The instrument systems are a new design for eddy-covariance measurements that consist of modular, largely self-contained units (approximately 1m x 0.6m x 0.2m) which house all key measurement and datalogging instrumentation. Units are directly mounted on the tower, minimizing sample tube length (~2m in our case) between air sampling ports and the closed-path measurement device (Licor 6262 infra-red gas analyzer). This system maintains the advantages of the closed-path design (e.g. precise instrument calibration) while also adding some of the advantages (e.g. minimal disturbance of the air sample before measurement) attributed to open-path designs. This system is particularly suitable for deployment in the very tall vegetation of the Santarem primary forest site where the problems posed by very long sample-tubes from the top of the tower to a ground-based measurement device would be exacerbated.

Each of the temperature-controlled units have the same basic hardware configuration, including a Licor infrared analyzer, CR-10x datalogger, custom multiplexer/filter electronics, power supply, and air pump and pressure and flow controllers for the sample air stream. Additional inputs to handle external signals from sonic anemometers (for the eddy covariance units) or from other associated instrumentation (radiometers, cup anemometers, wind direction sensor, etc., for the profile system) are tailored to each unit.