Very precise measurement of carbon dioxide atmospheric concentration by using TDL's

An instrument which will measure the atmospheric concentration of carbon dioxide with a resolution of one part in 10(4) will be realized in the frame of ''Environment and Climate'' program of the European Community [1]. The aims are the evaluation of global climate changes and the measurement of the flux at the interface air-sea. The requirements for such an instrument apart from resolution are stability and insensitivity to water. This instrument is based on room temperature tunable diode lasers at about 6350 cm(-1), a frequency region free from water absorptions, but only recently covered by laser sources with the required spectral characteristics. The atmospheric concentration of carbon dioxide is about 350 ppm and its absorbance along a path of 100 m is of the order of 1%. The measurement will be performed in a multipass cell. A second cell will supply the references for frequency stabilization and laser power monitoring. The detection is realized through frequency modulation techniques. The various aspects of the work presently in progress will be presented: spectroscopy, optical layout detection method and so on.