Underwater sounding systems and equipment

Marine Electronic Systems Department 21 I 2015

1 Operational and technical parameters in underwa- ter sounding

1.1 Polish Navy sonars (developed by the MES Department, ETI Faculty, GUT) Sonars developed by the MES Department, ETI Faculty, GUT All the MES sonar systems are in a fully operational service on board of Polish Navy anti-submarine warfare (ASW) and mine counter-measure (MCM) ships of both US and Soviet origin, meeting critical requirements of the highest technology readiness level (TRL 9).

I Long-range active ASW sonar II Medium-range MCM sonar III Helicopter dipping ASW sonar for submarine detection and tracking IV Passive ASW towed-array sonar V Side-scan MCM sonar

I Long-range active ASW sonar

The hull-mounted anti-submarine warfare (ASW) long-range, multi-beam sonar systems with full angular range of target track- ing are designed for the detection, localization and tracking of ships and other objects.

The long-range active ASW system is equipped with a cylindrical acoustic antenna cooperating with a beam-former, which allows simultaneous observation of the targets at all bearings around the ship. Automatic position stabilization of the antenna enables conducting a continuous survey of targets and determining their position with a good accuracy even at stormy weather. Very high energy, frequency- modulated sounding pulses used in sonar, combined with the correlation detection, assure a long range (up to 32 km), even in difficult propagation conditions with a high level of acoustic noise and reverberation. The system is equipped with a modern, ergonomic imaging assembly with 4 color display screens and control panels, operated by two operators.

1 R. Salamon & H. Lasota 21 I 2015 Echolocation Methods, Appendix A

Long-range active ASW sonar – operating consoles

Long-range active ASW sonar – parameters 1

Transmitter Operation frequency (nominal) 8,5 kHz Sweep frequency range 7,75 ÷ 9,25 kHz Transmitting beam horizontal width 360° Transmitting beam vertical width 12° ± 2,5° Number of transmitting channels 30 In-pulse electric power ≥ 10 kW Source level in dB re 1 Pa @ 1m ≥ 95 dB Antenna Ultrasonic transducer sensitivity 500 µV/Pa Receiving beam horizontal width 12° ± 2,5° Receiving beam vertical width 12° ± 2,5° Observation sector width 360°

2 R. Salamon & H. Lasota 21 I 2015 Echolocation Methods, Appendix A

Long-range active ASW sonar – parameters 2

Receiver Receiving band (3dB) 7,5 ÷ 9,5 kHz Number of receiving channels 30 Processing Beamforming technology digital, in the frequency-domain with second-order sampling Number of beams 90 Post-beamforming filtering for “chirp” signals digital correlation filtering in the time domain Post-beamforming filtering for “ping” signals envelope detection with digital low-pass filtering Operational range 1, 2, 4, 8, 16, 32 km Time-width of sounding pulses 50, 100, 200, 400, 800, 1600 ms Precision of distance measurement 1% of nominal range Precision of bearing measurement 1° Number of simultaneously tracked targets max. 12

II Medium-range MCM sonar

The mine counter-measure (MCM) sonar systems are designed for searching, detecting, and localizing bottom and contact mines, specifically in shallow waters with strong bottom reverberations and substantial deflection of acoustic wave propagation routes.

The MCM sonar is a multi-transmitting and multi-receiving beam systems designed using real-time microprocessor technology. On the transmitting side, the RDT technique of electronically rotated beam is used. The generation of sounding signals and rotation of electronic beam rotation is implemented using the direct digital synthesis (DDS) controlled by single-chip microprocessors. On the receiving side, a multi-processor DSP system is used for the algorithmic implementation of a beam-former. The latter is implemented in the frequency domain with the second order sampling and 14 bit resolution. A significant reduction of beam pattern side lobes both on the transmitting and receiving side is achieved. Two LCD monitors are used for supporting the console operators in detection, identification and tracking of objects. Information exchange between the sonar and other on-board systems is also provided.

3 R. Salamon & H. Lasota 21 I 2015 Echolocation Methods, Appendix A

Medium-range MCM sonar – operating consoles

Medium-range MCM sonar – parameters 1

Transmitter Operation frequency 41 ÷ 46 kHz Transmitting beam horizontal width 60° Transmitting beam vertical width 9° ± 1° Number of transmitting channels 36 In-pulse electric power ≥ 10 kW Source level in dB re 1 Pa @ 1m ≥ 110 dB Antenna Angular range of antenna declination (vertical) +5 lub -55° Angular range of antenna deflection (horizontal) ± 60° Receiving beam horizontal width 3° Receiving beam vertical width 9° ± 1° Angular width of simultaneous observation sector 60° Overall observation sector width 180°

4 R. Salamon & H. Lasota 21 I 2015 Echolocation Methods, Appendix A

Medium-range MCM sonar – parameters 2

Receiver Receiving band (3dB) 41 ÷ 46 kHz Number of receiving channels 36 Processing Beamforming technology digital, in the frequency-domain with second-order sampling Number of beams 61 Nominal operation ranges 100, 200, 400, 800, 1600 m Precision of distance measurement 0,5% of nominal range Precision of bearing measurement 1° A-type display target resolution 15, 37.5, 75 cm relative to the pulse-width after compression

III Helicopter dipping ASW sonar The dipping sonar for helicopters are new systems designed for detection and tracking submarines in both active and passive modes, equipped with an additional gradient passive array and a meter of speed velocity distribution in water. All electronic systems in the transducer, receiver and imaging system are designed using real-time microprocessor technology. The on-deck transmitter using a direct digital synthesis (DDS) modulator generates a broadband, frequency-modulated sounding signal. The sonar receives echo signals from a revolving ultrasonic transducer operating in the active mode and 4 signals from hydrophones of the passive array. After the first stage of preliminary magnification and analog filtering the received signals is subject to analog-to-digital conversion. Consequently, computer-aided processing and imaging is applied. The pulse compression technique used the in active mode significantly improves detection performance and increases the maximum range of detecting and tracking submarines, which can be displayed at console monitor.

Helicopter dipping ASW sonar – operating consoles

5 R. Salamon & H. Lasota 21 I 2015 Echolocation Methods, Appendix A

Helicopter dipping ASW sonar – parameters 1

Transmitter Center frequency of the sounding signal 15,5 kHz Sounding signal modulation linear frequency modulation (LMF) Sounding signal sweep range 14 to 17kHz Transmitting beam horizontal width 15° Transmitting beam vertical width 15° Number of transmitting channels 1 In-pulse electric power ≥ 1 kW Sounding pulse maximum energy 0.5 kJ Antenna Receiving beam horizontal width 15° Receiving beam vertical width 15° Observing sector angular range 360° Scanning technique mechanical rotation Receiver 3dB receiver band 14 to 17 kHz Number of receiving channels 1

Helicopter dipping ASW sonar – parameters 2

Processing Number of beams 1 Filtering for a “chirp” signal digital correlation filtering in the frequency domain Filtering for a “ping” signal envelope detection with digital low-pass filtering Operational range 1.5, 3, 6, 12 km Time-width of sounding pulses 50, 125, 250, 500 ms Precision of distance measurement 1% of nominal range Precision of bearing measurement < 5° Number of simultaneously tracked targets max. 4 Passive operation (intercept) Listening band 5 ÷ 300 Hz Listening time 1, 2, 4 s Bearing accuracy: SNR > 20dB, f = 100 Hz 1° SNR > 10dB, f = 100 Hz 3° Spectrum resolution 1, 0.5, 0.25 Hz

6 R. Salamon & H. Lasota 21 I 2015 Echolocation Methods, Appendix A

IV Towed-array passive sonar

The SQR-19PG is a passive anti-submarine warfare (ASW) towed- array side-scan sonar system designed for detecting and tracking submarines.

The SQR-19PG sonar is a low-frequency, broadband, passive real-time system designed using digital microprocessor technology. Increased angular resolution has been achieved by generating more receiving beams using effective methods of digital signal processing. New effective beam-forming algorithms for broadband signals, as well as methods for high-resolution spectrum estimation were developed and ap- plied. This results in a precise measurement of the incoming acoustic wave bearing. Novel algorithms for automatic tracking of selected targets were developed and applied. The adequate data transmission rate from the transducer array, thru the towing cable-line is assured by using the VDSL (Very High Speed Digital Subscriber Line) transmission technique.

Towed-array passive sonar

Towed-array passive sonar – parameters 1 Maximum operation depth 610 m Antenna modules filling liquid ISOPAR M Number of intercept bands 4 Frequency range of intercept bands: I: 10 – 175 Hz II: 175 – 350 Hz III: 350 – 700 Hz IV: 700 – 1400 Hz Effective antenna diameter in the specific bands: I: 195 m II: 97,5 m III: 48,8 m IV: 24,4 m Number of processed acoustic channels 120 Non-acoustic data transferred from the antenna immersion depth magnetic heading water temperature Number of beams formed 91 Observation sector 360° 7 R. Salamon & H. Lasota 21 I 2015 Echolocation Methods, Appendix A

Towed-array passive sonar – parameters 2

Bearing ambiguity port side / starboard ability to determine the heading side after a change of the course Target bearing accuracy from ± 2° in orthogonal axis up to ± 4° in sectors Motion parameters being measured current bearing bearing rate of change Listening time 1s, 2s, 4s Frequency resolution in specific bands for a given listening time: I: 1, 0,5, 0,25 Hz II: 1, 0,5 , 0,25 Hz III: 2, 1, 0,5 Hz IV: 4, 2, 1 Hz Resolution of analog-to-digital conversion 16 bis Sampling frequency of acoustic signals 4096 Hz Data transmission down-link band (to antenna) 1 ÷ 3,5 MHz Data transmission up-link band (from antenna) 3,8 ÷ 6 MHz Modulation scheme of digital signal transmission VDSL – QAM Number of simultaneously tracked targets max.. 16

V Side-scan MCM sonar

The side-scan mine counter-measure sonar systems use a very effec- tive underwater acoustic method for detecting and localizing mo- tionless underwater objects.

The side scan sonar is an active system designed using real-time microprocessor technology. Multi- element ultrasonic transducers are towed behind the ship above the bottom in a so-called tow fish. The beam patterns are diagonally directed to the bottom, on the right and left. The dynamic beam width control ensures constant linear resolution throughout the entire search operation. The echo signals from the towed transducers are converted into the digital form and sent to the on-board device using the VDSL (Very High Speed Digital Subscriber Line) data transmission technology. The survey results and other information are displayed on two-monitor operator console with such functions as zoom, short-term memory, dimensioning, multiple windows, etc. The side-scan method is used effectively in deep water and on the bottom (e.g. contact and bottom mines, shipwrecks, underwater structures). It enables identifying the bottom topography (for hydrographic purposes – making seabed maps) on the area of several hundred meters wide on both sides of the sounding vessel.

8 R. Salamon & H. Lasota 21 I 2015 Echolocation Methods, Appendix A

Side-scan MCM sonar – towfish and sounding exposition

Side-scan MCM sonar – parameters

Side-scan sonar: Source level (dB re 1 Pa @ 1m) ≥ 90 dB Time-width of sounding pulses 0.2, 0.5, 1, 2 ms Operation frequency on the left side of the towfish 154 ± 5 kHz on the right side of the towfish 175 ± 5 kHz Angular resolution in the horizontal plane dynamically varying with the range: 1° for 200 m constant 4° Linear resolution in the horizontal plane with dynamically varying beam width: ca. 3.5 m Range resolution: switched 0,5 or 1,5 m Vertical width of observation beam 50° Display exposition range 150 or 300 m Reservoir depth 5 to 100 m Towing speed max. 6 knots Echosounder: Operation frequency 200 kHz Reservoir depth 5 to 100 m

9 R. Salamon & H. Lasota 21 I 2015 Echolocation Methods, Appendix A

1.2 Acoustic camera Adaptive Resolution Imaging Sonar (Sound Metrics) http: ARIS camera http: Seeing with sound http: High-resolution sonar-images

Side-looking camera images

Acoustic camera parameters

10 R. Salamon & H. Lasota 21 I 2015 Echolocation Methods, Appendix A

Contents

1 Operational & technical parameters 1 1.1 Polish Navy sonars ...... 1 1.2 Acoustic camera ...... 10

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