Validation of wind speed retrieval from HY-2B calibration microwave radiometer data during tropical cyclones

ABSTRACT

In this letter, we present a validation of the wind speed retrieval from data from the calibration microwave radiometer onboard the Haiyang-2B (HY-2B) satellite against the observations from the stepped-frequency microwave radiometer (SFMR) onboard hurricane aircraft of the National Oceanic and Atmospheric Administration (NOAA) during 50 tropical cyclones (TCs). These data were collected during the cyclone season for the period from 2019 to 2022. The validation yields a root mean square error (RMSE) of 2.99 m s⁻¹, a correlation coefficient (r) of 0.69, and a scatter index (SI) of 0.21 for the wind speed at wind speeds of <25 m s⁻¹, which are worse than those achieved through the comparison with the HY-2B scatterometer, i.e. an RMSE of 1.15 m s⁻¹, an r value of 0.96, and an SI of 0.11. This is probably caused by the fact that the brightness temperature measurement from the calibration microwave radiometer is likely affected by whitecaps caused by wave breaking; however, whitecaps have less influence on the sea surface backscattering signal under a regular sea state. At wind speeds of >25 m s⁻¹, the accuracy is reduced to an RMSE of 2.19 m s⁻¹, an r value of 0.75, and an SI of 0.07. In the presence of rain, significant distortion was observed, i.e. a variation of 3 m s⁻¹ for a rain rate of 15 mm hr⁻¹. This behaviour was also observed in the analysis of the HY-2B scatterometer product at low-to-moderate wind speeds. In this sense, it is believed that correction associated with rain has to be conducted in wind retrieval from HY-2B data.

Acknowledgments

We appreciate the provision of the Haiyang-2B data by the National Satellite Ocean Application Service through an authorized account via https://osdds.nsoas.org.cn. The information on the tropical cyclone and measurements from the stepped-frequency calibration microwave radiometer (SFMR) onboard the hurricane aircraft were provided by the National Oceanic and Atmospheric Administration (NOAA) via https://www.aoml.noaa.gov.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was partially supported by the National Key Research and Development Program of China [No. 2023YFE0102400], the National Natural Science Foundation of China [Nos. 42076238 and 42376174], and the Natural Science Foundation of Shanghai [No. 23ZR1426900].