3.The bright lights of Tucson, Arizona, are more than matched by a flash of lightning far above the city skyline. The sunset scene shows a classic cumulonimbus cloud formation.
4.The scheme has a novel feature that the extraction location of the tracer is not fixed at the center location of the grid, but first optimized at the location where the gradient is maximum in the grid domain, and then by cumulonimbus and uniformity test, the final tracers can be decided.
