Verification of precipitable water vapor estimated from shipborne GPS measurements

Precipitable water vapor (PWV) was measured using a shipborne Global Positioning System (GPS) during a two month cruise in the equatorial Indian Ocean. More than 300 profiles were also observed by radiosondes released from the ship during the experiment. GPS atmospheric delay and PWV was estimated and compared to the radiosonde observations. The GPS‐PWV is in good agreement with the radiosonde PWV (RS‐PWV) with an rms error of 2.27 mm and a mean difference of less than 1 mm during the nighttime. In the daytime, the dry bias of RS‐PWV becomes 3.63 mm. Thus GPS‐PWV observed from a ship under way in the open ocean is sufficiently accurate. The ship based GPS‐PWV data are accurate to be useful for numerical weather predictions as well as for the calibration of the satellite remote sensors.