Multibeam Echosounders

Abstract

Multibeam echosounders have revolutionized our ability to resolve seabed geomorphology and regionally define its substrate. Using a fan of narrow acoustic beams, the slant ranges, angles and returned backscattered intensity can be employed to define the seabed elevation and infer the substrate. A corridor of data with a width proportional to the projected angular sector is acquired along a vehicle track. Before interpreting the resulting geomorphology, however, it is critical to understand the practical resolution and accuracy limitations that result from a particular system configuration. The spatial resolution of the data depend on a combination of the pulse bandwidth, the projected beam widths and their resulting spacing and stabilization. For a given configuration, the single biggest factor controlling the resulting resolution is the altitude of the platform. For surface mounted systems this results in degrading definition of morphology with depth. As multibeam systems improve, there is the potential to monitor temporal changes in submarine geomorphology. To do so, however, each survey has be positioned to a standard finer than the expected change. The total propagated uncertainty in the location of the resolved topography is a combination of the uncertainty in the position and orientation sensors and their integration as well as the bottom detection algorithm and sound speed field. When interpreting apparent change, it is critical to comprehend the realistic achievable accuracies.