Water Quality Monitoring in Orbetello Lagoon Using OceanAlpha USV

The Orbetello Lagoon is a semi-enclosed coastal basin at the southern end of the Tuscan coast in Italy. The lagoon is characterized by very shallow water, with an average depth of about 1 m. Over the past few years, high nutrient levels and algal blooms have raised concerns about water quality and the conservation of fish stocks, the most important species in this ecosystem. Orbetello municipal government worked with program Retralags to choose OceanAlpha SL40 USV as the autonomous platform for water quality monitoring in the lagoon.

Background

The Orbetello lagoon (Fig.1) has two stationary water quality monitoring stations, but how to quickly collect the necessary water quality parameters and monitor the changing trend is a problem, local governments need to take action before the water quality go worse in critical periods. So, an efficient water quality data collection tool is needed.

Fig. 1 Orbetello lagoon (in red circle)

Solution

The SL40 is an autonomous multi-function platform for water survey and monitoring, the YSI EXO2s probe was chosen for water quality monitoring including parameters Temperature, PH, Conductivity, DO, Turbidity, Chlorophyll, and BGA. Dual frequency single beam echo sonder adopted for bathymetry survey, underwater camera used for observation of the underwater
environment.

Fig. 2  SL40 USV, YSI EXO2s probe, echo sounder and underwater camera

Monitoring Work

OceanAlpha USV base station software (Fig. 3) provides a friendly user interface for water quality monitoring mission planning.

Fig. 3 Mission planning in USV base station software

The compact USV was easily mobilized with a trolley and launched by two people.(Fig.4).

The USV base station software monitors the mission status and controls the USV, sonar control interface to adjust echo sounder settings, and real-time video in monitoring the water environment.
① USV base station software and real-time water quality data
② Echo sounder interface
③ USV PTZ camera
④ USV camera

Fig. 6 Water quality monitoring interface

Monitoring Results

The USV acquired water quality data based on waypoints (Fig. 7), time, coordinates, and details of parameters were recorded. The monitoring data can be exported in a distribution map and also processed in QGIS to get the water quality map(Fig.8). This helps to understand the lagoon water quality quickly based on different parameters.

Fig.7 Water quality monitoring data (Data courtesy of Università di Siena, http://www.retralags.eu/)

Fig.8 Water quality data processed in QGIS (Data courtesy of Università di Siena, http://www.retralags.eu/)
 

Conclusion

SL40 USV plays an important role in the lagoon water quality monitoring with the key features below.
① The SL40 USV has a high level of manoeuvrability and automation, it is able to plan and optimize the monitoring waypoint with high precision, and has the ability to monitor
the entire lagoon in a short time.

② Compared with traditional manned ships, SL40 USV is a safe, economical, and efficient alternative.

③ The SL40 is convenient for repeated and long-lasting monitoring activities and can perform monitoring tasks in difficult-to-access waters.

SL40 is an innovative application in lagoon monitoring, according to the project’s agreement with Orbetello Municipal Government, SL40 USV will become an important tool for observing the ecological conditions of the lagoon.

In addition to water quality measurement at any time, regular monitoring operations from spring to early autumn can also be organized. These operations will allow for a detailed understanding of trends in certain water quality parameters and are particularly useful for observing changes in the lagoon during the critical period (July and August).

Some parameter values are often crucial to the survival of fish fauna. If abnormal data is monitored, the acquired data can be quickly sent to the management department to take prompt action to deal with these abnormalities.