Thursday, 16 January 2025: 9:15 AM
348 (New Orleans Ernest N. Morial Convention Center)
Handout (2.3 MB)
The Eddy Covariance (EC) Flux technique is a broadly accepted method to measure the exchange of greenhouse gasses between surface ecosystems and the atmosphere. The primary elements of an EC system are a 3D anemometer and a fast-response collocated gas analyzer for the species of interest. As greenhouse gas research has expanded to include the trace gasses Methane (CH4) and Nitrous Oxide (N2O), there is a need for suitable gas analyzers with a small physical size, low power, low cost, sufficient frequency response, and proven field ruggedness. The TGA300 series, developed by Campbell Scientific, are closed-path trace-gas analyzers for CH4 and N2O tailored to specifically meet the requirements of EC flux measurements.
The newly developed TGA300 trace-gas analyzers are built on the principles of tunable diode laser absorption spectroscopy (TDLAS) and leverage technologies from the TGA200A with a long track-record in the field. A tunable mid-infrared distributed feedback inter-cascade laser provides the light source for the measurement. The analyzer employs a 1 m single-pass sample cell with a small volume allowing the use of a low-power integrated vacuum pump system that maintains 30 kPa sample pressure to clarify the spectral absorption lines. The source laser beam is simultaneously split into a parallel reference gas cell fed by a constant concentration pressurized gas. The reference cell is maintained at the same pressure and temperature as the sample cell and the ratio of these signals cancels out the spectroscopic effects of pressure and temperature. This eliminates additional corrections and calibrations improving the spectral line tracking and stability of the instrument. The sample intake uses a vortex particle separator to clean the sample air and prolong the service life of filtration components. The intake also includes an integrated Nafion membrane and counterflow to stabilize water vapor fluctuations and eliminate the need for water vapor line broadening corrections. The intake components are designed to function without compromising the frequency response of the instrument and provide closed-loop control of sample flow and pressure.
In this study, we examine the sensor-level and system-level performance of the TGA300 instruments during field and laboratory trials. The sensor-level analysis considers the frequency response, noise performance, and accuracy of the analyzers. The instrument is shown to measure frequency response of verifiable atmospheric variation out to several Hertz. Instrument noise is low enough to accurately capture real agricultural flux events and differentiate those from periods without flux. Allan variance analysis shows system stability matching the short-term noise out to approximately 30 minutes. A system-level analysis of the TGA instrument looks at total data availability, power requirements, synchronization, maintenance routines, and logistics of a complete EC station. The conclusions of the analysis are framed from the perspective of practical field application and the specific data requirements of EC flux measurements.
The newly developed TGA300 trace-gas analyzers are built on the principles of tunable diode laser absorption spectroscopy (TDLAS) and leverage technologies from the TGA200A with a long track-record in the field. A tunable mid-infrared distributed feedback inter-cascade laser provides the light source for the measurement. The analyzer employs a 1 m single-pass sample cell with a small volume allowing the use of a low-power integrated vacuum pump system that maintains 30 kPa sample pressure to clarify the spectral absorption lines. The source laser beam is simultaneously split into a parallel reference gas cell fed by a constant concentration pressurized gas. The reference cell is maintained at the same pressure and temperature as the sample cell and the ratio of these signals cancels out the spectroscopic effects of pressure and temperature. This eliminates additional corrections and calibrations improving the spectral line tracking and stability of the instrument. The sample intake uses a vortex particle separator to clean the sample air and prolong the service life of filtration components. The intake also includes an integrated Nafion membrane and counterflow to stabilize water vapor fluctuations and eliminate the need for water vapor line broadening corrections. The intake components are designed to function without compromising the frequency response of the instrument and provide closed-loop control of sample flow and pressure.
In this study, we examine the sensor-level and system-level performance of the TGA300 instruments during field and laboratory trials. The sensor-level analysis considers the frequency response, noise performance, and accuracy of the analyzers. The instrument is shown to measure frequency response of verifiable atmospheric variation out to several Hertz. Instrument noise is low enough to accurately capture real agricultural flux events and differentiate those from periods without flux. Allan variance analysis shows system stability matching the short-term noise out to approximately 30 minutes. A system-level analysis of the TGA instrument looks at total data availability, power requirements, synchronization, maintenance routines, and logistics of a complete EC station. The conclusions of the analysis are framed from the perspective of practical field application and the specific data requirements of EC flux measurements.
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