As part of the Salinity Processes in the Upper-ocean Regional Study (SPURS-2) 2017 cruise to the eastern tropical Pacific, the Colorado State University SEA-POL (SEA-going POLarimetric) C-band radar made its first ever ship deployment. Previous ship-based experiments have used Doppler radars to map rainfall and the structure of oceanic convection, but SPURS-2 marked the first time the US research community deployed a dual-polarimetric radar at sea. Dual-polarimetric radar transmits and receives electromagnetic radiation in both horizontal (H) and vertical (V) polarizations simultaneously and thereby makes additional, important measurements of precipitation compared to a single polarization radar, which normally transmits horizontal polarization only. For H-polarization, the electric field vector of the transmit pulse is horizontal to the local Earth’s surface; for V-polarization, the electric field vector is perpendicular to Earth’s surface. Polarization measurements provide information about particle size, shape, and phase (water vs. ice). As a result, superior rain rate estimates are afforded by the dual-polarimetric technology. During SPURS-2, SEA-POL produced rain maps in real time to locate freshwater lenses forming on the ocean’s surface to develop context for oceanographic measurements of surface temperature and salinity.