Reliable optical measurement of water vapor in highly scattering environment

Based on tunable diode laser spectroscopy with direct absorption measurement, we developed a reliable measurement scheme which can precisely detect water vapor concentration independent of the scattering (attenuation) caused by the non-water dust particles inside the observed humidity chamber. The relative water vapor concentration was measured at 2ν1+ν32ν1+ν3 water vapor transition band by 938 nm distributed feed-back diode laser at different temperatures using the tunable diode laser spectroscopy technique. These relative water vapor concentrations are converted into the absolute water vapor concentrations and we confirmed that the experimental results at different temperatures are consistently independent of the attenuation. Our measurement system gives the consistent water vapor concentrations without regard to either high or low scattering caused by the non-water dust particles inside the observed humidity chamber.