Method and system for detecting acoustic phenomena

Abstract

The invention relates to a detection system (1) comprising N detection devices (10) distributed in an area to be monitored (Z), each comprising an acoustic sensor and a processing block; - a second operating mode where processing of the sounds captured by the detection device is carried out, corresponding to a second level of electrical consumption higher than the first level; each detection device (10) operates by default in a first mode corresponding to a first level of electrical consumption of the device, very low consumption, in which the processing block carries out the first analysis on the electrical signal delivered by the acoustic sensor, and in which the recording of said electrical signal is not authorized; and as soon as said first analysis detects a predefined acoustic phenomenon, said detection device (10) alerts the N-1 other detection devices (10) of the system;upon receipt of the alert, each of the N-1 other detection devices (10) then switches to a second mode, in which it is triggered: - the transmission, to a recording block, of the electrical signal delivered by its acoustic sensor after receipt of the alert; - the recording, by said recording block, of the transmitted electrical signal; and - a second analysis of the recorded electrical signal, to detect acoustic phenomena, implementing an algorithmic processing corresponding to a second level of electrical consumption higher than the first level. Figure for the abstract: Fig. 1;

Description

Title of the invention: Method and system for detecting acoustic phenomena Technical field

[0001] The invention lies in the field of monitoring acoustic phenomena. Prior art

[0002] The invention particularly relates to the monitoring of acoustic phenomena using a detection system comprising a network of acoustic sensors each coupled to a processing block, making it possible to detect acoustic signatures in real time.

[0003] Limiting the electrical energy consumed by such a system is a significant problem, especially when the sensors are on-board.

[0004] There is therefore a need for a solution for such a detection system that can continuously detect acoustic signatures, in real time, but with very low energy consumption. Summary of the invention

[0005] To this end, according to a first aspect, the present invention describes a method for detecting acoustic phenomena using a detection system comprising N detection devices distributed in an area to be monitored, N >2 and connected to each other by telecommunication links,

[0006] each detection device comprising an acoustic sensor capturing sounds and delivering an electrical signal as a function of the captured sounds and an electrical signal processing block,

[0007] each detection device is adapted to operate alternately according to:

[0008] - a first operating mode during which the detection device carries out an initial analysis to detect acoustic phenomena, corresponding to a first level of electrical consumption of the device, called very low consumption detection mode; and

[0009] - a second mode of operation during which sound processing captured by the detection device are carried out, corresponding to a second level of electrical consumption higher than the first level;

[0010] according to which:

[0011] each detection device operates by default in the first mode, in which the processing block performs the first analysis on the electrical signal delivered by the acoustic sensor, and in which the recording of said electrical signal is not authorized; and as soon as said first analysis detects an acoustic phenomenon predefined, said detection device alerts the Nl other detection devices of the system via the telecommunications links;

[0012] upon receipt of the alert, each of the N1 other detection devices then switches to the second mode, in which it is triggered:

[0013] - the transmission, to a recording block, of the electrical signal delivered by its acoustic sensor after receiving the alert,

[0014] - recording, by said recording block, of the transmitted electrical signal and

[0015] - a second analysis of the recorded electrical signal, to detect phenomena acoustics, implementing algorithmic processing corresponding to a second level of electrical consumption higher than the first level.

[0016] The invention exploits the coupling between the sensors and the propagation of the wave from one sensor to another to carry out in-depth analyses on the signal with extremely low energy consumption.

[0017] Following the alert triggered by one of the N detection devices, the N1 other devices can thus be switched to a second mode associated with the implementation by the system of in-depth detection processing, even before the acoustic signal that triggered the alert reaches them, allowing complete capture of the signal in question, whereas the detection device that first detected the signal cannot have recorded it (this would have required the signal to be perpetually recorded, which, in most situations, is not sustainable in terms of energy and storage).

[0018] In embodiments, such a method will further comprise at least one of the following features:

[0019] - the method comprises one of the following provisions:

[0020] when the detection device is in said second mode: the recording is carried out by an electronic recording block of said detection device and / or the second analysis is carried out by the processing block of said detection device;

[0021] when the detection device is in said second mode, it transmits the electrical signal to a remote analysis device via a teletransmission link and the second analysis is carried out by said remote analysis device;

[0022] - in the second mode, the electrical signals of the Nl devices are recorded in a synchronized manner, the detection devices having been previously synchronized with each other and / or a synchronization being implemented by said detection devices on the basis of the alert or another signal;

[0023] - the direction of arrival of an acoustic phenomenon detected by the second analysis in the second mode is determined based on the recordings of the electrical signals delivered by the sensors of several of the Nl detection devices following receipt of the alert;

[0024] - the relative positions of the sensors between them is determined as a function of at least of a temporal length of acoustic signatures sought and of the environment in which the detection devices are arranged, in which the sound propagates;

[0025] - the inter-sensor distance is chosen so that an audible signal can be detected by a detection device in very low power mode among the N detection devices before said sound signal reaches at least the sensor of one of the Nl other detection devices.

[0026] According to another aspect, the invention describes a system for detecting acoustic phenomena comprising N detection devices adapted to be distributed in an area to be monitored, N >2 and to be connected to each other by telecommunication links,

[0027] each detection device comprising an acoustic sensor, adapted to capture sounds and deliver an electrical signal as a function of the captured sounds, and an electrical signal processing block,

[0028] each detection device is adapted to operate alternately according to:

[0029] - a first operating mode during which the detection device carries out an initial analysis to detect acoustic phenomena, corresponding to a first level of electrical consumption of the device, called very low consumption detection mode; and

[0030] - a second mode of operation during which sound processing captured by the detection device are carried out, corresponding to a second level of electrical consumption higher than the first level;

[0031] in which:

[0032] each detection device is adapted to operate by default in the first mode, in which the processing block is adapted to carry out the first analysis on the electrical signal delivered by the acoustic sensor, and in which the recording of said electrical signal is not authorized; and as soon as said first analysis detects a predefined acoustic phenomenon, said detection device is adapted to alert the Nl other detection devices of the system via the telecommunications links;

[0033] upon receipt of the alert, each of the N1 other detection devices is adapted to then switch to the second mode, in which the following operations are triggered:

[0034] - the transmission, to a recording block, of the electrical signal delivered by its acoustic sensor after receiving the alert,

[0035] - recording, by said recording block, of the transmitted electrical signal and

[0036] - a second analysis of the recorded electrical signal, to detect phenomena acoustics, implementing algorithmic processing corresponding to a second level of electrical consumption higher than the first level.

[0037] In embodiments, such a system will further comprise at least one of the following features:

[0038] - the acoustic phenomena detection system comprises one of the dis following positions:

[0039] when the detection device is in said second mode: the recording is carried out by an electronic recording block of said detection device and / or the second analysis is carried out by the processing block of said detection device;

[0040] when the detection device is in said second mode, it is adapted to transmit the electrical signal to a remote analysis device via a teletransmission link and the second analysis is carried out by said remote analysis device;

[0041] - in the second mode, the electrical signals of the Nl devices are recorded in a synchronized manner, the detection devices having been previously synchronized with each other and / or a synchronization being implemented by said detection devices on the basis of the alert or another signal;

[0042] - the system is adapted to determine the direction of arrival of a phenomenon acoustic detected by the second analysis in the second mode based on the recordings of the electrical signals delivered by the sensors of several of the Nl detection devices following receipt of the alert. Brief description of the drawings

[0043] The invention will be better understood and other characteristics, details and advantages will appear more clearly on reading the following description, given without limitation, and thanks to the appended figures, given by way of example.

[0044] [Fig-1] [Fig.l] is an illustration of a phenomenon monitoring system acoustics in one embodiment of the invention;

[0045] [Fig.2] [Fig.2] is a schematic representation of a detection device in one embodiment of the invention;

[0046] [Fig.3] [Fig.3] represents the steps of a method for monitoring acoustic phenomena in one embodiment of the invention.

[0047] Identical references may be used in different figures when they designate identical or comparable elements. Description of the embodiments

[0048] [Fig.l] represents a system 1 for monitoring acoustic phenomena within a predefined area of ​​interest to be monitored, named Z. The system 1 comprises a network comprising N detection devices 10, N being an integer greater than or equal to equal to 2.

[0049] . Zone Z is, depending on the case, in one, two or three dimensions and can take various shapes and sizes.

[0050] In the present case, the area under surveillance Z is an underwater area and the monitored acoustic phenomena are underwater phenomena. The acoustic sensors 101 are, for example, hydrophones.

[0051] The detection devices 10 are distributed in the area under surveillance Z according to a predefined configuration, depending on the signals to be measured: in the example considered, the detection devices are 4 in number and are arranged relative to each other so as to each be on a respective vertex of the same tetrahedron. The sensors are at a known distance from each other and held rigidly together. The orientation of the assembly is also known, for example by using an inertial unit or any other positioning system.

[0052] Each detection device 10 comprises in the first embodiment considered and as represented in [Fig.2], in particular an acoustic sensor 101, a processing block 102, a control block 104, a memory 105, a power supply block 106 and a telecommunications block 107 (the sensor 101 and the processing block 102 are generally in the same place, integrated in the same hardware element); in the first embodiment considered and as represented in [Fig.2], it further comprises a recording block 103.

[0053] The power supply unit 106, comprising for example batteries or cells, is adapted to supply electrical energy to the acoustic sensor 101, the processing unit 102, the recording unit 103, the control unit 104, the memory 105, the power supply unit 106 and the telecommunications unit 107.

[0054] The telecommunications block 107 of a detection device 10 comprises a telecommunications transmitter and receiver and is adapted to implement telecommunications links in particular with the telecommunications block 107 of each other detection device 10. These telecommunications links are for example wireless links (for example UHF radio) or even wired links on wired telecommunications supports connecting the devices 10. In one embodiment, the telecommunications block 107 of at least one of the detection devices 10 is further adapted to communicate with a remote electronic supervision module (not shown), for example via satellite link or other.

[0055] Each detection device 10 is adapted to work alternately according to a first mode, corresponding to detection processing requiring very low consumption, called very low consumption detection mode and a second mode corresponding to the implementation, by the system 1, of detection processing requiring greater electrical energy consumption than the very low power detection mode, called deep detection mode and described below.

[0056] For illustration purposes only, the consumption of the detection device 10 in the very low power detection mode corresponds to an average consumption of the device of less than 100 uW, and the electrical consumption for the detection processing on a signal obtained by the device in the second mode is in the range 10 mW to 1 W. Or, in another example, the average consumption for a detection processing carried out on a signal in the second mode is more than 100 times the average consumption for a detection processing carried out on a signal in the very low power detection mode.

[0057] The recording block 103 is adapted to record - only in the second mode (deep detection mode) and not in very low consumption detection mode - the electrical signals at the output of the sensor 101 in the memory 105. In one embodiment, it is adapted to also record - only in deep detection mode - at least some of the results of the processing block 102 in the memory 105.

[0058] The detection devices 10 are adapted to implement the steps, which are their respective responsibility, of the method 200 now described with reference to [Fig.3].

[0059] In a step 201, each detection device 10 analyzes by default, continuously or periodically with a period T less than the duration of the phenomena to be detected, its acoustic environment in the very low consumption detection mode, and this as long as it does not detect a significant acoustic event or does not receive an alert from the N1 other detection devices 10. Thus: - the sensor 101 captures the ambient acoustic signals and delivers, to the processing block 102, an electrical signal depending on these acoustic signals; - the processing block 102 performs processing of the electrical signal making it possible to detect whether one (or more) acoustic phenomenon(s) of interest is present in the captured acoustic signals.

[0060] The acoustic phenomena of interest are predefined and depend on the application. Thus, the acoustic phenomena of interest in the case of surveillance relating to the underwater animal world will be the characteristic sounds of the animals being monitored (whales, dolphins, etc.). In the case of surveillance of marine vessels, these will be the sound signatures of the different types of ships and underwater devices, etc. The data defining these reference acoustic phenomena of interest have been previously stored in the memory 105 and are used in step 101 by the processing block 102.

[0061] When a detection device 10 is in this very low detection mode consumption, it is impossible to record signals from the acoustic sensor 101 (for example, the control block 104 prohibits the use of the recording block 103 of the device 10).

[0062] In one embodiment, the signal processing performed by the processing block 102 in this very low-power detection mode is, for example, low-complexity detection processing, thus consuming little electrical energy. For example, it is analog filtering bank type processing coupled with expert rules or a simple neural network.

[0063] As soon as the processing block 102 of a detection device 10 (named device 10_aierte) detects an acoustic phenomenon of interest during this processing, it notifies the control block 104 which then triggers the sending, via the telecommunication block 107, of an alert message to the other detection devices 10 (named 10_other) •

[0064] In a step 202, as soon as a detection device 10 receives, via its communication block 107, an alert message sent by one of the (N1) other detection devices 10 of the system 1, this detection device 10 switches from the very low consumption detection mode to the second mode (in-depth detection mode). The switch is for example triggered by its control block 104. The detection processing corresponding to the first mode is stopped.

[0065] In this in-depth detection mode, within the detection device 10 having received the alert, the recording block 103 then records the electrical signal coming from the sensor and the processing block 102 performs at least one processing operation on all or part of the recorded electrical signal: this processing operation this time comprises an analysis of the recorded signal (a posteriori analysis) using one or more complex algorithms for searching for and identifying acoustic phenomena consuming more electrical energy than the processing operation carried out in the very low consumption detection mode: for example algorithms of the FFT pattern analysis type, which are implemented based on convolutional neural networks or others (conventional networks, Long Short Terni Memories, expert rules, etc.), and having an energy cost that is too high to operate permanently when they are 'embedded'.

[0066] In one embodiment, as soon as a detection device 10 has detected a phenomenon, in addition to sending an alert message, it also switches to the second mode, here the in-depth detection mode, in addition to the other detection devices.

[0067] At the end of step 202, the processing block 104 of one or more of the N1 other devices in turn identifies the acoustic phenomenon already detected by the device having triggered the alert, and confirms it as a significant phenomenon or on the contrary concludes that it is not significant and, if it is confirmed, characterizes it in a more detailed manner. than the latter had done via its analysis in very low consumption mode. During this processing, data defining significant reference sound phenomena (for the detection application used) previously stored in the memory 105, are for example used during comparison with data extracted from the recorded signal.

[0068] Then, if the detection of a significant acoustic phenomenon is confirmed, for example:

[0069] - the signature determined by the analysis in deep detection mode is stored in memory 105; and / or

[0070] - a transmission, to the supervision module, of the alert accompanied by certain less results of in-depth detection are performed.

[0071] In one embodiment of the recording of the electrical signal, the data defining this electrical signal are recorded in a synchronized manner between the N1 detection devices: they are time-stamped (the reference time being the same for the detection devices) and stored with their time-stamping. To do this, the N detection devices have been synchronized in a prior step, or the alert emitted in step 201 (or any other agreed signal transmitted between them) is equivalent to a synchronization signal. A calibration of the synchronization may have taken place beforehand in the case of radio alerts for example.

[0072] At the end of the characterization, by each detection device 10, of the detected phenomenon (or when no more acoustic phenomenon is detected by this detection device), the switch from the in-depth detection mode to the very low consumption detection mode is triggered by the control block 104 of this detection device. The N detection devices then each repeat step 201.

[0073] In a step 203 (optional), the use of the signal recorded by one or more (for example at least three) of the detection devices and relating to the same detected acoustic phenomenon makes it possible, after synchronization, to measure the delays between the arrival times of the signals at each of these devices, and to deduce therefrom the direction of arrival of the signal (the relative positions of the devices between them being known). These calculations are carried out for example by the control block 104 of one of the detection devices or by a processor of the supervision module, after collection of the electrical signals relating to the acoustic phenomenon.

[0074] In a second embodiment, the second mode comprises a recording-only mode, in which the recording block 103 of the detection device 10 records signals from the acoustic sensor 101 of the device. In step 202, it is into this recording mode that the detection device 10 switches following receipt of the alert message, the in-depth detection signal processing being carried out subsequently, in deferred time, on the recorded signals. (by the processing block 102 of the detection device or otherwise as described below), for example after recovery of the detection devices.

[0075] In a third embodiment, the detection devices of the monitoring system 1 (or at least some of them) are, with respect to their structure shown in [Fig. 2], only provided with very low-power detection and alert capabilities allowing them to implement step 201, but do not have a recording block 103, nor in-depth detection capabilities. Instead, a recording and in-depth detection device of the monitoring system 1 and provided with a memory and a processor, is used, which performs the recording and in-depth detection tasks described, in the first embodiment, as performed in step 202 by the recording block 103 and the processing block 102. The recording and in-depth detection device is connected to each of these detection devices (via its communication block 107) by a telecommunications link, wireless or wired.For example, it is located at the center of the tetrahedron whose corners correspond to the locations of the devices, or it is integrated into one of the detection devices 10.

[0076] In this third embodiment, after step 2015 in a step 202_bis (replacing step 202 described above), as soon as a detection device (without recording block 103, nor in-depth detection capabilities), named 10_bis, receives, via its communication block 107, an alert message sent by one of the (Nl) other detection devices of the system 1, this detection device 10_bis switches from the very low consumption detection mode to the second mode: in this second mode, it then transmits the electrical signal coming from its sensor to the recording and in-depth detection device; the latter then records the received signal and it will carry out at least one processing of the signal described above as carried out for in-depth detection (in a variant, this device records in its memory the signals which are transmitted to it, the in-depth detection processing being carried out later, after recovery from the memory)..

[0077] In one variant, the recording block is kept in all the detection devices and only the “deep detection” part is centralized.

[0078] The transitions between the first and second modes correspond, whatever the embodiments, to a switching of the detection structure, the peripheral detection devices may or may not be equipped with recording and / or advanced analysis capabilities.

[0079] In one embodiment, the shape of the network is determined based on the intended application.

[0080] For example, if it is a question of detecting a source of acoustic phenomenon which can be placed anywhere in the monitored zone Z, a network of four devices of detection 10 will be used, the four corresponding sensors being for example arranged in a tetrahedral structure (not necessarily regular, cf. submarine instrumentation for example).

[0081] The structure can be anything other than tetrahedral, for example planar to analyze sources that may come from a 2D surface.

[0082] In the case where the detection is carried out in a linear waveguide (pipeline for example), only two sensors, each in a respective detection device 10, are necessary. The distance between the sensors depends on the characteristic time of the signature (or signatures) of interest sought and the medium in which the sound propagates.

[0083] Whatever the shape of the network, it is wise to choose the distance between the sensors so that the signal can be detected by a detection device in very low consumption mode before it reaches at least one of the other devices, which will make it possible to have the recorded acoustic signature in its entirety to carry out advanced analyses later on the signals recorded following the transition to the second mode.

[0084] The invention therefore describes a solution for detecting acoustic phenomena making it possible to limit the consumption of electrical energy, on the basis of a switch, from a first operating mode corresponding to very low consumption detection) to a second operating mode associated at least with the triggering of recording with a view to in-depth detection, requiring much more energy, and conversely of a switch, associated with a prohibition of recording, from the second mode to the very low consumption detection mode.

[0085] Each of the detection devices continuously analyzes the acoustic signals received in very low power detection mode so as to be able to wake up the entire network if an abnormal event occurs. Since the "wake-up" is carried out almost instantaneously via the telecommunications links, wireless or wired, the N1 other detection devices can thus be switched to the in-depth detection mode implemented by the system 1 even before the acoustic signal reaches them, allowing complete capture of the signal in question, whereas the detection device that first detected the signal cannot have recorded it (this would have required it to be perpetually recording, which is not sustainable in terms of energy and storage).The captures are then analyzed a posteriori by the embedded system using advanced algorithms (for example CNN) having an energy cost too high to run continuously, to confirm the alert. Thus, the invention allows, based on the coupling between the sensors and the Fonde propagation from one sensor to another, to carry out in-depth analyses on the signal with ultra-low energy consumption.

[0086] An embodiment of underwater monitoring has been described above, but the invention can be implemented in the monitoring of acoustic phenomena in environments other than water: in air, vacuum, a gas, a waveguide medium in general. This can be, for example, metal, for pipelines and in this case of one-dimensional phenomena, two sensors are sufficient: the first triggers the awakening of the second which can capture the shock or leak signal as soon as it appears and in its entirety, which facilitates and improves classification. For example, the invention is implemented to monitor factories in which machine defects can occur; in this case, detection is done in 3D.

[0087] At least some of the steps (for example those performed by the processing block and / or the control block and / or the recording block) may be implemented by the execution of software instructions on a processor in the detection device 10 (or in the recording and in-depth detection device), the software instructions being stored in a memory of the device. Alternatively, they may be implemented by dedicated hardware, typically a digital integrated circuit, either specific (ASIC) or based on programmable logic (for example FPGA / Field Programmable Gate Array).

Claims

1. Claims Method for detecting acoustic phenomena using a detection system (1) comprising N detection devices (10) distributed in an area to be monitored (Z), N >2 and connected to each other by telecommunication links (11), each detection device (10) comprising an acoustic sensor (101) capturing sounds and delivering an electrical signal as a function of the captured sounds and an electrical signal processing block (102), each detection device (10) is adapted to operate alternately according to: - a first operating mode during which the detection device (10) carries out a first analysis to detect acoustic phenomena, corresponding to a first level of electrical consumption of the device, called very low consumption detection mode; and - a second operating mode during which processing of the sounds captured by the detection device is carried out, corresponding to a second level of electrical consumption higher than the first level; according to which: each detection device (10) operates by default in the first mode, in which the processing block (102) performs the first analysis on the electrical signal delivered by the acoustic sensor, and in which the recording of said electrical signal is not authorized; and as soon as said first analysis detects a predefined acoustic phenomenon, said detection device (10) alerts the Nl other detection devices (10) of the system via the telecommunication links (11); upon receipt of the alert, each of the Nl other detection devices (10) then switches to the second mode, in which it is triggered: - the transmission, to a recording block, of the electrical signal delivered by its acoustic sensor after receipt of the alert, - the recording, by said recording block, of the transmitted electrical signal and - a second analysis of the recorded electrical signal, to detect acoustic phenomena, implementing algorithmic processing corresponding to a second level of electrical consumption higher than the first level.

2. Method for detecting acoustic phenomena according to claim 1, comprising one of the following provisions: - when the detection device is in said second mode: the recording is carried out by an electronic recording block of said detection device and / or the second analysis is carried out by the processing block of said detection device; - when the detection device is in said second mode, it transmits the electrical signal to a remote analysis device via a remote transmission link and the second analysis is carried out by said remote analysis device.

3. Method for detecting acoustic phenomena according to claim 1 or 2, according to which, in the second mode, the electrical signals of the N1 devices are recorded in a synchronized manner, the detection devices having been previously synchronized with each other and / or a synchronization being implemented by said detection devices on the basis of the alert or another signal.

4. A method for detecting acoustic phenomena according to any one of the preceding claims, wherein the direction of arrival of an acoustic phenomenon detected by the second analysis in the second mode is determined based on the recordings of the electrical signals delivered by the sensors of several of the N1 detection devices following receipt of the alert.

5. Method for detecting acoustic phenomena according to any one of the preceding claims, according to which the relative positions of the sensors between them are determined as a function of at least one temporal length of acoustic signatures sought and of the medium in which the detection devices are arranged, in which the sound propagates.

6. Method for detecting acoustic phenomena according to any one of the preceding claims, according to which the inter-sensor distance is chosen so that a sound signal can be detected by a detection device in very low consumption mode among the N detection devices before said sound signal arrives at least at the sensor of one of the N1 other detection devices.

7. System for detecting acoustic phenomena (1) comprising N detection devices (10) adapted to be distributed in an area to be monitored (Z), N >2 and to be connected to each other by telecommunication links (11), each detection device (10) comprising an acoustic sensor (101), adapted to capture sounds and deliver an electrical signal as a function of the captured sounds, and an electrical signal processing block (102), each detection device (10) is adapted to operate alternately according to: - a first operating mode during which the detection device (10) carries out a first analysis to detect acoustic phenomena, corresponding to a first level of electrical consumption of the device, called very low consumption detection mode; and - a second operating mode during which processing of the sounds captured by the detection device is carried out, corresponding to a second level of electrical consumption higher than the first level; in which: each detection device (10) is adapted to operate by default in the first mode, in which the processing block (102) is adapted to carry out the first analysis on the electrical signal delivered by the acoustic sensor, and in which the recording of said electrical signal is not authorized; and as soon as said first analysis detects a predefined acoustic phenomenon, said detection device (10) is adapted to alert the Nl other detection devices (10) of the system via the telecommunication links (11); upon receipt of the alert, each of the Nl other detection devices (10) is adapted to then switch to the second mode, in which the following operations are triggered: - the transmission, to a recording block, of the electrical signal delivered by its acoustic sensor after receipt of the alert, - the recording, by said recording block, of the transmitted electrical signal and - a second analysis of the recorded electrical signal, to detect acoustic phenomena, implementing algorithmic processing corresponding to a second level of electrical consumption more higher than the first level.

8. Acoustic phenomena detection system (1) according to claim 7, comprising one of the following provisions: when the detection device is in said second mode: the recording is carried out by an electronic recording block of said detection device and / or the second analysis is carried out by the processing block of said detection device; when the detection device is in said second mode, it is adapted to transmit the electrical signal to a remote analysis device via a teletransmission link and the second analysis is carried out by said remote analysis device.

9. An acoustic phenomena detection system (1) according to claim 7 or 8, wherein, in the second mode, the electrical signals of the N1 devices are recorded in a synchronized manner, the detection devices having been previously synchronized with each other and / or a synchronization being implemented by said detection devices on the basis of the alert or another signal.

10. Acoustic phenomenon detection system (1) according to any one of claims 7 to 9, adapted to determine the direction of arrival of an acoustic phenomenon detected by the second analysis in the second mode as a function of the recordings of the electrical signals delivered by the sensors of several of the N1 detection devices following receipt of the alert.

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