Technical Description - Interferometers and Beamformers


Both interferometric multibeams and beamforming multibeams measure range and angle to a series of points on the seabed. A beamformer mathematically forms a set of “beams”, and detects the range to the seabed in each beam. An interferometer measures the angle the incoming sound wave fronts in a time sequence of samples. Slant range is obtained from the time of the sample and speed of sound.

In summary, beamformers measure range for each of a set of angles, and interferometers measure angle for each of a set of ranges.




Wide Swath Width

An interferometer produces a swath width of 10 to 15 times water depth, depending on sonar conditions. This advantage is particularly clear in shallow water (less than 30 m).


Bathyswath measures thousands of depths along every profile, across a very wide swath. Its coverage of the seabed is thus unparalleled.


A beamformer requires digitized signals from each of dozens of transducer elements, which must then be highly signal-processed. This results in a requirement for many amplifiers, wires, connectors and processors. These components must either be present in the wet-end of the system, or highly complex cabling is required to pass through the hull of the platform. Such complexity must inevitably result in reliability problems. In contrast, Bathyswath requires only three or four individual signal channels. The innovative use of electronic processing limits the requirement for many processors. Only the transducers need to be placed in the water, and these are entirely passive: they contain no electronic components at all other than the piezo-electric elements and are completely potted in plastic compound. They are thus extremely compact and robust.

Weight and Size

The simplicity of Bathyswath results in a lightweight, portable package with a small footprint and simple cable requirements.


Interferometric systems can similarly be configured to work from a range of platforms, and in a range of configurations.


Effect of Beam Width at Far Range

Beamformers have a finite width of beam, detecting anything within this beam as signal. Their resolution is thus related to the width of beam. At far ranges, where the beams make a small angle with the seabed, horizontal resolution is poor. In contrast, Bathyswath produces a small pulse of sound and measures returns from this pulse across the seabed. The footprint of this pulse thus remains small, and the resolution of an interferometer remains good even at far range.

Angular Restrictions

Beamformers form a limited number of beams, in a limited angular sector. They therefore cannot survey up to the sea surface unless special mounts are used. In contrast, Bathyswath can survey a full 260° sector with 20° overlap in its standard configuration.

Lower Resolution

With less than a hundred depth measurements in each sonar cycle, it is often necessary for a beamformer to interpolate between measurements in order to simulate full coverage.

Roll Sensitivity

Beamformer profiles, being a much smaller percentage of water depth than an interferometer, are subject to large movements relative to vessel track. This can lead to unsurveyed areas at the swath edges if the survey vessel is subject to rolling motion from wave encounter.