Measurement of the isotopic ratio distribution of (HDO)-O-16 and (H2O)-O-16 in the 20-38 km altitude range from far-infrared spectra

The altitude distribution of the isotopic ratio between (HDO)-O-16 and (H2O)-O-16 in the stratosphere is derived by retrieving the mixing ratio profiles (from 20 km to 38 km of altitude) of the two isotopic species from far-infrared emission spectra. The measurements were made with a balloon-borne Fourier Transform Spectrometer capable of 0.0025 cm(-1) spectral resolution during the IBEX 92 campaign. The retrievals were carried out using the global-fit procedure on a statistically significant number of spectra for each isotope, in the 40-75 cm(-1) spectral region. This measurement determines the D/H ratio in stratospheric water over an altitude range larger than that of previous measurements. The value of the (HDO)-O-16/(H2O)-O-16 ratio, normalized to the standard value, ranges from 0.4 to 0.5 (with a 10% random error) in the altitude range studied and is in good agreement with the values previously measured.