Fourier and Moment Methods Applied to Two-Dimensional Raindrop Images

Abstract

Two-dimensional PMS precipitation probes mounted with horizontal optical axis have been previously used to study the shapes of hydrometeors such as raindrops and graupel. Fourier and moment descriptors have been applied to such images for the purposes of parameter estimation (axis ratio, canting angle) of raindrops, and for classifying raindrops in a raindrop/graupel mixture. Simulations have been used to evaluate these techniques. Our results show that axis ratios of raindrops can be accurately estimated using both Fourier and moment methods. We also show that the canting angle of the raindrop image can be accurately estimated using the moment method. Two image classification techniques were applied to data from below the melting level in a convective storm for classifying raindrops and graupel. The potential usefulness of such techniques is demonstrated in this paper.