Method and device for identifying unmanned aerial vehicles at low altitudes

Abstract

Methods and devices for detecting low-altitude unmanned micro aircraft (UAVs) are described. The method includes recording the mechanical vibrations of an electric motor and those acoustic signals caused by the rotation of the propeller. The method - Further, an optical signal is recorded in the visible (0.4 - 0.76 μm) and / or infrared (0.76 μm - 1 mm) range of the UAV, - The occurrence of parametric modulation of the optical signal caused by these same mechanical vibrations is detected, - The correlation between the acoustic signal and the optical signal of the UAV is registered, the presence of which indicates the detection of the UAV, and is characterized by this. The device - A passive acoustic sensor (2), - A passive optical sensor (4), - A correlator (3), - An active acoustic sensor (5) adjusted to operate at the wavelength of resonant scattering of sound waves on the UAV in the frequency range of 10 - 20 kHz, - An active radar sensor (6) that operates at a wavelength corresponding to the wavelength of resonant absorption of signals in the atmosphere within the range (1 mm - 15 mm) and detects the UAV at a flight altitude of 5 m - 50 m is provided.

Description

Technical Field

[0001] The present invention relates to a method as described in the preamble of the independent claim of the method, and a device as described in the preamble of the independent claim of the device. In particular, the present invention relates to the detection and localization of micro-aircraft. The present invention can be used to create technical means for protecting important ground objects according to the method of claim 1 [1].

Background Art

[0002] The modern international situation is characterized by new elements that have come to occupy a firm position in military conflicts. These are drones. Drones play an important role in reconnaissance, combat, defense, and attack. The manufacture of drones involves a number of state-owned companies and private enterprises. In fact, they are new types of weapons. Defense against these weapons is a difficult task.

[0003] However, the real problem is the protection against micro-drones, since the absolute development trend is to minimize their size to a few centimeters. A related problem is that such micro-drones are not very suitable for military conflicts and are more suitable for unprecedented terrorist purposes.

[0004] Micro-drones target cities and the people living there. Swarms of micro-drones do not jump into ditches to destroy soldiers, nor do they participate in battles on the battlefield. They fly into hotels, homes, offices, schools, and universities. If micro-drones fall into the hands of terrorists, cities like Singapore and Dubai will quickly become impoverished because no one protects their inhabitants. Also, people who are used for terrorism and coercion will give everything for their children.

[0005] In the context of urban development, with its overwhelming amount of interference from reinforced concrete structures, glass, mirrors, the entire urban infrastructure, various industries, and the lives of the city itself, the task of detecting microdrones is extremely difficult. Whatever the problem may be, the ultimate goal is the detection and identification of microdrones measuring 1-3 cm in size in dense urban environments.

[0006] The detection process involves the use of various active and passive sensors. Micro-drone detection in densely populated urban areas is characterized by widespread interference and, simultaneously, short distances to obstructing obstacles, buildings, and structures. Naturally, conventional radar detection devices and lasers are unlikely to be aimed at the windows of adjacent hotels.

[0007] This leads to the following requirement: that the active radar, near acoustic and optical spatial detection required for reliable detection of microdrones must have a limited range of physical boundary forms (and must not be controlled by software). This requirement allows for a short detection range of objects up to approximately 100m, on the one hand, and minimizes the effects of interference, including its own reflected acoustic signals, on the other hand.

[0008] This challenging requirement should be implemented in the claimed invention by using active radar and acoustic sensors that operate within the range of resonant absorption of radio waves in the atmosphere (in the case of millimeter-wave radar sensors) and resonant scattering of sound waves on micro UAVs (in the case of active acoustic sensors).

[0009] For example, since virtually all radar functions are performed within a so-called "transparent window," the operation of the vast majority of wireless devices does not interfere with the radar detection proposed in this invention. At the same time, if detection does not require long distances, i.e., if it fully complies with the requirements for detecting microdrones in urban areas, the problem can be solved with an opaque window. Detecting microdrones over long distances is not the intended target. This is impossible in urban areas, and microdrones must, in some cases, be detected in open spaces, typically less than 100 meters away, such as "in front of a neighbor's house."

[0010] At the same time, it is desirable to experimentally verify the required distance from the nearest urban object for each specific (protected) object in order to optimize the solution to the problem of reliable detection of microdrones and to minimize interference from adjacent buildings and structures.

[0011] The use of radar systems to detect flying objects is well known. However, low-altitude unmanned aerial vehicles (UAVs) are difficult targets for existing radar systems. Low-altitude UAVs have a small effective scattering area due to their small size (a few centimeters to tens of centimeters) and the use of low-reflectivity composite materials in their construction. Furthermore, active (radiation) radar stations are exposed to enemy electronic warfare systems. All of these factors reduce their effectiveness due to the short range and low reliability of detecting low-altitude UAVs in electronic warfare.[2]

[0012] The closest approach to the claimed invention is a passive acoustic method for detecting or sensing unmanned aerial vehicles [3]. For example, the Ataka-Shoroh acoustic reconnaissance module can detect approaching unmanned aerial vehicles at distances of tens to hundreds of meters, depending on the level of external noise and the size of the drone's propellers.

[0013] A drawback of this method is its susceptibility to interference from external acoustic noise, or ambient noise. These influences reduce the detection range of unmanned aerial vehicles, potentially leading to false detections.

[0014] U.S. Patent Application Publication No. 2015 / 0302858 discloses the use of one or more microphones to record short sequences of acoustic noise and decompose each of these sequences into its frequency spectrum. The frequency spectrum is compared to noise signatures stored in a database of various UAVs in different flight conditions (hovering, climbing, descending, approaching, and taking off) to identify the UAV. If a match is found, an alarm is triggered. The alarm may contain information about the UAV model. The use of multiple microphones enables direction detection of the UAV.

[0015] U.S. Patent Publication 2021 / 0383665 discloses a combination of acoustic and electro-optical detection for detecting UAVs. UAVs can be classified according to type and threat level. Acoustic sensors are positioned in settings adapted to terrain, terrain features, or artificial objects. Sound detected by one or more of the acoustic sensors is compared to known sound signatures to classify the sound source. The sound signatures contain information specific to the UAV. Acoustic detection can be combined with optical imaging, optical video, thermal imaging, electro-optical infrared, radio frequency detection, RADAR, LIDAR, and full-spectrum electromagnetic radiation detection, including any combination thereof to display video images or 3D visualizations of the field of view, for example, non-line-of-sight acoustic detection indicating a UAV as a noise source.

[0016] The technical objective of this invention is to improve detection reliability and expand the detection range of unmanned micro-aircraft equipped with rotating propellers (engines) at low altitudes in the presence of external noise.

[0017] In particular, an objective of the present invention is to improve the detection efficiency of low-altitude micro UAVs in urban areas by enhancing the reliability of detection and the confidentiality of operation in the event of external interference.

[0018] This problem can be solved by the features of the independent claims for the method, or by the features of the independent claims for the device.

[0019] The present invention can be implemented as follows: To detect low-altitude microdrones (UAVs), the mechanical vibrations of their electric motors and the acoustic signals caused by the rotation of their propellers are recorded. Simultaneously, the occurrence of parametric modulation of optical signals caused by the same mechanical vibrations is recorded in both the visible (0.4–0.76 μm) and infrared (0.76 μm–1 mm) ranges of waves reflected from the UAVs, while the correlation between these two low-frequency signals is recorded (its presence indicates UAV detection).

[0020] The detection of flying objects is performed using at least two independent search channels (sensors). That is, - At least one passive optical channel using visible wavelengths (e.g., 0.4–0.76 micrometers), and / or - At least one passive optical channel using infrared wavelengths (e.g., 0.76 micrometers to 1 mm), - At least one passive acoustic channel using a frequency range perceptible to the human ear (e.g., 10Hz to 20kHz), and optionally adjacent frequency ranges (e.g., 3Hz to 10Hz, 20kHz to 30kHz), and optionally further, - At least one active radar channel in the millimeter wavelength range, short millimeter detection range, and / or - At least one active acoustic channel, For example, three search channels (sensors) may be used.

[0021] An active acoustic channel operating at the wavelength of resonant scattering of sound waves on an unmanned aerial vehicle is preferably included in the detection process, and an active radar channel with a millimeter detection range whose wavelength matches the wavelength of resonant absorption of signals in the atmosphere is preferably included in the detection process.

[0022] To achieve the fundamental objectives of the present invention, it is evident that it may be provided to use active radar and acoustic sensors operating in the resonant absorption and resonant scattering window of sound waves on a micro UAV for millimeter-wave radar sensors, as well as optical sensors operating in the visible and IR ranges.

[0023] The wavelengths of resonant absorption in the atmosphere were obtained from reference data on the propagation of radio waves in various media (gases, liquids, solids, etc.) from known literature sources.

[0024] The aforementioned passive optical sensor operates in conjunction with the passive acoustic sensor.

[0025] Under favorable conditions, modern passive optical sensors are known to be able to detect low-altitude unmanned micro-aircraft at a distance of 500 meters during the day.[4] At night, the detection range of infrared thermal imaging cameras can reach tens or even hundreds of meters.[2] However, the use of only one optical channel makes the detection process unstable.

[0026] In particular, in passive detection channels of passive optics and passive acoustics, preferably in both detection channels (acoustic and optical), low-frequency modulation components are recorded. These are caused by the mechanical oscillations or vibrations of the electric motors and rotating propellers of low-altitude flying UAVs. At the same time, there is a fixed, stable correlation between the two components. The low-frequency match is due to the rotational speed of the rotating propellers, which generates low-frequency parametric "spiral" modulation of the optical signal [5]. The use of correlation greatly improves the range and noise immunity of the detection technique. Low frequencies can refer to signal changes in the range of 20 Hz to 20 kHz.

[0027] The claimed method further includes an active millimeter-wave radar sensor whose wavelength preferably matches the wavelength (1-15 mm) of the resonant absorption of signals in the atmosphere within a given altitude range of the unmanned aircraft. Millimeter-wave radio waves suffer the greatest attenuation in the atmosphere. This is due to the absorption lines in the millimeter range caused by oxygen and water vapor molecules present in the atmosphere. The absorption process is due to resonant quantum mechanical effects.

[0028] Water vapor molecules have a certain electric moment, and their interaction with the electromagnetic field causes resonant absorption of radio waves. The maximum absorption occurs in the range of 10-15 mm and at wavelengths shorter than 3 mm.

[0029] Oxygen molecules contained in the atmosphere have a magnetic dipole moment that causes the appearance of a single absorption line at a wavelength of 2.5 mm and a line complex (burst) at 5 mm.

[0030] The use of wavelengths having resonant absorption in the atmosphere (attenuation coefficients reaching 20-30 dB / km or more) in the active radar channel (radar sensor) enhances the secrecy of the operation of the radar sensor [7]. Furthermore, at these millimeter-range wavelengths, they are rarely used in various electronic systems, so the degree of interference is significantly low. The radar sensor registers the reflected microwave signals only within a specific altitude range of the unmanned aircraft, i.e., at short intervals (tens of meters). This avoids interference from large flying objects (aircraft, helicopters) located at a distance.

[0031] Preferably, this also includes active acoustic sensors that operate at wavelengths at which sound waves are scattered by unmanned aerial vehicles due to resonance [8]. Since the minimum dimensions (micro) are specified in centimeters, the wavelengths of the acoustic field must correspond to these to ensure resonant scattering. Given the speed of sound in air (approximately 340 m / s), this corresponds to frequencies of several tens of kHz. Therefore, the optimal frequency range for active acoustic sensors for distances up to 50 meters is 10–20 kHz. In this case, the attenuation coefficient is tolerable at 0.2–0.8 dB / m. The total loss over a distance of 100 meters is only 20–80 dB, which is within the tolerance range of the acoustic sensor. At the same time, the value of the acoustic depth signal at distances greater than 100 meters is not important, making it difficult for the “enemy” to register it.

[0032] The method for calculating resonant scattering signals is well known to those skilled in the art.

[0033] Similar to classical radar, the effective scattering region of an object (microdrone, UAV) in acoustics has three characteristic wave scattering regions. That is, - Rayleigh when the wavelength is much larger (at least 2-3 times) than the characteristic size of the object. - Resonance when wavelength corresponds to the size of the object (in the case of this invention), - If the wavelength of the acoustic field is much smaller (at least 2-3 times) than the characteristic size of the object, it is considered quasi-optical.

[0034] Calculating the reflective properties of actual drones with complex shapes is difficult. Therefore, approximations can be used, which may also be implemented according to the present invention. However, these are preparatory steps that do not necessarily occur during the detection method of the present invention, but can be obtained from a pre-coded database for a range of flying objects of different sizes and / or shapes.

[0035] When evaluating a drone, it is possible to replace the drone with a sphere whose diameter corresponds to the length of the drone's fuselage. In this case, the value of the acoustically effective scattering area ("force target") is close to the value of the lateral scattering area of ​​the sphere. The characteristic resonance deviation of the sphere's reflection properties is 35 dB or more. For example, for an object diameter of 3 cm (micro-drone), the resonant scattering range (wavelength of approximately 3 cm) is in the 10 kHz range.

[0036] Of the three typical characteristic ranges of sound wave scattering, in our case, there is preferably a resonance range where the wavelength corresponds to the size of the object, i.e., where the reflection is maximum.

[0037] Furthermore, since it is preferable to consider the detection of microdrones with a size of 3 centimeters, the wavelength is also approximately 3 centimeters. The corresponding frequency follows the following formula. F(Hz) = V(sound) / λ(wavelength) = 340(m / s) / 3 × 10^-2(m) ≈ 11(kHz), so the range is 10 to 20(kHz).

[0038] For example, if a 2cm microdrone is detected, the length of the acoustic wave corresponding to the characteristic resonant scattering is also approximately 2cm, or the frequency is approximately 17kHz. Through the detection of the corresponding resonant scattering, a scanning process can be performed in which the frequency is changed until the correct frequency for the correct microdrone is identified.

[0039] The preferred simultaneous use of four sensors with optimal signal processing (correlation of the first two sensors) and a common matching circuit for all four sensors allows for increased reliability of unmanned aerial vehicle detection under the influence of acoustic, optical, and electromagnetic microwave interference.

[0040] In this specification, to camouflage, conceal, or hide the execution of a method or the operation of a device performing a method, also referred to as operational secrecy or confidentiality, from external detection in particular, and to reduce energy consumption, active radar and acoustic detection are performed when a control signal for an additional passive acoustic channel operating in standby mode is turned on.

[0041] Field experiments were conducted to test the performance of the most complex components of the proposed method. The subject of the experiment was a small MJX Bugs3 quadcopter with low-noise brushless propellers. It weighed 447 grams and had overall dimensions of 44 × 44 × 15 centimeters. The quadcopter was mounted on a tripod 15 meters away from a Shure SM58 microphone and an optical sensor. The optical sensor used was a 12x monocular with an FD-7k silicon photodiode mounted on a vibration-resistant tripod. The photodiode was mounted on a broadband low-frequency matching amplifier. The photodiode operated in the visible and near-infrared range (λp = 0.4~1.1 μm).

[0042] The low-frequency spectra of the microphone and optical sensor were recorded using an S-48 spectrum analyzer. The operating mode was "narrowband" with a bandwidth of 5 Hz.

[0043] During the measurement, the rotational speed of the quadcopter's two-blade propeller varied from 6000 to 9000 rpm. In this case, the low-frequency spectrum (fundamental frequency F and its harmonics) was recorded, which is in the frequency band above 200 Hz and corresponds to a known dependency [6]. That is,

[0044] TIFF0007912161000001.tif12170, Hz Here, ω is the propeller speed in rpm. N: Number of sheets.

[0045] Experimentally, it has been established that the spectral components of acoustic and low-frequency signals in the output of an optical sensor match with an accuracy of 3–5%. This allows for the detection of signals from low-altitude unmanned aerial vehicles and micro-aircraft against a background of acoustic noise using a correlator.

[0046] Figure 1 shows a block diagram of a device (1) that implements the proposed method for detecting unmanned microaerial vehicles at low altitudes.

[0047] A device for detecting unmanned micro-aircraft in low-altitude flight may include a passive acoustic sensor (2), a passive optical sensor (receiver of modulated light radiation in the visible and infrared ranges) (4), a correlator (3), preferably an active acoustic sensor (5), preferably an active radar sensor (6). Preferably, a matching circuit (with actuators) (7) is included. The correlator (3) is intended to detect the correlation between signals from the outputs of the passive acoustic sensor and the passive optical sensor.

[0048] A device (1) for detecting an unmanned micro-aircraft at low altitude functions as follows, according to a non-limiting embodiment: An acoustic signal from an unmanned micro-aircraft at low altitude is received by a passive acoustic sensor (2). In this case, a modulated optical signal from the unmanned aircraft is simultaneously recorded by an optical sensor (4). Low-frequency signals from the outputs of the two sensors are fed into the input of a correlator (3). Their spectra match because they are produced by the same rotating propeller. In this case, the signals are fed into a matching circuit (7), and signals from two active sensors, acoustic (5) and radar (6), also enter the matching circuit. An actuator can then be triggered. The actuator is preferably understood as an addition to the detection method according to the present invention and is not required for detection itself.

[0049] It is important to note that the present invention includes a method for detecting unmanned micro-aerial vehicles (UAVs) at low altitudes, which includes recording the mechanical vibrations of an electric motor and the acoustic signals caused by the rotation of a propeller. - Furthermore, the optical signal is recorded in the visible (0.4~0.76 μm) and / or infrared (0.76 μm~1 mm) range of the UAV. - The occurrence of parametric modulation of the optical signal caused by these same mechanical vibrations was detected. This system is characterized by registering the correlation between the acoustic and optical signals of the UAV, and the presence of this correlation indicates the detection of the UAV.

[0050] Correlation can be performed in the (low) frequency range caused by the mechanical vibrations of the electric motor and the rotation of the UAV's propeller.

[0051] Accordingly, the present invention proposes the correlation of two low-frequency harmonic signals based on a known and well-developed mathematical apparatus that includes a simple specific formula for the correlation coefficient. The term "low frequency" encompasses the mechanical vibrations of UAV electric motors and refers to the frequency range caused by the rotation of their propellers. For this purpose, a direct mathematical expression that describes the specific physics of the process can be used without employing complex statistical methods. This helps in creating technical samples with better sensitivity and selectivity, which is an obvious advantage.

[0052] Furthermore, this method can provide millimeter-range active radar detection, the wavelength of which corresponds to the wavelength of atmospheric resonant absorption (micro UAV electromagnetic waves) reflected by the surface of the drone, preferably in the range of 1 mm to 15 mm, particularly preferably within a given (flight) altitude range of the drone, preferably between 5 m and 50 m.

[0053] A key feature of this design is that active radar detection is performed on micro-drones measuring 1-3 cm in size in urban areas. Based on this requirement, the active radar sensor must preferably scan space at a maximum distance of 100 m, while the detection signal must be significantly attenuated at longer distances to prevent reflected signals from surrounding buildings and structures from interfering with the radar receiver sensor. Another important purpose of this attenuation beyond a given distance to the detection line (approximately 100 m) is to achieve greater secrecy of the detection signal from "enemies". As a method to solve the problem (claim 2), the claimed invention proposes millimeter-range active radar detection, the wavelength of which matches the range of resonant absorption of atmospheric radio waves reflected from the surface of a micro-UAV (range of 1 mm to 15 mm). The atmospheric masking properties for depth sounding signals in this radio wave range are most suitable in the case of the present invention because absorption lines by oxygen molecules and water vapor in the atmosphere exist in the millimeter range. The absorption process is caused by resonant quantum mechanical effects. The use of atmospheric resonant absorption wavelengths (with attenuation coefficients reaching 20-30 dB / km or higher) enhances the secrecy of the radar sensor. Furthermore, interference levels at these millimeter wavelengths are significantly reduced because they are rarely used in various electronic systems. The radar sensor detects reflected microwave signals only within a specific altitude range of the unmanned aerial vehicle, i.e., only at short distances (tens of meters). This eliminates interference from large, distant flying objects (aircraft, helicopters).

[0054] The advantages are that it minimizes interference and enhances confidentiality when conducting active radar detection of microdrones measuring 1-3 cm in size in densely populated urban areas.

[0055] An advantageous embodiment of this method can further include active acoustic detection operating at the wavelength of resonant scattering of sound waves on an unmanned aerial vehicle in the frequency range of 10 kHz to 20 kHz.

[0056] Since the minimum dimensions of UAVs, also known as microdrones, are a few centimeters, the wavelength of the sound field must match these to ensure resonant scattering. Considering the speed of sound in air (approximately 340 m / s), this corresponds to a frequency of several tens of kHz. Therefore, the optimal frequency range for an active acoustic sensor at distances up to 100 meters is 10–20 kHz. In this case, the attenuation coefficient has a tolerance of 0.2–0.8 dB / m. The total loss over a distance of 100 meters is between 20 dB and 80 dB, which is within the tolerance limits of the active acoustic sensor.

[0057] The advantage is that it can significantly reduce all types of interference in urban environments. At the same time, the strength of the acoustic exploration signal is negligible at distances of 100 meters or more, making it difficult for the "enemy" to detect it.

[0058] In this case, effective detection of the microdrone involves "picking up" minimal acoustic interference and remaining hidden from the "enemy" at a distance of no more than tens of meters. This is certainly a significant advantage for the specific requirements of active acoustic detection of microdrones, which measure 1-3 cm at distances up to 100 m in a given UAV altitude range, preferably 5 m to 50 m.

[0059] It is also important to emphasize that the present invention may, as an alternative or addition, include a device (1) for detecting UAVs in low-altitude flight. Device (1) is - Passive acoustic sensor (2), - Passive optical sensor (4), - It is equipped with a correlation meter (3).

[0060] The correlation meter (3) is advantageously used to correlate acoustic and optical signals with respect to parametric modulation caused by the mechanical vibrations of the electric motor and the rotation of the UAV's propellers, and its presence indicates the detection of the UAV.

[0061] Device (1) enables the execution of a method for carrying out the present invention.

[0062] Furthermore, the device (1) may include an active acoustic sensor (5) configured to operate at the wavelength of resonant scattering of sound waves on an unmanned aerial vehicle in the frequency range of 10 to 20 kHz.

[0063] Alternatively or additionally, the device may include an active radar sensor (7). The active radar sensor (7) is advantageously tuned to operate at wavelengths corresponding to resonant absorption of atmospheric signals within a range (1 mm to 15 mm). The active radar sensor detects UAVs at flight altitudes of 5 m to 50 m.

[0064] The device (1) may further include a matching circuit (7) whose three inputs are connected to the outputs of a correlation meter and an active acoustic sensor (5) and a radar sensor (6).

[0065] Advantageously, passive acoustic sensors are selected as highly sensitive, wideband sensors, preferably operating in standby mode. They can potentially control the activation of active radar and acoustic sensors upon receiving signals from a micro UAV.

[0066] Simultaneously, by utilizing the atmospheric absorption (camouflage or masking) properties in an optimal range of radio and acoustic wavelengths, preferably using pulse or FM modulation, the active sensor has a fixed and limited detection range of preferably up to 100m, while receiving minimal interference and providing additional concealment for active acoustic and radar sensors (in urban areas), thus creating a detection zone for microdrones in the form of a "safety envelope" covering objects (that may be targets of microdrone attacks).

[0067] Advantageously, active radar and acoustic sensors are selected for the device. These preferably operate within an optimal range of radio and acoustic wavelengths, utilizing the atmospheric absorption (camouflage or masking) properties, preferably using pulse or FM modulation. They have a specific limited detection range, preferably up to 100m at a specific altitude range of 5-50m, so as to create a micro-drone detection zone in the form of a "radio-acoustic confinement envelope" with specific physical and geometric characteristics that cover objects (which may be targets for micro-drone attacks).

[0068] Preferably, the acoustic signal of the unmanned micro-aerial vehicle is received at low altitude by a passive acoustic sensor (2), and preferably, at the same time, the modulated optical signal of the unmanned aerial vehicle is detected by an optical sensor (4).

[0069] Preferably, the low-frequency signals from the outputs of both sensors are supplied to the input of the correlator (3), thereby allowing the signal from the output of the correlator (7) to be supplied to the input of the match determination circuit (7). Optionally, and preferably simultaneously, signals from the active acoustic sensor (5) and radar sensor (6) can be supplied to the other inputs of the match determination circuit (7). (Figure 2)

[0070] At the same time, they are subject to minimal radar and acoustic interference, providing additional secrecy to the source of depth sounding signals in densely populated urban areas, which is a clear advantage over devices (device elements) for detecting UAVs at the presented technical level.

[0071] It is important to emphasize that this invention provides correlation between two low-frequency harmonic signals. This can include pattern recognition in both the acoustic and optical ranges, e.g., the range of the electromagnetic spectrum visible to the human eye and / or the infrared range, caused by the mechanical vibrations of an electric motor and the rotation of a UAV propeller. Alternatively or additionally, to enhance the detection reliability of the UAV, radar signals, e.g., radar signals in the millimeter wavelength range, can be analyzed for such low-frequency ranges caused by the mechanical vibrations of an electric motor and the rotation of a UAV propeller.

[0072] It is important to emphasize that this invention is suitable for detecting so-called microdrones. The dimensions of the microdrones to be searched are 1 to 3 cm.

[0073] Advantageously, detection is limited to a distance of up to 100m and a specified height range of 5-50m.

[0074] Advantageously, the detection wavelength range for active radar is 1 mm to 15 mm, which corresponds to the range of resonant absorption of radio waves in the atmosphere.

[0075] The frequency range for active acoustic detection (which operates at the wavelength of resonant scattering of sound waves in the atmosphere) is advantageously 10 kHz to 20 kHz.

[0076] The advantages of this invention include the creation of a radio-acoustic security envelope, along with the secrecy of the source of the depth sounding signal. These are tactical and technical features that provide unparalleled advantages when using active radar and acoustic sensors to detect micro-drones.

[0077] Device (1) can utilize active radar and acoustic sensors that operate in an optimal range of radio and acoustic wavelengths, preferably using pulse or FM modulation, taking advantage of the absorption (masking) properties of the atmosphere. They have a fixed and limited detection range of preferably up to 100m within a specified altitude range of 5 to 50m, so as to create a detection zone for microdrones in the form of a “radioacoustic confinement envelope” with defined physical and geometric properties that cover objects (which may be targets for microdrone attacks).

[0078] At the same time, they are minimally exposed to radar and acoustic interference, providing additional secrecy to the source of the search signal in densely populated urban areas, which is a clear advantage over UAV detection devices (elements) at the presented level of technology.

[0079] source of information 1. Shcherbakov GN, Shlykov Yu.A., Protection of critical ground facilities from air terrorism, Special equipment, 2007, No. 1, pp. 17-22. 2.Filin ED,Kirichek RV,Methods for detecting small unmanned aerial vehicles based on electromagnetic spectrum analysis,Russian drones,2018,Electronic resource. Access mode: https: / / russiandrone.ru / publications / methody-obnaruz-heniya-malorazmer nykh-bespilotnykh-letatelnykh-apparatov-na-osnove-analiza-elektromagn / . 3. Rostec presented equipment for detecting spy drones, Rostec, 2020, Electronic resource. Access mode: https: / / rostec.ru / news / rostekh-predstavil-apparaturu-dlya-obnaruzheniya-dronov-shpionov / . UAV detection by optical positioning. Optical positioning, LLC "LAMET" Electronic Resources. Access mode: http: / / www.lamet.ru / 4988184368. 4. Shcherbakov G.N. Parametric location - a new method for detecting hidden objects, Special equipment, 2000, No. 4, pp. 52 - 58. 5. V.S. Frantskevich and A.S. Dorogokupets, Study of the acoustic characteristics of a radial fan, Proceedings of BSTU, 2017, series 2, no. 2, pp. 215 - 219, Electronic resource. Access mode: https: / / elib.belstu.by / bit - stream / 123456789 / 23346 / 1 / Franckevich_Akustich_haracteristiki.pdf. 6. Yakovlev O.I. et al., Propagation of radio waves, Chapter 10, Propagation of radio waves. 7. Waves through absorbing media, Section 10.5 Absorption of millimeter radio waves in the atmosphere, “LENARD”, Moscow, 2009, pp. 426 - 432. 8. Gorbatov AA et al., Acoustic methods for distance measurement and control, Section 2.3, Sound absorption in gases, Moscow, Energoizdat, 1981, pp. 39-43.

Claims

1. A method for detecting unmanned micro-aircraft (UAVs) at low altitude, including recording acoustic signals caused by the mechanical vibrations of an electric motor and the rotation of a propeller, - Furthermore, the optical signal of the UAV is recorded in the visible range (0.4 to 0.76 μm) and / or the infrared range (0.76 μm to 1 mm). - The occurrence of parametric modulation of the optical signal caused by these same mechanical vibrations is detected, A method characterized in that the correlation of the low-frequency components of the spectrum between the acoustic signal of a UAV and the modulated optical signal is recorded, and the persistent occurrence of said correlation indicates that a UAV has been detected.

2. The method according to claim 1, characterized in that the correlation is performed in a low-frequency range caused by the mechanical vibration of the electric motor and the rotation of the propeller of the UAV, and the change in the signal in the low-frequency range is in the range of 20 Hz to 20 kHz.

3. The method according to claim 1 or 2, further characterized in that a millimeter-range active radar detection is provided, the wavelength of which corresponds to the wavelength of atmospheric resonant absorption in the range of 1 mm to 15 mm within the flight altitude range of the UAV between 5 m and 50 m.

4. The method according to claim 1 or 2, further comprising an active acoustic detection system operating at the wavelength of resonant scattering of sound waves on an unmanned aerial vehicle in the frequency range of 10 kHz to 20 kHz.

5. The method according to claim 1 or 2, characterized in that the acoustic signal of the UAV is received at low altitude by a passive acoustic sensor (2) simultaneously with the modulated optical signal of the UAV via an optical sensor (4), the low-frequency signals from the outputs of both sensors are supplied to the input of a correlator (3), the signal from the output of the correlator (3) is supplied to the input of a match determination circuit (7), and simultaneously, signals from an active acoustic sensor (5) and a radar sensor (6) are supplied to other inputs of the match determination circuit (7).

6. A device (1) for detecting unmanned microaerial vehicles (UAVs) in low-altitude flight, - Passive acoustic sensor (2), - Passive optical sensor (4), - A correlation meter (3) whose input is connected to the output of the passive acoustic sensor (2) and the output of the passive optical sensor (4), and which is configured to detect the correlation of the low-frequency components of the spectrum of the acoustic signal and the modulated optical signal, - An active acoustic sensor (5) tuned to operate at the wavelength of resonant scattering of sound waves on a UAV in the frequency range of 10 to 20 kHz, - An active radar sensor (6) that operates at a wavelength matching the wavelength of resonant absorption of atmospheric signals within a range (1 mm to 15 mm) and detects UAVs at flight altitudes of 5 m to 50 m. A device (1) comprising:

7. The device according to claim 6, comprising a matching circuit (7) with three inputs connected, the three inputs being connected to the output of the correlator (3), the output of the active acoustic sensor (5), and the output of the active radar sensor (6), respectively.

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