CH715882A2 - Acoustic instrument and method for recognizing an acoustic signal emitted by a vehicle. - Google Patents

Abstract

The present invention relates to a method for recognizing an acoustic signal from a moving vehicle and consists of: - aiming with a sound level meter (20) in the direction of a noisy vehicle; - measuring by a sound sensor the sound intensity of the noisy vehicle (10) when it is in a first position P1; - determining the distance (D) between the sound level meter and one of the surfaces of the vehicle (10) which is in the first position P1; - Carry out a first measurement I1 of the sound intensity referred to a reference distance (Dr) pre-chosen relative to the vehicle (10); - identify the vehicle (10) if the standard sound intensity I1 at the reference distance (Dr) is higher than an authorized value. The invention also relates to an acoustic instrument (1) comprising a sound level meter (20), a system for measuring the distance between the sound level meter (20) and a noisy vehicle (10) and an identification system for this vehicle (10). ).

Description

Technical area

The present invention relates to the field of noise pollution, such as caused by noisy vehicles. More particularly, the invention relates to methods and systems for measuring the distance to a sound source and determining its intensity relative to a frame of reference. The invention also relates to the recognition and identification of a noisy vehicle.

State of the art

[0002] Noise pollution is a recurring problem in modern times. Huge amount of motor vehicles like cars, trucks, mopeds, trains and others are moving everywhere every day. Most of these vehicles are noisy because they use internal combustion engines. Pollution induced by sound from vehicles can have serious negative effects on health. The range of frequencies emitted can vary greatly depending on the type of vehicle. From near ultrasound to infrasound, a wide range of wavelengths can be a source of stress or have pathological consequences, depending on the intensity and duration of the noise as well as the sensitivity of people to animals.

[0003] In some countries vehicle noise is a major source of noise pollution. In France, for example, the human impact of transport noise pollution alone is estimated in 2016 at at least 50 billion euros per year. There are also special situations such as residential areas or areas close to hospitals or nursing homes where the excessive noise produced by vehicles may be difficult to tolerate or even strictly prohibited.

To limit this, laws and standards have been put in place, in most countries, for all approved vehicles, in terms of noise emissions.

[0005] However, said standards are not necessarily respected. Some people change parts between two noise checks on their vehicle so that they can be louder than allowed, and so they are difficult to identify.

[0006] There is therefore a need to acquire devices making it possible to detect whether a vehicle is in violation of the standards, directly at the time of the facts of the violation and to identify it. This information would make it possible to carry out a control without giving the owner time to redo any modifications.

[0007] There are a number of instruments for measuring vehicle noise, but these instruments are attached to a certain place and measure the noise of a vehicle passing over a range of relatively limited distances relative to the sound measuring instrument . One of the disadvantages of such systems is that drivers can easily reduce their speed when passing near them, as is done when approaching fixed speed cameras to measure speed.

The situation becomes more complicated when the vehicles in question are not vehicles which move on a road or a rail but they are aircraft such as for example helicopters or drones which will be increasingly no longer used for the transport of goods or people. Fixed or semi-mobile systems are not at all suitable for this type of vehicle.

Disclosure of the invention

A method and system for identifying a vehicle that produces noise above a defined standard is provided. The vehicle is understood in the broad sense and can include not only vehicles such as cars, motorcycles or trucks but any type of vehicle whether motorized or not.

In particular the invention is carried out by a method for recognizing an acoustic signal from a moving vehicle. The method of the invention consists in: identifying the passage of a noisy vehicle; - switch on a sound level meter on a portable acoustic instrument; - aim with the sound level meter in the direction of said noisy vehicle; - measure the sound level of the noisy vehicle when it is in a first position; - determine the distance between the sound level meter and one of the surfaces of the vehicle which is in the first position; - determining the sound intensity (11) of said noisy vehicle at a pre-selected reference distance (Dr) relative to said vehicle (10); - identify the vehicle (10) if the sound intensity (11) at the reference distance (dR) is higher than an authorized value.

[0011] In an implementation of the measurement of the sound level, the measurement of said distance, as well as the identification of the vehicle are carried out simultaneously.

[0012] In an advantageous implementation, after said sound measurements made in said first position, the sound level of the vehicle as well as the distance of the vehicle from the sound level meter are measured in a second position of the vehicle.

In a variant, a second value of the normalized sound intensity (12) is determined.

In a variant, the average of said first (11) and second (12) value of the normalized intensity is determined, said average being determined for a spectrum of predetermined frequencies.

[0015] In one embodiment, the identification of the vehicle is also made in said second position of the vehicle.

[0016] In a preferred embodiment, the identification of the vehicle is done by the identification of the vehicle registration number.

[0017] In one variant, the identification of the vehicle is done by recognizing the shape and / or the brand of the vehicle.

[0018] In a variant, the identification of the vehicle is done by recognizing the vehicle number and the shape and / or the make of the vehicle.

In a variant the identification of the vehicle is made by recognizing an identification code integrated into the vehicle, this identification code being other than the vehicle number.

[0020] In an advantageous mode, an alarm signal is sent to the vehicle indicating that the vehicle is too noisy.

In a variant, the alarm signal is displayed inside the vehicle in order to alert the driver of the noisy vehicle.

[0022] In an advantageous mode, said acoustic instrument comprises means for determining and recording the sound spectrum of the noisy vehicle.

The invention is also achieved by an acoustic instrument for recognizing an acoustic signal produced by a vehicle, the acoustic instrument include a sound level meter and also include: - means for measuring the distance of the vehicle from the sound level meter; A unit for storing sound level detection threshold criteria; A man-machine interface for displaying a representation of the normalized emitted sound level relative to a reference distance (dR) chosen beforehand; - means to identify the vehicle.

[0024] In one embodiment, said means for identifying the vehicle comprise a vision system making it possible to recognize the license plate of the vehicle.

In one embodiment, said means for identifying the vehicle comprise a vision system making it possible to recognize the make and / or the type of the vehicle.

[0026] In one embodiment, the acoustic instrument also comprises a display of a representation of the non-standardized sound level.

[0027] In one embodiment the acoustic instrument comprises at least two sound level meters and / or two means for measuring the distance from the vehicle relative to the sound level meter.

[0028] In one embodiment the means for measuring the distance from the vehicle relative to the sound level meter are optical means.

[0029] In one embodiment, the optical means comprise a laser.

[0030] In one embodiment the means for measuring the distance from the vehicle comprise a radar system.

[0031] In one embodiment, the means for measuring the distance from the vehicle comprise a system using triangulation techniques.

In one embodiment the sound of a vehicle can be detected up to a distance of 100m.

[0033] In one embodiment the acoustic instrument is the size of a mobile phone preferably having a length between 15cm and 20cm, a width between 7cm and 9cm and a thickness between 5mm and 15mm.

[0034] In one embodiment, the means for identifying the vehicle include lenses and the focal length of at least one of the lenses of the instrument has a focal length greater than the thickness of the instrument.

Brief description of the drawings

Other characteristics of the present invention will emerge more clearly on reading the following description, made with reference to the accompanying drawings, in which: - Figure 1a is a schematic view of the use of an instrument acoustics according to the invention; - Figure 1b is a schematic view of the use of a miniaturized acoustic instrument according to the invention; FIG. 2 is a schematic view of an aircraft comprising an identification code and of the implementation of sound and distance measurements made in two positions of the aircraft; FIG. 3 shows a block diagram of the method of the invention; FIG. 4 is a schematic view of a noise reference measurement configuration; FIG. 5 is a block diagram of the components and their communications for an audio measurement; FIG. 6 is an electronic diagram used to amplify the audio signal; - Figure 7 shows the directivity of a commercial microphone; FIG. 8 is a schematic view of an aliasing effect of a signal during sampling; FIG. 9 is an electronic diagram used with the PIC microcontroller; FIG. 10 is an electronic diagram used for reading / writing SRAMs; FIG. 11 and FIG. 12 show write and read signals on RAM in SP; FIG. 13 is a block diagram of the components of the acoustic instrument as well as their communication bus; FIG. 14 is a block diagram of the behavior of a PIC microcontroller during sampling; FIG. 15 is a block diagram of the behavior of a Raspberry Pi according to the action of the user; FIG. 16 shows experimental results obtained by a prototype of the invention; FIG. 17 shows an optical parallax pattern for determining a distance from an object; - Figure 18 illustrates the recognition of a registration of a vehicle; - Figure 19 shows the relationship between the focal length of an optic and its field of view; FIG. 20 shows a diagram of the relationship between the angle of view of an object, its dimension and its distance from an observation point; - Figure 21 shows a miniaturized acoustic instrument; - Figure 22 shows a diagram of the method of the sound measurement method and the identification of a noisy vehicle.

Embodiments of the invention

As emerges more specifically from Fig.1, the object of the invention relates to a new technique implemented using acoustic instrumentation to recognize an acoustic signal emitted by a vehicle. Vehicles such as cars, mopeds, trucks, even trains and planes must meet acoustic performance standards. There are different standards in different countries that allow setting the acoustic thresholds emitted by these vehicles. These thresholds can be determined by several criteria and in general a threshold is determined by a sound level not to be exceeded at a certain distance, for example a distance of 10 m. The invention relates not only to the measurement and sound detection of a stationary vehicle but above all to the measurement of the sound intensity emitted by a moving vehicle. The invention also relates in particular to the identification of the license plate of the vehicle which would produce too high noise. The invention also further relates to a method for summoning the owner of the excessively noisy vehicle to present himself for a check of his vehicle.

It is further understood that the invention is not limited to motor vehicles such as, for example, an automobile, a motorcycle or a moped, a coach, a tram, a boat. The term "vehicle" is understood here in its broadest sense and is here defined as any moving object which produces noise, independent of its nature, of its use or of the source of the device which is at the origin. noise to be measured by the method as well as the acoustic instrument 1 of the invention. The invention therefore also includes, for example, also any other vehicle propelled by other means such as for example propulsion by wind or gravity. The invention relates above all to moving vehicles but can also be applied, at least partially, to immobile or stationary vehicles which includes noisy vehicles that are difficult to access, such as for example a drone which remains stationary at a high distance from the instrument. acoustic, for example a distance of more than 50m.

It is understood that the method and the measuring instrument of the invention are applicable to measurements of noise emitted by vehicles located at least 100m from the measuring instrument of the invention as described herein. document.

It is also understood that the sound level, also defined as sound intensity or measured noise intensity, can be expressed in decibels (dB) or in another measure such as a pressure measurement expressed in Pascals for example.

Figure 1a illustrates an implementation configuration of the acoustic instrument 1 sound of the invention. In FIG. 1a, the noises represented by arrows B can come from different sources of noise B3-B5. In general, the major contribution of the noise generated by a vehicle 10 is produced by the engine of the vehicle 10. The noise of an engine can deteriorate with the maladjustment of the vehicle 10 but also by the deterioration of the insulation under the protective hood of the vehicle. engine. Other sources of noise can be added to engine noise, such as those produced by worn tires or the use of non-aerodynamic structures. The objective of the invention is to determine the cumulative noise of all the noise sources of a noisy vehicle. Of course, the aim of the acoustic measurement is to reduce the noise of vehicles 10, but also to reduce fuel consumption to protect the environment, since an excessively noisy engine will often be linked to excessive fuel consumption.

It is also included in the invention the detection of a vehicle 10 which comprises any other source of noise which is not produced by the vehicle itself but produced by accessories such as sirens or speakers, for just cite these 2 examples.

More precisely, the invention is carried out by a method for recognizing an acoustic signal B produced by a vehicle 10, in particular when this vehicle 10 is moving. This method comprises the following steps, illustrated in the block diagram of FIG. 22: - identifying a noisy vehicle 10; of course the passage includes the removal of the vehicle 10; of course it is understood that the noisy vehicle may be in motion or may be stationary; - Switch on a sound level meter 20 of a portable acoustic instrument 1 as described above; - Aim with the sound level meter 20 in the direction of said noisy vehicle 10; - measuring the sound level emitted by the noisy vehicle 10 when it is in a first position P1; - determining the distance D between the sound level meter 20 and one of the surfaces 10a, 10b, 10c of the vehicle 10 which is in the first position P1; Determining a first normalized sound intensity I1 with respect to a determined reference distance Dr, illustrated in FIG. 1; such a standardized measurement can be determined by various means such as electronic and / or computer means as discussed later; - identify the vehicle 10 if the normalized sound intensity I1 at the reference distance Dr is higher than a predetermined authorized standard, for example as described in https://publications.europa.eu/en/publication-detail/ - / publication / fe98a835-e656-11e3-8cd4-01aa75ed71a1 / language-fr.

In one embodiment, the measurement of the sound level, the measurement of said distance D, as well as the identification of the vehicle 10 are done simultaneously. It is understood that the term "simultaneously" is limited by what is possible to achieve taking into account the speeds of sound as well as the speed of the signal sent to the vehicle 10 and partially collected as in the case of a radar system using a laser. . It will be understood that the term "simultaneously" means that the measurement of the sound level, the measurement of the said distance D, as well as the identification of the vehicle are carried out in a period of time less than a second, preferably less than 500ms or even more preferably less than 100ms (0.1 sec).

FIG. 3 shows a block diagram of the method of the invention.

[0045] FIG. 23 illustrates a diagram of the steps of the method of the invention.

When a user hears a noisy vehicle 10, stationary or in motion, he turns on the instrument 1. The latter goes into stand-by. When the vehicle 10 passes, the instrument 1 is pointed at it and a trigger integrated preferably in a handle 1c of the instrument 1 is pressed. In one variant, the system 1 can be activated automatically, for example according to the sound level detected. In a preferred embodiment three data are taken simultaneously: the sound level coming from the pointed direction, the distance from the pointed source and an image of the vehicle 10, in particular of its license plate. It is understood that in variants the acoustic instrument 1 described below may comprise means for helping the instrument 1 to be oriented towards a noisy vehicle 10. These means may comprise, for example, a heat source detector.

A healthy human ear for hearing sound pressures ranging from 20 μPa to 20 Pa. This results in a ratio of 1: 1,000,000, impractical in current use. A logarithmic scale of sound levels in decibels [dB] was therefore implemented, which also better represents the perception of sound by humans. The sound propagating in waves having values sometimes positive, sometimes negative, it is necessary to take the effective value of this one over the duration of the measurement in order to be able to have an average. The relationship between sound pressure, effective pressure and a reference pressure is given by:

• p: sound pressure [Pa] • T: time interval treated [s] • prms: effective pressure [Pa] • pref: reference pressure [20 µPa] • Lp: sound level [dB]

When two sources of sound emit at the same intensity, the sound level in decibels is not doubled, due to the logarithmic nature of the decibels, the level will increase only by 3 decibels. This difference decreases if the additional noise is smaller than the basic noise. Ltot = 10 log [(p1 <2> + p2 <2> + p3 <2> + p4 <2>) / p0 <2>]; Ltot: Total sound level; pn: Sound pressure to add. P0: Reference pressure (20 µPa)

For example, if a level of 10dB and 15 dB are added, the result will be 16.2 (the highest level (15) + 1.2). This feature makes it possible not to have to isolate the measured sound source: the instrument being intended to sound the noisiest cars, they will cover the lower surrounding noises.

Frequency weighting:

The ear can hear frequencies ranging from 20 Hz to 20 kHz; however, it has a different sensitivity depending on the frequency and this factor is taken into account in the measurement. A standardized weighting (A weighting of standard IEC 61672-1 „Electroacoustics - Sound level meters“) has been established to have a better representation of the sound. This is the weighting used in most of the references on sound, including the legal values of automobile noise emissions

A sound level value evaluated in decibels according to the A-weighting can be expressed in dBA, even if most devices and documents simply indicate this in dB. The equation corresponding to the transfer function is presented as follows:

[0052]

A (f) = 20log10 (HA (f)) + 2.00 • HA (f): Gain as a function of frequency • A (f): Total gain [dB]

When the sound travels a distance, it becomes less and less audible. The loss of sound pressure over the distance makes the sound measurement unusable without the distance to the corresponding sound source. Thus, when measuring sound for controls and standards, a standardized distance is defined in order to be able to compare the results.

For an omnidirectional sound source, the sound intensity (expressed in W / m <2>) decreases according to the ratio 1 / r <2>, where r is the distance traveled by the sound. The energy is distributed evenly over the sphere of the sound wave, and its area increases with the square of the distance. Since the sound intensity is proportional to the square of the sound pressure p. As a result, the sound pressure p, unlike the intensity, decreases according to 1 / r.

It thus makes it possible to establish the relationship p2 / p1 = r1 / r2, or, in decibels:

In the method of the invention the aim is to have the same sound measurement regardless of the distance between the acoustic instrument 1 and the vehicle 10. To do so, a reference distance dR must be defined. Several possibilities are of course possible. For example one can base oneself on sound measurement methods as carried out during automobile checks according to Swiss ordinance RS 741.41. (https://www.admin.ch/opc/fr/classified-compilation/19950165/index.html)

As illustrated in Figure 4, the vehicle 10 must accelerate as much as possible from line AA 'to line BB'. The maximum intensity measured by the two microphones gives the result of the measurement. If we assume that the car is a point sound source with omnidirectional emission, the maximum intensity will be measured at 7.5 m from the source. Measuring the distance with the vehicle 10 simultaneously with the sound recording and reducing the sound intensity to what it would be at 7.5m would therefore make it possible to have a good approximation of whether or not the authorized values are respected.

There are various possibilities for determining a sound level at a certain reference distance, defined as a standardized level. For example, an electronic circuit can correct the sound level measured by the sound level meter 20 taking into account the measurement of the distance D between the sound level meter and one of the surfaces of the vehicle, knowing that the sound intensity decreases gradually by a factor which is inversely proportional to the square of said distance D. Said correction of the degression effect of the signal and the determination of the sound level at a reference distance Dr can also be done or at least partially by computer means.

It is understood that the uncertainty of the measurement of the distance D between the sound level meter 20 and one of the surfaces of the car 10 will be determined by the section of the signal which is incident on said surface. In the case of a laser radar, for example, this section may be less than 500 mm <2>. In the case of a distance measurement from a vehicle such as a car or a motorcycle, the accuracy of the measured distance D is about 20cm over a typical distance of 30m.

Of course, means can be implemented to be able to measure the sound level at distances greater than 100 m, for example 200 m or 300 m. In this case more sophisticated means must be deployed such as filtering of certain typical sound frequencies generated by the vehicle. In order to increase the sensitivity of the sound detection, several sound level meters can be integrated into the acoustic instrument, these sound level meters 20 can have different directivity or sensitivity characteristics.

The tolerated noise standards are of course different depending on the country. For example, according to ordinance RS 741.41 of the Swiss law on noise emission from motor vehicles, the authorized values for cars are directly linked to the European standards in force. A measurement of sound at a previously chosen reference distance is shown in figure 4, in which this distance Dr is 7.5m

In one embodiment, the sound level of the vehicle as well as the distance D of the vehicle relative to the sound level meter 20 are also measured in a second position P2 of the vehicle 10, as illustrated in FIG. 2 where the vehicle shown is a drone 10.

In one embodiment, at least a second value of the standardized sound intensity 12 is determined. Of course, several values of the normalized intensity can be determined for one or more positions of the vehicle 10.

In a variant, the average of said first 11 and second 12 value of the normalized intensity is determined, said average being determined for a spectrum of predetermined frequencies. This makes it possible to obtain a more reliable value of the normalized sound noise.

In one embodiment, the identification of the vehicle 10 is done by identifying the registration number of the vehicle 10, which is typically done when the vehicle 10 is a car or truck or motorcycle or even mopeds. Flying devices can also include a registration number or a code which identifies them.

In one variant, the identification of the vehicle 10 is done by recognizing the shape and / or the brand of the vehicle 10. This can have several uses, for example during the comparison test of several types of vehicles, as by example cars or drones.

Of course the invention is not limited to the recognition of a registration number 12. As illustrated, the identification of the vehicle 10 can be done by the recognition of the registration number 12 of the vehicle 10 and the shape and / or vehicle make 10.

In one embodiment, the identification of the vehicle 10 is made by recognizing an identification code C integrated into the vehicle 10. It is understood here that said identification code C is an apparent code on the vehicle or detectable by an instrument such as a bar code and may be other than the registration number 20 of the vehicle 10.

Said code C can be used to more easily recognize a vehicle. Code C can also be applied in a manner suitable to facilitate reading of the code such as in fluorescent material. Code C can also be designed to reduce the risk of the vehicle keeper modifying the vehicle to prevent reading the registration number or said code, for example by using an anti-reflective layer or a light scattering layer from the code recognition system. . In the future, for example, vehicles 10 such as drones will probably also be provided with a registration number or a code C making it possible to identify their owner or additionally other properties of the vehicle 10. Said properties may be optical properties. Advantageously, said C code can comprise structures which increase reflectivity. Said code C can be a bar code and can also include structures reflecting particularly well in a predefined spectral range such as, for example, a range of wavelengths between 550nm and 690nm.

The distance can be measured by different methods. A first direct method consists in using a radar system as illustrated in FIG. 1. Such a radar can be a radar based on an optical system comprising a laser. Such radar systems are known and are not discussed in more detail here. The method of the invention can be implemented in various ways making it possible not only to determine the new sound but additionally to determine at the same time the speed or the distance traveled by a vehicle. For example, FIG. 2 shows a noise measurement situation of a drone 10 which moves from a first position to a second position over a distance traveled P. By aiming the vehicle in both positions and measuring the distances in them. two positions P1, P2 it is possible to deduce the distance traveled by the vehicle 10 using an acoustic instrument 1 which includes a GPS system or an accelerometer. In a similar way there are situations where the distance traveled P by the vehicle is known (for example a train at constant speed) it suffices to point the acoustic instrument 1 in two directions to be able to deduce the distance d1, d2 of the vehicle sound level meter. Of course, advantageously, several distance measurement methods can be deployed by a single instrument 1, for example the combination of a triangulation technique and a radar measurement.

In an advantageous variant, an alarm signal can be generated and sent to the vehicle indicating that the vehicle 10 is too noisy.

In another variant, the alarm signal is displayed inside the vehicle 10 in order to alert the driver of the noisy vehicle 10.

In one embodiment, said acoustic instrument 1 comprises means for determining and recording the sound spectrum of the noisy vehicle 10. This makes it easier to identify the origin of the noise produced by the vehicle, which can be advantageously used to identify an improvement in the vehicle to be communicated to its driver. In luxury vehicles, for example, information such as the spectral content of the noise detected by the acoustic instrument 1 can be transmitted to its driver or to the autonomous piloting system of the vehicle.

In an advantageous variant the acoustic instrument 1 can comprise means for displaying the distribution of noise around a vehicle, similar to a thermographic analysis of heat leaks from a building. In this case, for example, red zones can show local exceedances of at least 50% of the standard, an orange color when the sound level is between + 30% and 50% of the authorized normalized sound level, and green zones would indicate areas where the sound level is far below the standards, for example less than 30% of the authorized standard.

The measurable noise level depends on the characteristics of the sound level meter, ie its directivity, and the measurable distance depends, ie on the technical means used to measure this distance. With the development of commercial microphones and lasers it can reasonably be expected that a noise measurement at distances greater than 100 m can be determined.

The invention is also produced by an acoustic instrument 1 for recognizing an acoustic signal produced by a vehicle 10. The instrument 1 of the invention corresponds to several desired criteria: - the instrument of the invention must be light and quickly usable when the situation arises; - the measurement must make it possible to have an estimate of the noise emitted in order to know whether the maximum emission standard is respected or not; - the noise value must correspond to the noise perceptible by the human ear within a radius of 7 to 10 meters around the source; - the acoustic instrument 1 does not necessarily have to be used as a reference for a contravention. It must above all determine whether a vehicle must pass a sound emission control according to legal standards; - the instrument must be usable up to a range of about 100 meters; - the system must operate without being recharged for at least 8h to 10h, corresponding to an operator's working day.

More specifically the acoustic instrument 1 of the invention, illustrated in Figure 1a, 1b, 2 comprises at least: - means for measuring the distance D of the vehicle 10 relative to the sound level meter 20; A unit for storing sound level detection threshold criteria; - correction means for determining the normalized sound intensity at a predetermined reference distance Dr; A man-machine interface 1a for displaying the normalized emitted sound level relative to a previously chosen reference distance Dr; - means for identifying the vehicle 10.

In one embodiment, said correction means are electronic means or computer means. In a variant, said correction means are a combination of an electronic circuit and computer means.

Said correction means make it possible to take into account the noise attenuation effects (also defined as degression effect). This correction is performed by a processor immediately after conversion to decibels with a digital filter. The formula used is the simple logarithmic addition previously mentioned, which is none other than 1 / (r <2>) converts to a logarithm. It is carried out in the step “Data processing” shown in fig.3, or more precisely in “Calculation of dBA + Display” in fig.15. This is a physical calculation performed by the computing unit (the processor) with the measured data. Unlike previous methods in this kind of calculation a programmed digital filter is used rather than an analog filter, as explained later.

In one embodiment, said means for identifying the vehicle 10 comprise a vision system 40 making it possible to recognize the license plate 12 of the vehicle 10 and / or to recognize the make and / or the type of the vehicle.

In one embodiment, the acoustic instrument 1 also comprises a display 1a of the non-standardized sound level. The instrument 1 can comprise an interface 1b comprising means for programming parameters of the instrument such as a keyboard 1e. The instrument 1 can also include warning elements 1d which can be sound or optical elements to indicate the level of sound detected.

In one embodiment the acoustic instrument 1 comprises at least two sound level meters and / or two means for measuring the distance D of the vehicle relative to the sound level meter 20. Said sound level meters and / or the two means for measuring the distance D can be different

In one embodiment the means for measuring the distance D of the vehicle 10 relative to the sound level meter 20 are optical means.

In one embodiment, the optical means 4 comprise at least one laser.

In one embodiment the means for measuring the distance D from the vehicle 10 comprise a radar system.

In one embodiment the means for measuring the distance D of the vehicle 10 comprise a system using triangulation techniques, as illustrated in FIGS. 2, 17.

In an advantageous variant, the acoustic instrument 1 of the invention can comprise at least two sound level meters 40, if necessary different. In another variant, the acoustic instrument 1 of the invention can comprise at least two distance measuring systems and / or at least two shooting systems. For example one of the viewing systems may have a wide viewing angle and the second may have a high magnification. The so-called two shooting systems can be integrated into one and include a zoom lens. In a variant, this zoom lens can be triggered according to a measured noise level and according to a predetermined level programmed in the acoustic instrument 1.

It is understood that the acoustic instrument 1 of the invention can be used for any parked vehicle. In a mode of use where the vehicle is stationary, the distance measurement may be inactive.

In one embodiment the acoustic instrument 1 is arranged so as to be able to carry out noise measurements at distances greater than 150 m or even more than 200 m.

In one embodiment the acoustic instrument has the size of a portable telephone preferably having a length between 10cm and 25cm, a width between 5cm and 15cm and a thickness between 3 and 20mm.

Example of an embodiment of a prototype of an acoustic instrument 1 according to the invention:

Implementation of sound measurement:

FIG. 5 shows an example of the implementation of a sound acquisition

The prototype is based on a single-board nanocomputer, in particular a Raspberry Pi 2 (ref: https://fr.wikipedia.org/wiki/Raspberry_Pi). The following steps are performed.

When the user wants to take a measurement, the Raspberry Pi sends a signal to a PIC microcontroller. The amplified signal from a microphone is connected to an analog-to-digital converter AD thereof, which samples it and stores it in a random access memory of the RAM type. When the PIC indicates that it has finished sampling, the Raspberry Pi retrieves the values from the memories and keeps them internally. The user can then choose to view the converted value in dBA or create a .wav file to listen to or process the recording.

Microphone implementation

The first step in recording sound is to measure the output of a microphone. The prototype microphone is a CMI-4537-SN69 model from CUI inc. for its low price, unidirectional directivity and ease of use. Its signal is amplified using Texas Instruments LM386 audio amplifier, as shown in figure 6.

The resistor R1 and the capacitor C1 constitute the conventional scheme for supplying and removing the DC component from the microphone. The potentiometer R2 makes it possible to adjust the gain of the input, the capacitor C2 makes it possible to have the maximum gain of the amplifier (200) while the capacitors C3 and C4 as well as the resistor R3 are recommendations of the manufacturer. The capacitor C5 makes it possible to filter the input to cut the disturbances resulting from the communication between other components (see sampling). It forms an RC filter with the potentiometer with a cutoff frequency of approximately 26.5 kHz. This value varies with the value of R2, but these variations are not large enough in our range of use to have an influence on the output. A second 25.5 kHz RC filter (R4 and C6) is placed at the output to eliminate the remains of noise which are amplified by the circuit.

The series capacitor offered for output by the manufacturer has been withdrawn. The purpose of this is to remove the DC component from the signal. However, to simplify powering the system to a single DC power supply, this component should be retained. Note that the output value of LM386 is not rail-to-rail. For a 3.3 V supply, the output range is 600 mV to 2.6 V, with a central value of 1.6 V acting as an offset.

The microphone used has a unidirectional directivity as illustrated in FIG. 7: it picks up sound well in front of it, slightly on the sides and hardly behind it. Loud noise will cover lower sounds. The use of a unidirectional microphone also makes it possible to attenuate the sounds coming from other directions than the pointed one, which further improves the accuracy of the measurement.

Sampling

To be able to record analog values such as sound, it is necessary to carry out sampling. According to the Nyquist-Shannon theorem, the minimum sampling frequency should be 40 kHz (twice the maximum measured frequency, in our case the maximum audible frequency 20 kHz). However, there is an aliasing phenomenon, illustrated in FIG. 8, which can occur if signals exist above 20 kHz: they would be mirrored on Fs / 2 to end up on the audible band and generate noise.

To limit this, the sampling frequency is increased to 100 kHz. Frequencies likely to fall back into the audible band would start at 80 kHz, at which frequencies signals are much better cut by filters. The sampling duration is defined at one second, a compromise between capture speed and data consistency: there will therefore be 100,000 samples per measurement.

PIC microcontroller implementation

[0100] A Raspberry Pi does not have a real time clock and its operating systems do not allow this kind of application. This task is therefore entrusted to a second processor. Due to its relative ease of use and access to the necessary programming hardware, a Microchip PIC32 MX170F256B microcontroller was used. This has an internal 10-bit AD converter, an SPI port and the possibility of using an external oscillator to accelerate its modules.

[0101] The PIC32 illustrated in FIG. 9 contains more module than it has legs; it offers the possibility of choosing the legs on which the modules are used. This includes the programming module (RB0 and RB1), the AD converter (RB3) and the SPI (RB11, RB13, RB14). The "Busy" and "Start" signals, used to communicate with the Raspberry Pi, as well as the RAM selection are placed on conventional I / O.

RAM memory implementation

[0102] The microcontroller does not have enough RAM memory to store all the samples. The sampling being done on 10 bits, the data would be stored on 2 bytes. This amounts to a total amount of data of 200,000 bytes per second at 100 kHz. To store these values during sampling, it is thus necessary to have recourse to very fast external memories. Two 128 KB SRAM 23LC1024 memories communicating in SPI (SPI: a serial communication interface, in English Serial Peripheral Interface), illustrated in figure 10, were chosen for the prototype; there was no memory in DIL box (for prototyping) with enough room to store all the data in one.

The two memories are connected in parallel on the SPI bus, they are each selected in turn by the processor.

The measurement of a write to RAM in SPI is illustrated in FIG. 11.

[0105] The MOSI and SCLK symbols in figures 11 and 12 are defined by: • MOSI: Master Out Slave In: The SPI uses a master-slave system, which means that a device makes the requests and gives the orders ( master) and that the other can only answer (slave). The MOSI pin represents the output tab for the master and thus the input tab for the slave (line where the orders are sent); • MISO: Master In Slave Out: Input tab for the master and output tab for the slave (line where responses are sent); • SCLK: Serial Clock: wire on which a "clock" rotates (ie a clock, periodic square signal of a defined frequency) used to synchronize the communication.

In the example above, the instruction arrives first (0x02 for a write), then the address concerned on 24 bits, and finally two bytes of data. Memory is configured to operate sequentially; when writing an additional byte without giving any order, it will be written in the following address. In this example, 0x01 will be written in the address 0x00D772 and 0xFF in 0x00D773. The data is 16 bits (10 bits from the AD converter rounded up), so it is stored in two bytes. The address must therefore be incremented two by two.

[0107] Reading takes place in a manner similar to writing and is illustrated in FIG. 12: the instruction is sent (0x03 for reading), then the address. Then the clock sends two groups of eight clock strokes to collect the two bytes on an MISO line not shown here. The first will be that of the requested address, and the second that of the following address.

Raspberry Pi implementation

[0108] As shown in the block diagram, the Raspberry Pi must communicate with the PIC microcontroller and with the RAMs as illustrated in FIG. 13. This has an integrated SPI module as well as various inputs-outputs. The Raspberry Pi also has a UART port which will be used during the implementation of the distance sensor. This part is discussed in the chapter dedicated to it.

[0109] For better accessibility and flexibility during the tests, software has been developed on a Linux operating system (Raspbian). This has been programmed using QT Creator in order to have a user-friendly graphical interface. This allows you to test and modify the code, as well as process the results directly on the operating system. The Raspberry Pi of the prototype requires a keyboard and a mouse connected to the USB ports as well as a screen on the HDMI port, which will no longer be necessary during the industrialization of the system.

PIC programming

[0110] When the system is activated, the main function waits until the Raspberry Pi asks it to do a sampling (figure 14). As soon as this sets the "Start" signal to 1, the PIC changes the "Busy" signal to high level. This is followed by the initialization and start-up of the SPI, ADC and timer modules, as well as the launch of the AD conversion and the initialization of the RAMs. The main function then goes back to standby until the sampling is complete. During this time, the timer will call its interrupt every 10 µs to retrieve the values. During the interruption, the value of the converter AD is first read and the PIC is asked to restart a conversion. Starting the conversion at this time allows it to be done in parallel with sending data to RAM, which saves time. It follows the selection of the RAM with which we want to communicate in SPI, then sends it the value read from the converter. The RAM address is then incremented by two (see section "RAM memory implementation"). Half of the 16-bit values (50'000) are sent to the first RAM. When this is done (address = 100,000), the second RAM is selected, the address is reset and the process starts over. When 50,000 new values have been sent to the second RAM, the timer and the PIC SPI communication stop and it indicates that sampling is complete. The PIC can therefore reset the "Busy" signal to the low level to allow the Raspberry Pi to recover the values and continue working. When the hand on the SPI is released, all the tabs relating to the SPI are configured as input to avoid having an influence.

Programming the Raspberry Pi

The functional diagram of the essential functions of a Raspberry Pi of prototype 1 is illustrated in FIG. 15, namely an acquisition function, making a sound.wav file, reading a sound.wav file, conversion into dBA. The user interface for managing audio capture consists of four buttons. The acquisition button sends a signal to the PIC for sampling, then retrieves the data for internal storage. Two buttons are intended to read and write to a * .wav file. The latter applies the A-weight filter to the data and outputs the value in dBA. ; "Acquisition" function; [0112] Pressing the acquisition button starts the measurement process. First, a “Start” line connected to the PIC is set high to indicate that it should start sampling. This responds by setting the "Busy" line to the high level during the acquisition. The Raspberry Pi waits for "Busy" to return to the low level so that the data is all stored in the RAMs. Then, it activates the SPI, reads 100,000 bytes from each RAMs in groups of two and stores them in an array of 100,000 signed 16-bit values. The data is 10-bit and has an offset (see section "Microphone implementation"). The offset is removed, then the values multiplied to cover the 16 bits (-32'768 to 32'767). ; [0113] In the above measurement is displayed the low active selection of the RAMs during the acquisition. During a read or write, the RAMs are quickly selected, then deselected. We can see in the first part the use of RAMs by the PIC for the sampling of one second (500 ms per RAMs), then in the second part the taking of the relay by the Raspberry Pi to read the two RAMs. Only the first part needs to be real time, the second part is just data recovery. After sampling, the "Convert into dBA" function is called automatically. ; Function "Make sound.wav"; [0114] For reasons of experimentation and control, a * .wav file (Waveform Audio File Format), single playable audio file is created from the computer. This format is composed according to the following table: 0 1 2 3 4 5 6 7 8 9 10 11 ChunkID ChunkSize Format 12 13 14 15 16 17 18 19 20 21 22 23 Subchunk1ID Subchunk1Size AudioFormat NumChannels 24 25 26 27 28 29 30 31 32 33 34 35 SampleRate ByteRate BlockAlign BitsPerSample 36 37 38 39 40 41 42 43 44 45 46 47 Subchunk2ID Subchunk2Size data 0 data 1 48 49 50 51 52 53 54 55 56 57 58 59 data 2 data 3 data 4 data 5 data 6 ...

[0115] Each number represents one byte. The file is separated into three sections (chunk), each containing its name (ID), size and content. The first is the RIFF (Resource Interchange File Format) header, common to the file corresponding to this model. There follows the format section, indicating the characteristics of the file. Finally, the data section contains all the audio values of the file.

[0116] The RIFF Header includes: • ChunkID: Contains the letters [RIFF] in ASCII (0x52494646) • ChunkSize: Total size of the file except the first two fields in bytes. The size of the first two sections being constant in our case, the value will be 36 + SubChunk2Size for an uncompressed file (PCM), which gives for our file 200'036 (0x30D64). • Format: Contains the letters [WAVE] in ASCII (Ox57415645)

[0117] Format section: • Subchunk1ID: Contains the [fmt] characters in ASCII (0x666d7420) • Subchunk1Size: Size of the section except the first two fields in bytes. For a classic PCM file, the size is 16 (0x10). • AudioFormat: Encoding format. The value for a typical uncompressed sample file is 1. • NumChannels: Indicates the number of channels. For mono as in our case, the value is 1. • SampleRate: Sampling frequency, here 100'000 (0x186A0) • ByteRate: Number of bytes per second. 16-bit values on a 100,000 Hz channel give 200,000 (0x30D40). • BlockAlign: Number of bytes per block. 16 bits on 1 channel gives 2. • BitsPerSample: Number of bits per sample, here 16 (0x10).

[0118] Given section: • Subchunk2ID: Contains the letters [data] in ASCII (0x64617461) • Subchunk2Size: Size of the section except the first two fields in bytes. For 100,000 16-bit values, the size is 200,000 (0x30D40) • Data: The sampled values are then written one after the other here. In 16 bits, the values must be signed.

[0119] When the button is pressed, the program creates a sound.wav file (or modifies it if it already exists) in the compilation folder, writes the header according to predefined values, then inserts the stored data internally. The file can then be read by an audio player or opened on Matlab.

"Read sound.wav" function

[0120] Given that we are working only with a single file format in the prototype (1 second at 100,000 16-bit samples), the file is read in a very simple way: the program searches for a sound file. wav in the build folder, skip the header and read the data. These thus become usable as if they had just been measured with the PIC.

Convert into dBA function

This button is used to apply the A weighting filter to the value table, to retrieve the effective value of the latter and to scale it to have a value in dBA. This filter is necessary to have a sound value representative of what the human ear hears. There were two possibilities to implement the filter: • Analogue, at the microphone output; • Digitally, from the Raspberry Pi.

[0122] The digital method has been favored. It allows the filter to be tested on a computer before implementation to ensure accuracy and to save on components. This also makes it possible to generate .wav files, the original unfiltered values being available on the program.

[0123] To avoid having to make too large a correction when applying the corrective offset, the values are first of all scaled to go from -1 to 1. filter application: this has been resized on Matlab to become a digital filter with a sampling frequency of 100 kHz. After applying the filter, the rms value is calculated and converted to dBA. Finally, an offset representing the gain of the microphone is defined at the time of the calibration so that the results correspond to reality.

Digital filter

[0124] The digital filter was first of all generated on Matlab using the basic filter cited in theory. The sample rate has been set at 100 kHz and the filter looks like this:

[0125] The base filter being of the 6th <th> order, it was separated using Matlab into 3 chain filters of the 2nd <th> order. The reason is that the higher the order of the filter, the more precise its coefficients must be. For comparison, the graph below compares the analog filter (blue), the 6 <th> order digital filter (red) and the three 2 <th> order digital filters put in series.

[0126] The coefficients of the digital filters are all on 32 bits; the processor of the Raspberry Pi being on 32 bits, this makes it possible to be faster for the calculation. The three 2nd order filters are sufficiently precise in the range used (20 Hz to 20 kHz), it is therefore not necessary to use coefficients on more bits. The three filters used are as follows:

[0127] The whole must also be multiplied by a gain of 0.1753793 to be similar to the analog filter. To be able to program these filters, they must first be transformed into difference equations. The purpose of the operation is to be able to calculate each of the output values from the current and previous values. For example, to get the 10th <th> output value, we apply coefficients to the input values 10, 9 and 8, as well as the output values 9 and 8, and then add the results. The filters being of order 2, we use values up to k - 2, k being the index of the value that we want to calculate. The exponent of z in the equations represents the offset of the index. Since future values cannot be used, the first step is to negate the exponents by dividing the numerator and denominator by z <2>:

[0128] It is then necessary to isolate the interesting output, that is to say Y (z): Y1 (z) = U (z <-1>) + 0.5884756 U (z <-2>) + 0.9295781 Y (z <-1>) - 0.2160289 Y (Z <-2>) Y2 (z) = U (z) - 2.0002375 U (z <-1>) + 1.0002375 U (z <-2>) +1.9479506 Y (z <-1>) - 0.9482561 Y (z <-2>) Y3 (z) = U (z) - 1.9997631 U (z <-1>) + 0.9997632 U (z <-2>) + 1.9974139 Y (z <-1>) - 0.9974147 Y (z <-2>)

Finally, we can replace z by the index k to obtain the final equations: Y1 [k] = U [k - 1] + 0.5884756 U [k - 2] + 0.9295781 Y [k - 1] - 0.2160289 Y [k - 2] Y2 [k] = U [k] - 2.0002375 U [k - 1] + 1.0002375 U [k - 2] + 1.9479506 Y [k - 1] - 0.9482561 Y [k - 2] Y3 [k] = U [k] - 1.9997631 U [k - 1] + 0.9997632 U [k - 2] + 1.9974139 Y [k - 1] - 0.9974147 F [k - 2]

[0130] Each of the functions therefore represents the way of calculating a specific element of the array. To program these functions, it is now sufficient to calculate each of the 100,000 values of the first output table with the values to be filtered as input, then of the second by taking the first as input, and finally of the third with the second as input. To finalize the application of the A-weighting filter, the previously mentioned gain must be applied to each of the values in the table.

Test of the prototype of the acoustic instrument 1 of the invention, outdoors

[0131] The prototype of the acoustic instrument 1 was tested in a real situation and mainly aimed at testing the application of the attenuation calculation. To avoid disturbing, the test is carried out in the forest rather than in the city, the test requiring that one source of sound must be strong enough to cover the others.

Material:

[0132] - 1 Bushnell Tour v3 laser distance sensor - 1 Sound source (Lawn mower) - 1 Roline RO-1350 sound level meter

Measurement configuration:

[0133] The vehicle 10 in question for the test was a lawn mower is placed on the roadside, turned on. The person taking the measurement stands at certain distances defined by the laser sensor, then measures the sound picked up. The measurements are carried out further and further away.

Result of measurements:

[0134] The measurements were taken every 10 m up to 70 m. Distance measurement with this laser to an accuracy of ± 1m, while the sound level meter remains within ± 1dB of fluctuation. The measurements are shown in the table below as well as in figure 17.

Table 1

[0135] Distance [m] 1 10 20 30 40 50 60 70 Sound [dBA] 81 66 60 55 52 50 48 47

It can be seen that the attenuation in dBA resembles type 1 / r in the shape of the curve, which suggests that the attenuation in Pascal is of type 1 / r in accordance with theory. This also means that the closer we are to the source, the more the tolerance on the distance will have an impact and the further we are from it, the more the tolerance on the sound will have of the impact.

[0137] To better understand this phenomenon, here is a table in which each line represents a measured value transferred to all the other distances (the first line is the value measured at 1 m transferred to the other distances, the second is the value measured at 10 m, etc.). The following table shows outdoor measurements over all test distances.

Table 2

[0138] Measure at 1 m [dBA] 81 61 54.9794 51.45757 48.9588 47.0206 45.43697 44.09804 Measure at 10 m [dBA] 86 66 59.9794 56.45757 53.9588 52, 0206 50.43697 49.09804 Measure at 20 m [dBA] 86.0206 66.0206 60 56.47817 53.9794 52.0412 50.45757 49.11864 Measure at 30 m [dBA] 84.54243 66.0206 58 , 52183 55 52.50123 50.56303 48.9794 47.64046 Measurement at 40 m [dBA] 84.0412 64.54243 58.0206 54.49877 52 50.06181 48.47817 47.13924 Measurement at 50 m [dBA ] 83.9794 63.9794 57.9588 54.43697 51.9382 50 48.41638 47.07744 Measurement at 60 m [dBA] 83.56303 63.56303 57.54243 54.0206 51.52183 49.58362 48 46 , 66106 Measurement at 70 m [dBA] 83.90196 63.90196 57.88136 54.35954 51.86076 49.92256 48.33894 47

It can be noted that the further one goes, the more the calculations correspond to the measurements. This indicates that the distance tolerance has more influence than the noise tolerance and that with a more precise distance measurement, one could take measurements closer to the source.

Correction of vehicle movement

[0140] It is necessary to take into account the displacement of the noise source that is being measured. The measurement is made over one second, so the vehicle will be further from the measuring instrument at the end of the sampling than at the beginning. At long distance, there will be little difference in sound level, but it becomes significant the closer you get to the source. The error can however be partially corrected by taking into account the temporality of the distance measurement. For the duration of the measurement, the sound attenuation can be approximated as a straight line. The average calculated for the sound would thus correspond approximately to the central value of the sampling if the sound level emitted by the car is constant, and the average output by the instrument would therefore represent the sound received from the vehicle when the sampling is halfway. executed. It is therefore at this moment that the distance measurement must be taken to limit the error.

Limitation of tolerances

[0141] The tolerance on the distance measurement has less influence by being further away. At 10m ± 1m may represent a few dB, while at 60-70m the difference is barely noticeable. If we resume the calculation of attenuation:

The value r2 is the distance to which we want to relate the sound and r1 is the measured distance. The tolerance of L1 is fixed and corresponds to the precision of the sound measurement of the instrument. Since r2 is a constant (7.5 m), it is therefore necessary to have a large value of r1 (and thus a small tolerance value in%) to improve the precision of the measurement. It is therefore preferable to measure at medium or long distance. The disadvantage of long-distance measurement is the increased influence of noise. Since the sound to be measured decreases, ambient noise will have more influence on the measurement. This phenomenon is however limited by the fact that the measured element is defined as being the noisiest of the surroundings. However, wind or too high a distance can still distort the results.

Conclusion

The test described above gives an idea of the performance of an acoustic instrument 1 of the invention. The results showed that despite the potential disturbances from the outside, the theoretical calculations remain applicable. The limit of sound level detection depends on the intensity of the sound source and the implementation of optical and electronic improvements to the instrument.

In the following chapter, various aspects of an embodiment of a distance measurement module are commented on.

Distance measurement

[0145] The acoustic instrument must be able to indicate, from a distance of up to 100 m, the sound produced by a car 7.5 m from it. For this, it is necessary to know the distance between the vehicle and the person measuring.

[0146] Distance measurement up to 100m has a limited number of possibilities and two of them (methods A, B) have been analyzed in more detail.

Comparison between two images (method A), illustrated in FIG. 17: in this technique two photo instruments are separated by about ten centimeters taking an image simultaneously. The difference between these two images makes it possible to calculate the distance separating us from the object in question. This method has proved to be complicated with the techniques of the state of the art and is not the best choice because of the complexity of the image analysis compared to the second solution (B).

[0148] Laser sensor (method B: this method consists of using an industrial laser sensor for distance measurement. These have a high range, high precision and standardized interfaces. This solution seems preferable for the acoustic instrument 1 The details of this system are described below.

Laser distance measurement (method B)

[0149] To confirm the viability of the laser solution, tests were carried out with a Bushnell Tour v3 laser sensor, initially designed for golf. It has been confirmed that it is possible with this technology to measure the distance of moving vehicles, even distant ones. On this observation, a laser from the same company was sought. When looking for a compact laser that can be used with the Raspberry Pi, the choice fell on the Truyens S210. The S210 is a long-distance laser that can measure from 46cm up to 750m for an accuracy of ± 4cm. It has a UART interface to be programmed and used with the Raspberry Pi. It measures 104.4 x 81.7 x 41.6 mm, which makes it integratable into a portable instrument. It also has a laser pointer that allows you to target the vehicle you want to measure. It is powered from 12 to 24 V, so a battery in this voltage range should be used.

[0150] Since there is currently no better alternative on the market, the laser is overqualified for acoustic instrument 1. It would be preferable in the future to use a cheaper laser with a smaller measuring range (100-150 m ) whenever possible.

Example of capturing an image: case of a license plate

In order to be able to follow up on the detection of a too noisy motorist, it must be possible to find him. It was discussed to insert a camera to capture the vehicle license plate at the time of measurement.

[0152] In the case of integrating a camera, it is necessary to check the resolution that the latter must have so that the license plate is readable. First, you have to define the minimum resolution that the plate itself can have. To do this, a license plate image was shrunk on a computer until it was no longer readable.

[0153] The plate in the image illustrated in FIG. 18 above has a width of 55 pixels. A photo taken in action will be of lower quality, so an increase to a minimum of 100 pixels is preferable as an approximation. A camera is defined by its resolution and the focal length of its lens. A standard lens has a focal length of 50mm, which represents the human field of view. The more the focal length increases, the more the field of vision decreases, and vice versa. For the same camera, photographing a plate at 100 meters will have a higher resolution with a longer focal length. Figure 20 illustrates the viewing angles according to the focal length of the imaging optics.

[0154] By setting the maximum distance for capturing the image at 100 meters and knowing that a license plate has a size of 50 cm x 11 cm at the rear, we can calculate the minimum resolution according to the focal length what a camera must have for the plate to represent 100 pixels at 100 meters away. This is illustrated in figure 21. Using the following formulas, we obtain the results shown in the table above for different focal lengths:

Table 3

[0155] Focal length (mm) 400 (6 °) 200 (12 °) 100 (24 °) 80 (30 °) 50 (47 °) Min width (px) 2096.311171 4204.169411 8502.262467 10717.9677 17392.495

It can be noted that with a conventional focal length (50 mm), a very high resolution is required in order to be able to read a license plate. With a focal length of 200mm or greater, the numbers become more reasonable. A 4k resolution for the camera would theoretically suffice to read a plate at 100 m. Keep in mind, however, that the higher the focal length, the more precise you need to be when capturing an image. It would be necessary to carry out tests to verify that this factor is not too disabling when used in a real situation. In order to be able to use the device in any light, it may be considered to take infrared photographs if the color is not necessary to recognize the offending vehicle.

[0157] In conclusion, the realization of the prototype of the acoustic instrument 1 and the tests carried out have shown that the improvements must relate to the elimination of the use of a screen and to replace the Raspberry Pi with a more suitable processor to an on-board system.

Miniaturization of the acoustic instrument 1 of the invention

[0158] In one embodiment the acoustic instrument 1 of the invention has a miniaturized size so as to have a dimension typical of a portable telephone.

[0159] FIG. 21 shows a non-exhaustive embodiment of such an embodiment. Dimensions and items shown in Figure 22 are examples only and do not correspond to actual dimensions. The different elements can have different dimension ratios according to variants. Also, the relative location of the various elements of the exemplary embodiment can vary and other elements can be added in the miniaturized acoustic instrument of figure 21. More precisely, in order to reduce the dimensions of the instrument various paths optics can be deflected using mirrors or beam splitters. In the embodiment of FIG. 21, two vision systems are integrated in the acoustic instrument 1. A first system is based on a short focal length lens 40a and a second system is based on a lens having a large focal length. The integration of at least two systems of different focal lengths makes it possible in particular to be able to capture an image with a wide field of view and an enlarged image of a detail of the vehicle.

[0160] Figure 21 shows a section along a line A-A 'of the optical system having a long focal length. The light picked up by the lens 48b is deflected by 45 ° by an at least semi-reflecting mirror and is transmitted to an image detector 404 by a second mirror 403. Such a configuration makes it possible to have a large focal length in one. system 1 which has a thickness e which may be 10% to 50% smaller than the focal length of at least one of the lenses 34, 40b, 32 of the system. In one embodiment, one of the optical channels, for example the channels 402, 406 in FIG. 21, comprises a beam which is deflected by 90 ° in the instrument 1. In a variant, using several mirrors, at least one of the optical paths could be designed to reach a length of 2 x L + yxw, L being the length of the instrument and w its width, y being a predefined number. By choosing for example y = 1.5 in the case of the optical system comprising the lens 40b, the detector 404 would be located in the vicinity of the lens 40b and 3 deflection mirrors would be positioned in the corners inside the instrument 1. In order to to optimize the geometric design of the zigzag-shaped optical paths can be implemented. The dimensions of a portable instrument are preferably: a length between 10cm and 25cm, a width between 5cm and 15cm and a thickness between 3mm and 20mm. Other dimensions are of course also possible, It is understood that certain detectors such as that of the receiver 34a of the backscattered light from the optical radar as well as the optical transmitter, for example a laser 32a can be placed in the plane of the instrument. or in the thickness as shown in figure 21.

[0161] In a variant, the optical instrument comprises an electronic layer which is placed on the back of the instrument as shown in the example of FIG. 21. Of course the electronics and the necessary power supplies can be placed in the spaces. gaps between the different elements. The instrument 1 may include a viewfinder 60 and may also include two viewers being arranged to allow binocular vision to the observer. Of course, certain elements such as the viewfinder or at least one of the lenses of the instrument can be arranged to allow movement of these elements. For example, the viewfinder can be retractable.

[0162] In an alternative embodiment, other optical systems can be integrated into the instrument 1, such as for example an infrared flash. Of course, the instrument 1 can include an external battery 5000 making it possible to increase the autonomy of the instrument.

The acoustic instrument 1 of the invention as well as the method for measuring a normalized sound intensity with respect to a reference distance Dr of a vehicle can be applied in the industrial field. For example, the instrument and the method of the invention can be used for acoustic measurements of an installation of machines producing noise. In particular, the instrument 1 of the invention is useful for measuring, controlling or monitoring the noise produced by noisy installations which are difficult to access. These installations can be static or comprising parts or elements which are in motion.

Claims (25)

1. Method for recognizing an acoustic signal from a moving vehicle, characterized in that it consists in: - aim with a sound level meter of a portable acoustic instrument (1) in the direction of a noisy vehicle; - measuring by a sound sensor the intensity of the sound level of the noisy vehicle (10) when it is in a first position (P1); - determine the distance (D) between the sound level meter and one of the surfaces of the vehicle which is in the first position (P1); - determining the sound intensity (11) of said noisy vehicle at a pre-selected reference distance (Dr) relative to said vehicle (10); - identify the vehicle (10) if the sound intensity (11) at the reference distance (Dr) is higher than an authorized value. 2. Method according to claim 1, characterized in that the measurement of the sound level, the measurement of said distance (D), as well as the identification of the vehicle are carried out simultaneously. 3. Method according to claim 1 or 2, characterized in that, after said sound measurements made in said first position (P1), the sound level of the vehicle as well as the distance (D) of the vehicle relative to the sound level meter (20 ) is measured in a second position (P2) of the vehicle (10). 4. Method according to claim 3, characterized in that at least a second value of the sound level of the noisy vehicle (10) is determined at said reference distance (Dr) relative to said vehicle (10). 5. Method according to claim 4, characterized in that an average of said first (11) and second (12) value of the normalized intensity is determined, said average being determined for a predetermined frequency spectrum. 6. Method according to one of claims 3 to 5, characterized in that the identification of the vehicle (10) is also made in said second position (P2) of the vehicle (10). 7. Method according to one of claims 1 to 6, characterized in that the identification of the vehicle (10) is done by the identification of the vehicle number (10). 8. Method according to one of claims 1 to 6, characterized in that the identification of the vehicle (10) is done by recognizing the shape and / or the brand of the vehicle (10). 9. Method according to claims 7 and 8, characterized in that the identification of the vehicle (10) is done by the recognition of the identification number (20) of the vehicle (10) and of the shape and / or the brand. of the vehicle (10). 10. Method according to one of claims 1 to 9, characterized in that the identification of the vehicle (10) is made by the recognition of an identification code (C) integrated optical vehicle (10), this code optical identification (C) being other than the registration number (20) of the vehicle (10). 11. Method according to one of claims 1 to 10, characterized in that an alarm signal is sent to the vehicle indicating that the vehicle (10) is too noisy. 12. The method of claim 11, characterized in that the alarm signal is displayed inside the vehicle (10) in order to alert the driver of the noisy vehicle (10). 13. Method according to one of claims 1 to 12, characterized in that said acoustic instrument (1) comprises means for determining and recording the sound spectrum of the noisy vehicle (10). 14. Acoustic instrument (1) for recognizing an acoustic signal produced by a vehicle (10), the acoustic instrument (1) comprising a sound level meter (20), characterized in that the acoustic instrument (1) comprises: - means for measuring the distance (D) of the vehicle (10) relative to the sound level meter (2); A unit for storing sound level detection threshold criteria; - a man-machine interface for displaying the sound level emitted by the vehicle (10) at a reference distance (Dr) chosen beforehand; - Means for identifying the vehicle (10). 15. Acoustic instrument (1) according to claim 14, characterized in that said means for identifying the vehicle (2) comprise a vision system (6) making it possible to recognize the license plate (20) of the vehicle. 16. Acoustic instrument (1) according to claim 14 or 15, characterized in that said means for identifying the vehicle comprise a vision system (6) making it possible to recognize the make and / or type of the vehicle (10). 17. Acoustic instrument (1) according to one of claims 14 to 16, characterized in that the acoustic instrument (1) also comprises a display of the sound level of the vehicle (10) at said distance (D). 18. Acoustic instrument (1) according to one of claims 14 to 17, characterized in that the acoustic instrument (1) comprises at least two sound level meters and / or two means for measuring the distance (D) of the vehicle relative to the sound level meter (20). 19. Acoustic instrument (1) according to one of claims 14 to 18, characterized in that the means for measuring the distance (D) of the vehicle (10) relative to the sound level meter (2) are optical means. 20. Acoustic instrument (1) according to claim 19, characterized in that the optical means (4) comprise a laser. 21. Acoustic instrument (1) according to claim 19 or 20, characterized in that the means for measuring the distance (D) from the vehicle (10) is a radar system. 22. Acoustic instrument (1) according to one of claims 18 to 20, characterized in that the means for measuring the distance (D) from the vehicle (10) comprise a system using triangulation techniques. 23. Acoustic instrument (1) according to one of claims 14 to 22, characterized in that the sound of a vehicle can be detected up to a distance of 100m. 24. Acoustic instrument (1) according to one of claims 14 to 23, characterized in that its dimension has the size of a mobile phone preferably having a length I between 10 cm and 25 cm, a width w between 5 cm and 15 cm and a thickness e between 3 mm and 20 mm. 25. Acoustic instrument (1) according to claim 24, characterized in that the focal length of at least one of the lenses of the instrument (34, 40b, 32) has a focal length greater than the thickness e of the 'instrument.