Precise orbit determinations in SLR and LLR results require corrections for the contribution of the atmosphere to the effective index of refraction. Despite the fact that the range measurements are obtained consistently, there is a discrepancy of approximately 4 cm reported in the comparison between optical and microwave based range measurements for the same GPS satellite target. As a conclusion from earlier work, the knowledge of the water vapour content of the atmosphere at least for some selections of the operation wavelength seems important. To overcome the lack of sensitivity for the measurement of water vapour profiles in the Earth's troposphere by means of remote sensing, a biaxial Rayleigh- and Raman-LIDAR has been set up on the Fundamentalstation Wettzell, making use of the still existing equipment of a former SLR facility. By operating the station as a Rayleigh-LIDAR, its geometrical characteristics and the overall sensitivity of this setup as a LIDAR system could be established and optimised. Observations in the spectral range of 607 nm and 660 nm are probing the troposphere for nitrogen and water molecules. By combining this information water vapour profiles of the lower troposphere were obtained.
|