APPLICATION OF DDS AND MAGNETIC BARRIER COOPERATING WITH ACOUSTIC BARRIERS AND TETHERED SONOBUOYS FOR HARBOUR AND ANCHORAGE UNDERWATER PROTECTION

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1 APPLICATION OF DDS AND MAGNETIC BARRIER COOPERATING WITH ACOUSTIC BARRIERS AND TETHERED SONOBUOYS FOR HARBOUR AND ANCHORAGE UNDERWATER PROTECTION ANDRZEJ ELMINOWICZ, LEONARD ZAJ CZKOWSKI OBR Centrum Techniki Morskiej S.A. 62, Dickmana St., Gdynia, Poland The underwater protection system that consists of wideband Acoustic Barriers (WAB) and wideband DDS (WDDS) is a very suitable acoustic device to operate in Littoral Water (LW) and Extremely Littoral Water (ELW). A new approach to underwater protection harbour and task group on the anchorage against AUV, DDV and torpedos is focused on designed stationary tethered sonobuoys with passive sonar, active multistatic sonar, intercept sonar and also possibility of jamming intercepted underwater objects. Passive omnidirectional sonar may be used for initial detection of intruder on the long distance (up to 5 km) and active multistatic sonar will be applied for detection and precise location of detected object. Intercept sonar is waiting for homing sonar signals generated by AUV, DDS, torpedos or submarines and received signals are basis generating jamming signals. The paper describes the WAB, WDDS and magnetic barrier integrated to short range (up to 1000 m) protection systems. The long range (up to 5000 m) sonobuoy for various technical parameters and environmental conditions has been studied. INTRODUCTION The article presents a new approach, method and equipment to underwater protection focused on application the WAB and WDDS that may operated both separately in monostatic mode or together in bistatic mode or also in multistatic mode (several WAB or WDDS depends on configuration of the protected sea/harbour area). The paper describes the wideband monostatic and bistatic acoustic barriers as well as wideband DDS specially designed for integration into protection bistatic systems. The devices have a sophisticated signal processing enabling their cooperation without mutual interferences. Results of investigation of stationary or portable acoustic barriers cooperating with stationary or portable DDS are also described. The aforementioned system should be treated as crucial in underwater protection of critical infrastructure. 39

2 HYDROACOUSTICS Volume 14 In today s changing high tech word, as intruders can be used effective lightweight AUV/DDV/torpedoes that are capable for operation in both shallow and deep water and in various acoustic environments. The results of modern technology are a substantial improvement in AUV/DDV/torpedoes performance at very low cost. Modern technologies with the latest COTS processing power which can accommodate and contains the common processor for sonar signal processing and tactical data processing give opportunity for designing very effective sonars with guidancecontrol functions. A sonobuoy is a device used to detect and identify objects moving in the water. Typically, a sonobuoy is used to detect submarines by either listening for the sounds produced by propellers and machinery (passive detection) or by emitting a sonar "ping" and receiving echo reflected from the surface of the submarine (active detection). For submarine detection and localization multistatic techniques are utilized also. Multi-static operations uses separate active source and passive received sonobuoys. Modern AUV/DDV/torpedoes provided by low self-noise planar array sonar with advanced wideband signal processing algorithm, target classification and filtration plus rejection processing and control tactics to provide new exceptional operation and performance possibilities which needs new concept for countermeasures. Only modern interceptingjamming (IJ) system which can use advanced wideband signal processing can by effective against these threats. An IJ system operates on the base of heading sonars jamming or heading sonars deceiving by false echoes generation. Great diversity of modern heading sonars are operating in wideband frequency range with different types of modulation and high processing gain. The article presents system of AUV/DDV/torpedoes countermeasures in which, on the basis of data from intercept sonar, optimal jamming are created and like noise signals matched to AUV/DDV/torpedoes homing sonars signals are generated also. 1. WIDEBAND ACOUSTIC BARRIER AND WIDEBAND DDS 1.1 WAB CONFIGURATION, TECHNICAL DATA AND APPLICATION The block diagram and technical data of WAB is presented in Fig. 1 [1, 3]. source level SL = 190 db re 1 Pa at 1 m central frequency f 0 = 60 khz; bandwidth B = 20 khz; pulse length T = 10 ms or 20 ms; pulse modulation LFM and HFM: up/down; beam (horiz./vert.) -3dB = 13,5 o /13,5 o ; detection range: swimmer up to 250 m, diver up to 400 m, DDV up to 600 m, maximal depth 30 m, monitor functions visual and audible alarm, operate fully automatic, location all types of harbour walls, quays, piers and other Fig. 1. WAB block diagram and technical data 40

3 Volume 14 HYDROACOUSTICS The wideband WAB comprises a lightweight transducer head and command workstation with a processor and display. The transducer head contains a wideband transducer, controlled transmitter, receiver with digitized output, reference sensors of the transducer head and indispensable electronics for communication (through cable) with shore equipment (command workstation). Received target echoes subject to sophisticated and specific data processing can give very useful information about the detected object: its position, velocity, target strength and course/azimuth the object can be classified with aforementioned data. 1.2 BISTATIC WAB On the basis of monostatic WAB, Bi-WAB was created using synchronization operation of two WAB by PPS (pulse-per-second) from GPS. Accuracy of PPS is ± 1 s. Research of bistatic WAB effectiveness has been performed on the marine range (Gda sk Gulf). The research displayed that bistatic reverberation are significantly smaller then monostatic reverberation then SRR (signal to reverberation) is significantly greater it is mean detection of weak objects in areas with high disturbances is easier and more reliable. It occurs only for some angles between transmitted and received beams [1]. 1.3 DDS CONFIGURATION, TECHNICAL DATA AND APPLICATION WDDS is the specialized sonar designed for detection and classification of small underwater objects i.e. a diver, a small underwater vehicle, a floating explosive charge, in the sea area with high reverberation level. Block diagram of the WDDS and her technical data is shown in Fig. 2 and 3 [2, 3]. WDDS has been designed with under and above water modules and both modules are connected by cable: power supply and data (ETHERNET) transmission. The piezocomposite transducer contains 64 elements covering 180 o. Fig. 2. Block diagram of the above water and underwater modules 41

4 HYDROACOUSTICS Volume 14 Fig. 3. Block diagram of the underwater modules) The basic features of the WDDS are: detecting of underwater targets up to 1000 metres range, built-in auto diagnostics system, tracking up to 10 underwater objects, able to cooperate with other sonar systems i.e. acoustic barriers mono, bi and multistatic system to make an integrated system. It can operate in a wide range of environments. The technical data are as follows: Antenna system cylindrical Observation sector (horizontal) 90 deg Central frequency 70 khz Bandwidth 20 khz Pulse length 10ms/20 ms Operating depth up to 30 m Source level 205 db re 1 Pa@1m Pulse modulation LFM/ HFM: up/down Location all types of harbour, walls, quays, piers, sea floor, Detection range: diver delivery vehicle (DDV) up to 1000 m diver with open BS up to 700 m BS breathing system diver with close BS up to 250 m 2. TETHERED SONOBUOY Anchored at defined places the sonobuoys are a tool of early warning on intruders functional block diagrams of sonobuoys are presented in Fig. 4 and 5. The sonobuoys operates automatic and are powered by solar panel/battery system. The sonobuoys multistatic operations are possible with synchronization by GPS or radio link and cooperation with Command Centre (harbour, ship) only. 42

5 Volume 14 HYDROACOUSTICS Fig. 4. Functional block diagram Fig. 5. Block diagram Passive LF omni directional sonar may be used for initial detection of intruder. Passive HF omni directional sonar in cooperation with active sonar may also allow relatively precise location of intruder by multistatic. Any noise and signal that an AUV makes is potential information about intruder. 3. WAB, WDDS AND TETHERED SONOBUOY IN UNDERWATER HARBOUR PROTECTION The principles of WAB, WDDS and sonobuoy operation/coverage are shown in Fig. 6 harbour protection system. The system contains three zones: First (I) zone is covered by few sonobuoys operating in passive, active/multistatic, intercept and jamming mode. The zone is the area of intruder warning and spread out over 5 km from harbour entry. The zone enables detection, localization and jamming of hostile (AUV/DDV/torpedoes) underwater object. Due to operation of passive sonar underwater objects may be detected from 5 km before harbour entry, Second (II) zone is covered by WDDS sonar and magnetic barrier for divers and AUV/DDV/torpedoes detection and localization. The zone is a semicircle with about 700 m radius and covers approach to harbour entry, 43

6 HYDROACOUSTICS Volume 14 Third (III) zone located in harbour entry contain acoustic barrier, set of loudspeakers and two Air Gun in order to deterrent of intruders (i.e. diver). Fig. 6. Harbour protection system The first protection zone is created by three sonobuoys operating as monostatic (areas of detection) and multistatic (areas of localization). The application WAB and WDDS as tools of threat detection in second and third zones is shown in the Fig. 5 for example of harbour approach and entry protection. The protection may be realized by: only WDDS, only WAB, WDDD and WAB in multi or bi mode. Due to first protection type is known and applied (with classic DDS usage) we focused our attention on application of WAB and protection system containing WAB and WDDS. 3.1 APPLICATION OF WAB WAB has been verified, in practice, during Tall Ship s Race 2009 in Gdynia Port (Poland). WAB has been installed as protection of entry to harbour channel see Fig. 7 and alarmed when any underwater or surface objects crossed the acoustic barrier. The echo signal of small passenger ships from Fig. 8 is shown on Fig

7 Volume 14 HYDROACOUSTICS Scuba divers echoes Fig. 7. WAB in Gdynia Port Fig. 8. Echo signal of ship from Fig. 7 Fig. 9. Scuba divers crossed the barrier (due to safety 2 scuba divers swimmed close each other) Due to small dimensions, easy installation, easy service and first of all high detection efficiency, WAB may be applied, as protection tool, in any places of harbour (basins, entries, ships at berth, etc.). WAB may operate both as individual device and as part of protection system. Fig. 9 demonstrates the possibilities of divers detection WAB has been installed at marina entry. 3.2 APPLICATION OF WDDS AND WAB It should be noted that (WDDS+WAB) system increase probability of detection and moreover each devices is the redundancy to second device for maritime critical high value assets (in times of Global War on Terror), installation this system should be obligatory; operation mode of the system should be settled after analysis configuration object to be protected, configuration of sea bottom and condition of propagation sound and environment (these condition should be monitored). 4. CONCLUSIONS 1. Presented devices, especially WAB and WDDS are the basic equipment especially designed to protect maritime critical infrastructure in the short range up to 1 km. Application of adaptative processing and possibility of matching parameters this devices to varying propagation condition as well as to configuration of a protected object enables the detection of underwater objects with small target strength in harsh acoustically environment both of shallow water and of very-shallow water (VSW up to 10 m depth). 2. Presented system of tethered sonobuoys with passive, active, multistatic and intercept sonars and jammer enables high probability of jamming or deceiving AUV/DDS/torpedoes sonar in the long range up to 5 km. The jammers generates the signals optimally matched to signal (frequency band and modulation) of threats ie. AUV/DDS/torpedo. The jammers possess the possibility of simultaneous jamming of homing sonar in few separated subbands. The jamming is effective for CW, FM and FSK signal modulation. 3. The effectiveness of tethered sonobuoys significantly increases if intercept sonar using multielements (high processing gain) array is applied. Received signal from homing sonar can be processed and generated as false echo. The deceiving effectiveness increases by processing gain improvement. 45

8 HYDROACOUSTICS Volume 14 REFERENCES [1] Elminowicz A., Okuniewski M., Rulaff B., Zaj czkowski L., A Comparison of Mono and Bistatic Acoustic Barriers Designed for Coastal Objects Protection, UDT Europe, Hamburg [2] Elminowicz A., M ci ski W., Okuniewski M., Wideband, Modular Diver Detection Sonar (DDS), SHA2010, Jurata. [3] Elminowicz A., Zaj czkowski L, Application of wideband DDS and acoustic barrier for underwater harbour protection, MAST 2010, Roma, November