Low Energy, Passive Acoustic Sensing

for Wireless Underwater Monitoring

Networks

Gavin Lowes

Jeff Neasham, Richie Burnett, Charalampos Tsimenidis

INTRODUCTION TO PROJECT

• EPSRC sponsored £1.3m three year project in

collaboration with Newcastle University, Heriot-Watt

University and the University of York

• Development of affordable technology for large

scale, smart wireless sensing networks to be

deployed in the oceans.

PROJECT DATA COMMUNICATION ENABLER

Low power, low cost miniature underwater

acoustic modem developed by Newcastle

University Sensors, Electromagnetics and

Acoustics Laboratory (SEALab)

Supply Voltage 3 – 6.5V

Supply Current Listening: 2.5mA

Receiving: 5mA

Transmitting: max 300mA

Standby/sleep: < 100uA

Acoustic

directivity

Near omnidirectional

Acoustic data

rate

640 bits/s, unicast and broadcast

data messages up to 64 bytes

Max range 3.6 km

Addressing Up to 256 units

Range variance ~10 cm

RS232

interface

9600 Baud, 8-bit, no parity, 1

stop bit, no flow control

AIMS AND OBJECTIVES

Research and develop the SENSOR PAYLOAD for the USMART project

• Detect acoustic signals of interest reliably and at low-power

• Classify successfully detected signals of interest

• Transmit compressed data through an underwater network of nodes

• Maintain a low-power, low-cost development approach

Signals of Interest include… Cetaceans, VESSEL DETECTION, Underwater Threats, Subsea Assets, Noise Pollution

LOW POWER VESSEL DETECTION

DETECTION SOURCE MOTIVATION

(1)Propeller Cavitation - Formation and

collapse of bubbles in water at or on the

surface of a rotating propeller, occurring

when the pressure falls below the

vapour pressure of water.

(1) https://www.maritime-executive.com/article/us-japan-and-germany-join-australian-stealth-research

(2) https://www.bbc.co.uk/news/uk-england-kent-46679414

(2)

• Detection of vessels which are being used

to carry out dangerous and illegal functions.

• Examples include – Drug trafficking,

defence related threat detection, border

control.

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=2ahUKEwi2g46EgpTlAhVCzoUKHVDxCuMQjRx6BAgBEAQ&url=https://www.logolynx.com/topic/bbc%2Bnews%2B24&psig=AOvVaw3opsn5rZbkf2CQIvW8BYV3&ust=1570876739478845https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=2ahUKEwi2g46EgpTlAhVCzoUKHVDxCuMQjRx6BAgBEAQ&url=https://www.logolynx.com/topic/bbc%2Bnews%2B24&psig=AOvVaw3opsn5rZbkf2CQIvW8BYV3&ust=1570876739478845

SIGNAL DETECTION METHOD

Cavitation Signal

Band Pass Filter

Rectifier

Envelope Tracker

Fast Fourier Transform

DEMON Spectrum

Detection of Envelope Modulation on Noise (DEMON)

VESSEL DETECTION CRITERIA

• The vessel detection algorithm searches for consistent DEMON spectral peaks.

• A linear fit is applied to the frequency peak history over a user defined time frame.

• Standard Error Of the Estimate (SEOE) is calculated to determine how well the actual recorded samples 𝑦 relate to the estimated samples ො𝑦.

• 𝑆𝐸𝑂𝐸 = σ( ෝ𝑦 −𝑦)2

𝑛 −2

• The acceptable SEOE value is one of a variety of user defined system thresholds to tune the algorithm to specific applications.

RECEIVE AND TRANSMIT SYSTEM DIAGRAM

VESSEL SIGNAL

DATA TRANSMITTED

DETECTION

ALGORITHM

DESIGN CHARACTERISTICS

• Integrated with existing acoustic

communication device via add-on signal

processing PCB

• Shared Transducer for Receive and Transmit

• Power consumption - 11.4mW using a 6V

supply.

• Cost - less than £40 in quantities of 200 units.

• Cable Connection to Depth Rated Battery

Pack

• Encapsulated in Acoustically Favourable

Polyurethane for Underwater Applications

DATA TRANSMISSION

RECEIVED SIGNALDATA TRANSMISSION

• Once the algorithm decides a vessel has been

detected, data is sent acoustically through the water

using the acoustic communication device developed by

Newcastle University.

FIELD TRIAL – BIOGRAD NA MORU, CROATIA

Positive detection

of RHIB at approx.

1.6km.

Detection data

transmitted

acoustically over a

200m range back

to the receiver

station.

DECODED DETECTION DATA

NORTH SEA DEPLOYMENT – NOVEMBER 2019

WIFI LINK University Marine Station Newcastle University CampusDATA BUOY

HYDROPHONE 1

HYDROPHONE 2

ACOUSTIC MODEM 1

ACOUSTIC MODEM 2

Newcastle University - Acoustic Network GatewaY (ANGY)

1km (potential for up to 3.6km in single hop)10m from

sea floor

Battery Pack

Vessel Detector/

Acoustic Modem

30

m d

ep

th

Acoustic Data Transmission

NORTH SEA DEPLOYMENT – NOVEMBER 2019

CONCLUSIONS

This presentation had demonstrated the following:

• Ability to detect propeller cavitation signals using DEMON methodology.

• Implementation of DEMON methodology using analogue electronics.

• The vessel detection criteria to decide whether a vessel is present.

• Low-power, low-cost project ethos has been maintained.

• Data communication using integrated underwater acoustic modem.

• Field trial results proving the system for vessel detection and communication.

FUTURE WORK

• Use Low-Power vessel detector to wake-up a higher power classification mode.

• Classification mode will perform time-frequency analysis on full spectrum signal.

• Spectral feature extraction will be used to classify specific vessels based on their

acoustic signature.

• Expand the current system to also detect divers.

• Explore other applications such as cetacean whistle detection/classification and

subsea asset monitoring.

• Research the feasibility of adding other sensors to the system (magnetometer,

temperature etc) to offer more data to the end user application.

• Test the system as part of the USMART underwater network.

THANK YOUhttps://research.ncl.ac.uk/usmart/ G.Lowes2@Newcastle.ac.uk