Acoustics Session at SUT 2009
The Acoustics Session at the Subsea Technical Conference 2009 was chaired by Scott Elsom of L3 Nautronix with presentations by Grant Pusey, PhD student at CMST, Curtin University followed by Sandro Ghiotto, also of L3 Nautronix, and myself, coincidentally an alumnus of L3 Nautronix, representing ACOSP.
Grant spoke about transmission of acoustic signals over horizontal ranges, his work being part of the CSIRO Wealth from Oceans Flagship Cluster on Pipelines. The move towards platform-free fields, deeper water, rugged terrain and subsea facilities drives the need for reliable subsea communications and fault reporting.
The aims of Grant's work include characterisation of the horizontal performance of commercial underwater acoustic modems, and to demonstrate the feasibility of real-time measurement retrieval from subsea facilities. Vertical propagation is relatively easy, exhibiting clean impulse response of first and second reflections with hemispherical propagation.
Deep horizontal propagation, on the other hand, has sound concentrated in surface duct, or within a deep sound channel, and a complex impulse response that requires protocols which have been adapted to avoid intersymbol interference. Grant carried out simulation using the Bellhop program for Gaussian beam ray tracing on a sound field, based on bathymetry from 40km off Rottnest. The result was a negligible decrease in amplitude, i.e. low transmission loss (TL). The plan is to simulate underwater acoustic channels to be able to predict responses for various protocols and symbol codings.
He reported the preliminary results from a sea trial, an upwardly refracting sound speed profile (SSP) from measured conductivity, temperature and density (CTD) measured in situ; the raw data showing snapping shrimp and minke whales as well as recorder clipping. There was a bandwidth discrepancy and need to fix the wrong location of the the recorder using recorder localisation, exploiting TL=20log(R) spherical spreading. Modem reception was unsuccessful over about 500m; ambient noise recorder extremely helpful in assessing performance; 32-sample FFT average over 5ms, 15-24kHz comm band.
Sandro spoke about underwater acoustic surveillance networking - Autonomous Surveillance Sonar Network (AUSSNet) as a Defence Capability Technology Demonstrator (CTD) project. Credits for the paper included my friends and colleagues Mal Cifuentes, Eve Clark and Richard Jarvis among others from L3, in addition to Sandro, and two authors from DSTO (Defence Science Technology Organisation).
The objective of AUSSNet is to report on acoustic events during windows of opportunity while remaining covert. The system comprises a ship-based control and monitoring system (CMS), shore-based CMS, cluster of sensor node hydrophone elements, popup gateway connected to comms satellite via an Iridium RF channel; low frequency passive array (and active source); mid-frequency (14kHz) acoustic modem; array data processing - recording, beam forming, broadband detection, event characterisation and data reduction.
The 150m flexible line array is lightweight, low noise, 48 low frequency 10-500Hz anti-aliasing frequency, three heading sensors used to determine the array orientation. A "ping" shaped signal gives times of arrival for each sensor node used to estimate hydrophone element positions - calibrated for beam forming. Surveillance mode requires acoustic data - data recording and beam forming giving "speckle diagrams", i.e. freq-time, freq-bearing and bearing-time; subset of FRAZ (freq-azimuth) - only send bearing and frequency components of interest, needs about 1kbps bandwidth after data reduction. Track data fusion (lat, long) of events (targets) over about 1 year.
Background and issues:
Western Australia has a uniquely rich marine environment which must be protected - even as it is exploited commercially for fisheries, tourism, oil and gas industries, and scientific exploration. Wireless technologies are flexible to deploy for various applications for which we can envisage a common architecture.
Underwater communications - copper and fibre cable, electromagnetic and acoustic each has pros and cons for any given application. Pitched at a fairly high level, the only technical slide was to introduce m-sequences,(*) also called pseudo-random noise because its energy is spread across a broad band, hence "spread spectrum" - enables covert communications.
A common network architecture can be conceived that satisfies the requirements for subsea systems integration for a range of applications, increasing flexibility and lowering costs. A common problem of subsea processing in oil and gas is subsea integration, i.e. software and systems integration in the subsea environment. One application scenario is a subsea communication network involving multiple submerged surface and other participants - true network needs standards for discovery, channel and protocol negotiation.
Over the course of the conference, we have been hearing there are numerous technical problems needing innovative solutions in subsea processing - particular interest in software and systems integration to support automation. Safety and integrity in remote or hazardous locations is drawing towards "intelligent" autonomous systems. Subsea systems are particularly difficult to access after they have been commissioned so very good telemetry is important for pipelines and multiphase systems.
Message in a bottle (MIB) is a concept invented by Chris Skinner, also an initiator of ACOSP, to collect spatially and temporally diverse data, cheaply, by exploiting miniaturisation and adhoc networking to deploy a low-cost network. The bottles will be dropped in the ocean and will disperse over a wide area with winds and tides. WiFi networking, GPS position and time stamps will slowly deliver data to fill gaps in very large, marine datasets.
Data fusion is important to enable informed decision making, including in the oil and gas industry. We envisage GIS overlays of relevant datasets to fulfil the need for comprehensive sea floor, environmental and benthic(**) studies. In order to deliver these and other innovations, ACOSP has been conceived as a science-based, not-for-profit to facilitate technology transfer and to undertake projects for industry.
(*) m-sequence - maximum length sequence generated by linear feedback shift register; m registers gives sequence of length 2^m - 1.
(**) benthic - living on the sea floor; cf. pelagic fauna meaning organisms that live in the open ocean.
[I note a creative suggestion by Scott Elson in private conversation for the development of a system of commercial acoustic sensors for monitoring fields during extraction operations to optimise flow and extraction, where it is usual to survey 1-2 times per year.]
Grant spoke about transmission of acoustic signals over horizontal ranges, his work being part of the CSIRO Wealth from Oceans Flagship Cluster on Pipelines. The move towards platform-free fields, deeper water, rugged terrain and subsea facilities drives the need for reliable subsea communications and fault reporting.
The aims of Grant's work include characterisation of the horizontal performance of commercial underwater acoustic modems, and to demonstrate the feasibility of real-time measurement retrieval from subsea facilities. Vertical propagation is relatively easy, exhibiting clean impulse response of first and second reflections with hemispherical propagation.
Deep horizontal propagation, on the other hand, has sound concentrated in surface duct, or within a deep sound channel, and a complex impulse response that requires protocols which have been adapted to avoid intersymbol interference. Grant carried out simulation using the Bellhop program for Gaussian beam ray tracing on a sound field, based on bathymetry from 40km off Rottnest. The result was a negligible decrease in amplitude, i.e. low transmission loss (TL). The plan is to simulate underwater acoustic channels to be able to predict responses for various protocols and symbol codings.
He reported the preliminary results from a sea trial, an upwardly refracting sound speed profile (SSP) from measured conductivity, temperature and density (CTD) measured in situ; the raw data showing snapping shrimp and minke whales as well as recorder clipping. There was a bandwidth discrepancy and need to fix the wrong location of the the recorder using recorder localisation, exploiting TL=20log(R) spherical spreading. Modem reception was unsuccessful over about 500m; ambient noise recorder extremely helpful in assessing performance; 32-sample FFT average over 5ms, 15-24kHz comm band.
Sandro spoke about underwater acoustic surveillance networking - Autonomous Surveillance Sonar Network (AUSSNet) as a Defence Capability Technology Demonstrator (CTD) project. Credits for the paper included my friends and colleagues Mal Cifuentes, Eve Clark and Richard Jarvis among others from L3, in addition to Sandro, and two authors from DSTO (Defence Science Technology Organisation).
The objective of AUSSNet is to report on acoustic events during windows of opportunity while remaining covert. The system comprises a ship-based control and monitoring system (CMS), shore-based CMS, cluster of sensor node hydrophone elements, popup gateway connected to comms satellite via an Iridium RF channel; low frequency passive array (and active source); mid-frequency (14kHz) acoustic modem; array data processing - recording, beam forming, broadband detection, event characterisation and data reduction.
The 150m flexible line array is lightweight, low noise, 48 low frequency 10-500Hz anti-aliasing frequency, three heading sensors used to determine the array orientation. A "ping" shaped signal gives times of arrival for each sensor node used to estimate hydrophone element positions - calibrated for beam forming. Surveillance mode requires acoustic data - data recording and beam forming giving "speckle diagrams", i.e. freq-time, freq-bearing and bearing-time; subset of FRAZ (freq-azimuth) - only send bearing and frequency components of interest, needs about 1kbps bandwidth after data reduction. Track data fusion (lat, long) of events (targets) over about 1 year.
Background and issues:
- Sea Wasp CTD - sensor array and RF buoy.
- HAIL (Hydro-Acoustic Information Link) CTD - reliable, long range, low data rate.
- AUSSNet shift from HAIL rate x10 at 1/10 range.
- Propagation analysis.
- Time independent/reverberation analysis.
- Short symbol swamped by multipath interference.
- Real-time channel simulator for water depth and surface roughness.
- Array position calibration signals - loud, low frequency sound, good amplitude and phase linearity (to avoid harmonics), about 150 dB re 1µPa, bandwidth about 80Hz (really?) in 1 cubic foot (!).
- Popup gateway buoy mechanical design; about 50kg buoyancy.
- DC modem (used in trucks), single core shield and sea water return.
- Stabilisation floats for popup gateway UHF comms.
- Jetty shallow water (20m) and deeper water (150m) demo.
- Batteries about 300h (2 weeks).
Western Australia has a uniquely rich marine environment which must be protected - even as it is exploited commercially for fisheries, tourism, oil and gas industries, and scientific exploration. Wireless technologies are flexible to deploy for various applications for which we can envisage a common architecture.
Underwater communications - copper and fibre cable, electromagnetic and acoustic each has pros and cons for any given application. Pitched at a fairly high level, the only technical slide was to introduce m-sequences,(*) also called pseudo-random noise because its energy is spread across a broad band, hence "spread spectrum" - enables covert communications.
A common network architecture can be conceived that satisfies the requirements for subsea systems integration for a range of applications, increasing flexibility and lowering costs. A common problem of subsea processing in oil and gas is subsea integration, i.e. software and systems integration in the subsea environment. One application scenario is a subsea communication network involving multiple submerged surface and other participants - true network needs standards for discovery, channel and protocol negotiation.
Over the course of the conference, we have been hearing there are numerous technical problems needing innovative solutions in subsea processing - particular interest in software and systems integration to support automation. Safety and integrity in remote or hazardous locations is drawing towards "intelligent" autonomous systems. Subsea systems are particularly difficult to access after they have been commissioned so very good telemetry is important for pipelines and multiphase systems.
Message in a bottle (MIB) is a concept invented by Chris Skinner, also an initiator of ACOSP, to collect spatially and temporally diverse data, cheaply, by exploiting miniaturisation and adhoc networking to deploy a low-cost network. The bottles will be dropped in the ocean and will disperse over a wide area with winds and tides. WiFi networking, GPS position and time stamps will slowly deliver data to fill gaps in very large, marine datasets.
Data fusion is important to enable informed decision making, including in the oil and gas industry. We envisage GIS overlays of relevant datasets to fulfil the need for comprehensive sea floor, environmental and benthic(**) studies. In order to deliver these and other innovations, ACOSP has been conceived as a science-based, not-for-profit to facilitate technology transfer and to undertake projects for industry.
(*) m-sequence - maximum length sequence generated by linear feedback shift register; m registers gives sequence of length 2^m - 1.
(**) benthic - living on the sea floor; cf. pelagic fauna meaning organisms that live in the open ocean.
[I note a creative suggestion by Scott Elson in private conversation for the development of a system of commercial acoustic sensors for monitoring fields during extraction operations to optimise flow and extraction, where it is usual to survey 1-2 times per year.]
posted by Daniel Berinson at 2:28 PM
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