Posted on 17.06.2010 - 11:00 UTC in SURVEY NEWS by Rons_ROV_Links
A range of factors in a water column influences the accuracy of sonar readings. To ensure that they are as precise as possible, they need to be calibrated to suit the exact conditions. A new system of underwater winches equipped with CTDs from MacArtney will measure conditions every 30 minutes, report those readings to computers based onshore in order to maintain the quality of sonar data.
Water conditions affect sonar readings
Sonar equipment is used for a multitude of underwater investigations, including monitoring underwater equipment and devices, environmental study and control, sea life and fisheries, archaeology and military and security surveillance. Gaining a good understanding of what is happening underwater often means getting a good view of details.
Detailed sonar observations underwater rely on a range of factors and precision can be enormously affected by the condition of the water in the observation area. Sonar images are made through sonar waves travelling through the water and bouncing back from an object. The precision of the data received can be affected by a multitude of factors, including pressure, changes in the concentration of salt particles suspended in the water or altered travel speed due to temperature. Computer software can manage the data to compensate for distortions but knowing of the state of the water through which sonar travels is enormously significant when digitally processing or correcting for distortions.
MacArtney system reads water column
Deploying CTD sensors regularly in the sonar observation area provides up to date information on the water column so that the sonar readings can be adjusted.
The CTD sensors provide onshore computers with the measurements they need to perform adjustments that make the sonar data as accurate as possible, processing the data digitally to account for any distortions caused by pressure, changes in the concentration of salt particles suspended in the water or altered travel speed due to temperature.
MacArtney is launching a new underwater winch system with CTDs on buoys. The underwater winches, installed on the seabed, reel out a buoy with a CTD installed. The CTDs will measure salinity, temperature, pressure, depth and density every 30 minutes and their continual real time bathymetry data to onshore computers will facilitate the precise calibration of the sonar readings to provide completely accurate sonar data without distortion caused by variations in the water column. They can be installed as single units or in a group or pattern of several systems.
Engineered, flexible design
The types and frequency of water column readings varies enormously from one project to another. Some applications require almost continual monitoring of water conditions, whilst others may need checking at longer intervals. MacArtney's underwater winch system can be programmed to run varying sequences according to the project, for example launch twice an hour or once a day. The oceanographic equipment can also be designed to suit requirements and the winch mounted with whichever sensor or monitor is most suitable for the project to monitor a wide range of conditions in fresh or sea water systems. The winch is stopped with the equipment close to the surface and the cable is spooled back into the winch as data readings are performed. At the top of the measuring equipment, a buoyancy aid helps the winch to rise from the winch on the seafloor up to the surface in a steady, even tempo when the cable is spooled out from the winch.
MacArtney has integrated several features into the system to help ensure that the winch works optimally from the sea floor. A foundation is positioned on the seabed so that the winch that is mounted on it sits as flat and evenly as possible and the winch drum material has been specifically chosen to be lightweight yet strong for extended lifespan in situ. The cable that links the winch to onshore provides both fibre communication and power supply. Oil compensation in the winch box ensures that pressure is correctly compensated, provides a cooling system for the equipment and allows the winch to function on the sea bed.
Regular maintenance ensures long lifespan
The challenges that fixed underwater winches face depend on where they are installed. Depth, water temperature, oxygen and other natural processes, such as fouling, can affect how a system works. Servicing at specific intervals and maintenance ensures that the winch works optimally and that the oceanographic measuring equipment functions correctly and continues to make precise readings. MacArtney's underwater winch systems are designed with a long lifespan of 20 years with the correct service and maintenance.