Nuno Cruz, a researcher at INESC Porto and project leader, explains that to test TriMARES’ acoustic positioning system, two buoys with acoustic beacons were placed 300 metres apart, so the vehicle can determine its own position through triangulation. These buoys can receive acoustic signals emitted by TriMARES and they can respond with signals that allow the vehicle to calculate its distance. The buoys also have GPS receivers and communicate with the mission control station via radio which makes it possible to visualize the AUV’s position and send emergency signals to abort missions.

With TriMARES in the water, the team conducted an automatic calibration of the acoustic navigation network to determine the best frequencies to use and the levels of noise in the operational zone. This made it possible to determine the location of the vehicle via radio from the control station. The automatic calibration made it possible to define the best frequencies and noise levels and this only needs to be conducted once. Following the calibration, it was possible to determine the vehicle’s position using the acoustic triangulation system. In agreement with the Brazilian consortium, TriMARES’ acoustic system will only be ready in the next few months and will not be sent with the robot to Brazil in June. 

Nuno Cruz notes that when the vehicle is connected and it is on the surface, “TriMARES has a wireless flash drive with a small antenna that is not submerged and, through collaboration with the Telecommunications and Multimedia Unit at INESC Porto, this will soon be replaced with an even smaller antenna that is about 3cm long” meaning this project can constantly be improved.

At the control station a router with a 18 dBi sector antenna was installed to communicate with TriMARES. “We were able to communicate with TriMARES via wi-fi every time it surfaced even though there were small waves caused by the wind and other boats in the area. We were able to maintain the broadband connection for up to 200 metres,” he confirms. 

Nuno Cruz describes the procedure for TriMARES’ in autonomous mode: “we started with simple missions, making the vehicle hover in the water at various depths. We tested the abort commands by sending acoustic signals to the buoys”. Next, we completed short underwater missions where TriMARES travelled in a determined direction in a straight line and at various depths.

TriMARES should arrive in Brazil at the beginning of June and will complete tests in the Atlantic Ocean around Rio de Janeiro in late July. 

Source: BIP May 2011