The first MARES water tests were conducted in a local pool in late 2006. Those tests served to validate the integrity of the system, adjust buoyancy and trim, and test simple maneuvers. During the first semester of 2007 a set of tests took place in a reservoir in the Douro river, with a maximum depth of 20 meters and about 200 meters wide. These tests allowed the fine tuning of motion control parameters as well as the final adjustments on the acoustic navigation system.

Fig. 7. Salinity map close to the sewage outfall diffuser.

MARES was first demonstrated at sea in November of 2007. This demonstration mission took place in the neighbourhood of a sewage outfall located 2 km off the Portuguese coast at Foz do Arelho. MARES was equipped with a Seabird Fastcat 49 CTD and collected 16 samples/second of CTD data for about one hour. Upon vehicle recovery, CTD data was analyzed to infer the location of the sewage plume in the vicinity of the diffuser. Fig. 7 shows a salinity map produced from CTD data, and although the salinity signature was very weak, it was also very consistent. This demonstrated the potential for detecting minute anomalies with the onboard CTD, which was the main objective for this mission at sea.

The success of the demonstration mission at sea proved that the initial requirements and the design decisions contributed to the development of an operational vehicle that can be effectively used in real application scenarios. One of the major advantages of the MARES AUV, when compared with other AUVs of similar size, is the ability to independently control the motion in the vertical and in the horizontal planes. This allows for some new primitives of motion, such as commanding the vehicle to be completely motionless in the water column (for example, waiting for some triggering event), or diving and emerging vertically, which greatly simplifies its launching and recovery.

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