Background

Wireless Sensor Networks (WSNs) cover a broad application range which includes monitoring of environment, healthcare, industrial, etc. In environmental monitoring, conditions such as temperature and pressure are measured and cooperatively passed through the network nodes to a central location. Wireless Sensor Network for Oceanographic Monitoring (WSNOM) is a particular instance of an environmental monitoring application.

An undergraduate project was conducted by the Department of Electronic & Telecommunication Engineering, University of Moratuwa, to provide a simple, scalable, power efficient and low cost solution for monitoring marine ecosystems in 2014. The prototype system implemented consists of four sensing nodes having an IEEE 803.15.4 (Zigbee) based Wireless Sensor Network (WSN), a one-wire protocol digital thermometer based monitoring mechanism, an Arduino based controlling system and a scalable buoy platform. The mobile network carries the data from the Zigbee WSN to the central location.

The project was carried out with the support of the Dialog-University of Moratuwa Mobile Communications Research Laboratory, in collaboration with the Department of Oceanography and Marine Geology, Faculty of Fisheries and Marine Sciences and Technology, University of Ruhuna and the Sri Lanka Police.

Currently the possibilities of continuing the project on a national scale are being considered as a collaboration of the parties mentioned above, SenzMate(Pvt)Ltd, Sri Lanka Navy and Dialog Axiata PLC.

Nature and Scope of the Problem

Sri Lanka has a coastal belt of 1750 km which supports unique and highly productive and sensitive marine ecosystems the starting point of the food chain for sea animals which is vital for the survival of all sea creatures. Therefore, it is very important to be vigilant about the environmental conditions of the sea continuously.

Marine ecosystems are frequently subjected to natural phenomena such as warm water currents and harmful human activities. Thus, their existence is seriously threatened. Study of marine ecosystems is hampered by lack of data, lack of trained personnel for data gathering and difficulty of access to relevant sites.

System overview

The objectives of the WSNOM are as follows:

• Using remote sensors for monitoring seasonal variations in physiochemical parameters within coral reefs.
  
  
• Providing critical information such as temperature variation in sea water to conserve and manage sensitive coastal and marine ecosystems and endangered marine organisms.
  
  
• Creation of a database accessible to oceanographers and scientists on the unique marine ecosystem around Sri Lanka.

System Architecture

The deployed WSN is a combination of communication nodes, a buoy platform, temperature sensors and a back-end consisting of a web server and a database. Communication nodes consist of a Coordinator with a Gateway and three End Devices. Temperature sensor measurements collected by the End Devices are routed to the Coordinator Node using the ZigBee Communication Protocol. The collected data is sent to the Web Server via the mobile network. Finally, clients/users can access and view the data over the internet. The envisaged WSNOM architecture is shown in Figure 2. The implemented buoy platform for a single node is shown in Figure 3.

Pilot Trial and Results

In an initial pilot trial, the buoys were placed in different locations with minimum of 50m separation at University of Moratuwa and temperature readings were observed. Results are illustrated in Figures 4 and 5. The system performed continuous monitoring for a month without any human intervention. The functioning and reliability of the communication platform was verified during this trial.

Future work will include the following:

• Testing of the system while being kept at sea for a long duration.
  
  
• Deploying other eleven sensing sites around the country.
  
  
• Adding new sensors to monitor more parameters such as salinity and pH levels.

Future scope of the system

Contribution of the deployed Oceanographic WSN can be seen in many areas. It can be used as an early detection and alarming system for hot water currents and other abnormal temperature variations that had destroyed coral-reefs and associated aquatic life in the recent past. Depending on the parameters being measured, the WSN could be used for pollution monitoring, marine meteorology, marine erosion and mining.

The collected data through the WSN is of high value for the marine biologists and oceanographers doing research in these areas. Marine biologists could also deploy the network with the intentions of marine life tracking, observation in population dynamics of marine organisms and effect of sea environment on aquatic life.