Passive remote sensing of columnar water vapour content above land surfaces. Part I: Theoretical algorithm development - Part II: Comparison of OVID measurements with radiosonde and DIAL measurements
Various efforts are currently being made to develop remote sensing techniques for high accuracy determination of atmospheric columnar water vapour content above land surfaces. Most of those algorithms are based on radiative transfer calcu lations, however, which have to be verified by spectral airborne or satellite measurements. Initial verification of a new algorithm with the aid of airborne spectral data using the spectrometer OVID (Optical Visible and near Infrared Detector), an airborne water vapour DIAL (Differential Absorption Lidar), an airc;raft humicap sensor and radiosonde data is performed dUIing a flight experiment over Southern Germany. This water vapour algorithm is also dedicated to the MERIS (MEdium Resolution Imaging Spectrometer) in strument on board ESA's satellite ENVISAT which will be launched 1999. Spatial water vapour gradients of &120 = 0.1 g/cm2 over a distance of 100 km were resolved by applying the OVID measurements. The error estimation of the absolute value of the retrieved water vapour contents poses· some problems due to insufficient additional temporal and spatial radiosonde data. However, the principal feasibility has been prove
