Evaluation of HY-2A satellite-borne water vapor radiometer with shipborne GPS and GLONASS observations over the Indian Ocean

The Chinese Haiyang-2A (HY-2A) altimetry satellite is equipped with a calibration microwave radiometer (CMR) for correcting atmospheric water vapor path delay in radar altimeter observations. To evaluate the satellite-borne CMR, we retrieved 1 Hz high-frequency precipitable water vapor (PWV) using shipborne GPS and GLONASS from a two-month cruise in the Indian Ocean. This open-sea evaluation of the satellite-borne radiometer is free of the contamination of the satellite footprints induced by coastal lands, which occurs inevitably in ground-based or coastal stations. The estimates and errors of the retrieved PWV from shipborne GNSS kinematic precise point positioning were analyzed and then compared to the CMR-retrieved PWV. The results show that the shipborne GNSS kinematic precise point positioning can obtain marine PWV with an uncertainty of about 2.8 mm. When the HY-2A sub-satellite point and the ship cross, the HY-2A CMR-retrieved PWV is in good agreement with the GNSS PWV with the difference of about 0.8 mm, which demonstrates that the HY-2A satellite can contribute high-precision precipitable water vapor measurements to weather and atmospheric studies.