EP3729111A1

EP3729111A1 - Interferometric lightning detection system

Info

Publication number: EP3729111A1
Application number: EP18839844.0A
Authority: EP
Inventors: Philippe CARDI; Jean-Yves Lojou
Original assignee: Selerys
Current assignee: Selerys
Priority date: 2017-12-20
Filing date: 2018-12-20
Publication date: 2020-10-28
Also published as: FR3075390B1; US20210072338A1; MA51313A; FR3075390A1; WO2019122763A1; CN111788490A

Abstract

The invention relates to a system (1) for interferometrically detecting an electromagnetic source, characterised in that it comprises two antenna modules (5), each antenna module (5) comprising two conductive elements (2), one planar reflector (6) having a first face (6i) and a second face (6ii), the first faces (6i) of the planar reflectors (6) of the antenna modules (5) engaging respectively and rigidly with the two conductive elements (2) of the antenna modules (5), the two antenna modules (5) being mutually arranged so that the second faces (6ii) of the planar reflectors thereof form a projecting angle (α).

Description

Interferometer lightning detection system

The invention relates to the field of devices or systems in application with the detection and / or observation of electromagnetic sources. Such devices or systems are used for all types of use and preferably but not exclusively, in connection with meteorological phenomena, and more particularly, to provide lightning detection functions, also known by the English name "lightning detection". ".

In the rest of the document, the invention will be described preferentially but not exclusively in the context of prevention against lightning, that is to say in the context of actions aimed at reducing or aborting eventual damage that can cause storms, more particularly, lightning phenomena in territories more or less sensitive than others, such as cultivated areas, or on infrastructures for example.

For the purposes of the invention and throughout the document, for purposes of simplification, the terms "lightning" and "lightning" will be used interchangeably.

For decades, lightning has fascinated men, especially scientists. Lightning is also the subject of many studies in the field of meteorology, since it has many dangers, which can cause serious damage, both in terms of material and human, such as, for example , the outbreak of fires, a possible electrocution of human beings and / or animals that could potentially lead to their death, electromagnetic interference possibly harmful to communications, aviation and / or navigation, destruction of electronic components in infrastructure and / or equipment.

During a storm, two phenomena are commonly observed: one or more flashes consisting of one or more electrical discharges generating an electromagnetic wave, visible results of the heating of the air, and thunder corresponding to a noise emitted during the abrupt expansion of the heated air during the passage of this current. Indeed, lightning consists of a natural phenomenon of discontinuous electrostatic discharge, such a phenomenon generally occurring in regions of storm clouds charged with static electricity, that is to say either in or between such clouds (" Cloud lightning "according to English terminology), or between such clouds and the air or the ground (" Cloud to Ground (CG) lightning "according to English terminology), the ground may include one or more zones land or sea. Whatever the nature of lightning, it is preceded and followed by electrical phenomena of lower intensity called respectively precursors ("leader" in English terminology) and "streamer". It is usually precursors that determine the path of lightning. There are two main families of precursors: the precursors or tracers in step ("stepped leader" in English terminology) that precede the first arc of the cloud-ground lightning and which progress towards the ground in leaps of fifty meters in length, and the leading precursors ("dart leader" in English terminology) that precede the subsequent arcs of lightning clouds-ground as well as different types of intra-cloud lightning. The systems capable of detecting both lightning and precursors and streamers are said to total detection ("total lightning" in English terminology). They generally operate in high frequency (VHF-UHF) bands in which the radiation of these phenomena is the most intense. The appearance of lightning causes the creation of a plasma, that is to say a medium consisting of a mixture of neutral particles, positive ions and negative electrons, produced in the air on the route of the discharge, resulting in the appearance of two previously mentioned phenomena: on the one hand the lightning, which spreads very rapidly, and on the other hand the thunder, which results from an explosive expansion of the air heated by the lightning, and spreads relatively slowly in comparison with the lightning. Typically, lightning tends to strike the ground close to the generating cloud, especially in high altitude areas, and / or more particularly buildings, trees, or any prominent objects on the ground or the sea. The thunder, as for him, can resound of a noise, such a crunching, dry and immediate, when the flash is near, or, alternatively, rumble more widely in the distance, more particularly when the storm takes place in a mountainous region, by echo effects in particular. Because light travels much more quickly in the air than sound, lightning is usually visible long before thunder is heard, allowing us to estimate the approximate distance to which lightning has fallen.

Storm clouds develop from cumulonimbus or cumulonimbus aggregates, also referred to as "storm clouds", such cumulonimbus clouds. which may contain a hundred thousand tons of water, hailstones and small ice crystals. The said cumulonimbus are generally subjected to speed shears, that is to say variations of the wind speed as a function of altitude, to directional shears, that is to say variations of the orientation. wind depending on the altitude, and intense ascendances and subsidies. This turbulence causes shocks between the particles constituting the cloud, in particular ice crystals and water droplets. The redundancy of these clashes leads to the removal of electrons from particles and thus the appearance of charges. The heavier particles harbor the negative charges while the lighter ones, supported by the updrafts, are positively charged. Inside the cumulonimbus (s), a complex electrification process leads to the separation of positive and negative electrostatic charges, and thus the creation of an intense electric field.

As soon as this field reaches a sufficient value, an ionized channel is formed, also called a descending tracer, corresponding to the lightning and propagating by successive leaps from the cloud towards the ground.

The physical processes causing thunderstorms are complex and include many unpredictable elements that are subject to constant change. In addition to the state of the atmosphere, the formation of storms also depends, for many, very variable local conditions, especially in terms of temperature and humidity, soils at the edge of which thunderstorms form, such conditions being more particularly conditioned by the nature of the soil, the type of vegetation, or the configuration of the relief itself depends on the presence of buildings. Moreover, in comparison with possible storms, the stormy phenomena are generally sudden, of short duration, ranging from a few tens of minutes to a few hours, and concern relatively limited areas, a few tens of kilometers. As a result, the detection and location of storm phenomena is particularly complex.

At the sight of the significant damage that can cause lightning or more generally thunderstorms, different researchers have tried to find methods or processes intended to detect, even to locate, the lightning, and this in order to prevent the possible damages that the lightning could cause, or even in some cases, to finally preserve infrastructure and living things. Such methods for detecting lightning are based on different technologies.

As already mentioned, lightning can be grouped into two main categories: lightning strikes on the ground, also known as "lightning strikes", and lightning strikes that do not hit the ground. Within these two categories, lightning can be subdivided into other subgroups, as a function, for example, of the specific trajectory of such flashes and / or the direction of the electric current flowing in the light channels associated with each flash. . The most common lightning usually does not hit the ground and is commonly referred to as "cloud lightning or intrafloud lightning". Such lightning, of lower intensity lightning strikes on the ground, in particular, make it possible to reduce space charge differences in a cloud or between clouds. The number of said intra-cloud flashes is a marker of convection of storm cells, well before the appearance of lightning strikes on the ground. Over the years, it has been essential to observe intra-cloud lightning for a number of reasons: the sharp increase in the intra-cloud rhythm, precursor of violent storm events, has already been made l 'object of study and is generally named by the Anglo-Saxon terminology' Lightning Jump '. Indeed, in most thunderstorms that can be described as ordinary, the flashes of clouds are generally more numerous than the flashes striking the ground, of a factor of about two to ten. Surprisingly, however, violent thunderstorms produce much higher rates of intran cloud lightning than lightning strikes on the ground, with some thunderstorms producing no lightning on the ground. Thus, intra-cloud lightning can provide interesting and important indications for thunderstorms, such as, for example, their rate of growth and / or intensity, leading consequently to important applications in the immediate prediction of thunderstorms. In most thunderstorms, one or more intra-cloud flashes precede the first lightning strike, while the storm may have already begun to develop and become electrified. Typically, a few minutes to a few tens of minutes may elapse between the first intraflat flash and the first lightning strike on the ground. This delay may be, in certain cases, essential, since it makes it possible to use the observations made in link with intra-cloud lightning to provide warnings or warnings about lightning strike on the ground, depending on the position of a storm.

Intra-cloud lightning and lightning strikes on the ground emit one or more electromagnetic waves, broadly defined as electromagnetic energy, over a wide range of frequencies. Depending on the type of lightning, the distribution of electromagnetic energy emitted as a function of frequency is different. Flashes striking the ground have, for example, a spectral distribution in frequencies at low frequencies, of the order of a few kilohertz. Intra-cloud lightning, on the other hand, has a spectral density in very high frequencies, even ultra-high frequencies. Such disparities in the spectral distribution come from the size of lightning, more particularly the wavelength. Thus, a flash striking the ground generally has a wavelength of the order of a few kilometers while an intra-cloud flash usually has a wavelength of the order of one meter.

Most of this energy is contained in pulses or "bursts" at very high frequencies or ultra high frequencies (known abbreviations and respective English terminologies "VHF-Very High Frequency and UHF-Ultra High Frequency") such pulses being more or less long and / or sudden. Such electromagnetic emissions can be categorized and generally treated in traditional radio frequency ranges relating to common signal processing bands. Due to significant differences in the frequencies and amplitudes of electromagnetic radiation at At these frequencies, several techniques have been developed to detect various processes in intrafloud flashes and lightning strikes on the ground.

Historically, a first relatively old technique, dating back to the end of the nineteenth century, first consisted in developing a system employing a detection device based solely on the magnetic field (also known as abbreviation and English terminology). "MDF - Magnetic Direction Finding") combined with one or more narrowband radio receivers in very low and low frequency ranges. The first experiments included understanding the electromagnetic fields produced by lightning and focused mainly on the detection of vertical flashes, ie lightning strikes on the ground. Such a first technique has notably demonstrated the importance of the calibration before triggering the electric field measurements and the importance of the detection direction. Subsequently, to try to respond to such constraints, around the 1950s, other researchers resorted to geolocation time-of-arrival techniques (also known as ToA abbreviations and terminologies). - Time of Arrival "or" ToF - Time of Flight ") for the first time in lightning geolocation. Such ToA-type geolocation techniques use the constant time difference between the arrival of low frequency signals and sensors positioned on the ground to calculate the location of meteorological events involving lightning strikes on the ground. However, these techniques also present a certain a number of limits and disadvantages, especially in terms of terrain and the effect of conductivity on the speed of propagation of lightning signals. In addition, each ToA-based detection system identifies a unique and specific function or shape of a signal to provide the most accurate arrival times of the order of one hundred nanoseconds. Such a function or signal form must thus be considered common through a number of systems widely separated from each other, said systems being advantageously networked. Any signal shapes or functions must then be sufficiently separated in time, in order to reduce, or even avoid, the correlation errors between the systems. In addition, such ToA-type detection systems are very sensitive in terms of signal-to-noise ratio.

The existence of intra-cloud lightning has been known for a long time, but the implementation of systems or equipment for detecting and locating electromagnetic waves, particularly intraflash lightning, still remains today. delicate and complex. Indeed, in the frequency range where such flashes radiate, more particularly in very high frequencies or ultra high frequencies, such electromagnetic waves propagate in a substantially direct direction. Consequently, the sites or locations selected for the installation or installation of systems for detecting said lightning must be free of any obstacle and / or any source emitting electromagnetic fields. In addition, the support or supports on which said systems are installed also have constraints, since they must to answer a certain number of specific characteristics, in particular in order to limit, or even to suppress, the mask effects, the multiple reflections, the phase shifts that the electromagnetic waves that one seeks to detect could undergo.

In storm cells, there are tens of thousands of electromagnetic sources in the form of intra-cloud lightning, unlike lightning strikes on the ground. When the detection of such intra-cloud flashes is carried out on the basis of ToA-type technologies, it is necessary to use a large number of stations in a small space, thus implying relatively long computing times due to a large volume of data. important information to process. It is thus impossible to obtain real-time information on intra-cloud lightning by using ToA-based technologies.

Thanks to the development of new technologies and knowledge, faced with the disadvantages mentioned above in connection with the technologies presented previously, other actors have tried to rely on alternative techniques to detect lightning by using for example systems based on detection. by interferometry. Interferometry consists of a measurement method exploiting the phase difference of a coherent electromagnetic wave, the phase then being measured by two receivers at two distinct points. The use of interferometry is particularly clever, since interferometry-based detection systems do not require a specific form of signal and operate relatively easily on noisy signals. Figure 1 shows a first example implementation of a known system for detecting an electromagnetic source by interferometry, already available on the market. Such a known system 1 for detecting an electromagnetic source, also called an antenna, aims to capture the lightning totally, whether it is intra-cloud lightning and / or lightning striking the ground, since it exploits a only high frequency interferometry technologies to detect intra-cloud lightning, but also technologies with magnetic orientation and low-frequency arrival time to detect lightning strikes on the ground.

Said detection system 1 consists of an unambiguous network, such a system or network being advantageously arranged to operate at very high frequencies, that is to say in frequency bands between one hundred eleven (111) and one hundred and ten seven (117) megahertz. To ensure the observation or location of intra-cloud lightning, said system 1 comprises at least five conductive elements in the form of five dipoles 2. The system 1 is thus described as unambiguous, that is to say that the distance between the dipoles is less than half a wavelength, such a distance depending on the coupling terms between the dipoles. For the purposes of the invention and throughout the document, the term "dipole", which can also be described as an antenna or dipole antenna module, any element or receiver object consisting of two metal strands, supplied in its middle 2m, that is to say between such two strands, and intended to receive all or part of the electromagnetic energy emitted by a flash or more generally by lightning. In order to ensure the cohesion of the different dipoles 2 according to a determined arrangement in all directions to three hundred and sixty degrees, said detection system 1 comprises a central portion 4, cooperating with each of the dipoles 2 respectively by means of an advantageously dimensioned dielectric element. The five dipoles 2 of said system 1 are advantageously positioned equidistant from said central portion 4. The latter is furthermore arranged to cooperate with a low-frequency sensor, said sensor using technologies with magnetic orientation at arrival time ( ToA) and / or magnetic gonometry at low frequency, said sensor being arranged to detect or locate lightning strikes. Such a central portion 4 may also be configured to cooperate simultaneously and severally with a GPS location-based receiver system (for "Global Positioning System" in English terminology), thus enabling synchronization, calibration and calibration. other detection systems positioned at other places of interest and spatially separated. The detection system 1 optionally comprises a mast 3 arranged to cooperate solidarily, that is to say according to a suitable mechanical connection, for example of the embedding type, the central portion 4 and also the detection elements of the system. Such a mast 3 makes it possible in particular to position the system 1 for detecting an electromagnetic source at various locations of particular interest, particularly at the top of the infrastructure.

However, such a system for detecting a known electromagnetic source, such as that described with reference to FIG. 1, has, like the other detection systems mentioned above, a number of disadvantages. First and as mentioned previously, a known system 1 comprises at least five conductive elements in the form of five dipoles. Such a system can thus be slightly redundant, since certain detections can provide identical information, resulting in identical or even superfluous treatments. In addition, the particular architecture or arrangement of such a system for detecting a known electromagnetic source, such as that described with reference to FIG. 1, imposes on said system to be implanted at the culmination point of the structure or of the infrastructure over which it is positioned. In addition to the difficulties that such an installation may impose in terms of time and number of operators to requisition for such an installation, but also the maintenance difficulties that can consequently inflict a known system of detection of a source, the arrangement The particularity of the latter thus leads to a restriction of the number of places or infrastructures on which said system can be installed. Moreover, as already mentioned, a system for detecting an electromagnetic source in the form of a network is advantageously arranged to operate at very high frequencies, that is to say in frequency bands. between one hundred eleven (111) and one hundred and seventeen (117) megahertz. Operating such a frequency band imposes a dimensioning accordingly the detection system and thus leads to the design of a cumbersome and heavy system. Indeed, the system in the form of an antenna array has the shape of a cylinder whose dimensions are substantially of the order of one hundred and twenty centimeters in diameter and one hundred and twenty centimeters in height. In addition to a large footprint, the system is thus complex to install and / or maintain and not adapted for some installations and / or often existing infrastructures. In addition, the arrangement of said system requires that no metal object can be positioned around the system at a distance substantially less than ten times the wavelength.

The invention thus makes it possible to respond to all or some of the disadvantages raised by the known solutions.

Among the many advantages provided by a system for detecting an electromagnetic source by interferometry according to the invention, we can mention that this one:

provides a system for positioning on any type of infrastructure, such a system being insensitive to mechanical variations and a coupling possibly occurring between different antennas of said system, freeing the operator of said system from a systematic calibration antennas prior to their jobs ;

proposes a simple and modular detection system, possibly mobile, can thus be used in many places, such a system being insensitive to possible ground reflections;

makes it possible to increase the accuracy of the localization and / or the detection of lightning by the use of one or more frequency bands for the same antenna module of a detection system. For this purpose, a system is especially provided for detecting an electromagnetic source by interferometry. In order to ensure the capture or detection of such an electromagnetic source and more particularly to ensure the observation of intra-cloud lightning, a system for detecting an electromagnetic source according to the invention comprises two physically dissociated antenna modules, each an antenna module comprising two conductive elements, a planar reflector having a first face and a second face, said first faces of the planar reflectors of said antenna modules cooperating respectively and severally with said two conductive elements of said antenna modules, the two modules antenna being mutually arranged so that the second faces of their planar reflectors form a salient angle.

Preferably, but not exclusively, the planar reflectors of the antenna modules of a system for detecting an electromagnetic source by interferometry according to the invention can be respectively oriented to be substantially vertical.

According to an advantageous but nonlimiting embodiment of a system for detecting an electromagnetic source by interferometry according to the invention, in order to facilitate the implementation of the latter, the two conducting elements of each antenna module of said system can advantageously be dipoles.

As a variant or in addition, in order to facilitate the manufacture, installation and maintenance, of a system for detecting an electromagnetic source by interferometry according to the invention, the two elements conductors of each antenna module of the latter may have quadrilateral conductive surfaces.

Advantageously, but not limitatively, in order to guarantee optimal operation of a system for detecting an electromagnetic source by interferometry according to the invention, the two conducting elements and the plane reflector of each antenna module of the latter can cooperate with the means of a dielectric element.

Alternatively or additionally, to facilitate the manufacture and installation of each antenna module of a system for detecting an electromagnetic source by interferometry according to the invention on various and varied supports, the planar reflector of each module of Antenna of the latter may consist of a metal mesh.

According to a preferred but nonlimiting embodiment, to guarantee an optimum accuracy of detection of an electromagnetic source, a system for detecting an electromagnetic source by interferometry according to the invention may comprise four physically dissociated antenna modules, each module being antenna comprising two conductive elements, a plane reflector having a first face and a second face, said first faces of the planar reflectors of said antenna modules cooperating respectively and severally with said two conductive elements of said antenna modules, the four modules of antenna being mutually arranged so that the second faces of their planar reflectors form, two by two, an angle of ninety degrees.

According to a preferred but non-limiting embodiment of a system for detecting a source electromagnetic interferometry according to the invention, in order to ensure optimum detection, and in particular to increase its accuracy, for example by avoiding unwanted pollution induced by other third-party electromagnetic sources, each antenna module of said system can be arranged to detecting an electromagnetic source producing an electromagnetic wave whose frequency band is selected from the set of frequency bands: between 111 and 117 megahertz, between 328.6 and 335.4 megahertz or between 1400 and 1427 megahertz.

To make it possible to combine an ambiguous and unambiguous network and thus to increase the accuracy of the measurements and to access a localization in three dimensions, even at low elevation, each antenna module of a system for detecting an electromagnetic source By interferometry according to the invention can be arranged to simultaneously receive a plurality of frequency bands.

Other features and advantages will emerge more clearly on reading the following description and on examining the figures that accompany it, among which:

FIG. 1, previously described, illustrates an exemplary embodiment of a known lightning detection system;

FIG. 2 illustrates a schematic view of a first embodiment of a system for detecting an electromagnetic source by interferometry according to the invention; FIGS. 3A and 3B show two schematic views of a second embodiment of a system for detecting an electromagnetic source by interferometry according to the invention;

- Figures 4A, 4B and 4C show schematic respective views of non-limiting embodiments of antenna modules of a system for detecting an electromagnetic source by interferometry according to the invention.

Figures 2, 3A and 3B respectively show first and second embodiments of a system for detecting an electromagnetic source by interferometry according to the invention.

For the purposes of the invention and throughout the document, the term "electromagnetic source", also referred to as a "radio source", any source or more generally any element capable of emitting an electromagnetic field, such an electromagnetic field comprising one or several electromagnetic waves. The best-known electromagnetic wave remains the light wave. Such electromagnetic sources, and more generally such electromagnetic fields, may advantageously be of natural origin, such as those at the origin of lightning or lightning, or created by human activity, such as those at the source of origin of x-rays used in radiography. The invention will be described through an example of a preferred but non-limiting application in which the electromagnetic source consists of lightning or even one or more lightning. For purposes of simplification, throughout the document, indiscriminately expressions "lightning" and "lightning" to define the electrostatic phenomenon observed by a system according to the invention.

For the purposes of the invention also, "interferometry" is understood to mean any measurement method making it possible to detect an electromagnetic source and / or an electromagnetic field as mentioned above, exploiting the phase difference of a coherent electromagnetic wave, the phase being then measured by two receivers at two distinct points, thus making it possible to evaluate the phase shift. The use of interferometry-based systems is particularly clever, since methods based on interferometry have the advantage of operating independently of the shape of the electromagnetic wave or waves radiated by lightning or lightning, increasing the robustness of the systems with regard to the deformations that can undergo the wave or waves. The accuracy of the location of an electromagnetic source is thus not dependent on the environment and / or the distance separating the system from the lightning or flashes. In addition, such systems based on interferometry are particularly effective for a large number of electromagnetic sources to observe and thus provide real-time information, unlike systems based on ToA techniques. Indeed, the ToA technologies impose to have knowledge a priori on forms of the electromagnetic waves to be observed and are limited in their use by the distances between the sensors composing a system of study, since the measurements of arrival time are limited by the travel time of distances between sensors of the same system. According to the sensors, the order of the electromagnetic waves can be possibly reversed or changed, directly impacting the measurements and consequently the location of the electromagnetic waves.

The principle of interferometry consists mainly in calculating the direction of an electromagnetic source by measuring the phase shift of one or more electromagnetic waves originating from the same source during their propagation, the measurement being carried out by means of a or several conductive elements. The equation defining any detection or measurement performed and / or performed by a conductive element or dipole of an interferometric system, composed of at least two conductive elements or dipoles, is given by the following formula:

f is the elevation, that is the angle between a horizontal plane defined by the ground and the direction of the electromagnetic source;

l is the distance between two conductive elements;

l is the wavelength;

Q is the azimuth, that is, the angle in the horizontal plane between the direction of the magnetic source and a reference direction;

F is the phase shift, that is to say the phase difference at the same time determined between two signals describing the electromagnetic wave per two conductive elements.

Such an equation shows a relation between said phase shift F of an electromagnetic wave and the azimuth Q and the elevation f, to locate the electromagnetic source. When two antenna modules, each with two conducting elements, of an interferometric system are combined in two different orientations, a system with two independent equations is then obtained. According to the phase or phase difference measured by the conductive elements of said interferometric system, whose resolution of the two-equation system then makes it possible to determine the azimuth Q and the elevation f, and finally the location of the electromagnetic wave. Also, the accuracy of such a location is only a function of the accuracy of the phase shift measurement, the accuracy of such a phase measurement depending solely on the signal level relative to the electromagnetic wave received and the integration time, that is to say the period of time during which the receiver must be exposed to the electromagnetic wave or the period of comparison time of the respective phases of the two signals coming from two conductive elements, thus making it possible to reduce or even remove the measurement noise, in this case between ten to a few hundred microseconds.

In the context of the invention, such a system based on interferometry will preferably but not exclusively be used to detect one or more electromagnetic sources, in this case for the detection of lightning, one or more lightning.

According to a first embodiment described in connection with FIG. 2, a system 1 for detecting an electromagnetic source by interferometry in accordance with the invention comprises two antenna modules. In the sense of the invention and throughout the document, we mean by "Antenna module" means any element, object or device, generally metallic and / or electrically conductive, capable of capturing or detecting one or more electromagnetic waves in space. Such an antenna module is thus considered as a juxtaposable or combinable element with other elements of the same nature or contributing to the same function, that is to say to one or more other antenna modules, able to detect one or more electromagnetic waves, making it possible to solve the interferometry equation and locate a flash. All the antenna modules present within a system for detecting an electromagnetic source by interferometry are advantageously physically dissociated, that is to say that they do not have a common mechanical connection between the different modules. antenna. Such an arrangement in the form of dissociated antenna modules is particularly advantageous, since said antenna modules are then directional and independent of their supports and therefore not subject to any interference due to their implantation sites. As already mentioned, to ensure the detection of an electromagnetic wave of an electromagnetic source by interferometry, at least two antenna modules are necessary to ensure such detection. Indeed, a system 1 according to the invention, advantageously comprising two antenna modules dissociated with two conductive elements, can easily locate a flash at a given moment. The location of a flash being performed in three dimensions, it is thus necessary to perform two phase shift measurements respectively from two different angles. Nevertheless, when several, at least two, flashes, are observable at the same time determined, it may be necessary to use a larger number of antenna modules within the system. The invention can not thus be limited to the use of this single number of antenna modules dissociated within a system 1 to detect an electromagnetic source by interferometry according to the invention. Also, the choice of a particular number of conductive elements or more broadly antenna modules with respect to another number, will depend mainly on the number of electromagnetic sources that can or wants to detect and locate concomitantly by a system 1 for detecting an electromagnetic source by interferometry according to the invention. Optionally, the number of antenna modules may also depend on the location of the electromagnetic source (s) to be observed. Thus, an antenna module comprising N conductive elements can locate Nl sources emitting concomitantly. The antenna modules of a system 1 for detecting an electromagnetic source by interferometry according to the invention are dissociated, that is to say that there is no physical and / or mechanical cooperation between the different modules. antenna 5 component said system. Such dissociation makes it possible to make observations by sector and to simplify the implementation of the systems. Indeed, such a system proves for example particularly effective in areas or on sites where it is not possible to monolithic antenna systems such as that described in connection with Figure 1. According to a first example, at the Aiguille du Midi site, the summit is already equipped with telecommunication transmitters and can not accommodate a monolithic system. A system 1 according to the invention thus allows to install antenna modules dissociated all around the nacelle and thus to overcome the radiation of different transmitters already existing and existing on site. According to a second example, said system 1 can be installed around or on any post, such as a pylon type structure.

To ensure interferometric detection of one or more electromagnetic waves, each antenna module 5 of a system 1 according to the invention comprises two conductive elements 2. For the purposes of the invention and throughout the document, we mean "Conductive element" means any object consisting mainly of a body, generally but not exclusively a metal, for example aluminum or copper, the physicochemical characteristics of which permit the passage of an electric current, such object being intended to receive all or part of the electromagnetic energy emitted by a flash or more generally by lightning or a radiating source. Such conductive elements are advantageously receivers and can thus be described as passive conductive elements. According to a preferred but nonlimiting example, the two conductive elements 2 of an antenna module 5 of a system 1 according to the invention can advantageously be separated by a distance substantially between ten and fifty centimeters, preferably twenty centimeters. . In addition, said conductive elements are advantageously positioned along the same horizon line. As previously stated, the presence of two conductive elements advantageously makes it possible to measure a phase shift, thus making it possible to determine the azimuth and elevation of a source electromagnetic generating an electromagnetic wave. Nevertheless, the invention can not be limited to the number of conductive elements present within each antenna module or the separation distance between such conductive elements.

One of the aims of the invention is in particular to propose a system for locating an electromagnetic source by interferometry, comprising at least two antenna modules, said system then having a directional emission diagram thus making it possible to overcome the infrastructures or, more generally, supports on which such antenna modules are installed and / or to avoid the coupling between the different antenna modules. Indeed, such a coupling between the antenna modules, more particularly the conductive elements, imposes a systematic calibration of the detection system, said system being very sensitive to mechanical variations. In addition, the invention also makes it possible to offer a system for detecting an electromagnetic source by interferometry, comprising at least two antenna modules, said system then having a directional emission diagram thus making it possible to avoid possible reflections of soil.

To do this, each antenna module 5 of a system 1 for detecting an electromagnetic source by interferometry according to the invention also comprises a reflector 6. For the purposes of the invention and throughout the document, the term "reflector Any device capable of reflecting one or more electromagnetic waves. In some cases, such a reflector may be responsible for concentrating the received electromagnetic wave or waves towards the conductive elements. According to the invention, such a reflector is preferentially but not exclusively planar. In accordance with various embodiments of antenna modules described with reference to FIGS. 3A, 3B, 4A to 4C, such a plane reflector 6 advantageously has a first face 6i and a second face 6ii. The definition of such first and second faces 6i and 6ii make it possible and advantageously the positioning of each dissociated antenna module within the system according to determined distances, of the order of a few centimeters, or even a few meters, to a few tens of meters, so as mentioned above, to overcome the constraints related to the installation of antenna modules, the coupling of conductive elements between said antenna modules and / or ground reflections of electromagnetic waves.

Moreover, in addition, according to a preferred but non-limiting embodiment (not shown in the figures for purposes of simplification) of a system for detecting an electromagnetic source according to the invention, the planar reflector 6 of each module of FIG. Antenna 5 of the latter may consist of a metal mesh. The use of a planar reflector in the form of a metal mesh is particularly advantageous, since such a reflector is relatively light, inexpensive and has a minimum wind catch, said antenna modules being generally installed outdoors and subject to possible weather constraints. Preferably, but not exclusively, such a metal mesh may have a network or mesh whose dimensions are ten times smaller than the wavelength, to ensure in particular the insulation of the conductive elements. The invention, however, can not be limited to the use of a specific arrangement, structure and / or composition of a reflector. The choice of a particular arrangement, structure and / or composition of a reflector 6 with regard to another arrangement, another structure and / or another composition may depend, advantageously but without limitation, the electromagnetic source to locate or even more widely the position or location of a system 1 for detecting such an electromagnetic source by interferometry according to the invention in particular to further reduce manufacturing costs, installation and / or maintenance of such a system 1.

FIGS. 4A, 4B and 4C show respective schematic views of non-limiting exemplary embodiments of antenna modules of a system for detecting an electromagnetic source by interferometry according to the invention.

FIG. 4A shows a first exemplary embodiment of an antenna module 5 of a system 1 for detecting an electromagnetic source according to the invention. According to this advantageous embodiment, the two conducting elements 2 of each antenna module 5 may consist respectively of dipoles. Within the meaning of the invention and throughout the document, any element or receiver object consisting of two metal strands, supplied in its middle 2m, that is to say between such two strands, and intended to receive all or part of electromagnetic energy emitted by a lightning or more generally by lightning. The use of conductive elements under the dipole form is particularly clever, since such dipoles are commonly used, so inexpensive, and what is more, easy to implement and insensitive to the coupling between conductive elements. According to FIG. 4A, such coplanar dipoles may advantageously have a substantially trombone shape (also known by the English terminology "folded dipole"). Dipoles having such a trombone shape offer a number of advantages: firstly, the dipoles, grounded, have no accumulation of capacitive effect and do not require to be discharged. In addition, such dipoles have a better mechanical strength, thus providing a permanent installation over time. According to a preferred but non-limiting example, when the conductive elements are in the form of dipoles, as in the example described with reference to FIG. 4A, and when the operating band of the antenna modules of a 1 system according to the invention is of the order of 332 megahertz, the two conductive elements 2 and the reflective plane of an antenna module 5 of a system 1 according to the invention can advantageously be separated from a distance substantially between ten and fifty centimeters, preferably twenty centimeters.

In a variant, FIG. 4B shows a second exemplary embodiment of an antenna module 5 of a system 1 for detecting an electromagnetic source according to the invention. According to this advantageous embodiment, the two conductive elements 2 of each antenna module 5 may respectively have quadrilateral conductive surfaces. According to this advantageous embodiment, such an antenna module 5 comprising two conductive elements 2 having quadrilateral conductive surfaces is considered a planar antenna, also called patch antenna according to English terminology. According to this embodiment, the planar reflector can also be conductive. The use of such antenna modules in the form of planar antennas is particularly advantageous, since such antenna modules, by their very simple design, are very easy to produce industrially. In addition, they can be used alone or as part of a network, in this case a system 1 for detecting an electromagnetic source by interferometry according to the invention. Finally, said antenna modules in the form of planar antennas have a small footprint compared to other antenna modules, thus allowing easy handling and installations, as well as easy integration against an existing structure, such as a building. Such antenna modules in the form of planar antennas, just like dipole antennas, have a specific resonance frequency. However, said planar antennas have the advantage of being able to resonate at different frequencies, for example three hundred megahertz and / or one thousand four megahertz. Such modules of antennas qualified multi-frequency allow to combine an ambiguous and unambiguous network and thus to increase the accuracy of measurements and to access a localization in three dimensions, even at low elevation.

The invention can not, however, be limited to the use of a specific conductive element arrangement or structure for the realization of a module antenna. The choice of a particular arrangement or structure of conductive element with regard to another arrangement or structure may depend, advantageously but not limitatively, on the altitude or trajectory of the electromagnetic source to be observed and / or locate or even more widely the position or location of a system 1 for detecting an electromagnetic source by interferometry according to the invention in particular to further reduce the costs of manufacturing, installation and / or maintenance of such a system. In addition, as already mentioned, the invention can not be limited to the number of conductive elements present within each antenna module. According to a third nonlimiting exemplary embodiment of an antenna module of a system 1 for detecting an electromagnetic source by interferometry according to the invention described with reference to FIG. 4C, an antenna module of the latter can comprise more than two conductive elements 2, in this case six conductive elements 2. The use of a large number of conductive elements within an antenna module makes it possible to refine the directional lobe of the antenna module and thus increase the scope of such a module.

In order to ensure a cohesion of the elements constituting the antenna modules of a system 1 for detecting an electromagnetic source by interferometry according to the invention, in this case, for each antenna module a plane reflector and at least two conductive elements, the first faces 6i of planar reflectors 6 of said antenna modules 5 cooperate respectively and severally with said two conductive elements 2 of said modules antenna 5. Such cooperation between the first face 6i of a planar reflector 6 and the two conductive elements 2 may be embodied by any suitable mechanical connection, preferably of embedding type, advantageously permanent or possibly reversible. Such an embedding connection can be achieved by any suitable fastening means, said first face 6i of a planar reflector 6 and the two conductive elements 2 being mutually arranged to ensure their assembly. By way of non-limiting example, when the conductive elements are in the form of dipoles 2, such dipoles can be kept parallel to the reflector 6 by means of respective rectilinear poles describing a "V" association whose base cooperates without degree of freedom with the reflector. The invention can not, however, be limited to this single embodiment. As a variant, according to FIGS. 4B and 4C in particular, the invention provides that the first face 6i of a planar reflector 6 and the two conducting elements 2 of a system 1 for detecting an electromagnetic source by interferometry according to the invention can form or consist of one and the same physical entity.

Alternatively or additionally, the invention provides that the two conductive elements 2 and the planar reflector 6, more particularly its first face 6i, of each antenna module 5 of a system 1 for detecting an electromagnetic source by interferometry according to the invention can cooperate by means of a dielectric element 8. The use of such a dielectric element proves particularly advantageous, since such a dielectric element does not conduct electricity and thus makes it possible to isolate the conductive elements of the first face 6i reflector, so that they can fully perform their function. In the context of an exemplary embodiment of an antenna module in the form of a planar antenna, as described in particular with reference to FIGS. 4B and 4C, the two conductive elements 2 and the plane reflector 6 of FIG. such an antenna module 5 are advantageously and respectively separated by a dielectric plate, said dielectric plate may consist mainly of an epoxy resin.

In order to overcome the infrastructure or, more generally, supports, on which such antenna modules are installed and / or to overcome the coupling between the different antenna modules of a system 1 to detect a source electromagnetic interferometry according to the invention, such as that described in connection with Figure 2, the two antenna modules 5 of the latter are advantageously dissociated, that is to say, preferably but not limited to a few centimeters apart, even from a few meters to a few tens of meters, and mutually arranged so that the second faces 6ii of their planar reflectors 6 form a salient angle, that is to say an angle between zero and one hundred and eighty degrees. Thanks to such a protruding angle, the conducting elements 2 of said system 1 for detecting an electromagnetic source by interferometry are arranged in such a way that they do not interfere with each other, unlike the antenna system described in connection with According to a preferred but nonlimiting embodiment, the second faces 6ii of the respective planar reflectors 6 of the two antenna modules of a system 1 according to FIG. the invention can form an angle substantially equal to ninety degrees, thus ensuring a better resolution and accuracy to finally locate and / or detect one or more electromagnetic sources.

In order to also overcome any ground reflections or infrastructures on which a system 1 for detecting an electromagnetic source by interferometry according to the invention is installed, the planar reflectors 6 of such a system 1 can be respectively oriented to be substantially vertical. Moreover, alternatively or in addition, always to overcome possible ground reflections, the planar reflectors 6 of such a system 1 may be respectively and also oriented to be substantially aligned on the same horizon line. In addition, the conductive elements of said system 1 for detecting an electromagnetic source by interferometry may also be aligned horizontally, in particular to avoid ground echoes inherent to possible reflections of one or more electromagnetic waves on the ground.

According to a preferred but non-limiting embodiment of a system 1 for detecting an electromagnetic source by interferometry according to the invention described with reference to FIGS. 3A and 3B, the latter may comprise four antenna modules 5, said modules of FIG. antenna 5 being themselves physically and mechanically dissociated from each other, thus allowing the formation of an exploded system or antenna. Like the first embodiment of a system 1 for detecting an electromagnetic source by interferometry according to the invention described in connection with the figures each antenna module 5 may comprise two conductive elements 2, able to measure a phase shift. Such conductive elements 2 may also and respectively consist of dipoles or have quadrilateral conductive surfaces. Each antenna module of the detection system further comprises a planar reflector 6 having a first face 6i and a second face 6ii, said first faces 6i of planar reflectors 6 of said antenna modules 5 cooperating respectively and severally with said two conductive elements. 2 of said antenna modules 5, possibly by means of a dielectric element. Still according to Figures 3A and 3B, the four antenna modules 5 may be mutually arranged so that the second faces 6ii of their planar reflectors 6 form in pairs at an angle of substantially ninety degrees. Arranged in this manner, the four antenna modules of a system 1 according to the invention can then scan an overlapping area of three hundred and sixty degrees. Such a configuration not only makes it possible to overcome the infrastructure or more generally the supports on which such antenna modules are installed and / or to get rid of the coupling between the different antenna modules, but also to ensure a wider area of coverage possible to detect an electromagnetic source, ultimately increasing the sensitivity of the system.

Finally, the invention provides that each antenna module of the system can be sized, in order to be able to use several frequency bands. Preferentially but not exclusively, each module An antenna 5 of a system 1 for detecting an electromagnetic source by interferometry according to the invention is arranged to detect an electromagnetic source producing an electromagnetic wave whose frequency band is selected from the following set of frequency bands: 111 and 117 megahertz, between 328.6 and 335.4 megahertz or between 1400 and 1427 megahertz. The higher the frequency band used, the smaller the size of each antenna module. In addition, the wider the frequency band, the lower the noise level. The use of a detection frequency band of between 111 and 117 megahertz is particularly advantageous, since the lower the spectral band observed, the better the electromagnetic wave radiates and the better the signal. However, such a detection frequency band between 111 and 117 megahertz has the disadvantage of being close to the FM radio transmission and reception (ie emitting in frequency modulation), limiting then the detection ranges. The use of a detection frequency band of between 328.6 and 335.4 megahertz or else between 1400 and 1427 megahertz is particularly advantageous, since said emission frequency bands are very restricted, or even forbidden, limiting thus noises or pollution. In addition, such frequency bands have global coverage.

As mentioned previously, the antenna modules have a specific resonance frequency. The invention further provides that said antenna modules can be arranged to resonate concomitantly at different frequencies, that is to say to be able to receive concomitantly several, at least two, frequency bands, for example three hundred megahertz and / or one thousand four megahertz. Such modules of antennas qualified multi-frequency allow to combine an ambiguous and unambiguous network and thus to increase the accuracy of measurements and to access a localization in three dimensions, even at low elevation.

According to a non-limiting exemplary embodiment, with the exception of the coupling between the conductive elements of each antenna module, such an antenna module may consist of two conductive elements, preferably separated by a distance of approximately one half wavelength, each conductive element having dimensions less than half a wavelength. According to different embodiments:

for a reception frequency of three hundred megahertz, the wavelength is substantially equal to one meter. The conductive elements of each module are then substantially positioned at fifty centimeters from one another. By the existence of coupling term, the conductive elements of each module are then substantially positioned at fifty centimeters from one another, for a receiving frequency of one thousand five hundred megahertz, the wavelength is substantially equal at twenty centimeters. The conductive elements of each module are then substantially positioned at ten centimeters from one another.

for a receive frequency of one thousand seven hundred megahertz, the wavelength is substantially equal to seventeen centimeters. The conductive elements of each module are then substantially positioned at eight centimeters from one another.

However, the sizing and / or adjustment of each antenna module of a system for detecting an electromagnetic source by interferometry according to the invention can not be limited to the frequency bands selected for such detection. Such dimensioning and / or adjustment of each antenna module may also depend on the phase excursion, also depending on the coupling effects, of the emission diagram of each antenna module corresponding to a directional lobe and / or any phase ripples, themselves dependent on the frequency.

The invention has been described when used in connection with lightning detection applications, more particularly the detection of intra-cloud lightning. It can also be implemented to act on any other type of lightning, such as lightning strikes, or more generally any type of electromagnetic waves to be detected and thus offer a fully qualified lightning detection system. To do this, a system for detecting an electromagnetic source according to the invention may also include devices for detecting lightning strikes on the ground, such devices using technologies with magnetic orientation and low-frequency arrival time. The invention can not be limited to the application in which the system 1 according to the invention is used. According to another embodiment, such a system for detecting a source Electromagnetic interferometry according to the invention could be used in connection with high voltage lines having one or more sections whose insulation is defective, thus making it possible to anticipate the maintenance of such high voltage lines.

In addition, a system for detecting an electromagnetic source according to the invention may comprise other accessories, in particular, by way of nonlimiting examples, to allow easy maintenance of the antenna modules on different supports or infrastructures or else processing means for adjusting, calibrating and / or adjusting the measurements. Such accessories may be as non-limiting examples, chosen from one or more pre-amplifiers, filters, amplifiers and / or digitizers. As a variant or in addition, in order to ensure the coherence of each acquisition line of an antenna module and to ensure adequate measurements between the antenna modules of a system for detecting an electromagnetic source conforming to the invention, each antenna module may comprise an emitter positioned between the conductive elements and the reflector plane, in order to regularly calibrate said system.

Claims

1. System (1) for detecting an electromagnetic source by interferometry, characterized in that it comprises two antenna modules (5) physically dissociated, each antenna module (5) comprising two conductive elements (2), a reflector plane (6) having a first face (6i) and a second face (6ii), said first faces (6i) planar reflectors (6) of said antenna modules (5) cooperating respectively and integrally with said two conductive elements (2 ) of said antenna modules (5), the two antenna modules (5) being mutually arranged so that the second faces (6ii) of their planar reflectors form a projecting angle (a).

2. System (1) according to the preceding claim, wherein the planar reflectors (6) are respectively oriented to be substantially vertical.

3. System (1) according to any one of the preceding claims, wherein the two conductive elements (2) of each antenna module (5) are dipoles.

4. System (1) according to any one of claims 1 or 2, wherein the two conductive elements (2) of each antenna module (5) have quadrilateral conductive surfaces.

5. System (1) according to any one of the preceding claims, wherein the two conductive elements (2) and the plane reflector (6) of each antenna module (5) cooperate by means of a dielectric element (8). ).

6. System (1) according to any one of the preceding claims, wherein the planar reflector (6) of each antenna module (5) consists of a metal mesh.

7. System (1) according to any one of the preceding claims, comprising four physically dissociated antenna modules (5), each antenna module (5) comprising two conductive elements (2), a plane reflector (6) having a first face (6i) and a second face (6ii), said first faces (6i) of planar reflectors (6) of said antenna modules (5) cooperating respectively and severally with said two conductive elements

(2) said antenna modules (5), the four antenna modules (5) being mutually arranged so that the second faces (6ii) of their planar reflectors (6) form in pairs an angle (a) substantially ninety degrees.

8. System (1) according to any one of the preceding claims, wherein each antenna module (5) is arranged to detect an electromagnetic source producing a wave electromagnetic whose frequency band is selected from the set of frequency bands: between 111 and 117 megahertz, between 328.6 and 335.4 megahertz or between 1400 and 1427 megahertz.

9. System (1) according to any one of the preceding claims, wherein each antenna module (5) is arranged to receive concomitantly a plurality of frequency bands.