A low-cost modular data-acquisition system for monitoring biometeorological variables

We describe the design and implementation of a low-cost electronic modular data-acquisition (DAQ) system in the context of the eddy-covariance technique. The system was fully tested under laboratory conditions and later installed on two eddy-covariance towers (ECTs) sited in natural terrestrial and marine environments, respectively. The system was divided in four parts: signal conditioning, data-acquisition, data-transfer and data-processing. A data-acquisition module (DAM) based on the ADuC848 microcontroller was designed in order to acquire these data. This DAM could transfer data directly to a computer or embedded system. By configuring a RS-485 network, a DAQ system could be expanded up to 8 DAMs working simultaneously. Due to its modular design, different parts of the equipment could be easily replaced without affecting the operation of the ECT. The system registered high-frequency (20 Hz) measurements of CO2, water vapor and wind velocity in the free atmosphere as well as additional ancillary biometeorological variables (1/60 Hz) such as air temperature, solar radiation, soil heat flux, precipitation, and others. Both towers were installed in remote sites using solar cells providing a continuous and autonomous source of energy. This DAQ system proved to be reliable and useful for long-term deployments (> 1 year). Due to its modularity and flexibility the system can be used for any other application involving data recording.