نبذة مختصرة : International audience ; This paper presents a first demonstration of range-resolved differential absorption LIDAR (DIAL) measurements of the water vapor main isotopologue H 2 16 O and the less abundant semi-heavy water isotopologue HD 16 O with the aim of determining the isotopic ratio. The presented Water Vapor and Isotope Lidar (WaVIL) instrument is based on a parametric laser source emitting nanosecond pulses at 1.98 µm and a direct-detection receiver utilizing a commercial InGaAs PIN photodiode. Vertical profiles of H 2 16 O and HD 16 O were acquired in the planetary boundary layer in the suburban Paris region up to a range of 1.5 km. For time averaging over 25 min, the achieved precision in the retrieved water vapor mixing ratio is 0.1 g kg −1 (2.5% relative error) at 0.4 km above ground level (a.g.l.) and 0.6 g kg −1 (20%) at 1 km a.g.l. for 150 m range bins along the LIDAR line of sight. For HD 16 O, weaker absorption has to be balanced with coarser vertical resolution (600 m range bins) in order to achieve similar relative precision. From the DIAL measurements of H 2 16 O and HD 16 O, the isotopic abundance δD was estimated as −51%₀ at 0.4 km above the ground and −119%₀ in the upper part of the boundary layer at 1.3 km a.g.l. Random and systematic errors are discussed in the form of an error budget, which shows that further instrumental improvements are required on the challenging path towards DIAL-profiling of the isotopic abundance with range resolution and precision suitable for water cycle studies.
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