In-Orbit Measurement of Antenna Pattern of the WindRAD scatterometer onboard FY-3E satellite

The WindRAD onboard the Fengyun-3E satellite is the world’s first dual-frequency scatterometer (SCA) for sea surface wind field observation. Simultaneous dual-frequency observation offers advantages such as a wider wind speed measurement range and higher wind direction accuracy. The primary function of WindRAD is high-precision quantitative measurement, where antenna pattern uncertainty is one of the main errors affecting its accuracy. Additionally, WindRAD’s high range resolution means that even minor changes in the antenna pattern can impact the calculation of high-resolution backscattering coefficients. This paper introduces an optimized in-orbit test method for the antenna pattern of the spaceborne microwave scatterometer using ground-based active radar calibrators (ARC). The methodology, process, and results were refined to enhance efficiency. Evaluation shows minimal deviation between the in-orbit antenna pattern and pre-launch measurements, verifying the correctness of key radar antenna parameters for the first time, with a test accuracy better than 0.5 dB. External active references confirmed the in-orbit stability of the WindRAD antenna.