The massive development take place in the field of IoT (Internet of Things) has enabled generation of large set of real time environmental data from low cost sensor networks. This has enabled developing nations to monitor their environments with more economical options. The environmental monitoring network of Sri Lanka is mainly handled by the government bodies such as Meteorological Department, Irrigation Department and Central Environmental Authority. Most of the systems are manually operated and sparsely distributed. The automated systems are restricted to certain main cities of the country. Thus, the data provided by the existing network not capable enough to generate reliable climate or disaster specific forecasts. The available data is mostly retained as hard copies and they are not freely and publicly available. Hence, every time, the researchers and decision makers need to purchase data and required to undergo redundant data collection procedures. In this context, the 4ONSE research project on developing an experimental, open-source, low cost and non-conventional Environmental Monitoring System (EMS) can be considered as the 1st initiative in Sri Lanka which creates a new revolution in the country for environmental data viewing and sharing without any charge. 4ONSE is the acronym for 4 times Open and Non-Conventional technology for Sensing the Environment, which is a joint research between University of Moratuwa and University of Applied Sciences and Arts of Southern Switzerland (SUPSI). Deduru Oya river basin area is the selected study area to deploy the 4ONSE systems. The Deduru Oya is 115km long and covers 2687km2 of catchment area. It carries flash floods during rainy seasons and very low flow during the dry seasons. Hence, the selected case study area is ideal for developing any forecasting application based on the real time environmental data. The project team has already deployed 27 systems in the basin. Temperature, rainfall, atmospheric pressure, solar radiation, relative humidity, soil moisture, wind speed and direction are the parameters measured by the system. In this research we attempt to present the state of the art of open source based environmental monitoring, architecture of the 4ONSE system, motivations behind deployment of the 4ONSE system and finally the lessons for the future research and development.
