Do you want to remove rain, or use CNN? Because here is an image processing algorithm developed by the University of Dayton that removes rain: https://www.udayton.edu/engineering/centers/vision_lab/video_preprocessing/rain_removal.php
To learn CNN, see the Mathworks portal to Deep Learning: https://www.mathworks.com/solutions/deep-learning.html?s_tid=hp_solutions_deep
