Detecting Tropical Cyclone Formation from Satellite Infrared Imagery

An objective technique to differentiate developing from non-developing cloud clusters during the formation of tropical cyclones is described. As the tropical cyclone develops from an unstructured cloud cluster, the wind field intensifies, and the cloud structures become more axisymmetrically organized around a center. This technique performs a statistical analysis of the brightness temperature gradient to measure the level of symmetry of cloud structures, which characterizes the degree of cloud organization of the tropical cyclone. To quantify the level of axisymmetry of a weather system structure, the deviation angle of each gradient vector relative to a radial line projected from the center is calculated. The variance of the set of deviation angles enclosed by a circular area around the center indicates the level of axisymmetry of the system. The formation of tropical cyclones is detected by calculating the deviation-angle variance technique using every pixel in the scene as the center of the cloud system. Low angle variances pinpoints structures with high levels of axisymmetry, these values are compared to a set of thresholds to determine whether a cloud structure can be considered as a tropical cyclone. The first detection in a sequence indicates a nascent storm. In the presentation we will describe the technique and show performance statistics.