A new mini TDL for open‐path measurement of CO2 fluxes in situ

Most current CO2 flux measurement sites are equipped with a single set of instruments above the plant canopy due to the cost of instruments and maintenance. Here we introduce a new sensor being developed at Lawrence Livermore National Laboratory that will reduce the cost of flux and concentration measurements thus allowing for multiple points of measurement throughout a canopy. This is especially important at canopies with a vertical stratification of fluxes (i.e. 2-layered canopies) or a high canopy storage term (i.e. tall forests). The sensor uses a vertical cavity surface‐emitting laser (VCSEL) tuned to a narrow spectral range targeting CO₂ absorption lines according to the HITRAN 2012 database. The multipass sample cell measures 5cm x 4cm x 1cm with a path length of 1.5 m and can sample at ≥10Hz. We show data from laboratory testing of the sensor at a range of CO₂ concentrations from 5 ppm to pure CO₂. We also will demonstrate sensor performance across a range of temperature and humidity in the lab. Finally, we will show the first data from deploying the instrument into the field alongside traditional IRGA sensors.

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.