The proposal was divided into three phases, which have been successfully processed. Phase I: Performance improvement: A first-generation prototype laser spectrometer was installed as part of the CARIBIC payload on a commercial aircraft to perform autonomous in-situ measurements of δD. A versatile and all digital data acquisition unit based on FPGA technology was developed, tested, and implemented into a second-generation prototype laser spectrometer. Phase II: Instrument characterization and airborne employment: Operation of the first prototype continued onboard IAGOS-CARIBIC, where (δD) isotope ratio measurements were performed in-situ in the upper troposphere. The early version second-generation prototype was employed onboard HALO during the TACTS and ESMVal campaigns, where measurements of UT humidity were performed. The final second-generation prototype was operated onboard a research aircraft during the MUSICA remote sensing validation campaign. Isotope ratio measurements (δD) with unprecedented spatial resolution and well-documented accuracy were obtained. The measurements led to the empirical validation of groundbased and satellite-based remote sensing measurements of δD. Phase III: Data analysis and publication of results: The data analysis and post processing tools have been successfully improved towards higher data accuracy at lower humidity. The isotope ratio data are presently scientifically analyzed.