Technical Description - Hardware



The main components of the Bathyswath are sonar transducer(s), Transducer Electronics Module(s) (TEM), Bathyswath software and a PC computer (not included in the package). Data is recorded by the PC computer onto disk. Data may be archived onto standard PC media, e.g. USB disk. There is one TEM for each transducer; all TEMs are inside the TIU (Transducer Interface Unit)


Sonar transducers are available in three frequencies: 117, 234 and 468 kHz.



The Transducer Electronics Modules connect the sonar transducers to the PC computer. One Transducer Electronics Module is used for each sonar transducer, so a typical system is supplied with two TEMs. Each Transducer Electronics Module (TEM) contains a single printed circuit board (PCB), with flexible connections to the computer and sonar transducer. It is thus extremely robust. The TEM on-board data processing is implemented in a large FPGA. The TEM PCB has sub-sections performing the following functions:

  • Transmitter, which sends an electrical pulse to the sonar transducers. This makes the sonar pulse.
  • Analogue Receiver, which amplifies the returned echo signals, and produces sidescan amplitude data. The Bathyswath analogue circuits provide very high gain and low noise, enabling signals below acoustic sea noise to be measured. The limiting factor to performance is therefore determined only by the external environment.
  • Phase Interface, which receives the amplified sonar signals, measures the phase differences between them and converts the sidescan data into digital form.


Each Transducer Electronics Module (TEM) is connected to the PC computer using an industry-standard USB connection. Up to 15 TEMs can be connected to one PC, with up to four of them being used simultaneously.

If the sonar system needs to be mounted at a distance from the computer, then the USB interface can be extended using a commercial USB extender or USB-to-Ethernet converter. Alternatively, a remote compact computer unit can be installed close to the sonar system and auxiliary sensors, which then acts as a data storage and control unit for the sonar. This remote unit can then be operated over a network link, either cable or Wireless, using standard remote interface software. This latter option is useful for remote systems, such as USVs (unmanned surface vehicles), UUVs (unmanned underwater vehicles) and towed vehicles.


The Bathyswath software operates in Microsoft Windows. Commands may be entered via the mouse and keyboard. A wide range of displays is available, which allow the operator to monitor and control the operation of the sonar system.


The operating software supports ports to allow real time interfaces to other survey suite sensors, including Motion Measurement, Position (DGPS / RTK DGPS) and Heading (NMEA 0183 format). It also supports multiple information streams from integrated systems. Tide height information can be input manually either from a telemetry system or in post processing. Water speed of sound profiles may be input manually after speed of sound dips or in post processing.


Ship Hull Mount Configuration

Pole mount configuration – Side mounting Pole mount configuration – Bow mounting

This configuration is used where Bathyswath is to be permanently mounted on a vessel, and where a pole mount is not required.









This configuration is used when a permanent hull mount is not required. The “wet end”, consisting of the transducers and the motion reference unit in a watertight pod, is mounted on a special plate at the end of a rigid pole. The pole is deployed over the side, or on the bow, of the vessel. The pole can be hinged or retractable, so that the system and the ship are not at risk in shallow water. Alternatively, Bathyswath can be deployed through a moon pool or gate valve. For the reasons implied in the advantages of a bow mount, it should ideally be possible to stow a side mount away during transit to site or when coming alongside. A rigid side mount is usually acceptable for a few days, but after that, the time wasted in slow transits to site, or in mounting and de-mounting a rigid mount at sea, is greater than the time taken to prepare a movable mount. Another consideration with side-mounts is that good fixing points are often not available along the side of small vessels. It is sometimes possible to use the side rails for the mountings, but this should be discouraged on safety grounds.

For use on small ships of opportunity, the best mounting position is usually on the bow, because:

  • It is rigid and mechanically stable, even at speed when making transits to site.
  • The transducers have a clear view of both sides of the vessel, and therefore the transducers can be mounted above the bottom of the keel. This means that the transducers do not need to be lifted when coming alongside or operating in shallow water.


This needs to be done with caution, as aeration from the propellers severely reduces sonar range. It can sometimes work when outboard motors are used.


Bathyswath has been used on a range of remote and underwater platforms, including unmanned surface vehicles (USVs) and unmanned/autonomous underwater vehicles (UUVs/AUVs). It is also ideal for use on remotely operated vehicles (ROVs).


Bathyswath can be used from very small boats such as rigid-inflatable boats (RIB), and can be configured to use DC power from a battery, rather than mains power. The higher frequency transducers are smaller and lighter than the low frequency ones, and are thus more suitable for this application. A carefully selected system of Bathyswath with laptop and lightweight auxiliary sensors can weigh less than 10kg and consume less than 20 Watts. The plank is fixed across the inflatable hulls and the pole is rotated out of the water for fast transits.