C14-015 Rigby.indd - Informit

technical paper

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Real-time marine observing systems: Challenges, benefits and opportunities in Australian coastal waters* P Rigby†, CR Steinberg, DK Williams, G Brinkman, R Brinkman and H Tonin Australian Institute of Marine Science, Townsville, Queensland D Hughes CSIRO Wealth from Oceans Flagship, Hobart, Tasmania

ABSTRACT: The Australian Integrated Marine Observing System (IMOS) is funded by the Australian Government, and designed to be a fully-integrated national array of observing equipment to monitor the open oceans and coastal marine environment around Australia. IMOS delivers physical, chemical and biological data comprising of observations from a wide spectrum of platforms including weather stations, oceanographic moorings, underway ship observations, seagliders, ocean surface radar, satellite image reception and reef based sensor networks. When data from ocean observing systems can be provided in near real-time, the operational aspects are further enhanced and provide potential for a range of value added products to be developed. Here we provide three examples of co-invested partnerships that have facilitated the development of real-time moored ocean observing systems in the coastal zone, operated by the Queensland IMOS node. For each of these examples, the project is introduced, a detailed technical description of the system is provided, operational aspects are summarised, and the uptake of data from stakeholders is discussed. These examples demonstrate the benefits of having a national collaborative approach to marine observing with a clear focus on open access to data. It is also demonstrated that the benefits and opportunities offered by real-time ocean observing can outweigh the technical challenges of developing and maintaining these complex systems. KEYWORDS: Ocean observing system; marine measurements; real-time observations; oceanography; hydrodynamic modelling; moorings; instruments; sensors; metocean. REFERENCE: Rigby, P., Steinberg, C. R., Williams, D. K., Brinkman, G., Brinkman, R., Tonin, H. & Hughes, D. 2014, “Real-time marine observing systems: Challenges, benefits and opportunities in Australian coastal waters”, Australian Journal of Civil Engineering, Vol. 12, No. 1, pp. 83-99, http://dx.doi.org/10.7158/C14-015.2014.12.1.

1

INTRODUCTION

The wellbeing and prosperity of Australia is strongly linked to the ocean, with most of the population living in highly urbanised centres along a narrow coastal strip. Infrastructure development and population growth along the coast has already, and will continue to place growing pressure on the marine environment and its natural resources, requiring a *

Reviewed and revised version of paper first presented at Coast and Ports Conference 2013, 11-13 September 2013, Sydney.

†

Corresponding author Paul Rigby can be contacted at [email protected].

© Institution of Engineers Australia, 2014

knowledge-based approach to the management of risks to these assets. Decision making around sea level rise, storms and extreme events, shipping and maritime operations, fisheries and aquaculture, and marine park zoning must be informed by an understanding of coastal ocean processes, their drivers, and ecosystem responses. This requires both coastal and open ocean observations (Moltmann et al, 2013). Since 2007, these observations have been provided by the Integrated Marine Observing System (IMOS) (IMOS, 2014a). IMOS was established under the National Collaborative Research Infrastructure Australian Journal of Civil Engineering, Vol 12 No 1

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“Real-time marine observing ...” – Rigby, Steinberg, Williams, Brinkman, Brinkman, Tonin & Hughes

Strategy (NCRIS), extended and enhanced through the Education Investment Fund in 2009, and further extended under the Collaborative Research Infrastructure Scheme and NCRIS in 2013. It is a nationally managed and distributed set of equipment established and maintained at sea, providing streams of in-situ oceanographic data and information services that collectively will contribute to meeting the needs of marine research in both open oceans and coastal oceans around Australia. Combined with satellite data, it provides essential in-situ data to understand and model the role of the oceans in climate change, and data to initialise seasonal climate prediction models. If sustained in the long term, it will permit identification and management of climate change in the coastal marine environment. In the shorter term, it will provide an observational nexus to better understand and predict the fundamental connections between coastal biological processes and regional/oceanic phenomena that influence biodiversity. While IMOS was originally designed to support research, the data streams are also useful for many societal, environmental and economic applications, such as management of marine natural resources and their associated ecosystems, support and management of coastal and offshore industries, safety at sea, marine tourism and defence. Under direction of the IMOS Office, nine national facilities make the observations using different components of infrastructure and instruments. The observing facilities include three for bluewater and climate observations, three for coastal ecosystems and three for coastal currents and water properties. One of the largest facilities in terms of deployed assets is the Australian National Moorings Network (IMOS, 2014b), which comprises a series of National Reference Stations (NRS) and regional moorings designed to monitor particular oceanographic phenomena in Australian coastal ocean waters. The moorings network as a whole measures physical, chemical and biological parameters of these waters. The NRS are designed to deliver long-term time series observations and they significantly increase the number of such observations available for Australia both in terms of variables recorded, temporal distribution and geographical context. Prior to IMOS, existing reference stations were simple waypoints where regular boat-based water samples were taken. The inclusion of moored instrumentation at these sites significantly improves the quality and quantity of data that can be collected and used to inform management. The regional moorings monitor the interaction between boundary currents and shelf water masses and their consequent impact upon ocean productivity and ecosystem distribution and resilience. Depending on the site, the moorings remain in-situ for 3-12 months, at which time the mooring is recovered and the data is downloaded, processed Australian Journal of Civil Engineering

into a standard format, quality controlled and published in the public domain (IMOS, 2014c). These standard moorings are referred to as delayed mode, as there can be a delay of up to 15 months from the time that an observation is made, to the time when this observation is made available to an end user. For a subset of these moorings, it was deemed highly beneficial to the community if the data could be broadcast in near real-time. These key sites have been upgraded with the addition of a telemetered surface buoy for data transmission; this allows data to be published online minutes after the observation is made. The next three sections describe and discuss three examples of operating real-time oceanographic stations situated at Darwin Harbour, the Yongala wreck near Townsville, and the Palm Passage site on the Great Barrier Reef (GBR). 2

DARWIN NATIONAL REFERENCE STATION

2.1

Background

Darwin Harbour is the main shipping port for the Arafura Timor Seas region of northern Australia. It provides a major transport hub and has links to Asian markets. Over the past 15 years there have been rapid developments within the Port of Darwin. A major expansion of port facilities was begun in 1995 with the construction of the East Arm Wharf, which is linked with southern Australia via the Darwin to Adelaide rail link. Four residential marinas have been developed providing stable sheltered moorings for the ever growing recreational boating fleets. One liquefied natural gas terminal has been completed and another is under construction. These developments have seen an order of magnitude increase in dredging requirements. A marine supply base attached to the East Arm wharf is also under construction and will serve increasing activity in the Arafura Timor Seas. Overall the Port of Darwin is deep enough to handle Panamax class ships but at present cannot do so at all stages of the tide cycle. Darwin Harbour has tide ranges of up to 8 m and these are responsible for generating currents of over 4 knots in places. The entrance to the harbour is restricted in depth through an area of sand waves known as Charles Point Patches. Investigations are presently underway to examine the feasibility of dredging a channel through this area to enable shipping access throughout the entire tidal cycle; if successful this will increase the allowable traffic of ships into and out of the harbour. Even though the harbour has undergone rapid development, the water quality and health of the marine environment is very good. Darwin Harbour still retains over 90% of its mangrove areas and these contain 35 of the 52 species found Vol 12 No 1


in Australia. The Northern Territory Government is committed to preserving the environmental and cultural values of the harbour while also allowing for non-environmentally degrading economic development. However, monitoring of key processes in the harbour such as tidal currents, waves, water depth, sediment and nutrient transport has not been undertaken continuously; much of the knowledge of the physical, chemical and biological behavior of the harbour has only been collected on a project by project basis. Darwin has one of Australia’s national reference network tide gauges with over 50 years of record that is the only existing long term record of tidal behaviour for the area. With the introduction of IMOS that has now changed. An IMOS NRS has been established at the entrance to Darwin Harbour and in concert with the Darwin Port Corporation (DPC) has been set up using an existing channel navigation marker. The station measures tidal currents, waves, chlorophyll-a, turbidity, wind vectors, temperature and rainfall. The system is telemetered and the data is available in near real time. The system is being used now to provide boundary conditions for a numerical model of the harbour as well as provide data to mariners for ship handling. The system has recently expanded into the Beagle Gulf region with the deployment of a second mooring. The Beagle Gulf mooring is currently operating in delayed mode but will soon be upgraded to a real-time station in an extension of the partnership between IMOS and the DPC. 2.2

Observing system overview

2.2.1 Platform The Darwin NRS has been deployed by adapting an existing channel marker buoy known as Buoy 5, situated in approximately 26 m of water at the entrance to the Port of Darwin and owned by the DPC. The platform is a Tideland SB-285P Sentinel Buoy, which provides ample room for the mounting of all the required hardware and instrumentation, and is large and stable enough for two technicians to board for field servicing. The system described below is readily adaptable for installation on different platforms, and to date has also been deployed on two other buoys of comparable size. The Darwin NRS provides three mounting points for instrumentation: 1. A horizontal arm approximately 3 m from the sea surface which holds meteorological instruments. The arm can be lowered to enable a technician to access the instruments for servicing. 2. A vertical boom mounted on the side of the buoy which holds near surface oceanographic instruments. This boom can be raised and lowered from the surface to enable servicing of instruments without the need for divers. 3. A separate tripod situated on the seabed, offset by approximately 100 m from the buoy to avoid the Australian Journal of Civil Engineering

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sweep zone of the mooring chain. This tripod can relay the data from two oceanographic instruments to the surface buoy using acoustic modem telemetry. The tripod also features a gimballed mount for an acoustic Doppler current profiler (ADCP), and an acoustically activated pop-upbuoy and rope canister used for frame recovery. The general arrangement of the buoy and tripod are shown in figures 1 and 2. 2.2.2 Sensor suite The suite of sensors installed on the buoy have been selected to answer the scientific questions discussed in section 2.1, and also provide the real-time data streams required to improve maritime safety and navigation for the larger ships likely to service Darwin. For the measurement of wave parameters, a bottom mounted ADCP with wave measuring capability was selected over a wave buoy. Combining the required functionality to measure both waves and currents in a single compact package offers significant operational benefits, and it has been shown by Strong et al (2000) that ADCP wave measurements compare favourably with competing techniques. Battery life is a major constraint on the frequency of wave sampling bursts; with two double battery packs connected to the ADCP we are able to measure waves every 2 hours over a 6-month deployment. The full sensor suite is summarised in table 1. 2.2.3 Control system A Campbell Scientific CR1000 serves as the measurement and control system for the buoy. An extensive modular code library has been developed which enables instruments to be interchanged or added to the system relatively easily. The system is compatible with numerous types of measurement input. With the current arrangement of instruments, RS-232, SDI-12 and analogue channels are employed. 2.2.4 Power system As the channel marker is a relatively large and stable platform, it has been possible to install four solar panels with a total power rating of 160 W, which provide ample power for the system with some redundancy. These panels charge a 12 V, 105 Ah deep cycle battery via a Morningstar Sunsaver MPPT regulator. The regulator provides a serial output of the charging status, and so variables such as panel voltages, charging current and load current can be logged and viewed in real time. 2.2.5 Communications A Teledyne Benthos acoustic modem is installed on both the tripod frame on the seafloor and on the instrument boom attached to the side of the Vol 12 No 1

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Figure 1:

The Darwin NRS channel marker buoy showing the scientific instrumentation.

Figure 2:

The NRS seafloor tripod used at the Darwin Buoy 5 and Yongala Wreck sites.

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Table 1:

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Darwin NRS sensor suite.

Instrument

Manufacturer Mount Parameters measured

Sample interval

CNR1 Net Radiometer

Kipp and Zonen

Arm

Upwelling and downwelling long and shortwave radiation

10 minutes

WXT520

Vaisala

Arm

Air temperature, humidity, air pressure, precipitation, wind velocity

10 minutes

Boom

Conductivity, water temperature, pressure, 15 minutes turbidity, chlorophyll, fluorescence, dissolved oxygen

Tripod

Current velocity profile, directional wave parameters

Tripod

Conductivity, water temperature, pressure, 15 minutes turbidity, chlorophyll, fluorescence, dissolved oxygen

Water quality monitor

Wetlabs

Workhorse ADCP with waves upgrade and NEMO Teledyne RDI wave processing card SBE16plusV2 SEACAT

Seabird

surface buoy. As measurements are taken by the instruments mounted on the tripod, they are stored within the internal memory of the acoustic modem. Every 30 minutes, the near surface modem polls the tripod modem and current, wave and water quality measurements are transmitted acoustically to the surface. The frequency of interrogation is constrained by the battery power available on the tripod; a 30 minute acoustic transmission interval allows for 6-month deployments. In terms of surface telemetry, the station is close enough inshore to make use of the NextG mobile phone network. A Cybertec Series 2000 modem and router is used to allow a server to connect to the station and perform a scheduled download of new data. While this router draws a large portion of the power budget, it allows full remote access to the station for troubleshooting, diagnostics and software changes. 2.3

Operations

The station is routinely serviced by AIMS oceanographic technicians at typical intervals of 6 months. This time period is deemed the longest that the instruments should be left deployed before the data begins to severely degrade due to bio-fouling. The bio-geochemical instruments which have moving parts in their pump assemblies and optical sensors are particularly susceptible to bio-fouling, and these instruments are generally the limiting factor in setting an appropriate deployment duration. The service is also an opportunity to download the full data sets from the instruments. Due to bandwidth limitations, only summary data is broadcast in real time with the complete high fidelity datasets (eg. raw wave data) being stored on the instruments internal memory until they are physically retrieved. During a full service, the pop-up buoy on the tripod frame is acoustically released, and the tripod is Australian Journal of Civil Engineering

10 minutes currents, 120 minutes waves

recovered and redeployed using a research vessel with a suitable A-frame. The surface buoy is not recovered, all servicing can be carried out in-situ by personnel boarding the buoy. The inherent difficulties of working on the buoy while in the water have steered the design towards a modular, ergonomic system. The battery housing, electronics housing and sensors can be swapped out individually and easily if required. Diving operations have been engineered out and all buoy mounted sensors can be accessed from the surface by retracting the vertical boom. In addition to these scheduled services, the real-time stream is monitored throughout the deployment and reactive repair operations can be initiated if failures are detected. The channel marker buoy is periodically replaced by DPC, and will typically remain in position for 3-5 years. 2.4

Uptake and opportunities

2.4.1 Maritime operations and incident response Since inception, the real-time data from this station has been assisting DPC with their shipping operations and overall understanding of the environment. A range of value added products are also under discussion and development, which are only possible due to the realtime data provision. The data from the IMOS buoy will contribute to a dynamic under-keel clearance system for enhanced ship handling management. Realtime data streams from stations such as the Darwin NRS can also support operational management of dredging activities, and provide vital information in the event of incidents such as ship grounding or oil spills. Improved web interfaces and “apps” will be developed to improve the dissemination of data from this facility. This will also include access to an operational forecast model for Darwin Harbour. Vol 12 No 1

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2.4.2 Environmental monitoring and modelling AIMS undertake coastal research in the region and are continually developing and refining numerical models (Williams et al, 2006) with the NRS now providing the boundary conditions for Darwin Harbour. In concert with a new delayed mode mooring situated in Beagle Gulf, the Darwin NRS provides a data assimilation point for the broader Beagle Gulf model. Data from the Darwin NRS ADCP shows that currents are bi-directional with maximum current magnitude of approximately 1.5 m/s. There is a subtle dominance of ebb flows during the wet season, and flood flows during the dry season. Coupling the discharge measures (calculated from the ADCP data) with the suspended sediment concentration (inferred by optical instruments and ADCP backscatter data) has allowed the determination of net flux of sediment loads into Darwin Harbour. This information provides context to understand the sediment dynamics within the harbour, which has relevance for maintenance dredging and harbour operations. The wave climate that influences Darwin Harbour exhibits a strong seasonality that is tied to the tropical northwest monsoon that occurs between November and March. During this period, north westerly winds blow over the uninterrupted fetch of the Timor Sea, increasing incident wave energy in Beagle Gulf and at

the entrance to Darwin Harbour. Due to the alignment and narrow nature of the harbour entrance and the presence of the Tiwi Islands to the north, the interior of the harbour is sheltered from long period swell, and any swell that does enter the harbour is quickly dissipated by the generally shallow bathymetry and indented nature of the harbour shoreline. Tropical cyclones regularly influence the region during the northwest monsoon, and lead to episodes of severe, but short-lived, increases in wave energy. During the months of April to October, the harbour experiences south-easterly trade winds, which, due to the limited fetch within the harbour, have little impact on the local wave climate. Wave observations from the Darwin NRS are used below to highlight the general characteristics of the wave climate in Darwin Harbour. Observed significant wave height (Hs) during January to July 2012 shows the distinct influence of episodic weather events during January and March 2012. Significant wave heights exceeding 3.5 and 2.5 m were recorded during the passage of tropical lows on 24 January and 13 March, respectively (see figure 3). During these events the peak period of wave energy also increased from typical values of 3-5 to 6-8 seconds. Outside of these episodic events, wave height in the harbour is generally below 1.0 m for 90% of the time (figure 4). Wave directions are aligned with the direction of the main entrance channel to the harbour, and occur from the northwest quadrant for 67% of the time (figure 5).

Figure 3:

Observed significant wave height (Hs) and peak period (Tp) at the Darwin NRS.

Figure 4:

Histogram of wave height occurrence.


Figure 5:

Histogram of wave direction occurrence. Vol 12 No 1


Wave propagation into and within Darwin Harbour was modelled with the SWAN shallow water wave model (Ris et al, 1999). SWAN is a third-generation spectral model that contains implicit shallow water routines to allow for shoaling, frictional dissipation, wave breaking and refraction. The model grid was a regular, rectilinear mesh with 50 m spatial resolution, and extended into Beagle Gulf. Simulations were performed with a swell from the northwest, with significant wave height and peak wave period of 2 m and 4 s, respectively. Model results show limited propagation of wave energy into the harbour (figure 6). Development of the Darwin harbour wave model is continuing, and the present focus is to couple the wave and hydrodynamic models. The aim is to simulate wave-current interactions, which are particularly important in macro tidal environments where large tidal currents have the potential to significantly influence local wave conditions at tidal time scales. Analysis of the wind and wave observations from the Darwin NRS demonstrate that local wave conditions are predominantly driven by local winds. An examination of coincident wind and wave observations show that, outside of periods of extreme weather, local waves are proportional to local wind strength, and wave action ceases shortly after the cessation of local winds, indicating the absence of remote influences on the local wave

Figure 6:

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climate. Wind fetch based models of surface gravity waves are therefore able to adequately simulate the observed wave climate within Darwin Harbour, and present an efficient means to provide wave climate forecasts, based on forecast winds. With the delivery of near real-time wave, water level and current data, the coupled wave-current model will ultimately be configured to run in near real-time, using observations and weather (wind) forecast to provide short-term (hours to days) forecasts of wave conditions within the harbour and harbour approaches. A diagram of the proposed modelling system in shown in figure 7. 3

YONGALA NATIONAL REFERENCE STATION

3.1

Background

Close to Townsville on Australia’s northeast coast, the Yongala NRS has had a subsurface mooring or bottom frame in place since 2007. The site lies in the centre of the GBR lagoon, between the mainland and the reef itself and is representative of a large region of the Continental Shelf between the predominantly outer shelf reef matrix and the coastal waters. The Yongala NRS is therefore well located to sample the competing influences of the southeastward lagoonal branch of the East Australian Current (EAC)

Darwin Harbour SWAN wave model.


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Figure 7:

Operational model diagram.

(Brinkman et al, 2002) and the opposing southeasterly trade wind forced coastal current (Burrage et al, 1991). Constraints in selecting the site were twofold: firstly, the location had to be reasonably readily accessible by a small vessel to allow the monthly biogeochemical sampling; and secondly, due to the multiple use zoning established by the Great Barrier Reef Marine Park Authority (GBRMPA) it was best sited in a protected zone free of trawling. The presence of the Yongala Wreck meant that an isolated green zone was established by GBRMPA as it supports a recreational diving and tourism industry and it is in the middle of commercial shipping lanes. The Australian Maritime Safety Authority (AMSA) required the installation of an IALA Isolated Danger Mark (IDM) which provided the ideal platform upon which the NRS instrumentation could be installed. The IDM is a co-investment between the following stakeholders: Museum of Tropical Queensland, Department of Environment and Resource Management, Department of Environment, Water, Heritage and the Arts, IMOS, AIMS and AMSA. 3.2


3.2.1 Platform The general arrangement of the Yongala buoy is shown in figure 8. The buoy is secured in approximately 28 m of water by a three point mooring system designed to minimise the swing radius, essential due to its proximity to the historic wreck. The mooring has been designed by Deltex to a standard that complies with generally accepted Australian Journal of Civil Engineering

marine mooring recommendations. The securing lines are made of polyester monofilament wires making it easier to deploy, and allowing for greater performance in tensile strength, energy absorbance and memory feedback. This synthetic cable has a low weight in sea water and thus is close to neutral buoyancy. The buoy was secured to the seabed via the Deltex Cables and using a 5000 kg cast iron weight to secure each leg of the mooring. Buoy and mooring design aside, the instrumentation platform is very similar to the Darwin NRS system described above. The designs for the horizontal arm, retractible sensor boom and gimballed tripod were all reused in this system with only slight customisation required. The sensor suite, control system and power system is also virtually identical and so for details on these the reader is referred back to section 2.2. The mooring was severely damaged in 2011 by tropical cyclone Yasi, which generated swell heights of around 10 m and was sufficient to pick up the three 5-tonne anchor weights, arranged in a triangular fashion, and tangle the mooring lines. A replacement surface mooring was deployed in 2013, in the interim the data records were maintained by deploying a subsurface delayed mode mooring. 3.3

Operations

As with the Darwin NRS, a full service is completed at 6-monthly intervals. The monthly biogeochemical sampling trips give an opportunity for troubleshooting and inspection throughout the deployment period. Vol 12 No 1


Figure 8: 3.4

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The Yongala Wreck Isolated Danger Mark showing the scientific instrumentation.


3.4.1 Maritime operations The Yongala NRS is located close to shipping lanes and could be used to better assess environmental conditions to support operational management of shipping in this region of GBR World Heritage Area. As with the Darwin NRS, sites such as this could also support management of dredging activities and provide vital information in the event of incidents such as ship grounding or oil spills. 3.4.2 Local operators The NRS is in the region of a recreational sailfish and marlin sport fishery and when added to the large scale dive tourism at the Yongala historic wreck site, the website displaying the real-time data from the mooring has attracted significant local interest. Recreational diving and sport fishing businesses are monitoring the weather and sea state via the NRS webpage, and using this information to plan their operations. 3.4.3 Water quality modelling Since European settlement, changed land use practices have meant increased sediment, nutrients and pesticide delivery to the coastal and reef waters (Brodie et al, 2001; 2009; McCulloch et al, 2003). The Australian Journal of Civil Engineering

dynamics and fate of freshwater plumes delivered by the many rivers draining into the GBR area are a critical determinant of the health of coral reef ecosystems, and data from the Yongala NRS are proving critical to tuning and assessing the ability of the models to simulate the transport of this freshwater and associated dissolved and suspended material. The Yongala NRS informs a number of coastal monitoring programmes focussed on water quality including the Reef Rescue Marine Monitoring Program funded by Reef and Rainforest Research Centre and GBRMPA (Schaffelke et al, 2009). The data is also used to validate remotely sensed sea surface temperature (SST) and ocean colour products and provide validation of a number of hydrodynamic and biogeochemical modelling efforts: Bluelink, OceanMAPS and the eReefs project, which is described in more detail in the next section. Of particular interest is the Burdekin river plume. The Burdekin is Australia’s 4th largest river by volume, largest in Queensland and second to the Murray in terms of economic importance. Occasionally, during the monsoonal wet season flooding, the Burdekin plume occupies a large portion of the shelf and impinges on the Yongala site. The eReefs models have been evaluated during the 2010-2011 wet season, during which significant flows from the Burdekin occurred from mid-December through to late January (figure 9). During this period the Yongala NRS was recording salinity at 3-5 and Vol 12 No 1


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Figure 9:

Comparison of observed and simulated salinity at 3 and 23 m depth at the Yongala NRS. Observations are denoted “NRS” and model outputs are denoted “SHOC”.

Figure 10:

The full Q-IMOS GBR mooring array consists of four pairs of moorings. They are located in the vicinity of Lizard Island in the northern GBR at Jewel Reef and Cormorant Passage; Myrmidon Reef and Palm Passage in the central GBR; Elusive Reef and Capricorn Channel either side of the Swains Reefs; and near Heron Island and One Tree Reefs in the southern GBR.

23 m depth. The eReefs hydrodynamic model reproduced the timing of observed large salinity changes (eg. the fresh water events that come though during the period between late December and midJanuary), however magnitude of salinity change is exaggerated in the pilot model. Agreement in timing of events between model and observations is particularly evident in the near-bed salinities. 4

PALM PASSAGE MOORING

4.1

Background

Impacts on the GBR from phenomena ranging from weather events to longer term climate change have Australian Journal of Civil Engineering

in the past been based on very sparse observation and modelling tools. This has led to considerable uncertainty as to how the GBR will respond over long time-scales (Steinberg, 2007). In an attempt to address this, the Queensland IMOS node has an array of moorings along the GBR (Babcock et al, 2011) designed to monitor the flow of oceanic water along and into the reef matrix. Eight of the moorings are deployed as four pairs as shown in figure 10 with an offshore deep continental slope mooring paired with one outer shelf mooring. The moorings have a bottom mounted ADCP for measuring currents and waves (either Teledyne RDI Workhorse or Nortek AWAC), and a series of SeaBird SBE39s and WetLabs Water Quality Monitor (WQM) instruments to give Vol 12 No 1


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a vertical profile of temperature, salinity, turbidity, chlorophyll and dissolved oxygen. Historically these moorings have all been operated in delayed mode with data recovered every six months. In 2013 the mooring at the Palm Passage site in the central GBR was upgraded to real-time in order to inform the eReefs project, which is introduced below. 4.1.1 eReefs eReefs is a project sponsored by the Great Barrier Reef Foundation, which is being implemented through the Bureau of Meteorology (BoM) and developed collaboratively with CSIRO, AIMS and the Queensland Government. Its aim is to provide vital tools for decision making and communication across the entire GBR, from catchment to ocean (Bureau of Meteorology, 2014). A key component of eReefs is the development of an integrated suite of hydrodynamic, sediment and biogeochemical models, downscaled from global to regional to local levels. While the modelling teams have access to satellite observations and delayed mode data from IMOS and other sources, the lack of near real time sub-surface data has emerged as a significant impediment to reducing uncertainties and improving model skill. Through co-investment by IMOS and CSIRO, and with logistical support from AIMS, the delayed mode mooring at Palm Passage has been upgraded to realtime and coastal glider missions have commenced from Heron Island. The data collected is being used to assess and improve eReefs hydrodynamic, sediment and biogeochemical modelling for the GBR region. The incremental cost of enhancing existing IMOS infrastructure to create this near real time observing capability is a fraction of what it would have cost to establish it from scratch. 4.2


Up until January 2013 the Palm Passage mooring has been operating in delayed mode with a general arrangement similar to other Queensland IMOS moorings (see for example, figure 11). Since then, a second mooring with a surface buoy designed and built by CSIRO (Hughes et al, 2010) has been deployed to allow data to be sent back to shore via satellite communications. The Myrmidon Reef in-line mooring configuration showing detailed instrumentation attached along the wire throughout the water column.

4.2.1 Platform

Figure 11:

The real-time observing system deployed at Palm Passage is markedly different from the two NRS systems described above, in that the surface expression was purpose built and deployed as a telemetry buoy. In the two examples above, existing infrastructure (channel marker and isolated danger mark buoys) were opportunistically used.

The system consists of two distinct moorings, a subsurface mooring which contains the majority of the scientific instrumentation, and a second mooring with a surface buoy for telemetry, shown in figure 12.


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to the electronics canister made with standard subsurface oceanographic-type connectors. With these improvements the unit can be pulled down to a calculated maximum of 250 m depth without leakage into the electronics canister. 4.2.4 Control system A CR1000 datalogger provides control of the float electronics. Running a 1-minute scan rate, each hour the surface floats SBE39 is first polled to collect “near” SST and the returned temperature, together with samples of platform battery voltages are packaged along with header information into a platform information-type file which is added to the file stack.

Figure 12:

The Palm Passage surface buoy.

4.2.2 Sensor suite The subsurface mooring has a bottom mounted ADCP for measuring currents and waves, a series of SeaBird SBE39 temperature loggers and WetLabs WQM instruments to give a vertical profile of temperature, salinity, turbidity, chlorophyll and dissolved oxygen. The surface mooring is fitted with an additional Seabird 39 and has the capacity to host a Vaisala WXT520 Weather station if required. 4.2.3 Communications For in-water communications between the two moorings which comprise this system, Teledyne Benthos acoustic modems are used as per the two NRS systems detailed above. For transmission of data back to shore, the nextG solution used for the NRS stations was not suitable for this site due to the absence of any mobile phone signal. An iridium based telemetry system has been developed for IMOS and previously implemented on two platforms in offshore and coastal waters (Hughes et al, 2010), and this system was also adopted for the Palm Passage upgrade. This system has a novel design feature where flat aircraft-type antennas are mounted internally in the electronics canister, rebated into the Delrin lid, with minimal effect on signal strength or reported GPS position. This has enabled the construction of a much more robust telemetry system, with both piston and facetype o-rings seals in the lid and all penetrations Australian Journal of Civil Engineering

The acoustic modem is then powered up and each remote acoustic modem in the system is polled sequentially. Error correction routines parse the returned data, with up to three retries allowed to obtain a complete and correct dataset from each modem. Once data is retrieved successfully, the remote modems are commanded to clear their data storage. The data is packaged with header information and added to the file stack, and the acoustic modem is powered down. The remote acoustic modems have a large storage capacity relative to the size of the data records stored and the float systems parsing routines can handle up to 380 data records per hourly cycle. As such, with two WQMs, acoustic communications can fail for up to 48 hours without risk of loss of data. In practice, monitoring of the acoustic communication has indicated few failures attributable to poor acoustic path conditions, and these were for a maximum of one reporting period. Finally, the CR1000 powers up the Iridium modem and the system attempts to acquire a satellite connection for 2 minutes. If this is unsuccessful, the system will enter sleep mode until the next hourly cycle. If acquisition occurs, the system will poll the modem for up to 2 minutes until it reports a received signal strength of greater than 2 out of 5 to ensure the best chance of achieving a successful upload. It will then attempt to sequentially upload all un-transmitted files in the stack, checking signal strength between each transmission. The CR1000 will power down the Iridium modem and terminate the active cycle once all files are transmitted or the signal strength test fails. Every 24 hours, the CR1000 also polls the remote acoustic modems on each instrument frame to obtain their on-board voltage levels, and adds this information together with an appropriate header to the file stack. The addition of this data along with other file information ensures all battery voltages in the system can be monitored remotely to help plan mooring rotation requirements. GPS positional information is reported regularly by both the main float electronics and by an independent Vol 12 No 1


Iridium tracker (containing both Iridium modem and GPS). This ability to track a breakaway mooring in the vicinity of a shipping channel is critical, and so a second isolated battery system for the tracker provides redundancy. The positional data has also been useful in modelling mooring wear based on the change in surface location relative to the nominal anchor position. The independent tracker also provides an important “beacon” function to indicate that the mooring float is on the surface and in its correct location in the event of main power failure. 4.2.5 Power system Unlike the two NRS stations, this system does not harvest any power from on-board solar panels. Sufficient power for a 6-month deployment is contained within a battery within the main canister. This is possible because a low power modem is used instead of the higher power modem and router used in the two NRS stations above. The trade off with this approach is a loss in full two way remote access with the station; at present communications are restricted to small pre-configured data packets only. 4.3

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portal to enhance the real time summary data that has been released throughout the deployment period. 4.4


4.4.1 Stratification One of the goals of the observing system is to observe cross shelf flows and impacts from Coral Sea waters. During summer the EAC accelerates and results in the thermocline becoming shallower near the shelf break. This allows colder nutrient rich water to travel up onto the shelf (Berkelmans et al, 2010) and if sustained can form a lagoonal branch of the EAC (Brinkman et al, 2002). Figure 13 reveals many occasions of colder water running past the temperature loggers on the Palm Passage Mooring over the 2010-11 summer. This combined with strong insolation results in stratification that allows internal tides to form. These can be seen as the large daily ranges of the loggers in the mid-section of the mooring. There are also periods where it becomes well mixed, however these coincide with periods of strong winds and receding intrusions from the Coral Sea.

Operations 4.4.2 eReefs model of the GBR

Both the surface and subsurface moorings are recovered at 6-monthly intervals for service and instrument download. Typically a second buoy controller electronics canister with fresh batteries is prepared in advance. Once the buoy is recovered onto the deck of the vessel this canister can then be quickly and easily swapped for the old one, thus reducing the time on site. After download, the data are processed and quality controlled and published on the IMOS

Figure 13:

The eReefs hydrodynamic model is built upon SHOC (Sparse Hydrodynamic Ocean Code), which is a finite difference hydrodynamic model developed by the Environmental Modelling group at CSIRO Division of Marine Research (Herzfeld & Waring, 2008). The model domain covers the entire GBR (figure 14) at a spatial resolution of approximately 4 km and up to 47 layers in the vertical, with accurate boundary

A six-month time series of temperature measurements throughout the water column at the Palm Passage Site.


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Figure 14:

The eReefs grid extending along the east coast of Queensland, showing surface currents and temperatures during tropical cyclone Yasi.

forcing for offshore ocean boundaries provided by a global, data-assimilating, eddy-resolving model. The model was nested in BRAN2.3 which is a data assimilating global model with 10 km resolution in the Australasian region, using MOM4p1 as the code base (operated by BoM; OceanMAPS) (Schiller et al, 2008). These data were used as initial conditions for temperature, salinity and sea level, and currents for boundary forcing. A tidal signal using the OTIS tidal model was superimposed on the low frequency sea level oscillation provided by BRAN2.3 on the grid open boundary and river gauge data provides the runoff needed to model the plumes. 5

DISCUSSION AND CONCLUSIONS

The IMOS moored infrastructure which has been the focus of this article has manifold applications to a wide variety of users. The advent of near real time observations and higher resolution 3D operational models of the ocean environment provide timely information to better inform decision makers, industry and the general public. Data can be obtained publicly and freely from IMOS (imos.org.au) data portal. The transmitted data is advantageous as it is not reliant on information being manually retrieved from instruments post-deployment. It is therefore released as a timely and continuous stream, rather than staggered discrete downloads with a lag of several months. A long-term aim of oceanographic research is to incorporate forcing into predictive models and real-time observing systems are a fundamental Australian Journal of Civil Engineering

prerequisite to this objective. Also, with the multiple data streams being developed encompassing a wide range of environmental variables, numerous models including those run by meteorologists and biologists can also use the data. The real time telemetry systems also provide ease of access to the data for a wide cross-section of the community. In particular water temperatures, weather conditions and wave height are data streams with broad community applications. In other, international examples of oceanographic moorings the building of a wide stakeholder community on the back of telemetry has been cited as the reason for the program’s success and longevity. Transmitted data assists with quality control, as sensor failures and drifts can be identified almost immediately facilitating a prompt response to fix the problem. Transmitting the data also lowers the risk of complete data loss in the event of a catastrophic instrument failure, eg. an instrument housing floods or a mooring is lost. The above case studies show that there is increasing confidence in our ability to simulate the oceanographic conditions over broad regions of the GBR. Observations show, as never before, the details in circulation, temperature and salinity throughout the water column. The 3D modelling is getting closer to reproduce the actual observations of this complex stratified shelf system. Efforts are underway to assimilate the data streams from the near real time moorings with a goal to improve the operational now-cast and forecast modelling. Vol 12 No 1


ACKNOWLEDGEMENTS Data was sourced from the IMOS, which is supported by the Australian Government through the NCRIS and the Super Science Initiative. Q-IMOS is funded by the Australian Government’s NCRIS, the Super Science Initiative and the Queensland Government. AIMS operate the Queensland and Northern Australian sub-facility of the Australian National Mooring Network. eReefs is a collaboration between the Great Barrier Reef Foundation, BoM, CSIRO, AIMS and the Queensland Government. Support funding is provided by the Australian Government’s Caring for our Country, Science Industry Endowment Fund and the BHP Billiton Mitsubishi Alliance. Field deployments and servicing completed by the AIMS oceanography group: Chris Bartlett, Shaun Byrnes, John Luetchford, Felicity McAllister, Ruth Patterson, Simon Spagnol, Jonathan Windsor and Juergen Zier. Thanks to the crew of the RV Solander and RV Cape Ferguson. REFERENCES Babcock, R., Bainbridge, S., Brinkman, R., Griffin, D., Heron, M., Lemckert, C., Hill, K., Lough, J. Ribbe, J., Ridgway, K., Richardson, A., Steinberg, C., Tomlinson, R. & Weeks, S. 2011, Queensland’s integrated marine observing system (q-imos) node science and implementation plan (nsip), technical report, IMOS, http://imos.org.au/plansreports.html. Berkelmans, R., Weeks, S. & Steinberg, C. 2010, “Upwelling linked to warm summers and bleaching on the great barrier reef”, Limnology and Oceanography, Vol. 55, pp. 2634-2644. Brinkman, R., Wolanski, E., Deleersnijder, E., McAllister, F. & Skirving, W. 2002, “Oceanic inflow from the coral sea into the great barrier reef”, Estuarine Coastal and Shelf Science, Vol. 54, No. 4, April 2002, pp. 655-668. Brodie, J., Furnas, M., Ghonim, S., Haynes, D., Mitchell, A. & Morris, S. 2001, “Great barrier reef catchment water quality action plan”, technical report, Great Barrier Reef Marine Park Authority. Brodie, J., Lewis, S., Bainbridge, Z., Mitchell, A., Waterhouse, J. & Kroon, F. 2009, “Pollutant discharge management target setting for rivers in the great barrier reef catchment area”, Marine and Freshwater Research, Vol. 60, pp. 1141-1149. Bureau of Meteorology, 2014, “eReefs”, August, www.bom.gov.au/environment/activities/coastalinfo.shtml. Burrage, D. M., Church, J. A. & Steinberg, C. R. 1991, “Linear systems analysis of momentum on the continental shelf and slope of the central great barrier reef”, Journal of Geophysical Research, Vol. 96, No. C12, December, pp. 22169-22190. Australian Journal of Civil Engineering

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Herzfeld, M. & Waring, J. R. 2008, SHOC: Sparse Hydrodynamic Ocean Code Users’ Manual, CSIRO. Hughes, D., Lynch, T. P., Pender, L. & Sherlock, M. 2010, “A robust satellite telemetry system for imos moorings”, IEEE Oceans 2010, Sydney. Integrated Marine Observing System (IMOS), 2014a, “Introducing IMOS”, August, http://imos.aodn.org. au/imos. Integrated Marine Observing System (IMOS), 2014b, “Australian National Moorings Network”, August, http://imos.org.au/anmn.html. Integrated Marine Observing System (IMOS), 2014c, “IMOS Ocean Portal”, August, http://imos.aodn. org.au/imos123/. McCulloch, M., Fallon, S., Wyndham, T., Hendy, E., Lough, J. & Barnes, D. 2003, “Coral record of increased sediment flux to the inner great barrier reef since European settlement”, Nature, Vol. 421, pp. 727-730. Moltmann, T., Proctor, R. & Donoghue, S. 2013, “The integrated marine observing system: observations to support research and applications in the coastal zone”, Coasts and Ports 2013, Sydney. Ris, R. C., Booij, N. & Holthuijsen, L. H. 1999, “A third-generation wave model for coastal regions, part ii, verification”, Journal of Geophysical Research, Vol. C4, No. 104, pp. 7667-7681. Schaffelke, B., Thompson, A. A., Carleton, J. H., Davidson, J., Doyle, J. R., Furnas, M. J., Gunn, K., Skuza, M. S., Wright, M. M. & Zagorskis, I. E. 2009, Reef rescue marine monitoring program: Final report of aims activities 2008/09, technical report for Reef and Rainforest Research Centre, Australian Institute of Marine Science. Schiller, A., Oke, A. P. R., Brassington, G. B. & Entel, M. 2008, “Eddy resolving ocean circulation in the Asian Australian region inferred from an ocean reanalysis effort”, Progress in Oceanography, Vol. 76, pp. 334-365. Steinberg, C. 2007, “Impacts of climate change on the physical oceanography of the Great Barrier Reef”, Climate Change and the Great Barrier Reef, Great Barrier Reef Marine Park Authority & Australian Greenhouse Office, pp. 51-74. Strong, B., Brumley, B., Terray, E. A. & Stone, G. W. 2000, “The performance of ADCP-derived directional wave spectra and comparison with other independent measurements”, OCEANS 2000 MTS/ IEEE Conference and Exhibition, Vol. 2, pp. 1195-1203. Williams, D., Wolanski, E. J. & Spagnol, S. B. 2006, “Hydrodynamics of Darwin Harbour”, The Environment in Asia Pacific Harbours, Springer, pp. 461-476. Vol 12 No 1

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PAUL RIGBY Dr Paul Rigby is an Oceanographic Engineer at the Australian Institute of Marine Science. He has 10 years’ experience in the design, development and deployment of a wide range of ocean observing systems including autonomous and remotely operated vehicles, oceanographic moorings and surface telemetry buoys.

CRAIG STEINBERG Craig R. Steinberg is a Physical Oceanographer at the Australian Institute of Marine Science, and Integrated Marine Observing System Queensland and Northern Australia Sub-facility manager for the Australian National Mooring Network and Satellite Remote Sensing. Craig has 25 years’ experience undertaking research in interdisciplinary studies including observation, analysis and numerical modelling from scales that range from individual reefs to seas, and phenomena ranging from waves to large-scale ocean circulation.

DAVID WILLIAMS David K. Williams is a Coastal Oceanographer at the Australian Institute of Marine Science, and has 35 years of experience in tropical estuaries and coastal zone dynamics. His specialities include hydrodynamic, sediment transport, water quality and ecological modelling. David is also an expert in data collection using moored and underway acoustic Doppler current profiler systems.

GARY BRINKMAN Gary Brinkman is the Engineering & Field Operations Manager at the Australian Institute of Marine Science. He has extensive experience in the design of oceanographic observing systems, and in the management of large-scale marine measurement programs.


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RICHARD BRINKMAN Dr Richard Brinkman is the Lead Physical Oceanographer at the Australian Institute of Marine Science. Richard’s research interests fall within the broad topics of coastal oceanography and physical-biological interactions on continental shelves. He has significant expertise in conducting observational and modelling based research on shelf dynamics, coupling of shelf and ocean circulation, and physical-biological interactions at regional and local scales on Australia’s tropical coasts and marginal seas.

HEMERSON TONIN Dr Hemerson Tonin is a Physical Oceanographer at the Australian Institute of Marine Science (AIMS), specialised in numerical modelling of nearshore and coastal processes of estuarine, coastal and continental shelf regions including hydrodynamics, waves, sediment transport and pollutant transport. Before joining AIMS, Hemerson worked for several years as a physical oceanographer for an environmental consulting company, developing skills in planning, collection and data analysis, numerical modelling and environmental impact assessments.

DAVID HUGHES David Hughes is the Coastal Moorings Team Leader within CSIRO Marine & Atmospheric Research. He has extensive experience in the design, development and deployment of a wide range of marine instrumentation and ocean observing systems.


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