A novel approach to measuring rainfall in the ocean is presented. The method is based on the remote sensing of rain by navigational radar and subsequent calibration of the radar signal against the upper ocean salinity changes. The estimate of the area-average precipitation is obtained as the product of the calibration factor and the fraction of area covered by rainfall. We describe an application of this technique in the field during a recent voyage of the Australian R/V Franklin to the eastern tropical Indian Ocean. It is suggested that with further refinement of radar signal processing, navigational radar can be used to routinely measure open ocean precipitation from research vessels and ships of opportunity. ¿ 1999 American Geophysical Union