High-resolution sea surface wind speeds of Super Typhoon Lekima (2019) retrieved by Gaofen-3 SAR

Abstract

Gaofen-3 (GF-3) is the first Chinese spaceborne multi-polarization synthetic aperture radar (SAR) instrument at C-band (5.43 GHz). In this paper, we use data collected from GF-3 to observe Super Typhoon Lekima (2019) in the East China Sea. Using a VH-polarized wide ScanSAR (WSC) image, ocean surface wind speeds at 100m horizontal resolution are obtained at 21:56:59 UTC on 8 August 2019, with the maximum wind speed, 38.9 m·s⁻¹. Validating the SAR-retrieved winds with buoy-measured wind speeds, we find that the root mean square error (RMSE) is 1.86 m·s⁻¹, and correlation coefficient, 0.92. This suggests that wind speeds retrieved from GF-3 SAR are reliable. Both the European Centre for Medium-Range Weather Forecasts (ECMWF) fine grid operational forecast products with spatial resolution, and China Global/Regional Assimilation and Prediction Enhance System (GRAPES) have good performances on surface wind prediction under weak wind speed condition (<24 m·s⁻¹), but underestimate the maximum wind speed when the storm is intensified as a severe tropical storm (>24 m·s⁻¹). With respect to SAR-retrieved wind speeds, the RMSEs are 5.24 m·s⁻¹ for ECMWF and 5.17 m·s⁻¹ for GRAPES, with biases of 4.16 m·s⁻¹ for ECMWF and 3.84 m·s⁻¹ for GRAPES during Super Typhoon Lekima (2019).

Graphical abstract

Keywords

synthetic aperture radar / wind speed / numerical weather predication (NWP) / typhoon

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