Multiple-beam Acoustic Transducers: Differentiating Beam Signals
A new approach to seabed mapping using Multiple-Beam Echo Sounders (MBES) has been highlighted in a reprinted paper published in 1961 in The International Hydrographic Review. The paper, titled "Beam identification in multiple-beam echo sounders" by M. J. Tucker, delves into the benefits of tilting transducers to enhance the clarity of port and starboard seafloor areas in 3D maps.
In traditional MBES systems, an array emits fan-shaped acoustic pulses across a wide swath of the seabed. Port and starboard beams are identified by their angle relative to the vessel's centerline. However, overlaps can occur, leading to ambiguity in lateral positioning.
Tilting transducers address this issue by physically biasing the beam angles, thereby separating port and starboard beams more distinctly. This orientation improves the accuracy of lateral positioning in the resulting 3D seabed map.
One of the key advantages of using a tilted transducer is the ability to differentiate port and starboard beams by their different intensities. This is particularly useful when the transducer has a stronger axial beam.
The paper also discusses the application of multiple side-lobes to echo sounding for determining the bathymetry of the sea floor, a topic previously explored by Tucker (1960) and Howson and Dunn (in press).
The record shown in Fig. 3, taken approximately 30 miles ESE of Cape St. Vincent, illustrates the benefits of this approach. It depicts a submarine canyon, with the outside lobe crossing the canyon bed before the one directly under the ship, providing additional information that aids in understanding the canyon's geometry.
The extra information from a multiple-beam sounder can also help in deciding whether humps on adjacent runs are isolated or connect together to form a ridge.
For surveyors, this new approach offers an efficient way to create accurate 3D maps distinguishing port and starboard seafloor areas. Care must be taken, however, to ensure that fore and aft side-lobe beams do not interfere with the picture, and the transducer should be at least twice as long as it is wide.
Further studies, as outlined in the papers "A narrow-beam echo ranger for fishery and geological investigations" by Tucker and Stubbs, and "Directional echo sounding trials; trials with interferometric and sector scanning systems" by Howson and Dunn (in press), are expected to provide more insights into this promising technique.
The original paper can be found at this link: https://journals.lib.unb.ca/index.php/ihr/article/view/26493. For those interested in the history of this development, the paper "An acoustic aid to sea-bed survey" by Chesterman, Clynick, and Stride was published in 1958 in the journal Acustica.
Data-and-cloud-computing can be leveraged to store and analyze vast amounts of seabed mapping data collected by Multiple-Beam Echo Sounders (MBES). Technology plays a crucial role in processing this data into high-resolution 3D maps.
With the increased usage of MBES in seabed mapping, cloud-based solutions can facilitate real-time collaborative analysis, improving the efficiency and accuracy of geological investigations.
