A study of the performance of open- and closed-path fast infrared sensors for humidity and CO₂ fluctuations

In order to investigate the reliability of some of the instruments most used to measure humidity and CO_2 concentration fluctuations in field campaigns, two identically equipped meteorological measuring stations were operated for 30 days in the autumn 1995. Each mast was equipped with three different types of fast infrared sensors to measure fluctuations of humidity and CO_2.

Moreover the masts were equipped with standard instrumentation to measure wind speed, wind direction, temperature, humidity, pressure and solar radiation and with a Gill sonic anemometer/thermometer to measure turbulent fluctuations of temperature and wind components. Turbulent data were recorded with an effective sampling rate of 10 Hz.

Thirty-minute averaged statistics of the atmospheric turbulence were derived. In this paper we analyse two periods of three days each and present some results of the comparisons among the absolute values of concentrations measured by fast and slow instruments. Moreover the inter comparison of fluxes estimated by different types of instruments obtained by the eddy correlation method is presented. (au).