Aircraft based Stereographic Reconstruction of 3D Cloud Geometry.

This work describes a method to retrieve location and geometry of clouds using RGB images from a video camera on an aircraft and data from the aircraft's navigation system. Opposed to ordinary stereo methods where two cameras with fixed relative position at a certain distance are used to match images taken at the exact same moment, this method uses only a single camera and the aircrafts movement to provide the needed parallax. Advantages of this approach include a relatively simple installation on an aircraft and the possibility to use different image offsets, even larger than the size of the aircraft. Detrimental effects are the evolution of observed clouds during the time offset between two images as well as the background wind. However we will show that to some extent usable wind information can also be recovered. Our method allows the derivation of cloud top geometry which can be used, e.g., to provide location and distance information for other passive cloud remote sensing products. In addition it can also improve retrieval methods by providing cloud geometry information useful for the correction of 3D illumination effects. We show that this method works as intended by comparson to data from a simultaneously operated lidar system. The stereo method provides lower heights than the lidar method, on average by 126 m. This behaviour is expected as the lidar method has a lower detection limit (leading to greater cloud top heights for the downward view) while the stereo method also retrieves data points on cloud sides and lower cloud layers (leading to lower cloud heights). Systematic errors across the measurement swath contribute less than 50 m. [ABSTRACT FROM AUTHOR]