels 3 on the roadway 2, and the vibrations of the vehicle 1 transmitted to the roadway 2 via the wheels 3, cause the roadway 2 to vibrate. These vibrations propagate along the roadway 2, as indicated by a double arrow 4. The propagation of the vibrations along the roadway 2 is faster and covers greater distances than the propagation of airborne sound 5 emanating from the vehicle 1. A laser vibrometer 6 directs a laser beam 7 onto the roadway 2 and registers and analyzes the portion 8 of the laser beam 7 returning from the roadway 2. In this way, the vibrations of the roadway 2 are detected by the laser vibrometer 6.The temporal evolution of these oscillations, for example the increase in their intensity, as well as their spectral composition, allows conclusions to be drawn about whether vehicle 1 is approaching or moving away and what type of vehicle 1 it is. In particular, vehicle 1 can be identified as approaching.

[0042] Fig. Figure 2 illustrates the detection of the approaching vehicle 1 using the laser vibrometer 6 from another vehicle 9, on which the laser vibrometer 6 is mounted. By detecting the vibrations of the road surface 2, which are excited by the wheels 3 of the vehicle 1 traveling ahead, with the laser vibrometer 6 from the other vehicle 9, the vehicle 1 is detected even if there is no line of sight 10 between the other vehicle 9 and the vehicle 1. As an example of how this line of sight 10 can be interrupted, Figure 2 shows... Fig. 2 Heavy rain 11 is indicated. The relative approach of vehicle 1 to vehicle 9 is of interest, regardless of whether this relative approach is due to opposite directions of travel or different speeds in the same direction. In any case, the intensity of the vibrations of the roadway 2 detected by the laser vibrometer 6 increases as vehicle 1 approaches the other vehicle 9. It is understood that the wheels 12 of the other vehicle rolling on the roadway 2 also cause vibrations in the roadway 2. However, these vibrations do not change their intensity, or only depending on a condition of the other vehicle 9 that can be detected in another way. Furthermore, the heavy rain 11 can also cause vibrations in the roadway 2.The vibrations resulting from these excitations are, however, distinguishable from the vibrations of the road surface 2, which are excited by the wheels 3 of vehicle 1 rolling on it, by their different frequency spectrum and also their different temporal profile. Furthermore, the output signal of the laser vibrometer 6 is influenced by vibrations of the other vehicle 9, which lead to relative movements of the laser vibrometer 6 with respect to the road surface 2. These influences can, however, be separated, in particular by detecting vibrations of the other vehicle 9 using an accelerometer and / or by directly measuring the relative movements of the other vehicle 9 with respect to the road surface 2.

[0043] Fig. Section 3 explains how, by detecting vibrations of the road surface 2 propagating in all directions from vehicle 1, as indicated here by some arrows 13, the approach of vehicle 1 to an intersection 14 can be detected by the other vehicle 9, by detecting the vibrations of the road surface 2 from vehicle 9 using the laser vibrometer 6. This detection is independent of whether an obstacle 15 obstructs the view of vehicle 1 from the other vehicle 9. Fig. Figure 3 further indicates the possibility that the laser beam 7 from the laser vibrometer 6 is not only directed at a single point 16 on the roadway 2, defined relative to the other vehicle 9, in order to detect the vibration of the roadway 2 at this point 16, but is directed successively at various points 16 to 20 using a scanner of the laser vibrometer 6 (not shown separately here). The laser beam 7 can be pulsed such that at each of the points 16 to 20, a pulse of precisely the length required to measure the vibrations of the roadway 2 occurs. By detecting the vibrations of the roadway at multiple points 16 to 20, a spatial development of the vibrations of the roadway 2 can be recorded and analyzed with regard to the information it contains about the vehicle 1 and its approach.

[0044] Fig. Figure 4 illustrates how, with the aid of the laser beam 7 of the laser vibrometer 6, directed in particular at a point 16 of the roadway 2 located in front of the other vehicle 9, the vehicle 1 can be detected even if it is not directly visible from the other vehicle 9 due to a curve 21 of the roadway 2. The vibrations of the roadway 2, indicated here by curved wavefronts 47 and excited by the vehicle 1, precede the vehicle 1 by a considerable distance, thus allowing the approaching vehicle 1 to be detected long before it is visible from the other vehicle 9.

[0045] Fig. Figure 5 illustrates the possibility of directing the laser beam 7, which is again not shown separately, onto a fixed point 16 on the roadway 2 despite the movement of the other vehicle 9, using a scanner of the laser vibrometer 6. This shows Fig. 5A the other vehicle 9 at an even greater distance from this point 16 and Fig. 5B the vehicle 9 at a shorter distance from the same point 16. In this way, the influence of the road surface 2's elevation profile on the output signal of the laser vibrometer 6 can be suppressed. Different intensities of the component 8 of the laser beam 7 returning from the road surface 2 can be compensated for by varying the intensity of the laser beam 7.

[0046] Fig. Figure 6 illustrates a heterodyne laser Doppler vibrometer 22 as a specific embodiment of the laser vibrometer 6. The laser beam 7 is provided by a laser 23 and directed via the scanner 24 onto point 16 of the roadway 2. The component 8 of the laser beam 7 returning from the roadway 2 is scanned by the laser 24 and then separated from the beam path of the laser beam 7 in a beam splitting device 25. The beam splitting device 25 can be a beam splitter cube; however, it can also, for example, spatially separate the component 8 from the laser beam 7, which is highly localized in the area of ​​the beam splitting device 25. The component 8 is then superimposed with a reference beam 26.For this purpose, both the component 8 and the reference beam 26 are split into two mutually orthogonal polarization directions using a polarization beam splitter 27, and the resulting interference signals in both polarization directions are then detected by detectors 28 and 29. The components of component 8 that are orthogonal with respect to their polarization are statistically independent of each other and thus typically are not simultaneously affected by changes in a speckle pattern that the laser beam 8 forms when it strikes point 16 of the roadway 2. The frequency of the reference beam 26 is shifted relative to the laser beam 27 by a fixed frequency difference. For this purpose, the reference beam 26 can be branched off from the laser beam 7 and frequency-shifted using a Bragg cell or another frequency modulator.Here, a further laser 30 is provided for the reference beam 26, which is coupled to the laser 23 via a coupling device 31 such that the desired frequency difference between the reference beam 26 and the laser beam 7 occurs. The frequency difference is the fundamental frequency of the signals from detectors 28 and 29, which, however, is modulated by Doppler shifts of the component 8 relative to the laser beam 7, which occur due to relative movements of the roadway 2. The frequency modulation of the signals from detectors 28 and 29 therefore contains the information about the vibrations of the surface 2, which can be extracted from this by demodulation.

[0047] Fig. Figure 7 illustrates how the output signals 32 and 33 of the detectors 28 and 29 are fed to separate demodulators 34 and 35, with signal strength detectors 36 and 37 assessing the signal strengths of the output signals 32 and 33. A summing device 38 then determines a signal strength-weighted sum 39 of the output signals 40 and 41 of the demodulators, which is a robust output signal of the laser Doppler vibrometer 22.

[0048] Fig.Figure 8 illustrates an application of laser vibrometry for traffic monitoring at an airport 42, where the runway 2, whose vibrations are detected, is a taxiway 43. The vibrations can be detected with the laser vibrometer 6 from an aircraft 44 performing a taxiing maneuver or stationary on the taxiway 43, in order to detect an approaching ground vehicle 45. Alternatively or additionally, traffic monitoring on the taxiway 43 can be carried out from a control tower 46 using a stationary laser vibrometer 6. For example, a ground vehicle 45 obscured by the aircraft 44 can be detected from the control tower 46, and its movement on the taxiway 43 can be tracked. REFERENCE MARK LIST 1 vehicle 2 lanes 3-wheeler 4 Double Arrow 5 Airborne sound 6 Laser vibrometers 7 Laser beam 8 Returning portion of the laser beam 7 9 other vehicles 10 Line of sight 11 Heavy rain 12 Wheel of the other vehicle 9 13 Arrow 14 Intersection 15th obstacle 16 points of the roadway 17 points of the roadway 18 points of the roadway 19 points of the roadway 20 points of the roadway Curve 21 22 Laser Doppler vibrometers 23 lasers 24 scanners 25 Beam separation device 26 Reference beam 27 Polarization beam splitters 28 Detector 29 Detector 30 lasers 31 Coupling device 32 Output signal of the detector 28 33 Output signal of the detector 29 34 Demodulator 35 Demodulator 36 Signal strength detection device 37 Signal strength detection device 38 summing device 39 weighted sum 40 Output signal of the demodulator 34 41 Output signal of the demodulator 35 42 Airport 43 Runway 44 aircraft 45 Ground vehicle 46 Control tower 47 Wavefront

Claims

[1] Method for detecting a vehicle (1) approaching on a roadway (2), wherein vibrations of the roadway (2) are detected, wherein the vibrations of the roadway (2) are detected by laser vibrometry, wherein a laser beam (7) is directed at the roadway and a portion (8) of the laser beam returning from the roadway (8) is analyzed, characterized by , that the vibrations of the road surface (2) are detected by laser vibrometry from another vehicle (9). [2] Method according to claim 1, characterized by , that the vibrations are detected at several points on the roadway (2). [3] Method according to claim 2, characterized by , that the vibrations at the several points (16 - 20) of the roadway (2) are detected simultaneously or quasi-simultaneously. [4] Method according to any one of the preceding claims, characterized by , that the laser beam (7) is pulsed. [5] Method according to any one of the preceding claims, characterized by , that the intensity of the laser beam (7) varies depending on the intensity of the component (8) of the laser beam (7) returning from the roadway. [6] Method according to any one of the preceding claims, characterized by , that several components (8) of the laser beam (7) returning from the roadway, which are statistically independent of each other, are analyzed at least partially separately. [7] Method according to any one of the preceding claims, characterized by that laser vibrometry is heterodyne laser Doppler vibrometry. [8] Method according to any one of the preceding claims, characterized by , that to detect the approaching vehicle (1) the vibrations of the road surface (2) are considered which are excited by the wheels (3) of the vehicle (1) rolling on the road surface (2). [9] Method according to claim 8, characterized by, that the detected vibrations of the road surface (2) are evaluated with regard to the type and / or mass and / or speed and / or direction of travel of the approaching vehicle (1). [10] Method according to any one of the preceding claims, characterized by , that the vibrations of the roadway (2) are evaluated with respect to a surface condition of the roadway (2). [11] Method according to any one of the preceding claims, characterized by , that at least one point (16 - 20) of the roadway (2) where the vibrations are detected is arranged in the direction of travel of the other vehicle (9) at a distance in front of the other vehicle (9). [12] Method according to any one of the preceding claims, characterized by, that the laser beam (7) directed at the roadway (2) is swivelled relative to the other vehicle (9) depending on a speed and a steering angle of the other vehicle (9) such that the laser beam (7) remains directed at a constant point (16 - 20) of the roadway (2) for a vibration detection period. [13] Method according to any one of the preceding claims, characterized by , that vibrations of the other vehicle (9) are detected and taken into account when detecting the vibrations of the road surface (2) by laser vibrometry. [14] Method according to any one of claims 1 to 12, characterized by , that when detecting the approaching vehicle (1), the vibrations of the road surface (2) are correlated with a position of the other vehicle (9) determined by satellite navigation on a road network and / or with signals from other methods for detecting approaching vehicles (1) from the other vehicle (9). [15] Vehicle (9) with a laser vibrometer (6) which is configured to carry out the method of one of the preceding claims from the vehicle (9). [16] Vehicle (9) according to claim 15, characterized by that the laser vibrometer (6) has a scanner (24). [17] Vehicle (9) according to claim 15 or 16, characterized by , that the laser vibrometer (6) is a heterodyne laser Doppler vibrometer (22) which has two coupled lasers (23, 30) of different laser frequencies to provide the laser beam (7) and a reference beam (28).

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