H2O from GOME Water vapour is one of the most abundant atmospheric gases. More than 99% of water vapour is located in the troposphere where it significantly contributes to atmospheric chemistry, weather, and climate. Its large spatial and temporal variability makes water vapour a tracer for tropospheric changes and especially important for global models which aim to predict climate. The importance of water vapour has generated the need for global water vapour data. The main sources for water vapour data are currently in-situ radio sonde measurements, space borne IR measurements, for example by the TIROS-N Operational Vertical Sounder (TOVS), and microwave soundings, for example with the Special Sensor Microwave Imager (SSM/I). Recently it has been shown that measurements of the Global Ozone Monitoring Experiment (GOME) may provide an additional source of global water vapour data. The algorithm to derive water vapour total column amounts from GOME data is based on the well known Differential Optical Absorption Spectroscopy (DOAS) approach. This approach has been modified to handle the strongly wavelength dependent absorption of water vapour, which is not resolved by the GOME instrument because of its limited spectral resolution. Furthermore, a special Air Mass Factor correction is performed using additional information from O2 absorption features. It is a general problem of space based measurements in the UV-VIS-NIR spectral region  that no information can be obtained from below clouds. For the retrieval of water vapour this is a serious issue, because most of the water vapour is located near the surface and thus not visible in the presence of clouds.  Therefore, only the water vapour column above the clouds may be derived directly from GOME measurements. An example for these results is shown in Fig.1.   Fig. 1: Water vapour column amounts determined from GOME measurements between 1 August 2000 and 3 August 2000. No dedicated cloud correction has been performed, and a tropical reference atmosphere has been used.   To obtain the total vertical column (up to the surface),  a dedicated cloud correction has to be performed, which estimates the "hidden" water vapour amount using additional information from e.g. a climatology. Such cloud correction algorithms are currently under development; however, first results have shown that the cloud-corrected water vapour columns are very sensitive to the choice of cloud top height and cloud coverage. If you are interested in more information on GOME H2O, please contact Stefan Noël.  References: S. Noël, M. Buchwitz, H. Bovensmann, R. Hoogen, and J. P. Burrows, Water vapour retrieval from GOME data, Proc. European Symposium on Atmospheric Measurements from Space, vol. 1, 375-381, 1999. (PS file, ca. 425 kB) S. Noël, M. Buchwitz, H. Bovensmann, R. Hoogen, and J. P. Burrows,  Atmospheric Water Vapor Amounts Retrieved from GOME Satellite Data , Geophys. Res. Lett., vol. 26(13), pp. 1841-1844, 1999. (PS file, ca. 217 kB) S. Noël, M. Buchwitz, H. Bovensmann, and J. P. Burrows,  Retrieval of Total Water Vapour Column Amounts from GOME/ERS-2 Data , Adv. Space Res., submitted. (PS file, ca. 885 kB) S. Noël, H. Bovensmann, J. P. Burrows, Water vapour retrieval from GOME data including cloudy scenes, Proc. ENVISAT/ERS Symposium, Gothenburg, 2000. (PDF file,  ca.1.7 MB)   © 2000 written by Stefan Noël last update: 2000/12/20 Institute of Environmental Physics, University of Bremen