Swath surveys (sidescan and 3D bathymetry)
Acquisition of both bathymetric and side scan data can be achieved through the use of IHO standard compliant interferometric swath bathymetry systems capable of producing both Digital Terrain Models (DTM) and side scan imagery of the seafloor. Integration of both data outputs is possible, giving the 3D model realistic surfaces added by the side scan data. The system is able to perform swaths as wide as 20% of the total depth, although maximum swath widths of 1000 metres or 10% of the total depths are more common. The interferometric swath bathymetry system is capable of reaching IHO Special Order stantards.
The system is configured with dual 117 KHz transducers with an effective operating depth of 350 metres. Pulse repetition frequency can be adjusted depending on survey conditions while proper ensonification of the bottom can be achieved by altering this parameter. The 117 KHz transducers feature a slant range of 500m for normal conditions and 200m for poor conditions while swath ranges can reach 600 metres in the horizontal range and 200 metres deep without compromising accuracy. For extra accuracy in shallow areas, high frequency transducers can be used. All data outputs are compatible with industry standard GIS and mosaicing applications.
The Rozi wreck - Cirkewwa, Malta
Side Scan Sonar Survey with Accurate Horizontal Positioning
Side scan sonar is a method of underwater imaging using narrowbeams of acoustic energy transmitted from the side of the towfish and across the seabed. Sound is reflected back from the seabed and from objects in the water to the towfish. Certain frequencies work better than others: high frequencies such as 500 kHz to 1MHz give excellent resolutions but the acoustic energy only travels a short distance. Lower frequencies such as 50 kHz or 100 kHz give lower resolution but the distance that theenergy travels is greatly improved. For benthic habitat mapping, short ranges are used (i.e. 100m or less) which allow relatively small objects to be detected. For deep water work the time taken for a vessel to navigate the predefined line pattern can be greatly increased due to the time it takes to perform a turn at the end of each line. During the survey vessel and sensor positioning were maintained using specialised marine navigation software with high presicion GPS units. Positions were logged in realtime and used to derive a survey path during final data processing and visualisation.
Sub bottom profiling is another acousting imaging method, which is used to acquire stratigraphic data from the layers below the seabed. Sub bottom profilers make use of low-frenquency sound pulses to penetrare layers of sediment and provide information on their composition based on the strenght of the returning sound signal. Commonly, the AquaBioTech Group employs a combination of sidescan sonar, sub-bottom profiling and swath bathymetry to provide the client with the largest amount of data possible within a single survey.
Multiport DTS Drop Down Camera System
Digital drop camera system, with real time video link to the surface allows video monitoring without the need for expensive fibre optic cables. This unique system is ideal for any job that requires real-time high quality photographic images. At the heart of the system is a digital video telemetry system, the telemetry unit provides power and control for the cameras/lights as well as a real time video uplink with bi-directional instrumentation data channels to allow the operator to monitor the seabed parameters. Video images are recorded directly to DVD media with an additional overlay of positional and depth data. Environmental survey operations are mostly undertaken with combined video and deep water stills camera (up to 10mega pixel resolution). The information captured during these survey are used to provide high resolution data for habitat identified by the sonar survey and provide evidence for the presence/absence of potential habitats.
RoxAnn GDx Ground Discrimination System
The RoxAnn system is a remote acoustic sounder that can be used to develop sediment classifications and bathymetry of the sea floor. The single beam transducer operates in the range of 50-200kHz at a rate of one cycle per second and can be used in depths of one to 200 meters. The transducer for the RoxAnn generates sound waves that come into contact with the seafloor, and the way these sound waves, or echoes, are reflected are utilised to classify various bottom types (e.g., sandy vs. muddy). The properties (e.g., amplitude & shape) of a sound wave reflected from the seafloor are determined mainly by the roughness and hardness of the bottom, the change in acoustic impedance between water and sea floor materials, and how sound reverberates within materials at the water/sea floor.