A system to make atmospheric measurements from a moving trolley suspended by a stretched cable has been developed. At present, these measurements consist of wind velocity, temperature, humidity, and carbon dioxide concentration, though other sensors may be added. The track consists of cable segments attached to turns mounted on standard triangular towers. Using this approach, the path can be a closed (three dimensional) polygon of arbitrary length. This tool allows continuous, high spatial and temporal resolution sampling in environments, such as within forest canopies, not possible with other platforms. This system was used at the Niwot Ridge AmeriFlux site to obtain insight into the spatial and temporal structure of CO2, wind, and humidity fields in a natural forest ecosystem. Specifically, cool, moist, and CO2-rich air was observed to move in thin blobs downslope along the local water drainage through the subcanopy space at night.