Is there underwater GPS technology

GPS system for underwater navigation

Arlington (USA) - Submarines or divers have to surface in order to use their GPS receiver: The radio signals of the Global Positioning System no longer run underwater. A GPS extension below sea level is neither expensive nor complicated, US researchers are now explaining: They rely on acoustic signals that a single, precisely positioned transmitter sends on request. From the position of the transmitter, the depth of the receiver and the angle of the signal, it is easy and inexpensive to calculate your own exact location.

"The invention provides a single point reference for underwater acoustic modem systems to obtain the distance, direction, and geolocation of independent divers or underwater vehicles," wrote Maurice D. Green and Kenneth F. Scussel of the State Military Office of Naval Research in their in-submission the US Patent and Trademark Office. The heart of the system are base stations positioned exactly under water, which react to the acoustic request of the diver or submarine: If they receive a corresponding sound wave signal, they react with a signal about their own GPS coordinates, their depth and the angle, from which she reached the request signal. The angle is provided by a clever arrangement of hydrophones and underwater sound sensors. From the response signal, your own diving depth and the running time of the two signals, a program can then precisely calculate your own position in three dimensions. According to the researchers, the system also takes into account that the speed of sound waves in water varies slightly with temperature and salinity.

So far, underwater vehicles have been navigating using a combination of four different techniques, which are more or less time-consuming, complicated, expensive or imprecise: so-called inertial navigation measures and analyzes the acceleration and rotation of the vehicle and calculates exactly where it should be from the starting point. In addition, there are simple Doppler speed systems near the sea floor that register the distance to the sea floor and calculate the position of the vehicle to the ground - if there is too much water under the keel, they can hardly be used. Thirdly, the conventional GPS system is used when surfacing and helps to correct the position data if necessary.

And in special cases - such as military operations - the Long Baseline technology helps: a field of fixed underwater buoys reacts like the new system to the vehicle's signals and sends response signals. Here, however, several transmitter points distributed in a relatively close-meshed network are necessary, such as the GPS satellites over water, so that the distribution and positioning of these buoys is again expensive.