RO137287A0 - Aerial platform for detecting and locating explosions or other terrestrial and aerial military or civil acoustic sources - Google Patents

Abstract

The invention relates to an aerial platform for detecting and locating explosions or other terrestrial and aerial, military or civil acoustic sources. According to the invention, the platform consists of a balloon (100) filled with helium or other alternative gases, on the surface of which a continuous optical fiber (101) is applied continuously, in a single pass, with broadband Bragg grating elements as acoustic elements applied on the balloon (100), which continues its winding through a Sagnac-type gyroscope module (102) which allows the orientation of the balloon (100) to be determined, a detection module (103) which is located on the ground and consists of a narrowband laser source (105) generating high-coherence pulses modulated in time at nanoseconds, an acoustic and optical amplifier (106) with the role of optical amplifier and modulator , an acquisition system (112), filtered and digitized which receives the signal and a computer (113) which processes the information.

Description

RO 137287 AO

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Invention patent application

AERIAL PLATFORM FOR THE DETECTION AND LOCATION OF EXPLOSIONS OR OTHER LAND AND AERIAL ACOUSTIC SOURCES, MILITARY OR CIVIL

The invention relates to an aerial platform for the detection and localization of explosions or other ground and air, military or civil acoustic sources.

The sound source detection systems used so far are generally aerial platforms, which use current sources as a means of operating sensors and data processing and transmission modules on the ground. These are precise systems for detecting and locating acoustic sources, but at the same time they are sensitive to the action of atmospheric factors, especially electro-magnetic charges from the atmosphere or from the ground (electro-magnetic impulses). By comparison, the system presented in this patent application is immune to such interferences due to the fact that it uses light pulses, electromagnetically inert, as a medium of detection and transmission of information related to acoustic parameters, offering instead similar results from the point of view of sound source detection.

Aerial platforms were used as a support to lift the sensors into the air, but the equipment used was only electronic and thus susceptible to being influenced or damaged by electromagnetic waves. Gunfire and explosion detection systems have been applied using sensors distributed over large areas of land.

An optical communication system using a high altitude tethered balloon is known according to US 7046934 B2. This document presents an optical communications system using a high-altitude tethered balloon for high-data-rate communications between ground-based and space-based or high-altitude instruments.

A system and method for acousto-optical location of weapons is known according to document US 5970024 A. this document presents a system comprising an acoustic module for locating weapons for determining the location of fire from hostile weapons and an optical detection module for detecting energy of a second frequency originating from said hostile weapons fire, the means for transmitting data describing the location of said hostile weapons fire; and a processing one coupled to said acoustic and optical detection means.

PRESIDENT GENERAL DIRECTOR

DR.ENG. VALENTINE SYLVESTER

RO 137287 AO

A platform for multiple uses in the stratosphere is known, according to document WO 2015152897 Al. This paper presents some apparatus and some methods for placing a large, rigid, floating platform in the lower stratosphere of the Earth's atmosphere, at an altitude of about 20 km, above clouds, moisture, dust and wind. The platform can serve many uses, either individually or in any combination. These uses include non-stop radio and light communications, radar and optical observation, including very powerful radars, and solar electricity generation.

Some lighter-than-air (LTA) platform systems and applications are also known, according to US 9632503 B2. Disclosed herein are systems and methods of operating the systems, comprising an airborne platform comprising an unmanned balloon; a payload that is separate from the unmanned balloon; a transceiver; first and second flight determination devices; at least two separate power supplies for the first and second flight termination devices; a sensor; a processor; a pump; a valve; and a link that, when broken, separates the unmanned balloon and payload.

A location identification balloon system is known, according to document US 6164239 A. This document discloses a location identification balloon system (balloon) for use by lost or injured hikers and the like, which includes a helium-filled balloon that is secured with a grip and floated to allow a search plane or helicopter to easily locate a missing person.

A balloon antenna is known, according to the document US 7224322 Bl.l in this document a phased array balloon antenna is presented having an inner membrane coupled to an outer membrane and a phased array antenna connected to an inner membrane. The phased array antenna transmits energy to a reflective film on the outer membrane, reflecting the energy outward and illuminating a smaller area than that illuminated by the phased array alone.

A low altitude detection floating platform is also known, according to document CN 104309795 A. this document presents a low altitude detection floating platform comprising a balloon, a synthetic aperture radar, an optical equipment, a cabin system work, a power system, a flight control system,; the balloon used to provide buoyancy comprises a main balloon and an auxiliary balloon; synthetic aperture radar is used for ground detection; optical equipment is used for soil monitoring; the work booth system is arranged at the bottom

PRESIDENT GENERAL DIRECTOR

DR.ENG. VALENTINE SYLVESTER

RO 137287 AO of the balloon and comprises a first mounting platform; the synthetic aperture radar and optical equipment are mounted on the first mounting platform; the power system provides power for the floating platform; the flight control system is used for flight control; the flight control system and the power system are arranged on the second mounting platform; the tail fin system is used to control the ascent, descent and turn of the floating platform; the flight control system is connected with the synthetic aperture radar, optical equipment, power system and tail fin system. The floating low-altitude detection platform has the advantages that the detection means are more comprehensive, the operation is more comprehensive, the use is safer, and the detection of positions and paths can be corrected in real time.

An intelligent monitoring system and method for monitoring atmospheric pollution is also known, according to document CN 114720210 A. this document presents an intelligent system for monitoring atmospheric pollution and a monitoring method and relates in particular to the technical field of monitoring atmospheric.

A method of attaching the circular view radar construction to the balloons is known, according to document RU 2652512 CI. This document presents a method of building the circular view radar. To build a radar station, placing the radar in the gas-filled shell of a liaison balloon, driving the radar antenna in a continuous rotation around the axis of the radial joint of the radar with the bearing platform of the balloon, forming the flywheel of the gyroscopic pendulum, causing the bearing angle to increase , depending on the readings of the laser goniometer connected to the antenna, determining the origin of the coordinate system by episodic measurements of the direction of the ground object with known coordinates relative to the balloon coordinates.

Some systems and methods for detecting the locations of gunners in an aircraft are also known, according to document US 8437223 B2. The systems and methods described in this invention relate to an airborne shooter detection system having a plurality of sensors coupled to the body of an aircraft such as a helicopter. The system includes at least five sensors configured and arranged to disambiguate a shooter's location. By measuring the arrival times of the projectile shock waves at each of the sensors and determining the differences in arrival times between the sensors, the systems and methods can determine the location of one or more projectile sources.

PRESIDENT GENERAL DIRECTOR

DR.ENG. VALENTIN S1LIVESTRU

RO 137287 AO

Another method of detecting a trajectory of a supersonic projectile is known which is achieved by means of acoustic detection signals, according to document US 11294022 B2. From these acoustic detection signals, two or more shock wave-derived trajectory estimates can be derived. Moreover, the trajectory derived from the firing can be estimated, from which the disambiguation of the shock wave-derived trajectory estimates can be performed.

An acoustic array sensor network system for positioning the location of an explosion is known according to CN document 102215603 A. This document refers to an acoustic array network system for positioning an explosion point, comprising at least two nodes of acoustic matrix sensors. Acoustic array sensor nodes are placed near an explosive container and form a self-organized network; acoustic network sensor nodes are used to acquire the azimuth information of the blast point and send the azimuth information to a monitoring terminal; and the monitoring terminal fuses the data received from each sensor node of the acoustic array to obtain the position information of the blast point. The acoustic array network system provided by the invention can be used for rapid detection and positioning of the location of an explosion.

Systems with distributed acoustic sensors (Distributed Acoustic Sensing - DAS) have been studied and applied in monitoring critical infrastructures or the health of civil structures (bridges, pipelines, dams, railways, buildings, etc.) due to the multiple advantages of distributed measurement, such as , small dimensions of the detection elements, the possibility to cover very long measuring lengths, response in broadband frequencies (of the order of MHz), high sensitivity or immunity to the influence of electromagnetic waves.

Acoustic sensors are used in the defense industries as part of distributed sensor solutions for large-area, unattended detection of noise sources, particularly impulse noise from military firing or munitions detonation. Compared to other detection systems, acoustic sensors have many advantages such as omnidirectionality, the possibility of being easily hidden, they are passive, they have a low cost, also low consumption, weight and small dimensions. They allow the detection, localization, classification and tracking of an acoustic source. Military, they can be used to detect ground sources of continuous quasi-random noise (tanks, trucks, various armored vehicles, etc.) or air sources (drones, helicopters, etc.) or those of impulse type (artillery fire, mortars, machine guns, rifles with

PRESIDENT GENERAL DIRECTOR

DR.ENG. VALENTINE SYLVESTER

RO 137287 AO rear sight, etc.). Acoustic sensors also make it possible to determine the rate of fire of artillery and an estimate of the trajectory of heavy artillery projectiles. in civil applications, acoustic sensors are used in meteorological applications or to identify lost people while hiking through hard-to-reach areas.

The acoustic signal is highly dependent on atmospheric conditions, both for ground and airborne sources. Considering that sound propagation is in the air, acoustic detection is influenced by atmospheric conditions, such as wind direction and speed or temperature. The sound absorption of the terrain, the presence of vegetation or variations in the height of the terrain are other factors that influence sound propagation.

Therefore, the use of the balloon as a sensor-carrying platform, compared to ground-based systems, presents the advantage of direct sound detection, without built-up or vegetation obstacles and without the negative influence of ground height variations.

The present invention relates to a system for identifying and monitoring acoustic sources located on the ground or in the air, using a helium balloon of low or medium altitude, maintained in a quasi-stationary position, which operates as a sound signal sensor and source location identification. The identification of the location of an acoustic source is achieved by triangulating the signal coming from the different locations of the sensitive elements placed on the surface of the balloon and which act as acoustic sensors.

The advantage of this system is that it is inert to the action of atmospheric factors, the optical fiber that operates as an acoustic sensor being immune to the influence of electromagnetic waves present in the atmosphere. The fact that there are no electrical or electronic components on the aerial platform means that its operation cannot be influenced by atmospheric electromagnetic phenomena or possibly induced by a possible enemy. The system can also aim for meteorological identification and monitoring activities, civil rescue activities or military activities for identifying acoustic sources from the ground and from the air.

The acoustic detection system is completed with one for identifying the geographical direction in order to be able to correlate the orientation of the balloon with the acoustic source, in the variable operating conditions generated by atmospheric factors, especially wind. This is done using the Sagnac effect through fiber optics, and the same fiber optic line is used for this.

Compared to similar systems of acoustic detection by aerial platforms (balloons), which are carriers of electronic equipment and thus there is a danger of being damaged or

PRESIDENT GENERAL DIRECTOR

DR.ENG. VALENTINE SYLVESTER

RO 137287 AO lost, the proposed system carries only the sensitive elements of optical fiber, so a possible failure, loss or damage is less likely and suffers significantly lower costs.

Distributed Acoustic Sensing - DAS technology is based on the phase-sensitive time-domain optical reflectometry (φ-OTDR) technique. Coherent laser pulses are fired into the fiber to monitor changes over time in the resulting Rayleigh backscatter. Dynamic deformation changes of the physical support lead to small displacements of the scattering/scattering elements and thus to variations in the relative phases of the backscattered photons. The fiber to which sensitive FBG (Fiber Bragg Gratings) elements have been applied behaves as a series of interferometers whose response is sensitive to small changes in the deformation existing in them.

The advantage of using an acoustic detection system using fiber optic sensors, compared to similar electrical/electronic systems, is the fact that it is not sensitive to atmospheric conditions, being inert from the point of view of natural or artificial electromagnetic field influences (electromagnetic impulses used as weapons). At the same time, such a system offers the possibility of omnidirectional detection, the detection of sources located beyond the direct observation line, being a passive system that uses low current sources. Using the system offers the advantage of detecting the direction of acoustic sources, estimating their location and their possible subsequent classification. It is thus possible to identify impulse-type acoustic sources, such as artillery, mortar or rocket fire, or quasi-random sources, such as those generated by the engines of military vehicles in motion. The frequency of artillery fire can also be indicated. By incorporating a large number of sensors, the system offers an increased resolution of acoustic detection. Due to the fact that the sensitive elements are applied on the circumference of the balloon, and it is raised high, the acoustic attenuation effect of the ground is reduced. Other phenomena that influence the propagation of acoustic waves are also reduced, such as the dispersion and diffusion of vegetation elements or the variation of ground height (Figure 6).

By identifying both artillery fire and the explosion of projectiles, it makes it possible for the system to provide data for estimating their trajectory and classifying the type of projectile/weapon from the temporal and spectral acoustic character of the fire. Not least,

PRESIDENT GENERAL DIRECTOR

DR.ENG. VALENTINE SYLVESTER

RO 137287 AO the possibility of the aerial platform to fail is minimal, compared to platforms carrying electronic equipment, and the cost of production and maintenance is also low.

Next, an example of the invention is given, also in connection with figures 1...6.

The aerial platform for the detection and location of explosions or other land and air acoustic sources, military or civil, according to the invention and as can be seen from fig.l, consists of a balloon 100 filled with helium or alternatives, on the surface of which is continuously applied, in a single pass, an optical fiber 101, with FBG inserts as a sensing element. The optical fiber continues its winding, as can be seen from fig.2 through a gyroscopic module of the Sagnac type 102 that allows the orientation of the balloon to be established and is finally connected to the detection module, which is also the optical pulse generator 103, located to the ground.

The balloon 100 is tethered to the ground by a cable 104, which allows the balloon's position to be stored and estimated and returned to the ground. It can be raised in the air from several tens of meters, up to several hundred meters, to be effective in detecting ground sources, or even thousands of meters, for aerial ones. Also, the balloon 100 can have different sizes, from a few meters to tens of meters, depending on the area to be covered and the determination accuracy in the frequency domain. Thus, for signals containing a spectrum of frequencies as low as possible, a balloon with a larger diameter is required.

The optical fiber acoustic detection system DAS (Distributed Acoustic Sensing) uses a Bragg FBG (Fiber Bragg Grating) network that uses the principle of optical time-domain reflectometry, phase-sensitive Φ-OTDR (Phase-sensitive Optical Time-Domain Reflectometry). The Φ-OTDR module injects a series of optical pulses into the fiber and extracts, from the same end of the fiber, scattered (Rayleigh backscatter) or back-reflected light from various locations along the fiber. The scattered or reflected light is received back and used to characterize the acoustic parameters in the optical fiber. The characteristics of the pulses to be collected are measured and integrated as a function of time.

The Φ-OTDR detection system (Error! Reference source not found.) is composed of a narrowband laser source 105 generating high-coherence pulses modulated in time at nanoseconds, an acousto-optical amplifier 106 that acts as a modulator and optical amplifier . Phase control and compensation is performed by a system 115. A second optical amplifier 107 (Erbium-doped fiber amplifier) additionally amplifies the optical pulses that have lost power and are sent through the optical fiber. They pass through some sensitive areas

PRESIDENT GENERAL DIRECTOR

DR.ENG. VALENTINE SYLVESTER

RO 137287 AO

108 FBG, and the pulses reflected by them due to the micro-deformations of the support layer return back, pass through a circulator 109 where they interfere with the signal initially generated in a coupling 110 and collected by a photodiode 111 that transforms the optical signal into an electrical one.

Subsequently, the signal is taken by an acquisition system 112, filtered and digitized, and the information is processed by a computer 113. The computing unit also controls the pulse control module 114. The number of sensitive FBG elements influences the sensitivity of signal detection. This number is restricted by the balloon size and the generation and acquisition frequency of the optical pulse trains.

The optical fiber initially passes through the Sagnac 102 type gyroscopic module (Figure 4) coupled to the bottom of the balloon and which aims to determine its angular position with respect to a reference. The incident light generated in the optical fiber is split into two pulses that reach the gyroscope winding, one clockwise (CW) and the other counterclockwise (CCW) and propagate along the fiber optic loop, ending up in a 50:50 optical coupling, where the pulses interfere. When a change in the angular position of the balloon occurs, there is also a phase shift between the two pulses. After demodulation by the photodetector, the data string describing the change in light intensity, therefore also renders the angle with respect to the reference.

After leaving the gyro module, the pulse train successively arrives at the sensitive elements 108, distributed circularly on the balloon, at known locations, according to Figure 5, so as to cover all directions that converge omnidirectionally on the balloon surface. Thus, a train of optical pulses successively traverses all the sensitive elements arranged on the optical fiber and implicitly on the surface of the balloon. The spatial resolution of the sensitive elements is rated at a minimum of 50 cm at an optical signal frequency of 2 GHz.

Through triangulation, the signals received by the sensitive elements 108 make it possible to detect the direction, estimate the location, and by analyzing the signal in time and frequency, the firing rate, the possible trajectory of the heavy artillery projectiles and possibly the classification of the acoustic source are determined.

The Φ-OTDR system allows playback of an acoustic signal carrying amplitude and phase information. Transient impulse signals are determined by amplitude analysis of the signal in the time and frequency domains. The system is able to detect

PRESIDENT GENERAL DIRECTOR

DR.ENG. VALENTIN SIL1VESTRU

RO 137287 AO pulse-type signals whose acoustic energy is predominantly located in the 0500 Hz frequency band, the area in which large-caliber artillery fire is contained.

For the detection of quasi-stationary continuous acoustic signals characteristic of heavy vehicles in motion or in stationary operation, it is necessary that the time signal be processed and the identification spectral signatures extracted. Considering that heavy military vehicles and tanks have a spectrum up to 1,000 Hz, with a concentration of acoustic energy up to 150 Hz for medium and large tanks, the area of interest for extracting identification spectral signatures is reduced to this range.

PRESIDENT GENERAL DIRECTOR

DR.ENG. VALENTINE SYLVESTER

Claims (1)

RO 137287 AO CLAIM Aerial platform for the detection and localization of explosions or other terrestrial and aerial acoustic sources, military or civil, characterized in that it consists of a balloon (100) filled with helium or other alternatives, on the surface of which it is continuously applied, through -a single pass, a continuous optical fiber (101) with broadband Bragg grating elements as acoustically sensitive elements applied to the balloon which continues its winding through a gyroscopic Sagnac module (102) that allows the orientation of the balloon (100) to be determined and finally it is connected to a detection module (103) located on the ground, of a Φ-OTDR detection system which is composed of a narrowband laser source (105) generating nanosecond time-modulated high-coherence pulses, an acousto-optical amplifier (106) which acts as a modulator and optical amplifier, the signal being received by an acquisition system (112), filtered and digitized, and the information is processed by a computer (1 13). yo PRESIDENT GENERAL DIRECTOR DR.ENG. VALENTINE SYLVESTER