Cloud mapping with ground-based photogrammetric cameras

Ground-based digital imager systems in the visible and near infrared region of the solar spectrum have the potential to nicely complement existing instruments and observation networks of National Weather Services with very accurate, high spatial and temporal resolution, 2D and 3D macroscopic cloud data such as cloud amount, cloud-base height and 3D cloud-base motion. This paper discusses two current approaches to ground-based cloud sensing: the prototype instrument used at ETH/MeteoSwiss within Cloudmap and Cloudmap2 for stereoscopy tests, and a Daylight Visible/NIR Whole Sky Imager (WSI) system developed and fielded by the Scripps Institution of Oceanography (SIO). The article includes descriptions of the radiometric and geometric calibration methods. Cloud amount, cloud-base height and cloud-base motion results from two ETH/ MeteoSwiss measurement campaigns and from the operational WSI use at the German Weather Service (DWD) are shown. Finally, a case study with coincident satellite and ground data illustrates that ground-based digital imager systems are an interesting technique to validate satellite-based cloud-top heights and cloud-top motion winds of vertically thin clouds.