A LOW-COST SUBMERSIBLE DATA LOGGER SYSTEM FOR ENVIRONMENTAL MONITORING NETWORKS

The cost of commercial hydrological sensors poses a significant barrier, often limiting the number of sites and temporal scope of monitoring projects. We present a data logging system designed for monitoring projects that require more than one year of continuous operation. These units are relatively easy to build for $50-$150 using Arduino microcontrollers housed in standard PVC fittings. They are powered by standard AA batteries, and save csv formatted data on removable SD cards. Variables such as sampling frequency are user adjustable, and the driver software is easily modified to support a variety of different analog or digital sensors.

Two beta model configurations will be presented. The first records water flow using the principle of the hydro-metric pendulum, where drag-force induced tilt of a freely swinging body allows current speed and direction to be derived. This design has already survived more than three months of salt water submersion at 5 m depth in a flooded cave environment, and has been pressure tested to greater than 30 m. A second prototype, designed to study vadose hydrology, records the number of individual drops of water on the housing using an accelerometer.

The goal of this open source project is to provide a robust platform that is inexpensive enough to bring large scale monitoring networks within the range of modest research budgets. In addition, exploratory “tattle-tale” deployments of these loggers is a low risk strategy for identifying locations within complex systems that are worthy of more intensive study with commercial equipment. Working physical models will be presented, and links to the construction plans and software provided.