A method for the construction of cloud trajectories from series of satellite images
Knowledge of the trajectories of atmospheric structures is useful in meteorology, in particular for the study of the persistence of clouds at mesoscale and for studies of the large-scale atmospheric circulation. For this purpose, a method for the construction of cloud trajectories has been developed and is presented in this article. This method extends traditional techniques used to calculate cloud motion vectors from satellite images, representing the wind at a single instant and the motion over a short time interval (typically ½h), to the measurement of the motion of the same clouds over a long duration, up to 60 h. Trajectories of clouds have been constructed from series of Meteosat images in the thermal IR, the WV (water vapour) and the VISible channels. Similarly, pure WV structures have been tracked in the WV channel. The duration of a trajectory is mainly related to the lifetime of the tracked structure, but also dependent on its spatial scale. A lesser image quality or a larger time interval between images reduces this duration. The use of severe quality tests enables reliable tracking of a limited number of clouds or WV structures, whereas more tolerant tests lead to larger groups of less precise trajectories nevertheless suitable for the study of large-scale motions.