Retrieving the Velocities of Motion of Air Masses from Digital Images of Clouds
Dimitar Bakalov(1) and Kalinka Bakalova(2)
(1) Institute for Nuclear Research and Nuclear Energy, 72, Tsarigradsko ch., 1784 Sofia, Bulgaria
(2) Solar-Terrestrial Influences Laboratory, BAS, Bl.3, G. Bonchev str. , 1113 Sofia, Bulgaria
An interdisciplinary project, aimed at developing tools for the determination of the physical characteristics of the atmosphere by means of ground-based digital imaging in the visible range is now in progress. Determining the 3-dimensional field of velocities of motion of the air masses from digital images of clouds is among the central tasks. The idea of the approach is to identify patterns of the cloud structure with characteristic shape and to measure their angular displacement by tracking them in series of consecutive digital images, taken at optimal time intervals.
To do this, methods for the choice of appropriate patterns in the image of a cloud (that depends on the type of the cloud) and for recognizing these patterns on later images under the condition of continuous deformation of the cloud shape needed to be developed. We present here some results, obtained with the first versions of the computer codes we are now developing. A few images of relatively simple cloud systems have been digitally processed to: (a) automatically determine the cloud type; (b) automatically choose a few characteristic patterns in the image of the cloud, and (c) recognize each of these patterns in a sequence of images of the same cloud by adopting a parametric model of the deformations of the cloud shape with time (an assumption that is valid for sufficiently small time interval between the consecutive images). We also discuss the algorithms for obtaining the 3-dimensional field of velocities by means of parallel processing of synchronous images of the sky taken from distant points of view, and give an estimate of the accuracy of the method.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,