An important partner in the retrieval of atmospheric water vapor and cloud liquid water - derived over oceans only - is the 31-GHz window channel (37 GHz for SSM/I). The 31-GHz channel is even more sensitive to the absorption of microwave radiation by cloud liquid water and relatively insensitive to precipitation particles. This makes the 31-GHz channel ideally suited for providing additional cloud water information for both water vapor and cloud liquid water retrievals. Notice how water clouds over the ocean stand out even more than the same clouds in the 23-GHz channel.