Centre for Marine Science and Technology

Potential Research Topics for Prospective Higher Degree by Research Students

The Centre for Marine Science and Technology (CMST), at Curtin University of Technology, is a research centre active in the fields of hydrodynamics, marine acoustics and underwater technology (see www.cmst.curtin.edu.au ). With Curtin University offering a number of Postgraduate Scholarships (including APA and CUPS scholarships) for study commencing in 2005, this is a good opportunity to start a Masters or PhD degree at CMST.

Marine Acoustics

Professor Alexander Gavrilov's research interests are in experimental and theoretical underwater acoustics, oceanography, and signal processing. Possible research topics include:

Dr Rob McCauley is interested in supervising a PhD student on the following topic:

Hydrodynamics

Underwater Technology


Please note that APAs and CUPS scholarships are very competitive, and you will need a good first class honours degree (in a relevant area). For further information on Scholarships at Curtin, see http://www.cmst.curtin.edu.au/employment/index.html . Applications for APA and CUPS scholarships close in October each year. Other Scholarships have different closing dates.


See also:
* CMST Educational Activities
* Scholarships


For further details on our services please contact:

The Director
Centre for Marine Science & Technology
Curtin University of Technology
GPO Box U1987
Perth   Western Australia 6845
Tel: 08 9266 7380
Fax: 08 9266 4799
Email: Director

 

TITLE OF THE PROJECT:
Acoustic Observations of Indonesian Throughflow in the Timor Sea

OBJECTIVE:
The main objective of the project is to study the feasibility and efficiency of long-term, continuous remote acoustic observations of mesoscale and climatic oceanographic processes in the Timor Sea connected with variations in Indonesian Throughflow. This study will be performed by means of oceanographic data analysis and numerical acoustic modelling.

RATIONALE:
The water mass transport through the Timor Passage contributes roughly half of the integral transport from the Pacific to the Indian Ocean occurring within the Indonesian Seas [1], which is referred to as the Indonesian ThroughFlow (ITF). The ITF is an important element of the global conveyor belt which links the Pacific and Indian Oceans in the tropical latitudes [2]. Variable oceanic heat and freshwater flux into the Indian Ocean at the expense of the Pacific substantially affects atmosphere-ocean coupling with potential impact on the El Niño Southern Oscillations (ENSO) and monsoon phenomena. Observational and modelling studies suggest the IFT transport fluctuates in tune with ENSO: larger transport during La Niña conditions, smaller transport during El Niño [3]. The existing estimates of the climatic ITF transport varying from 10 to 15 Sv, are insufficiently definite until further more accurate and regular observations and determination of the IFT mean and variability are made. Furthermore, as shown from the Arlindo Makassar Strait time series [4], the ITF transport is linked to the thermocline depth and temperature: transport is smaller and thermocline shallower during El Niño [5]. An analysis of the XBT data collected for nearly 15 years, has shown that the upper thermocline temperature in the Indonesian Seas is highly correlated with ENSO (0.77 for the Southern Oscillation Index) [6]. Thus the ITF transmits equatorial Pacific El Niño and La Niña temperature variations into the Indian Ocean. Derived from sparse observations, the estimates of energy transport in the ITF are widely dispersed [7].
The Indonesian Seas are not just a passive channel linking the two oceans. Within the seas the ITF temperature and salinity stratification is significantly modified by tidal and wind-induced mixing and by sea-atmosphere fluxes, so that the thermohaline profile of the ITF waters entering the Indian Ocean is different from that at the Pacific entrance of the ITF. Moreover, strong variations of currents due to coupling of variable Indonesian Throughflow and the local sea/atmosphere processes produce strong internal wave activity and cause generation of strong solitons in the Indonesian Seas, which influences greatly the marine environment and may have a strong impact on the oil, fishing, and defence industries over the shelf zones.
Knowing long-term climatic changes and the shorter term mesoscale, seasonal and interannual variations of the heat flux and fresher Pacific water transport via the ITF is important for (1) building adequate models of atmosphere-ocean coupling in the Pacific and Indian Oceans, (2) more accurate prediction of climatic changes over South-eastern Asia and Australia, and (3) prediction of mesoscale activity (tidal, internal waves) within the seas. Local direct observations of the water temperature/salinity and currents with the use of moorings equipped with ADCPs, current meters and CTDs, and deployed within the Indonesian passages can provide us with some estimates of the ITF transport and thermohaline fluxes. Such observations in the Timor Sea are planned for a 5-year special project as part of the West Australia Global Ocean Observation System (WAGOOS) program. However, local and sparse oceanographic measurements via conventional means cannot give us sufficiently accurate estimates of the integral oceanographic characteristics (water temperature, thermohaline structure, current) over large regions of the seas and may be incapable of detecting some important local phenomena that arise aside from moorings’ locations.
Up-to-date methods of ocean acoustic tomography allow us to remotely observe variations of the integral temperature within water layers over hundreds and even thousands of kilometres [8] along the acoustic paths. Acoustic methods are also capable of resolving the thermocline depth and, under certain conditions, horizontal gradients in the temperature field [9]. Moreover, acoustic observations on a pair of adjacent acoustic paths across a passage give us a way to monitor the average currents along the passage using either tomography or the so-called shadowgraph [10] and scintillation [11] methods. Reciprocal acoustic transmissions along a single path that crosses the passage diagonally may yield even more accurate measurements of the integral current along the passage [12].
Equipped with long-life autonomous acoustic sources and autonomous receive arrays at the opposite brims of the passage, the acoustic tomography observational system may operate for years, providing us with regular measurements of the water transport and integral heat flux. Such a system may also give us a way to monitor internal wave activity and remotely detect passages of solitons. The feasibility and advantages of an acoustic thermometry system built with the use of an autonomous acoustic source have been proven by the results of the Arctic Climate Observations using Underwater Sound (ACOUS) experiment [9]. In contrast to the Arctic Ocean with a year-round ice cover, the sea surface in the Indonesian seas is always free, which makes it possible to transmit the acoustic data from the receiving array via a radio-buoy to the shore.
The Timor Passage is assumed to be a suitable testing area to examine the method of acoustic tomography for remote observations of the Indonesian Passages. The width of the deep-water Timor Trough at its western sill is about 50-60 km. For acoustic tomography measurements on such relatively short paths, it is appropriate to transmit low-level signals at frequencies of hundreds of Hz. The low-power acoustic sources operating at such frequencies are of high efficiency, reliable, and not expensive. They can be powered from batteries for many years. The transmitted signals will be received on vertical arrays. If the array spans most of the water column, filtration of separate acoustic modes in the received signals will be used. For shorter arrays, the acoustic ray approach to the inverse problem of acoustic tomography can be applied [13].

PROJECT DETAILS
The project proposed is a new research program in Australia. Although the objectives of this project are related to some extent to those of the WAGOOS Timor Sea oceanographic project, it is not a part of the WAGOOS program at this first stage of feasibility research. The next step of feasibility research will be experimental studies in the Timor Sea on one-two acoustic paths, which would be conducted in cooperation with the U.S. partners (SAIC, Scripps, WHOI, and MIT) and the Russian partners (Russian Academy of Science). If the results of feasibility research are positive, the further long-term acoustic installations and observations could be conducted in the framework of the Timor Sea project of the WAGOOS program.

RESEARCH PLAN:
The study requires the following tasks to be performed:
1. Analysis of historical oceanographic data collected in the Timor Sea. The typical (climatic) temperature, salinity, and sound speed profiles in the Timor Sea will be determined. The variations of the thermohaline parameters relative to the mean climatic values, due to the tidal fluctuations, seasonal cycles, and interannual changes, will be estimated. The data on currents (mean values, vertical profiles of magnitude and direction) will be assembled and analysed. Also the bathymetry and acoustic properties of the sea floor in the Timor Sea will be analysed.
2. Modelling of acoustic propagation across the Timor Passage at different frequencies. Both the acoustic normal mode theory and the acoustic ray approximation will be used for numerical modelling. The effects of mode coupling on the results of acoustic tomography measurements will be examined. Acoustic fluctuations due to probable variations of the T-S and sound speed profiles will be modelled.
3. Modelling of the acoustic tomography scheme. The optimum frequency band and the form of the acoustic tomography signal to be transmitted across the Timor Passage will be determined. The methods of signal processing on the receiving array will be considered and up-to-date approaches to solving the inverse problem of acoustic tomography will be examined for the Timor Sea environmental conditions.
4. Modelling of acoustic observations of the integral current along the Timor Passage. A system of two adjacent acoustic paths that cross the passage will be considered to determine the most robust method of acoustic measurements of the integral currents both over the main part of the water column and within particular layers, such as thermocline and intermediate water layer.

REFERENCES:
1. R. Molcard and M. Fiuex, “The Indo-Pacific throughflow in the Timor Passage ”, J. Geophys. Res., v.101(C5), pp.12,411-12,420 (1996);
2. A.L. Gordon, “Interocean exchange of thermocline water ”, J. Geophys. Res., v.91, pp.5,037-5,046 (1986);
3. G. Mayers, “Variation of the Indonesian throughflow and the El Niño Southern Oscillation ”, J. Geophys. Res., v.101(C5), pp.12,255-12,263 (1996);
4. A.L. Gordon, R.D. Susanto, A. Ffield, and D. Pillsbury, “Makassar Strait transport: preliminary Arlindo results from MAK-1 and MAK-2 ”, WOCE Newsletter, issue 33 (1998);
5. N. Bray, S.L. Hautala, and J.L. Reid, “The distribution and mixing of Pacific water masses in the Indonesian Seas”, J. Geophys. Res., v.101(C5), pp.12,375-12,390 (1996);
6. A. Ffield, K. Vranes, A.L. Gordon, R.D.Susanto, and S.L. Garzoli, “Temperature variability within the Makassar Strait”, Geophys. Res.Lett., 27, pp.237-240 (2000);
7. A.L. Gordon, “Interocean exchange”, in Ocean Circulation and Climate, chapter 4.7, Academic Press, 2001, pp.307-310;
8. B. Dushaw, et al, “Observing the Ocean in the 2000’s: A Strategy for the Role of Acoustic Tomography in Ocean Climate Observation”, Proceedings OCEANOBS 1999, St. Raphael, France;
9. A.N. Gavrilov and P.N. Mikhalevsky, “ Recent results of the ACOUS (Arctic Climate Observations using Underwater Sound) Program ”, Acta Acustica united with Acustica, v.88, No.5, pp.783-791 (2002);
10. B.J. Ushinsky and B. Pruin, “A shadowgraph method for ocean acoustics”, Waves in Random Media, 1999, pp. R1-R24;
11. S. F. Clifford and D. M. Farmer, “Ocean flow measurement using acoustical scintillation”, J. Acoust. Soc. Am. 74, pp. 1826-1832 (1983);
12. O.A. Godin, “Sound in a time-dependent ocean: Implications on acoustic tomography of currents”, J. Acoust. Soc. Am., v. 108, N 5, pp. 2544-2550 (2000);
13. W. Munk, P. Worcester, and C. Wunsch, Ocean Acoustic Tomography, Univ. Press, Cambridge, 1995;
14. P. N. Mikhalevsky, A. N. Gavrilov, and A. B. Baggeroer, “The Transarctic Acoustic Propagation Experiment and Climate Monitoring in the Arctic”, IEEE J. Oceanic Eng., v. 24, No. 2, pp. 182-202 (1999);
15. A. J. Duncan and R. D. McCauley, “Modeling seismic survey noise exposure in the Timor Sea”, Centre for Marine Science and Technology, Curtin University of Technology, Report number C99-2, February 1999.

TITLE OF THE PROJECT:
Long-range acoustic observation of Antarctic ice rifting and calving events using the CTBT hydroacoustic listening station off Cape Leeuwin

Abstract
The project involves the use of the Comprehensive Nuclear-Test-Ban Treaty hydroacoustic listening station off Cape Leeuwin, Western Australia, to remotely detect and analyse rifting and calving events on the Eastern Antarctic ice shelves. This new type of observation is expected to provide an efficient method for long-term continuous monitoring of climatic change in the Antarctic ice sheet.

Objectives
The objective of the project is to study the feasibility and efficiency of long-term, continuous remote acoustic detection, classification and statistical analysis of the rifting and calving events on the Antarctic ice shelves using the Comprehensive Nuclear-Test-Ban Treaty (CTBT) listening station HA01 deployed south-west of Cape Leeuwin. The calving activity of the Antarctic ice shelves is one of the major indicators of global climate change [1]. The ice shelf calving events observed for the past two decades have been extraordinary, and have led to dramatic changes in the Antarctic ice sheet. The total ice mass discharge due to those events is considerably greater than the average Antarctic snow accumulation [2]. The enormous amount of ice discharged from several recent, most dramatic events of ice calving is of major concern for scientists. However, it is still a subject of discussions whether the calving rate is staying within the natural bounds or steadily increasing. While the massive calving events are well observed post factum from satellites, numerous ice shelf breaks of smaller volumes are not monitored and statistically analysed. Moreover, the calving events are preceded long before by ice rifting, which is not remotely observable by conventional means [3]. To predict the further disintegration of the Antarctic ice sheet, it is expedient to gather statistics of ice cracking all around the Antarctic shelf. Seismo-acoustic observations on the Antarctica ice sheet are capable of monitoring the events of ice cracking. A network of seismo-acoustic stations deployed all over the regions of intense ice motion and calving can provide data for a statistical analysis of ice rifting. In the joint Australian-US experiment on the Amery Ice Shelf, seismo-acoustic recordings are accompanied with geodetic observations of ice shelf fractures by measuring the horizontal and vertical movements across the fracture zone with the use of GPS units [4].
An additional and potentially, very efficient approach to monitoring ice shelf cracking in Antarctica is long-distance acoustic observations using existing hydroacoustic listening stations installed in the Pacific, Indian and Atlantic Oceans. Cracking and calving of the ice shelves produces intense low frequency elastic (both compressional and shear) waves that are transformed into acoustic signals in the surrounding water. These low frequency acoustic signals can propagate over thousands of kilometres in the ocean. The source of the signal, i.e. the ice cracking event, can be located using either a pair of remote hydroacoustic receiving stations or a single station that consists of several receivers separated horizontally enough to form a sharp directivity pattern.
The HA01 CTBT hydroacoustic station off Cape Leeuwin consists of 3 individual hydrophones that are horizontally separated from each other and are continuously listening to the ocean at low frequencies. The acoustic recordings have been collected since April 2002. In the framework of this project, it is planned to process and analyse both the recordings previously accumulated and the current recordings for the subsequent years.
The results of a statistical analysis of the detected ice cracking events will be compared to the data of the current ASAC Project No.2338 (Rifting and Calving on the Amery Ice Shelf).
The results of signal processing and the statistical analysis will be published in well-known, peer-reviewed national and international scientific journals in accordance with CTBT regulations on the data distribution.
Conclusions on the capability of long-distance acoustic observations of Antarctic ice shelf rifting and calving will be formulated in the final report.

Project design
1) Data Collection
The hydroacoustic listening station HA01 was installed south-west of Cape Leeuwin in the Indian Ocean as part of the International Monitoring System of the CTBT Organization [5]. The station consists of three hydrophones (triad) spaced approximately 1 km from each other. The hydrophones are submerged near the SOFAR acoustic channel axis so that they are capable of long-range reception. The spectrum bandwidth of the receivers is from fractions of 1 Hz to 100 Hz, which is optimum for reception of pulse-like signals of ice cracking. The sampling rate of the recordings is 250 Hz. The acoustic sensitivity of the station is high, because the dynamic range of the receiving system is 110 dB. The station is continuously listening to the ocean and has an expected operating lifetime of at least 25 years. The acoustic signals are transmitted in real time to the International Data Centre of CTBT Organisation in Vienna and Geoscience Australia where they are stored. The recordings will be copied on DVD/CD-R disks and forwarded to CMST, Curtin University of Technology for processing and analysis.

2) Data analysis
The spectrum of ice cracking signals is broad. It is expected that the spectrum of those signals propagated over thousands of km in the ocean acoustic channel will be bounded within approximately 5 to 60-70 Hz due to interaction with the seabed at lower frequencies and scattering by the surface waves at higher frequencies. The HA01 triad geometrics are good enough to enable accurate bearings of the acoustic sources with such broad spectra using correlation analysis. Also it will be possible to estimate the range from the source, if the high frequency component of the signal spectrum (of tens Hz) is not scattered and decorrelated.
The first step of signal processing includes detection and preliminary identification of the hydroacoustic signals from the ice cracking events on the Antarctic ice shelves, which is based upon the azimuthal location of the signal arrivals and the estimation of range from the signal sources. Then a spectral and correlation analysis will be conducted to determine the peculiarities of the signals from the ice cracking/calving events. Finally, those events will be statistically analysed to determine their spatial and temporal distribution.

3) Rationale
The overall parameters of the CTBT station HA01 are nearly ideal for long-term acoustic observation of ice cracking events along the Antarctica shelf within the sector from approximately 50E to 150E. The range from the station to the Antarctica shore varies within this sector from 3800 km to 5000 km. Several experiments in the ocean have proven that it is possible to receive and process low frequency signals at such long distances from acoustic sources which have signal levels considerably lower than those expected for the ice cracking events [6-9]. Moreover, a preliminary analysis of the HA01 and HA08 (off Diego-Garcia Island) acoustic recordings has shown that some of the registered acoustic signals arrived from the Antarctica shore and could be identified as signals from the ice shelf disintegration events [10]. Signals from the icebergs in the Ross Sea were detected by the seismic stations of the Polynesian network and in the Cook Islands [11].


Research Plan:
Year 1:
1. Collection and processing of HA01 acoustic recordings. The aim of the signal processing will be to distinguish the acoustic signals generated by ice cracking and calving events from other natural signals in the ocean, including biological noise, and signals from volcanic and seismic events. This will include location of the detected signals in both azimuth and range using spatial processing of the signals from the triad.
Preprocessing of the acoustic recordings and preliminary sorting of the detected events will be carried out by a research assistant. The final acoustic analysis of the detected events will be performed by the chief investigator.
2. Modelling of acoustic propagation from the Antarctica shelf to the HA01 hydroacoustic station. Adiabatic and coupled-mode models of acoustic propagation will be used for numerical prediction of acoustic transmission loss, spectral and correlation characteristics and dispersion effects for the signals propagated from different locations of possible ice cracking events along the Antarctic ice shelf sector that can be observed from Cape Leeuwin. Blockage of the acoustic propagation from Antarctica to the HA01 station by islands and seabed ridges will be investigated.

Year 2:
1. Collection and processing of HA01 acoustic recordings. Processing and analysis of the accumulated and current HA01 signal recordings will be continued with the use of the results of acoustic propagation modelling. Collection and processing of the acoustic recordings will be performed by a research assistant.
2. An algorithm for automatic recognition and processing of the signals from the ice cracking/calving events will be developed.

Year 3:
1. Collection and processing of HA01 acoustic recordings. Processing and analysis of the current HA01 signal recordings will be continued with the use of the results of acoustic propagation modelling.
Collection and processing of the acoustic recordings will be performed.
2. A statistical analysis of recorded ice cracking events will be carried out.

5) Details of shared resources
The objective of Antarctic Science Project No. 2338 is to monitor the processes of ice shelf rifting and calving using GPS receivers deployed on ice for observations of the horizontal and vertical movements across the ice fracture zone. These observations are planned to be accompanied by seismo-acoustic recordings of ice cracking. The data recording time is about 2 months. The Amery Ice shelf lies within the zone of acoustic vision from Cape Leeuwin. Therefore it will be possible to compare the results of remote hydroacoustic observations with those obtained locally via seismometers, which would provide an excellent test of the hydroacoustic method.

References:
1. Doake, C.S.M. & Vaughan, D.G., “Rapid disintegration of the Wordie Ice Sheet in response to atmospheric warming”, Nature, v.350, pp. 328-330 (1991);
2. Allison, I., “The Antarctic cryosphere: evidence of the impacts of change and strategies of detection”, in Impact of Climate Change on Antarctica – Australia, AGPS, Canberra, 1992
3. Perkins, S., “An armada of ice sets sail for the new millennium”, Science News, v.159, No.14, p. 298 (2001);
4. http://www.aad.gov.au/default.asp?casid=4883 ;
5. http://www.css.gov/HYDRO/doc/Cape_Leeuwin.html ;
6. Munk, W. & Baggeror, A., “The Heard Island papers: A contribution to global acoustics”, J. Acoust. Soc. Amer. V.96, pp. 2327-2329 (1994);
7. Burenkov, S.V., A.N. Gavrilov, A.Y. Uporin, A.V. Furduev, "Heard Island Feasibility Test: Long Range Sound Transmission from Heard Island to Krylov Seamount", J.Acoust.Soc.Am., v.96, No. 4, pp.2458-2464 (1994);
8. Dushaw, B. D., Bold, G., Chui, C.-S., Colosi, J., Cornuelle, B., Desaubies, Y., Dzieciuch, M., Forbes, A., Gaillard, F., Gould, J., Howe, B., Lawrence, M., Lynch, J., Menemenl is, D., Mercer, J., Mikhaelvsky, P., Munk, W., Nakano, I., Schott,F., Send,U., Spindel,R.,
Terre, T., Worcester, P. & Wunsch, C., “Observing the ocean in the 2000's: A
strategy for the role of acoustic tomography in ocean climate observation”, in C. J.
Koblinsky and N. R. Smith (Eds.) Observing the Oceans in the 21st Century, pp.391-418.
GODAE Project Office, Bureau of Meteorology: Melbourne (2001);
9. Mikhalevsky, P. N., Gavrilov, A. N. & Baggeroer, A. B., “The Transarctic Acoustic
Propagation experiment and climate monitoring in the Arctic”, IEEE Journal of Oceanic
Engineering, 24(2), pp.183-201 (1999);
10. Lawrence, M., Presentation at the CTBT Hydroacoustic Workshop, Hobart, May 2003;
11. Okal, E.A., Talandier, J. & Hyvernaud, O., “Hydroacoustic signals detected in Polynesia from mega-icebergs drifting in the Ross Sea, Antarctica”, Annual Meeting of the Seismological Society of America, Victoria, B.C., April 2002

TITLE OF THE PROJECT:
ESTIMATING DIRECTIONAL WAVE SPECTRA WITH AN ARRAY OF NON-DIRECTIONAL CMST WAVE RECORDERS AND WIND WAVE SPECTRAL MODELLING NEARSHORE

Abstract
The knowledge of the state of sea surface is important in a number of marine applications. Particularly, it is vital for evaluating loads to and predicting motions of surface vessels, as well as for coastal and ocean constructions. A thorough estimate of the sea state is usually obtained through the two-dimensional distribution - in the space of frequency and direction - of wave energy. A record of water surface elevation at one point can provide sufficient information for estimating one-dimensional frequency spectrum. To derive an exact directional spectrum, the observations of surface elevation from an infinite number of wave recorders are needed. In practice, directional spectra estimates of acceptable accuracy are produced using measurements of a limited number of wave gauges. A low cost easy-to-deploy ocean wave recorder and processing software, which have been developed and refined at the Centre for Marine Science and Technology, can be readily adopted for such explorations. The instrument is in regular use for ships trials and research projects, which include verification of the ERS-1 satellite synthetic aperture radar spectral estimates. Directional wave spectra obtained from the wave records can readily be used either as the verification data to compare with outcomes of global wave models (e.g. AUSWAM) or as the forcing function in numerical experiments with spectral phase-averaging (e.g. SWAN) and/or phase-resolving (e.g. REF/DIF) models to study wind wave propagation at fine scales in coastal areas, harbours and ports.

Therefore, this study aims at following:
1) To collect and process measurements from field campaigns with deployments of CMST wave recorders. This will result in forming data archives prepared for further investigations.
2) To study the theoretical background of the directional spectra computation and to develop computer programs to estimate the wave spectra from the CMST recorders’ observations. The computer codes and spectra estimates will be the major outcomes at this stage.
3) To compare the estimated wave spectra with global wave modelling results in order to correct the latter on the basis of the former.
4) To refine coarse grid global wave modelling output for local spatial scales using phase-averaging and/or phase-resolving wind wave models.

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