RU2154841C1 - Technique for detection of underwater target in guarded water area - Google Patents

Abstract

FIELD: underwater acoustics, detection and tracking of underwater target in defended water area. SUBSTANCE: surface of water area is irradiated in correspondence with invention with use of modulated laser radiation on wave length 9- 11 μm. Radiation of this wave length is completely absorbed by surface layers of water. Zone of heating turns to be source of acoustic waves. Waves reflected from target are received by sonic detectors. Received signals are processed and then command to irradiate location of presumed position of target with additional modulated laser radiation with wave length 0.6-1.1 μm is given. Radiation of this wave length is capable of reaching target and of heating its surface which becomes additional source of acoustic waves. These acoustic waves are also received by sonic detectors. Processing of information from sonic detectors makes it possible to determine coordinates of target, its speed and direction of movement and to track target by way of corresponding movement or by scanning of laser radiation. EFFECT: increased precision in determination of coordinates of target and in its tracking. 6 cl, 1 dwg

Description

 The invention relates to the field of hydroacoustics and can be used to detect and track an underwater target in a protected marine area.

 There is a known method of the same purpose, according to which an explosive underwater charge is dropped from a surface vehicle (ship or aircraft) in a protected area. Acoustic waves generated by a charge explosion are detected by a sonar detector (hydrophone). And according to the results of detection, they judge the presence of an underwater target in a protected area [1].

 The disadvantage of this method is the inability to determine the exact coordinates of the target and its tracking, as well as the lack of stealth detection of the target.

 A known method for detecting targets in a protected area, which consists in irradiating the water surface with a surface vehicle (for example, a helicopter) with modulated laser radiation at a wavelength (9 - 11) μm, completely absorbed by the surface layers of water, and detecting acoustic waves excited by hydroacoustic receivers in water by its heated zone, according to the results of which they judge the presence or absence of a target in a protected area [2].

 This method is adopted as a prototype.

 The disadvantage of the prototype is the low accuracy of determining the coordinates of the target and the difficulties in its maintenance.

 The technical result obtained from the implementation of the invention is to eliminate the disadvantages of the prototype, i.e. improving the accuracy of determining the coordinates of the target and its support.

 This technical result is achieved due to the fact that in the known method of detecting an underwater target in a protected area, which consists in irradiating the water surface with a surface vehicle with modulated laser radiation with a wavelength of (9 - 11) microns and detecting acoustic waves excited in water with its heated surface zone, according to the results of which they judge the presence or absence of a target in a protected area, after detecting a target in a protected area, the water surface after it is irradiated above the intended target location with additional modulated laser radiation with a wavelength of (0.6 - 1.1) μm and acoustic waves are detected that are excited by the heated surface of the irradiated target, with the same or additional hydroacoustic receivers, and based on the results of joint detection of acoustic waves, reflected from the target and excited by its surface as a result of laser irradiation at different wavelengths, specify the location of the target.

 The laws of modulation of the primary and secondary laser radiation can be the same or different.

 In the latter case, the depth of the target is determined by the difference in the times of arrival of acoustic waves to sonar receivers.

 Scanning a laser beam with a wavelength of (0.6 - 1.1) μm allows target tracking.

 Additional laser radiation is obtained using ruby or neodymium lasers, respectively, with wavelengths of 0.69 and 1.06 μm.

 As hydroacoustic receivers, you can use hydrophones mounted on buoys discharged to the water surface from a surface craft.

 The invention is illustrated in the drawing, which shows a diagram of the implementation of the method.

 To implement the method, there is a surface craft 1, for example, a helicopter, with a radio antenna transceiver 2 and a laser system (not shown in the drawing), which includes two lasers at a wavelength of 10.6 μm and 1.06 μm, respectively, on carbon dioxide and ruby, focusing systems for each of the lasers, modulators, scanners and optical detectors. Such laser systems for irradiating objects are well known in the scientific and technical literature and from the prototype [2], therefore, their description is not given.

 There are also hydroacoustic receivers in the form of hydrophones 3, 4, 5.

 Hydrophones 3, 4 can be fixed on buoys 6, 7 with transmitting radio antennas 8, 9, and hydrophone 5 is fixed on the bottom 10 of the protected water area 11 using the anchor device 12.

 Received signals from hydrophones 3, 4 can be transmitted over the air to a coastal signal processing point 13 equipped with a radio transmitting antenna 14.

 From the hydrophone 5, the received acoustic signals can be transmitted via cable 15 to the same coastal signal processing point 13.

 The coastal signal processing point can be performed on the basis of a processor with a display as in the prototype [2].

 A method for detecting an underwater target in a protected area is implemented as follows.

 From helicopter 1, buoys 6, 7 with hydrophones 3, 4 and transmitting radio antennas 8, 9 are dropped onto the surface of the water area 11. At the same time, additional hydrophones 5 can be mounted on anchor devices 12 at the bottom 10 of the protected water area 11.

 The number of hydrophones 3, 4, 5 is dictated by the size of the controlled water area 11 and the necessary accuracy of detection and tracking of the target, indicated in the drawing by 16.

Using a laser system, the surface of the water area 11 is irradiated with modulated laser radiation 17 at a wavelength of 10.6 μm. (For example, laser radiation follows with a pulse frequency f ₁ ). At a wavelength of 10.6 μm, water has a metallic opacity for laser radiation [3], which causes heating of its surface layers.

 The heated surface zone 18 becomes a source of acoustic waves 19 (dashed line in the drawing), which, when hit on target 16, are reflected from it. And the waves 20 reflected from the target are received by hydrophones 3,4.

 The signals from the hydrophones after preliminary processing are transmitted over the air to the coastal point 13 signal processing.

 From the coastal point 13, also via radio channel, the helicopter 1 receives a command to turn on additional laser radiation 21 at a wavelength of 1.06 μm, at which the laser radiation is only partially absorbed by water [4]. Therefore, it reaches goal 16 and heats its surface in zone 22.

Laser radiation at a wavelength of 1.06 μm can be modulated by the pulse law at a frequency f ₁ or f ₂ not equal to f ₁ .

 Acoustic waves 23 (solid line in the drawing) will also be modulated according to the same law as laser radiation.

 If the laws of modulation of acoustic waves 20, 23 are different, then by the difference in the times of their arrival at hydrophones 3 or 4, it is easy to determine the depth of the target 16 (since the waves travel a different path in the water, equal to the depth of the target). Doppler frequency in the usual way determine the speed of the target. In this case, you can additionally use information from the hydrophone 5.

 The coastal processing point 13 allows, based on the information received, to determine not only the coordinates of the target 16 and speed, but also the direction of its movement. This information is transmitted via a radio channel to a helicopter 1, which provides target tracking by periodically irradiating its surface with additional laser radiation 21.

 If the depth of the target 16 is such that the energy of the laser pulse at a wavelength of 1.06 μm is not enough to achieve the goal, switch to the ruby laser at a wavelength of 0.69 μm. At this wavelength, the water absorption coefficient is much smaller [4], which allows reaching depths of hundreds of meters.

 Since the pressure level of the acoustic waves 20, 23 can be made lower than the level of sea noise, the detection and tracking of the target will be carried out covertly. And the well-known laws of wave modulation nevertheless allow them to be distinguished at the level of sea noise.

 Compared with the prototype, it becomes possible to accurately determine the depth of the target, its speed and direction of movement, and this in turn allows tracking the target, thereby achieving the technical result.

Sources of information
1. P. J. Urik. Basics of sonar. - L .: Shipbuilding, 1978, p. 26, 27.

 2. US patent N 5646907, CL. 367 - 93 (G 01 S 15/00), 1997 - prototype.

 3. A. M. Trokhan, V. A. Belogolsky, and Yu. N. Vlasov. On the surface boiling of a liquid. Doklady AN SSSR, 1971, 196, N 5, p. 1069-1071.

 4. Yu. N. Vlasov et al. Optical visual method for studying fluid flows. Thermophysics of high temperatures, 1972, 10, N5, 1135-1137.

Claims (7)

 1. A method for detecting an underwater target in a protected water area, which consists in irradiating the water surface of the water surface with a surface vehicle using modulated laser radiation with a wavelength of (9 - 11) microns and detecting acoustic waves excited in water by its heated surface zone using hydroacoustic receivers, according to the results which is judged on the presence or absence of a target in the protected area, characterized in that after the detection of the target in the protected area, the water surface of the latter is irradiated over the intended month the location of the target with additional modulated laser radiation with a wavelength of (0.6 - 1.1) μm, and acoustic waves are detected that are excited by the heated surface of the irradiated target, with the same or additional hydroacoustic receivers and based on the results of joint detection of acoustic waves reflected from the target and excited its heated surface as a result of laser irradiation at various wavelengths, specify the location of the target in a protected area.  2. The method according to p. 1, characterized in that the laws of modulation of the primary and secondary laser radiation coincide.  3. The method according to p. 1, characterized in that the laws of modulation of the primary and secondary laser radiation are different.  4. The method according to claim 1 or 3, characterized in that by the difference in the arrival times of acoustic waves with different modulation laws to hydroacoustic receivers, they judge the depth of the target.  5. The method according to p. 1, characterized in that by scanning additional laser radiation on the water surface, tracking of the detected target is carried out.  6. The method according to claim 1, characterized in that as additional laser radiation using radiation from ruby or neodymium lasers, respectively, at wavelengths of 0.69 and 1.06 μm.  7. The method according to p. 1, characterized in that as hydroacoustic receivers use hydrophones mounted on buoys of positive buoyancy, discharged to the water surface of the water from the surface means.