Data Collection in Marine Systems

The amount of data available from marine systems and programmes is growing. New information is gathered every day on environmental conditions, pollution and physical properties to name just a few. The demand for new real-time (NRT) data is increasing rapidly as a result of the need to see and to be able to act, on changes in conditions, within a short time frame. This need may be driven by legislation (to comply with regulations), safety, competitive advantage or for research.

There are thousands of sources of near real-time marine environmental data in the public domain, many of which are available via the Internet. These include meteorological and sea state measurements in the open ocean, coastal waves and inshore waters.

Ocean Scientific International Ltd (OSIL) has been involved in a wide range of monitoring and measurement programmes in port/harbour, coastal waters and in the deep waters of the open sea, all of which have contained some requirement for near real-time data.

PORTS & HARBOURS

Increasing focus on efficiency and emergency response has lead to a greater demand for real-time monitoring of environmental factors such as waves, currents and tides. Tighter controls on pollution have placed higher demand on the quantity and quality of analyses of water and sediment, and many of these data can now be provided in real-time.

The Port of Mostyn in North Wales, UK required a port monitoring system to service the needs of two large ferries operated by P&O. One of the problems associated with this operation was the shallow water over a sand bar on the approaches to the port. OSIL installed a range of Aanderaa tide and current meters on the quayside at Mostyn and on a pile located in the harbour approach. Data on tidal height, currents and meteorological conditions are transmitted, at 2 minute intervals to both the P&O ferries at sea and the Harbour Masters office. It enables the ferry to adjust speed ‘en route’ from Ireland to Mostyn in order to arrive when there is sufficient water to berth. This provides P&O with considerable operational advantages and fuel savings. Data is transmitted using VHF radio to the ships and to the shore. However, local conditions were not suitable for radio reception at the Harbour Master’s office so a ‘wireless modem’ link was used for this function. Wireless modems have become useful tools in the transmission of data. They have a working range of around 2 km and can be quickly and easily installed.

The ABP Marine Environmental Research group (ABPMER) required real-time turbidity data from Southampton Water during a long-term dredging campaign. It was important to collect near real-time data in order to maintain turbidity levels below a specified threshold. If turbidity reaches that threshold then an alarm is activated and dredging is stopped. In this case a suite of YSI turbidity sensors were networked at the site with Sontek acoustic current meters to provide a ‘view’ of the sediment dynamics. Data transmission by radio was problematic at the site due to obstruction by large buildings and structures so the preferred method was by GSM. This allows the user to autodial the sensor suite at pre-determined intervals to access the data. The cellular telephone network in the Southampton region is well supported and therefore provides a reliable means of data collection.

COSTAL REGIONS

The diverse environment that makes up coastal regions experiences ever changing conditions. It is a dynamic situation which requires close attention to be paid to the robustness of the equipment used and its means of deployment. Wave measurement has always been a key element in coastal monitoring. Recent requirements in the oil industry have included wave measurements around Floating Production Supply Offload (FPSO) vessels as a safety measure. The FPSO vessels are becoming more widely used as a means of extracting oil offshore but transfer of the oil from the FPSO to a tanker needs to be carefully controlled. OSIL have installed wave-measuring buoys for BP at 2 sites where FPSO’s are in operation. One is the Schiehallion site off the West Coast of Scotland and the other is at the Chirag site in the Caspian Sea. In both cases the wave buoy is moored in a dynamic environment and close attention was paid to the design and installation of the mooring. OSIL utilises the expertise and facilities of the mooring group at the Southampton Oceanography Centre (SOC) for much of their mooring work. In both cases data is transmitted from the wave buoy to the FPSO using VHF radios. Tankers are instructed on their approach to the FPSO, with regard to the safe berthing and off-loading of oil, according to the wave data received.

OPEN OCEAN

Production and transmission of data from the open ocean presents problems mainly associated with scale. Deployment and installation of instruments in deep waters (greater than 1000m) and transmission of data over hundreds or thousands of miles presents a new set of problems. Deep-water moorings are successful in the hands of a relatively small number of experienced teams. The remote nature of the location requires the mooring design to cope with a wide range of conditions over relatively long periods of time. In addition the instrumentation used must be reliable and able to operate for a considerable time scales without maintenance or calibration.

The most practical method for transmitting near real-time data from remote places such as the open ocean is via satellite. There are a number of systems available which operate using satellites in geostationery (altitude ca 35,000km) earth orbit (e.g. Inmarsat), mid-altitude (ca 10,000km) earth orbit (e.g. ICO) and low earth orbit (e.g. Argos, Orbcomm). Each have advantages and disadvantages in terms of data volume coverage and costs. The paper ‘Development in Satellite Communcations Systems’ by David Meldrum and Oli Peppe (SAMS) provides a comprehensive overview of systems available.

Some seabed studies, by their very nature, require long-term data sets and near real time collection is not possible. However, the use of additional devices can help to achieve successful data recovery from the long term deployments.

An example of this is Bathysnap, a free-fall camera and current meter system, which can operate on the deep sea floor for periods in excess of 1 year. It is programmed to repeatedly photograph the seabed to monitor changes in seabed appearance, feeding behaviour of animals and their effect on the benthic environment. However, the siting of Bathysnap can be crucial to the overall success of this long-term dataset. In one project, data was required on seabed topography and conditions prior to the long-term deployment of Bathysnap. OSIL developed, together with Geotek Ltd, a deep-water ‘drop camera’ which permitted a quick local survey of the area to be undertaken. The drop camera takes uses an altimeter-activated flash that is triggered within a specified distance (altitude) from the sea bed. OSIL also produce a deep-sea video camera which operates from a pressure switch and programmable timer which again allows operation from a non-conducting cable. Although not strictly near-real-time, these drop cameras allow the user to obtain information on the conditions in the water and on the sea-bed much more quickly than was possible using traditional mooring techniques.

The demand for real-time and near real-time data is increasing rapidly. Progress in communications for everyday applications (e.g. mobile phones, GPS, satellites) offers many opportunities for larger amounts of data to be transmitted reliability in relatively short time periods. However, it should be remembered that transmission of the data is only one piece of the jigsaw. Reliable instrumentation properly installed and maintained are essential components in the achievement of meaningful data.

By Paul Ridout, Chairman, OSIL.