Identifying Beams in Multi-Beam Sonar Systems
In a recent study titled "Beam identification in multiple-beam echo sounders" by M. J. Tucker, the design and application of multiple-beam echo sounder transducers are explored to enhance the examination of the sea floor. The paper, which can be accessed here, discusses various techniques to distinguish between port and starboard beams and highlights the benefits of using side-lobe beams.
The design of a multiple-beam echo sounder transducer involves precision multi-element arrays, sophisticated beamforming with phase and amplitude control, high-frequency operation for resolution, and physical placement and array segmentation to cover port and starboard sectors distinctly. The study cites several works related to directional echo sounding, including papers by Tucker, Stubbs, Howson, and Dunn.
Key design elements include array configuration, beamforming, beam separation, high frequency and resolution, physical layout, and signal processing. Array configurations consist of multiple linear or 2D arrays with elements spaced to cover a wide field of view. Beamforming involves phase shifting (time delay) and amplitude shading (weighting) across elements, steering beams and suppressing sidelobes. Beam separation is achieved by designing transmit and receive beams with different widths and directions, and receive arrays with multiple elements enhance angular resolution. High-frequency transducers enable high axial and lateral resolution, improving discrimination between echoes from port and starboard directions.
Physical layout often involves multi-element arrays mounted so that the transmit beam covers the desired swath, splitting into multiple receive beams pointed port and starboard for high spatial resolution bathymetry or imaging. Signal processing algorithms interpret phase differences and Time of Flight from each beam for target localization, enhancing port/starboard discrimination.
These techniques are implemented in commercial multibeam echo sounders like the BII7660 series and Surveyor 240-16 MBES, which utilize phased arrays, amplitude shading, and beam steering to produce multiple, well-separated beams covering port and starboard sides with minimal crosstalk.
The study also discusses the application of multiple side-lobes to echo sounding for determining the bathymetry of the sea floor. The outside lobe crossed the bed of the canyon before the one directly under the ship in the record shown in Fig. 3. Care must be taken that fore and aft side-lobe beams do not interfere with the picture, and the transducer should ideally be at least twice as long as it is wide.
The extra information provided by multiple-beam echo sounders can help fill gaps between soundings obtained on normal survey runs and allows a more detailed examination of interesting features on the records. The manuscript is a reprint of a paper published in 1961 in The International Hydrographic Review. Tucker and Stubbs have an upcoming paper titled "A narrow-beam echo ranger for fishery and geological investigations" in the Brit. J. Applied Physics, while Howson and Dunn have an upcoming paper titled "Directional echo sounding trials; trials with interferometric and sector scanning systems" in the J. Inst. Nav.
The depth at the position where side-lobe beams hit the sea bed can be determined without a geometrical construction, as it bears a fixed ratio to the range measured from the recorder chart. The record shown in Fig. 3 was taken approximately 30 miles ESE of Cape St. Vincent and shows a submarine canyon. Using a transducer with several secondary beams, or side-lobes, can further enhance the examination of the sea floor using echo rangers.
- The exploration of the sea floor using multiple-beam echo sounders includes the implementation of advanced science, such as high-frequency operation and sophisticated beamforming, which are significant components of technology.
- The study's discussion on the use of multiple side-lobes in echo sounding is an example of how science and technology intertwine, as the side-lobes can be considered a technological application of scientific principles to enhance the examination of underwater terrain.
