Measurements of Evapotranspiration and Carbon Dioxide Exchange Using New Compact Open-Path Gas Analyzer and Eddy Covariance Technique.

Open-path and closed-path designs of the fast CO₂/H₂O gas analyzers are well-established  and  widely used to measure concentrations and fluxes of carbon dioxide and water vapor in agricultural and natural ecosystems. Both designs have their advantages and deficiencies. Open-path analyzers have excellent frequency response, long-term stability, and low sensitivity to window contamination. They are pump-free and require infrequent calibrations. Yet they are susceptible to data loss during precipitation and icing-over, and may need instrument surface heat flux correction when used in cold conditions. Closed-path analyzers can collect data during precipitation, can be climate-controlled, and are not susceptible to surface heating issues. Yet they experience significant frequency loss in long intake tubes, especially problematic when computing water vapor flux. They may require frequent calibrations and need powerful pump. Here we present field data from third kind of a design: a compact  enclosed analyzer enabled for operation with short intake tube, intended to maximize strengths and to minimize weaknesses of both traditional open-path and closed-path designs. The new gas analyzer has number of  advantages over open-path analyzers. Similar to the closed-path analyzers, it has minimal data loss during  precipitation events and icing, it does not have surface heating issues, and it has improved water specs due absence of solar filter. The new gas analyzer also has a number of advantages over traditional closed-path analyzers. It has good frequency response (close to that of open-path analyzers) due to  small and easily correctable flux attenuation loss in short intake tube. Similar to open-path analyzers, the new analyzer does not need frequent calibration, has minimal maintenance requirements, and can be used in low power configuration with short intake tube. It is also small, light-weight and weather-proof.