Positioning Systems For Unmanned Underwater Vehicles: A peek into future development
This entry is based on the work done by Jeremiah Sullivan, published in IEEE Potentials. Sullivan, J. (2017). An acoustic positioning buoy. IEEE Potentials, 36(2), 16–19. doi:10.1109/MPOT.2016.263037.
Communication underwater can be achieved via tethered communication lines (wired), lights (wireless) and acoustics (wireless). A cost effective wireless communication system that can enable data transfer, positioning and tracking for Autonmous Unmanned Vehcles (AUV), is a subject of tremendous research and development interests. This blog entry summarizes advancement in this field.
Unmanned Aerial Vehicles (UAVs) and Unmanned Ground Vehicles (UGVs) benefit a great deal from GPS and other terrestrial microwave communication system. One of such benefit is to coordinate navigation for an individual or a swarm of vehicles. The tremendous advantage of being able to ascertain the precise location of an aerial or ground vehicle is a complex challenge for Unmanned Underwater Vehicles (UUVs). Radio wave transmissions do not work under water and as such pose significant challenges for under water vehicles.
Communication underwater is achieved, cheifly, via accoustic signals. Data is transmitted via sound through hydrophones where both the transmitter and the receiver are equipped with modems that are designed to convert data to sound and vice-versa. It is worth mentioning that the data rate of accoustics transmissions is in the order of kilo bits per seconds. Automous Underwater Vehicles (AUVs), a category of a UUV, are designed to carry out their mission without real-time command and control intervention from a human operator. As a consequence of being untethred and working autonmously, an AUV could get lost as it travels great distances while on its mission. Worst of all, an idle or an AUVs in low power mode can glide and drift with water currents making it difficult for operators to search to retrieve it.
A level of system tracking similar to what is used for aerial and ground vehicles is needed to keep track, locate and provide precise positioning information to underwater vehicles. Sullivan proposes a design based on using buoys to act as positioning nodes for AUVs. The design models terrestrial (as can be found with cellular tower triangulation) and satellites (as used in GPS) to determine the planar coordinates of AUVs. The significant of this approach is the potential in cost savings since the current way of communicating, tracking and providing tracking references to AUVs is through a ship or a network of ships. This approach can be cost prohibitive and as such limits the duration and type of mission to be carried out.
A network of buoys capable of communicating with AUVs underwater can provide reference positions to the AUVs. They can be linked to command and control stations ashore via sattelites. In addition they can communicate with above water surface vehicles via WiFi or even UHF signals. Much like cellular towers, a newtork of buoys can serve as relay nodes for underwater navigation and communication systems.
I agree with this approach in providing AUVs with positioning information. It must be noted, however, that untethered buoys drift with water current so measures must be taken to ensure that the network stays intact. An interesting approach, if anchorage is not an option, will be to use a semi-submersive autonomous (ASV) vehicle that is equipped with the same communication apparatuses as the buoys(Sesano, 2016). The advantage of the ASV is that it can follow a completely submerged AUV or school of AUV to while providing uninterrupted link between surface entities and the AUV or AUVs.
Bruzzone, G., Bibuli, M., Zereik, E., Ranieri, A., & Caccia, M. (2017). Cooperative adaptive guidance and control paradigm for marine robots in an emergency ship towing scenario.International Journal of Adaptive Control and Signal Processing, 31(4), 562–580. doi:10.1002/acs.2667
Sasano, M., Inaba, S., Okamoto, A., Seta, T., Tamura, K., Ura, T., . . . Suto, T. (2016). Development of a regional underwater positioning and communication system for control of multiple autonomous underwater vehicles. Paper presented at the 431–434. doi:10.1109/AUV.2016.7778708
Sullivan, J. (2017). An acoustic positioning buoy. IEEE Potentials, 36(2), 16–19. doi:10.1109/MPOT.2016.2630378