Physical validation activities collect targeted datasets that describe precipitation physics: the size, type, shape and number of raindrops throughout the air column from the cloud to the ground. Scientists use ground validation measurements to evaluate specific assumptions or hypotheses related to the physical behavior of precipitation, and the manner in which those characteristics are, or are not, well represented in a given retrieval algorithm. The goal of this validation process is to improve and fully develop physically-based precipitation retrieval algorithms. These algorithms are the...