Analysis of spark paths in air using three-dimensional image capturing and processing

Abstract

The tortuous paths of sparks in air need capturing in three dimensions in order to analyse their shapes and, ultimately, to gain a greater understanding of the process by which sparks and, indeed, lightning propagate. For short gaps (45 mm), the method used was to obtain two orthogonal images by means of a 45°/45°/90° prism and then to record them with a video camera, but for larger gaps (100–400 mm) the two orthogonal images had to be obtained by means of two vertical plane mirrors with an angle of 135° between them. The images from individual video frames were filtered by application of a threshold, removal of isolated points and thinning. Finally the images were combined and reduced to a single small file consisting of the xyz coordinates of the centre-line of the path.

As examples of the use of these path data, a brief explanation is given of the analysis of some 700 of these image files to yield the fractal dimension of each path, and the relationship of one section of path to the previous section; this was determined as (a) a probability distribution for its direction and (b) its most probable direction with respect to that of the previous section.

Keywords:

• spark paths
• image capturing
• image processing