Multi-beam echo sounders (MBES) have gradually taken over a fair slice of the bathymetric survey cake. MBES is nowadays a
common survey tool for offshore surveyors, civil authorities, dredgers and military users. It has proved an efficient alternative to single-beam systems, even in combination with side-scan sonar.

Since its first introduction, the number of beams used in MBES has gradually grown. As a result, the volume of data produced has become a critical issue, not only in data acquisition itself but in processing too. A MBES with 240 beams pinging at a rate of twenty times per second, for example, produces a dataset of over 34 million XYZ points per hour. Nowadays, processing time for these high-density datasets is approximately equal to data-acquisition time.

Editing to remove erroneous observations and decrease data volume consumes the major part of total processing time. These procedures are applied off-line, although (more advanced and hence more expensive) new software is available which makes possible real-time processing. This is quite important, for example, in dredging operations where (near) real-time production of DTMs minimises time spent by an expensive vessel in passively waiting before it can start or continue dredging.

MBES has quickly proven its superior capabilities over previous systems used to provide complete coverage of a sea bottom. The unique capabilities of the MBES allow it to provide 100% coverage of the bottom, even exceeding IHO specifications. The fact that the MBES transducer is rigidly mounted to the hull enables the user to calculate its position as accurately as the positioning system in use, contrary to the ever-present little errors so well known with towed systems such as side-scan sonar.

MBES may also have caused acceleration in the development of motion-sensing systems and Real Time Kinematic GPS systems and applications. Indeed, no MBES system is complete without accurate positioning, motion sensing and a signal-through-water propagation speed measurement system. Add to this a good data collection/storage and processing system with adequate software and capable, qualified survey staff and you have a perfect package for executing the most challenging survey in very short time.

Since one has to start with the hardware, we have asked the manufacturers of MBES systems for a detailed description of MBES systems up to 300m depth; all information may be found in this month’s Product Survey. In February 2007, the Product Survey will describe Deep Water MBES systems.

Participating suppliers:

• Kemijoki Aquatic Technology: AquaticSonar Swathe Surveyor
• Kongsberg maritime: EM3002 (D)
• L-3 Communications: Sea Beam 1185
• Reson: Seabat 8125