Estimates of error will be a formal part of the Global Precipitation Mission (GPM) product set. The goal of these error products is to increase the utility of satellite precipitation retrievals for operational and research applications. Over the global oceans, errors will be estimated by comparing relative error among observed and derived fields from the GPM core satellite's dual frequency radar and microwave imager. The proposed approach will decompose error characterization into amplitude error, displacement error, representativeness error (also known as rescaling error) and residual error. The physical assumptions required to estimate vertically-integrated LWC from passive microwave observations represent a subset of those needed to estimate surface rain rate. By comparing relative errors in both vertically-integrated and surface retrievals, sources of error within the algorithms may be able to be diagnosed.