Description Divers and ROV navigation systems based on hydro-acoustic emissions have been successfully used in the offshore industry for several decades. They allow the supervisor to guide the diver or the ROV according to a map regularly updated by the surveyor and displayed on a monitor in the dive or ROV control. Thus, we can consider that their use has become common in most offshore underwater operations, and most teams consider their use essential. However, most systems in service on vessels are voluminous and require the boat to be specifically designed or adapted for this purpose and to be of a size sufficient to accommodate components such as the poles and their deployment systems, in addition to transceiver units, responder driver units, the operator station, etc. As a result, these systems cannot be used on small surface support units such as those used for scuba replacement diving and ROV operations with class 1 & 2 machines in areas not accessible to ships commonly used offshore. However, several electronic equipment manufacturers propose technical solutions that can be implemented on light surface support units or from a jetty to compensate for this void. Even though they are less powerful than the units used on offshore ships, these systems provide sufficient precision to guide a diver or an ROV efficiently and are easy to transport and implement. It is, for example, the case of the MicronNav 200, sold by Maritech, a company based in Pertuis, France (https://www.maritech.fr/), and built by Tritech (https://www.tritech.co.uk/). The Tritech MicronNav system is an Ultra Short Base Line (USBL) acoustic tracking system using a 20-28 kHz band. It is designed for tracking or marking the position of underwater vehicles or objects with 180° hemispherical coverage from the surface unit and 360° omnidirectional coverage from the subsea unit enabling continuous tracking even in very shallow water. Its tracking range is up to 500 m horizontal and 150 m vertical, with up to 20 cm accuracy, depending on whether environmental conditions that may degrade the signal are present or not (thermoclines, acoustically reflecting surfaces, ambient noise, change of salinity, surface and seabed reflectivity, etc.). The system is capable of monitoring up to 15 transponders. The MicronNav system works through the Seanet Pro software package, which can be installed onto a desktop computer or a laptop, a MicronNav interface hub, a lightweight surface USBL transducer, and one or more small subsea MicronNav Modem/transponder heads. The picture below shows that the size of the subsea unit is small enough to be fitted to most small observation class vehicles. It can also be fitted on the diver bail out. The system can be used stand-alone in transponder mode in which case the subsea unit only requires power, or be used with Tritech's range of imaging SONARs in responder mode in which case the subsea unit is powered by and communicated with through the SONAR auxiliary (AUX) port (See the scheme below). The data displayed on the computer screen vary according to the functions selected. They can be limited to the distance and direction from the transducer (see example #1 below) or provide a lot of additional elements such as sonar picture, roll, pitch, depth, and more. Maps such as those from Google Maps can be added to visualize the position of the transducer and the diver or ROV on them (see example #2 below). To conclude, we can say that this device allows for the control of many ROV parameters and can also be used for monitoring divers. It must not be seen as a competitor of the systems traditionally used on offshore vessels but as a complement allowing to organize operations in areas not accessible to these systems. Tritech provides a video that illustrate some of the possibilities of this equipment. Click here to open it Other divers and ROVs navigation systems Diver6: Diver6 is a monitoring system, initially designed for scuba divers, that uses hydroacoustic technology to transmit data between topside and diver modems. The topside modem is an acoustic modem and an Ultra Short Base Line (USBL) transceiver that can detect the diver's transducer and calculate his geo-position by combining his relative position to the topside modem and the GPS position of the topside modem. The modem also transmits data such as cylinder gas pressure, depth, descent/ascent rate, and water temperature to the topside. Contact: https://diver6.azimuthinc.com