New field experiment: A new kind of environmental sensor that can measure the barometric pressure and its fluctuation at a very fast rate and with very high precision was deployed today. The sensors were deployed in a network consisting of 3 identical instruments mounted in a vertical profile on a 140 ft tall tower in a dense Douglas-fir forest in the Oregon Coast Range. It is part of the Advanced Resolution Canopy FLow Observation (ARCFLO) 2013 experiment funded by the National Science Foundation as the central experimental activity of Chris Thomas' CAREER award. The series of ARCFLO experiments aims at identifying the spatial and temporal dynamics of weak-wind flows in vegetated canopies to help build an integrative theoretical framework for airflow and transport that is valid for a continuous variation of surface conditions and stratification.
As inlet for the barometric pressure signal serves a so-called pressure port (white instrument on the left in the upper picture), which consists of 4 parallel discs around a cylinder to align the airflow horizontally and to minimize artifacts from the fluctuating airflow. The pressure sensors are interrogated 20 times per second (at 20 Hz) and have a resolution of 1/100 of one Pascal (N m-2). Each pressure port is paired with a sonic anemometer (instrument on the right in the picture) to combine the pressure signal with that of the velocity of the airflow.
The particular goal of these novel observations is to better understand the pressure transport and its role in creating turbulence kinetic energy (TKE) in forests that are characterized by weak winds. The transport and mixing in weak-wind environments such as forests and urban areas is poorly understood, and can, e.g., aggravate the computation of ecologically meaningful estimates of carbon and water exchange between the forest and the atmosphere.
Precise measurements of barometric pressure fluctuations are very challenging and the methodology is still under development, very few studies have been reported in the literature. Prior to field deployment, the sensors were tested on the roof of Weniger Hall on the OSU campus (picture to the right).