Color Analysis of Lightning Leaders: Application of Astronomical Photometry

In this paper, lightning leaders have been analyzed from a digital still image, by using our new color analysis method. Applying astronomical photometry, color indices B-G, B-R and G-R of the lightning leaders were defined by B-G G= -2.5 log(10) F-B/F-G, B-R = -2.5 log(10) F-B/F-R and G-R = -2.5 log(10) F-G/F-R. Using the brightness V and color indices B-G, B-R and G-R of the lightning leaders, the brightness-color relations (V, B-G), (V, B-R) and (V, G-R) were obtained. To represent the lightning image using the color indices B-G, B-R and G-R, 2D color index images (B-G)(2D), (B-R)(2D) and (G-R)(2D) were obtained. It was indicated that the lightning channels emit mainly the B and R band light from the brightness-color relations, though the intensity of the G-band light is low. From the 2D color index images, it was found that the color of the lightning leaders changes spatially. Furthermore, it was suggested that the spatial variability of the color of the lightning leaders is related to the lightning channel current, from the 2D color index images (B-G)(2D), (B-R)(2D) and (G-R)(2D).