This standard describes the determination of heightresolved profiles of atmospheric backscattering by means of active optical sounding. The measurements allow the following properties of the atmosphere up to several kilometres above ground to be derived: ? cloud bases ? upper boundaries of optically thin clouds ? upper and lower boundaries and internal structures of particle layers: ?C the height of thermal structures@ e. g. inversions ?C boundary layer height@ mixing layer height (under suitable conditions) ? backscatter coefficients of the particles ? extinction coefficient (requires further assumptions) The standard goes on to discuss the depolarisation lidar and the use of multi-wavelength systems. This allows further parameters to be determined: ? particle size classification (?ngstr?m exponent@ colour ratio) ? shape classification (linear depolarisation degree) The following fields of application are particularly important: ? air quality monitoring (vertical structure of the boundary layer) ? aviation safety (cloud base) ? particle content and transport (e. g. volcanic dust) ? weather forecasting and climate modelling (e. g. atmospheric boundary layer@ cloud base) ? satellite remote sensing (validation) Examples that illustrate these applications are discussed in Section 11. This standard does not describe extended lidar techniques that capture the following effects quantitatively: inelastic scattering effects (Raman scattering)@ Doppler shift@ multiple scattering@ modulation techniques and spectral separation of molecular and particle backscattering (HSRL = high spectral resolution lidar). Some of these extended techniques have already been or will be described in other parts of this VDI Series of Standards and the DIN ISO 28 902 series. This standard does not deal with the special features of airborne or satellite-aided systems nor those of scanning systems.